1 @c -*- mode: texinfo; coding: utf-8 -*-
2 @c This is part of the GNU Emacs Lisp Reference Manual.
3 @c Copyright (C) 1990-1995, 1998-2016 Free Software Foundation, Inc.
4 @c See the file elisp.texi for copying conditions.
8 This chapter describes a number of features related to the display
9 that Emacs presents to the user.
12 * Refresh Screen:: Clearing the screen and redrawing everything on it.
13 * Forcing Redisplay:: Forcing redisplay.
14 * Truncation:: Folding or wrapping long text lines.
15 * The Echo Area:: Displaying messages at the bottom of the screen.
16 * Warnings:: Displaying warning messages for the user.
17 * Invisible Text:: Hiding part of the buffer text.
18 * Selective Display:: Hiding part of the buffer text (the old way).
19 * Temporary Displays:: Displays that go away automatically.
20 * Overlays:: Use overlays to highlight parts of the buffer.
21 * Size of Displayed Text:: How large displayed text is.
22 * Line Height:: Controlling the height of lines.
23 * Faces:: A face defines a graphics style for text characters:
25 * Fringes:: Controlling window fringes.
26 * Scroll Bars:: Controlling scroll bars.
27 * Window Dividers:: Separating windows visually.
28 * Display Property:: Enabling special display features.
29 * Images:: Displaying images in Emacs buffers.
30 * Xwidgets:: Displaying native widgets in Emacs buffers.
31 * Buttons:: Adding clickable buttons to Emacs buffers.
32 * Abstract Display:: Emacs's Widget for Object Collections.
33 * Blinking:: How Emacs shows the matching open parenthesis.
34 * Character Display:: How Emacs displays individual characters.
35 * Beeping:: Audible signal to the user.
36 * Window Systems:: Which window system is being used.
37 * Tooltips:: Tooltip display in Emacs.
38 * Bidirectional Display:: Display of bidirectional scripts, such as
43 @section Refreshing the Screen
44 @cindex refresh the screen
45 @cindex screen refresh
47 The function @code{redraw-frame} clears and redisplays the entire
48 contents of a given frame (@pxref{Frames}). This is useful if the
51 @defun redraw-frame &optional frame
52 This function clears and redisplays frame @var{frame}. If @var{frame}
53 is omitted or nil, it redraws the selected frame.
56 Even more powerful is @code{redraw-display}:
58 @deffn Command redraw-display
59 This function clears and redisplays all visible frames.
62 In Emacs, processing user input takes priority over redisplay. If
63 you call these functions when input is available, they don't redisplay
64 immediately, but the requested redisplay does happen
65 eventually---after all the input has been processed.
67 On text terminals, suspending and resuming Emacs normally also
68 refreshes the screen. Some terminal emulators record separate
69 contents for display-oriented programs such as Emacs and for ordinary
70 sequential display. If you are using such a terminal, you might want
71 to inhibit the redisplay on resumption.
73 @defopt no-redraw-on-reenter
74 @cindex suspend (cf. @code{no-redraw-on-reenter})
75 @cindex resume (cf. @code{no-redraw-on-reenter})
76 This variable controls whether Emacs redraws the entire screen after it
77 has been suspended and resumed. Non-@code{nil} means there is no need
78 to redraw, @code{nil} means redrawing is needed. The default is @code{nil}.
81 @node Forcing Redisplay
82 @section Forcing Redisplay
83 @cindex forcing redisplay
85 Emacs normally tries to redisplay the screen whenever it waits for
86 input. With the following function, you can request an immediate
87 attempt to redisplay, in the middle of Lisp code, without actually
90 @defun redisplay &optional force
91 This function tries immediately to redisplay. The optional argument
92 @var{force}, if non-@code{nil}, forces the redisplay to be performed,
93 instead of being preempted if input is pending.
95 The function returns @code{t} if it actually tried to redisplay, and
96 @code{nil} otherwise. A value of @code{t} does not mean that
97 redisplay proceeded to completion; it could have been preempted by
101 Although @code{redisplay} tries immediately to redisplay, it does
102 not change how Emacs decides which parts of its frame(s) to redisplay.
103 By contrast, the following function adds certain windows to the
104 pending redisplay work (as if their contents had completely changed),
105 but does not immediately try to perform redisplay.
107 @defun force-window-update &optional object
108 This function forces some or all windows to be updated the next time
109 Emacs does a redisplay. If @var{object} is a window, that window is
110 to be updated. If @var{object} is a buffer or buffer name, all
111 windows displaying that buffer are to be updated. If @var{object} is
112 @code{nil} (or omitted), all windows are to be updated.
114 This function does not do a redisplay immediately; Emacs does that as
115 it waits for input, or when the function @code{redisplay} is called.
118 @defvar pre-redisplay-function
119 A function run just before redisplay. It is called with one argument,
120 the set of windows to be redisplayed. The set can be @code{nil},
121 meaning only the selected window, or @code{t}, meaning all the
125 @defvar pre-redisplay-functions
126 This hook is run just before redisplay. It is called once in each
127 window that is about to be redisplayed, with @code{current-buffer} set
128 to the buffer displayed in that window.
133 @cindex line wrapping
134 @cindex line truncation
135 @cindex continuation lines
136 @cindex @samp{$} in display
137 @cindex @samp{\} in display
139 When a line of text extends beyond the right edge of a window, Emacs
140 can @dfn{continue} the line (make it wrap to the next screen
141 line), or @dfn{truncate} the line (limit it to one screen line). The
142 additional screen lines used to display a long text line are called
143 @dfn{continuation} lines. Continuation is not the same as filling;
144 continuation happens on the screen only, not in the buffer contents,
145 and it breaks a line precisely at the right margin, not at a word
146 boundary. @xref{Filling}.
148 On a graphical display, tiny arrow images in the window fringes
149 indicate truncated and continued lines (@pxref{Fringes}). On a text
150 terminal, a @samp{$} in the rightmost column of the window indicates
151 truncation; a @samp{\} on the rightmost column indicates a line that
152 wraps. (The display table can specify alternate characters to use
153 for this; @pxref{Display Tables}).
155 @defopt truncate-lines
156 If this buffer-local variable is non-@code{nil}, lines that extend
157 beyond the right edge of the window are truncated; otherwise, they are
158 continued. As a special exception, the variable
159 @code{truncate-partial-width-windows} takes precedence in
160 @dfn{partial-width} windows (i.e., windows that do not occupy the
164 @defopt truncate-partial-width-windows
165 @cindex partial-width windows
166 This variable controls line truncation in @dfn{partial-width} windows.
167 A partial-width window is one that does not occupy the entire frame
168 width (@pxref{Splitting Windows}). If the value is @code{nil}, line
169 truncation is determined by the variable @code{truncate-lines} (see
170 above). If the value is an integer @var{n}, lines are truncated if
171 the partial-width window has fewer than @var{n} columns, regardless of
172 the value of @code{truncate-lines}; if the partial-width window has
173 @var{n} or more columns, line truncation is determined by
174 @code{truncate-lines}. For any other non-@code{nil} value, lines are
175 truncated in every partial-width window, regardless of the value of
176 @code{truncate-lines}.
179 When horizontal scrolling (@pxref{Horizontal Scrolling}) is in use in
180 a window, that forces truncation.
183 If this buffer-local variable is non-@code{nil}, it defines a
184 @dfn{wrap prefix} which Emacs displays at the start of every
185 continuation line. (If lines are truncated, @code{wrap-prefix} is
186 never used.) Its value may be a string or an image (@pxref{Other
187 Display Specs}), or a stretch of whitespace such as specified by the
188 @code{:width} or @code{:align-to} display properties (@pxref{Specified
189 Space}). The value is interpreted in the same way as a @code{display}
190 text property. @xref{Display Property}.
192 A wrap prefix may also be specified for regions of text, using the
193 @code{wrap-prefix} text or overlay property. This takes precedence
194 over the @code{wrap-prefix} variable. @xref{Special Properties}.
198 If this buffer-local variable is non-@code{nil}, it defines a
199 @dfn{line prefix} which Emacs displays at the start of every
200 non-continuation line. Its value may be a string or an image
201 (@pxref{Other Display Specs}), or a stretch of whitespace such as
202 specified by the @code{:width} or @code{:align-to} display properties
203 (@pxref{Specified Space}). The value is interpreted in the same way
204 as a @code{display} text property. @xref{Display Property}.
206 A line prefix may also be specified for regions of text using the
207 @code{line-prefix} text or overlay property. This takes precedence
208 over the @code{line-prefix} variable. @xref{Special Properties}.
212 If your buffer contains only very short lines, you might find it
213 advisable to set @code{cache-long-scans} to @code{nil}.
215 @defvar cache-long-scans
216 If this variable is non-@code{nil} (the default), various indentation
217 and motion functions, and Emacs redisplay, cache the results of
218 scanning the buffer, and consult the cache to avoid rescanning regions
219 of the buffer unless they are modified.
221 Turning off the cache speeds up processing of short lines somewhat.
223 This variable is automatically buffer-local in every buffer.
228 @section The Echo Area
229 @cindex error display
232 @c FIXME: Why not use @xref{Minibuffers} directly? --xfq
233 The @dfn{echo area} is used for displaying error messages
234 (@pxref{Errors}), for messages made with the @code{message} primitive,
235 and for echoing keystrokes. It is not the same as the minibuffer,
236 despite the fact that the minibuffer appears (when active) in the same
237 place on the screen as the echo area. @xref{Minibuffer,, The
238 Minibuffer, emacs, The GNU Emacs Manual}.
240 Apart from the functions documented in this section, you can print
241 Lisp objects to the echo area by specifying @code{t} as the output
242 stream. @xref{Output Streams}.
245 * Displaying Messages:: Explicitly displaying text in the echo area.
246 * Progress:: Informing user about progress of a long operation.
247 * Logging Messages:: Echo area messages are logged for the user.
248 * Echo Area Customization:: Controlling the echo area.
251 @node Displaying Messages
252 @subsection Displaying Messages in the Echo Area
253 @cindex display message in echo area
255 This section describes the standard functions for displaying
256 messages in the echo area.
258 @defun message format-string &rest arguments
259 This function displays a message in the echo area.
260 @var{format-string} is a format string, and @var{arguments} are the
261 objects for its format specifications, like in the @code{format-message}
262 function (@pxref{Formatting Strings}). The resulting formatted string
263 is displayed in the echo area; if it contains @code{face} text
264 properties, it is displayed with the specified faces (@pxref{Faces}).
265 The string is also added to the @file{*Messages*} buffer, but without
266 text properties (@pxref{Logging Messages}).
268 The @code{text-quoting-style} variable controls what quotes are
269 generated; @xref{Keys in Documentation}. A call using a format like
270 @t{"Missing `%s'"} with grave accents and apostrophes typically
271 generates a message like @t{"Missing ‘foo’"} with matching curved
272 quotes. In contrast, a call using a format like @t{"Missing '%s'"}
273 with only apostrophes typically generates a message like @t{"Missing
274 ’foo’"} with only closing curved quotes, an unusual style in English.
276 In batch mode, the message is printed to the standard error stream,
277 followed by a newline.
279 When @code{inhibit-message} is non-@code{nil}, no message will be displayed
280 in the echo area, it will only be logged to @samp{*Messages*}.
282 If @var{format-string} is @code{nil} or the empty string,
283 @code{message} clears the echo area; if the echo area has been
284 expanded automatically, this brings it back to its normal size. If
285 the minibuffer is active, this brings the minibuffer contents back
286 onto the screen immediately.
290 (message "Reverting `%s'..." (buffer-name))
291 @print{} Reverting ‘subr.el’...
292 @result{} "Reverting ‘subr.el’..."
296 ---------- Echo Area ----------
297 Reverting ‘subr.el’...
298 ---------- Echo Area ----------
302 To automatically display a message in the echo area or in a pop-buffer,
303 depending on its size, use @code{display-message-or-buffer} (see below).
305 @strong{Warning:} If you want to use your own string as a message
306 verbatim, don't just write @code{(message @var{string})}. If
307 @var{string} contains @samp{%}, @samp{`}, or @samp{'} it may be
308 reformatted, with undesirable results. Instead, use @code{(message
312 @defvar inhibit-message
313 When this variable is non-@code{nil}, @code{message} and related functions
314 will not use the Echo Area to display messages.
317 @defmac with-temp-message message &rest body
318 This construct displays a message in the echo area temporarily, during
319 the execution of @var{body}. It displays @var{message}, executes
320 @var{body}, then returns the value of the last body form while restoring
321 the previous echo area contents.
324 @defun message-or-box format-string &rest arguments
325 This function displays a message like @code{message}, but may display it
326 in a dialog box instead of the echo area. If this function is called in
327 a command that was invoked using the mouse---more precisely, if
328 @code{last-nonmenu-event} (@pxref{Command Loop Info}) is either
329 @code{nil} or a list---then it uses a dialog box or pop-up menu to
330 display the message. Otherwise, it uses the echo area. (This is the
331 same criterion that @code{y-or-n-p} uses to make a similar decision; see
332 @ref{Yes-or-No Queries}.)
334 You can force use of the mouse or of the echo area by binding
335 @code{last-nonmenu-event} to a suitable value around the call.
338 @defun message-box format-string &rest arguments
340 This function displays a message like @code{message}, but uses a dialog
341 box (or a pop-up menu) whenever that is possible. If it is impossible
342 to use a dialog box or pop-up menu, because the terminal does not
343 support them, then @code{message-box} uses the echo area, like
347 @defun display-message-or-buffer message &optional buffer-name action frame
348 This function displays the message @var{message}, which may be either a
349 string or a buffer. If it is shorter than the maximum height of the
350 echo area, as defined by @code{max-mini-window-height}, it is displayed
351 in the echo area, using @code{message}. Otherwise,
352 @code{display-buffer} is used to show it in a pop-up buffer.
354 Returns either the string shown in the echo area, or when a pop-up
355 buffer is used, the window used to display it.
357 If @var{message} is a string, then the optional argument
358 @var{buffer-name} is the name of the buffer used to display it when a
359 pop-up buffer is used, defaulting to @file{*Message*}. In the case
360 where @var{message} is a string and displayed in the echo area, it is
361 not specified whether the contents are inserted into the buffer anyway.
363 The optional arguments @var{action} and @var{frame} are as for
364 @code{display-buffer}, and only used if a buffer is displayed.
367 @defun current-message
368 This function returns the message currently being displayed in the
369 echo area, or @code{nil} if there is none.
373 @subsection Reporting Operation Progress
374 @cindex progress reporting
376 When an operation can take a while to finish, you should inform the
377 user about the progress it makes. This way the user can estimate
378 remaining time and clearly see that Emacs is busy working, not hung.
379 A convenient way to do this is to use a @dfn{progress reporter}.
381 Here is a working example that does nothing useful:
384 (let ((progress-reporter
385 (make-progress-reporter "Collecting mana for Emacs..."
389 (progress-reporter-update progress-reporter k))
390 (progress-reporter-done progress-reporter))
393 @defun make-progress-reporter message &optional min-value max-value current-value min-change min-time
394 This function creates and returns a progress reporter object, which
395 you will use as an argument for the other functions listed below. The
396 idea is to precompute as much data as possible to make progress
399 When this progress reporter is subsequently used, it will display
400 @var{message} in the echo area, followed by progress percentage.
401 @var{message} is treated as a simple string. If you need it to depend
402 on a filename, for instance, use @code{format-message} before calling this
405 The arguments @var{min-value} and @var{max-value} should be numbers
406 standing for the starting and final states of the operation. For
407 instance, an operation that scans a buffer should set these to the
408 results of @code{point-min} and @code{point-max} correspondingly.
409 @var{max-value} should be greater than @var{min-value}.
411 Alternatively, you can set @var{min-value} and @var{max-value} to
412 @code{nil}. In that case, the progress reporter does not report
413 process percentages; it instead displays a ``spinner'' that rotates a
414 notch each time you update the progress reporter.
416 If @var{min-value} and @var{max-value} are numbers, you can give the
417 argument @var{current-value} a numerical value specifying the initial
418 progress; if omitted, this defaults to @var{min-value}.
420 The remaining arguments control the rate of echo area updates. The
421 progress reporter will wait for at least @var{min-change} more
422 percents of the operation to be completed before printing next
423 message; the default is one percent. @var{min-time} specifies the
424 minimum time in seconds to pass between successive prints; the default
425 is 0.2 seconds. (On some operating systems, the progress reporter may
426 handle fractions of seconds with varying precision).
428 This function calls @code{progress-reporter-update}, so the first
429 message is printed immediately.
432 @defun progress-reporter-update reporter &optional value
433 This function does the main work of reporting progress of your
434 operation. It displays the message of @var{reporter}, followed by
435 progress percentage determined by @var{value}. If percentage is zero,
436 or close enough according to the @var{min-change} and @var{min-time}
437 arguments, then it is omitted from the output.
439 @var{reporter} must be the result of a call to
440 @code{make-progress-reporter}. @var{value} specifies the current
441 state of your operation and must be between @var{min-value} and
442 @var{max-value} (inclusive) as passed to
443 @code{make-progress-reporter}. For instance, if you scan a buffer,
444 then @var{value} should be the result of a call to @code{point}.
446 This function respects @var{min-change} and @var{min-time} as passed
447 to @code{make-progress-reporter} and so does not output new messages
448 on every invocation. It is thus very fast and normally you should not
449 try to reduce the number of calls to it: resulting overhead will most
450 likely negate your effort.
453 @defun progress-reporter-force-update reporter &optional value new-message
454 This function is similar to @code{progress-reporter-update} except
455 that it prints a message in the echo area unconditionally.
457 The first two arguments have the same meaning as for
458 @code{progress-reporter-update}. Optional @var{new-message} allows
459 you to change the message of the @var{reporter}. Since this function
460 always updates the echo area, such a change will be immediately
461 presented to the user.
464 @defun progress-reporter-done reporter
465 This function should be called when the operation is finished. It
466 prints the message of @var{reporter} followed by word @samp{done} in the
469 You should always call this function and not hope for
470 @code{progress-reporter-update} to print @samp{100%}. Firstly, it may
471 never print it, there are many good reasons for this not to happen.
472 Secondly, @samp{done} is more explicit.
475 @defmac dotimes-with-progress-reporter (var count [result]) message body@dots{}
476 This is a convenience macro that works the same way as @code{dotimes}
477 does, but also reports loop progress using the functions described
478 above. It allows you to save some typing.
480 You can rewrite the example in the beginning of this node using
484 (dotimes-with-progress-reporter
486 "Collecting some mana for Emacs..."
491 @node Logging Messages
492 @subsection Logging Messages in @file{*Messages*}
493 @cindex logging echo-area messages
495 Almost all the messages displayed in the echo area are also recorded
496 in the @file{*Messages*} buffer so that the user can refer back to
497 them. This includes all the messages that are output with
498 @code{message}. By default, this buffer is read-only and uses the major
499 mode @code{messages-buffer-mode}. Nothing prevents the user from
500 killing the @file{*Messages*} buffer, but the next display of a message
501 recreates it. Any Lisp code that needs to access the
502 @file{*Messages*} buffer directly and wants to ensure that it exists
503 should use the function @code{messages-buffer}.
505 @defun messages-buffer
506 This function returns the @file{*Messages*} buffer. If it does not
507 exist, it creates it, and switches it to @code{messages-buffer-mode}.
510 @defopt message-log-max
511 This variable specifies how many lines to keep in the @file{*Messages*}
512 buffer. The value @code{t} means there is no limit on how many lines to
513 keep. The value @code{nil} disables message logging entirely. Here's
514 how to display a message and prevent it from being logged:
517 (let (message-log-max)
522 To make @file{*Messages*} more convenient for the user, the logging
523 facility combines successive identical messages. It also combines
524 successive related messages for the sake of two cases: question
525 followed by answer, and a series of progress messages.
527 A question followed by an answer has two messages like the
528 ones produced by @code{y-or-n-p}: the first is @samp{@var{question}},
529 and the second is @samp{@var{question}...@var{answer}}. The first
530 message conveys no additional information beyond what's in the second,
531 so logging the second message discards the first from the log.
533 A series of progress messages has successive messages like
534 those produced by @code{make-progress-reporter}. They have the form
535 @samp{@var{base}...@var{how-far}}, where @var{base} is the same each
536 time, while @var{how-far} varies. Logging each message in the series
537 discards the previous one, provided they are consecutive.
539 The functions @code{make-progress-reporter} and @code{y-or-n-p}
540 don't have to do anything special to activate the message log
541 combination feature. It operates whenever two consecutive messages
542 are logged that share a common prefix ending in @samp{...}.
544 @node Echo Area Customization
545 @subsection Echo Area Customization
546 @cindex echo area customization
548 These variables control details of how the echo area works.
550 @defvar cursor-in-echo-area
551 This variable controls where the cursor appears when a message is
552 displayed in the echo area. If it is non-@code{nil}, then the cursor
553 appears at the end of the message. Otherwise, the cursor appears at
554 point---not in the echo area at all.
556 The value is normally @code{nil}; Lisp programs bind it to @code{t}
557 for brief periods of time.
560 @defvar echo-area-clear-hook
561 This normal hook is run whenever the echo area is cleared---either by
562 @code{(message nil)} or for any other reason.
565 @defopt echo-keystrokes
566 This variable determines how much time should elapse before command
567 characters echo. Its value must be a number, and specifies the
568 number of seconds to wait before echoing. If the user types a prefix
569 key (such as @kbd{C-x}) and then delays this many seconds before
570 continuing, the prefix key is echoed in the echo area. (Once echoing
571 begins in a key sequence, all subsequent characters in the same key
572 sequence are echoed immediately.)
574 If the value is zero, then command input is not echoed.
577 @defvar message-truncate-lines
578 Normally, displaying a long message resizes the echo area to display
579 the entire message. But if the variable @code{message-truncate-lines}
580 is non-@code{nil}, the echo area does not resize, and the message is
584 The variable @code{max-mini-window-height}, which specifies the
585 maximum height for resizing minibuffer windows, also applies to the
586 echo area (which is really a special use of the minibuffer window;
587 @pxref{Minibuffer Misc}).
590 @section Reporting Warnings
593 @dfn{Warnings} are a facility for a program to inform the user of a
594 possible problem, but continue running.
597 * Warning Basics:: Warnings concepts and functions to report them.
598 * Warning Variables:: Variables programs bind to customize their warnings.
599 * Warning Options:: Variables users set to control display of warnings.
600 * Delayed Warnings:: Deferring a warning until the end of a command.
604 @subsection Warning Basics
605 @cindex severity level
607 Every warning has a textual message, which explains the problem for
608 the user, and a @dfn{severity level} which is a symbol. Here are the
609 possible severity levels, in order of decreasing severity, and their
614 A problem that will seriously impair Emacs operation soon
615 if you do not attend to it promptly.
617 A report of data or circumstances that are inherently wrong.
619 A report of data or circumstances that are not inherently wrong, but
620 raise suspicion of a possible problem.
622 A report of information that may be useful if you are debugging.
625 When your program encounters invalid input data, it can either
626 signal a Lisp error by calling @code{error} or @code{signal} or report
627 a warning with severity @code{:error}. Signaling a Lisp error is the
628 easiest thing to do, but it means the program cannot continue
629 processing. If you want to take the trouble to implement a way to
630 continue processing despite the bad data, then reporting a warning of
631 severity @code{:error} is the right way to inform the user of the
632 problem. For instance, the Emacs Lisp byte compiler can report an
633 error that way and continue compiling other functions. (If the
634 program signals a Lisp error and then handles it with
635 @code{condition-case}, the user won't see the error message; it could
636 show the message to the user by reporting it as a warning.)
638 @c FIXME: Why use "(bytecomp)" instead of "'bytecomp" or simply
639 @c "bytecomp" here? The parens are part of warning-type-format but
640 @c not part of the warning type. --xfq
642 Each warning has a @dfn{warning type} to classify it. The type is a
643 list of symbols. The first symbol should be the custom group that you
644 use for the program's user options. For example, byte compiler
645 warnings use the warning type @code{(bytecomp)}. You can also
646 subcategorize the warnings, if you wish, by using more symbols in the
649 @defun display-warning type message &optional level buffer-name
650 This function reports a warning, using @var{message} as the message
651 and @var{type} as the warning type. @var{level} should be the
652 severity level, with @code{:warning} being the default.
654 @var{buffer-name}, if non-@code{nil}, specifies the name of the buffer
655 for logging the warning. By default, it is @file{*Warnings*}.
658 @defun lwarn type level message &rest args
659 This function reports a warning using the value of @code{(format-message
660 @var{message} @var{args}...)} as the message in the @file{*Warnings*}
661 buffer. In other respects it is equivalent to @code{display-warning}.
664 @defun warn message &rest args
665 This function reports a warning using the value of @code{(format-message
666 @var{message} @var{args}...)} as the message, @code{(emacs)} as the
667 type, and @code{:warning} as the severity level. It exists for
668 compatibility only; we recommend not using it, because you should
669 specify a specific warning type.
672 @node Warning Variables
673 @subsection Warning Variables
674 @cindex warning variables
676 Programs can customize how their warnings appear by binding
677 the variables described in this section.
679 @defvar warning-levels
680 This list defines the meaning and severity order of the warning
681 severity levels. Each element defines one severity level,
682 and they are arranged in order of decreasing severity.
684 Each element has the form @code{(@var{level} @var{string}
685 @var{function})}, where @var{level} is the severity level it defines.
686 @var{string} specifies the textual description of this level.
687 @var{string} should use @samp{%s} to specify where to put the warning
688 type information, or it can omit the @samp{%s} so as not to include
691 The optional @var{function}, if non-@code{nil}, is a function to call
692 with no arguments, to get the user's attention.
694 Normally you should not change the value of this variable.
697 @defvar warning-prefix-function
698 If non-@code{nil}, the value is a function to generate prefix text for
699 warnings. Programs can bind the variable to a suitable function.
700 @code{display-warning} calls this function with the warnings buffer
701 current, and the function can insert text in it. That text becomes
702 the beginning of the warning message.
704 The function is called with two arguments, the severity level and its
705 entry in @code{warning-levels}. It should return a list to use as the
706 entry (this value need not be an actual member of
707 @code{warning-levels}). By constructing this value, the function can
708 change the severity of the warning, or specify different handling for
709 a given severity level.
711 If the variable's value is @code{nil} then there is no function
715 @defvar warning-series
716 Programs can bind this variable to @code{t} to say that the next
717 warning should begin a series. When several warnings form a series,
718 that means to leave point on the first warning of the series, rather
719 than keep moving it for each warning so that it appears on the last one.
720 The series ends when the local binding is unbound and
721 @code{warning-series} becomes @code{nil} again.
723 The value can also be a symbol with a function definition. That is
724 equivalent to @code{t}, except that the next warning will also call
725 the function with no arguments with the warnings buffer current. The
726 function can insert text which will serve as a header for the series
729 Once a series has begun, the value is a marker which points to the
730 buffer position in the warnings buffer of the start of the series.
732 The variable's normal value is @code{nil}, which means to handle
733 each warning separately.
736 @defvar warning-fill-prefix
737 When this variable is non-@code{nil}, it specifies a fill prefix to
738 use for filling each warning's text.
741 @defvar warning-type-format
742 This variable specifies the format for displaying the warning type
743 in the warning message. The result of formatting the type this way
744 gets included in the message under the control of the string in the
745 entry in @code{warning-levels}. The default value is @code{" (%s)"}.
746 If you bind it to @code{""} then the warning type won't appear at
750 @node Warning Options
751 @subsection Warning Options
752 @cindex warning options
754 These variables are used by users to control what happens
755 when a Lisp program reports a warning.
757 @defopt warning-minimum-level
758 This user option specifies the minimum severity level that should be
759 shown immediately to the user. The default is @code{:warning}, which
760 means to immediately display all warnings except @code{:debug}
764 @defopt warning-minimum-log-level
765 This user option specifies the minimum severity level that should be
766 logged in the warnings buffer. The default is @code{:warning}, which
767 means to log all warnings except @code{:debug} warnings.
770 @defopt warning-suppress-types
771 This list specifies which warning types should not be displayed
772 immediately for the user. Each element of the list should be a list
773 of symbols. If its elements match the first elements in a warning
774 type, then that warning is not displayed immediately.
777 @defopt warning-suppress-log-types
778 This list specifies which warning types should not be logged in the
779 warnings buffer. Each element of the list should be a list of
780 symbols. If it matches the first few elements in a warning type, then
781 that warning is not logged.
784 @node Delayed Warnings
785 @subsection Delayed Warnings
786 @cindex delayed warnings
788 Sometimes, you may wish to avoid showing a warning while a command is
789 running, and only show it only after the end of the command. You can
790 use the variable @code{delayed-warnings-list} for this.
792 @defvar delayed-warnings-list
793 The value of this variable is a list of warnings to be displayed after
794 the current command has finished. Each element must be a list
797 (@var{type} @var{message} [@var{level} [@var{buffer-name}]])
801 with the same form, and the same meanings, as the argument list of
802 @code{display-warning} (@pxref{Warning Basics}). Immediately after
803 running @code{post-command-hook} (@pxref{Command Overview}), the Emacs
804 command loop displays all the warnings specified by this variable,
805 then resets it to @code{nil}.
808 Programs which need to further customize the delayed warnings
809 mechanism can change the variable @code{delayed-warnings-hook}:
811 @defvar delayed-warnings-hook
812 This is a normal hook which is run by the Emacs command loop, after
813 @code{post-command-hook}, in order to to process and display delayed
816 Its default value is a list of two functions:
819 (collapse-delayed-warnings display-delayed-warnings)
822 @findex collapse-delayed-warnings
823 @findex display-delayed-warnings
825 The function @code{collapse-delayed-warnings} removes repeated entries
826 from @code{delayed-warnings-list}. The function
827 @code{display-delayed-warnings} calls @code{display-warning} on each
828 of the entries in @code{delayed-warnings-list}, in turn, and then sets
829 @code{delayed-warnings-list} to @code{nil}.
833 @section Invisible Text
835 @cindex invisible text
836 You can make characters @dfn{invisible}, so that they do not appear on
837 the screen, with the @code{invisible} property. This can be either a
838 text property (@pxref{Text Properties}) or an overlay property
839 (@pxref{Overlays}). Cursor motion also partly ignores these
840 characters; if the command loop finds that point is inside a range of
841 invisible text after a command, it relocates point to the other side
844 In the simplest case, any non-@code{nil} @code{invisible} property makes
845 a character invisible. This is the default case---if you don't alter
846 the default value of @code{buffer-invisibility-spec}, this is how the
847 @code{invisible} property works. You should normally use @code{t}
848 as the value of the @code{invisible} property if you don't plan
849 to set @code{buffer-invisibility-spec} yourself.
851 More generally, you can use the variable @code{buffer-invisibility-spec}
852 to control which values of the @code{invisible} property make text
853 invisible. This permits you to classify the text into different subsets
854 in advance, by giving them different @code{invisible} values, and
855 subsequently make various subsets visible or invisible by changing the
856 value of @code{buffer-invisibility-spec}.
858 Controlling visibility with @code{buffer-invisibility-spec} is
859 especially useful in a program to display the list of entries in a
860 database. It permits the implementation of convenient filtering
861 commands to view just a part of the entries in the database. Setting
862 this variable is very fast, much faster than scanning all the text in
863 the buffer looking for properties to change.
865 @defvar buffer-invisibility-spec
866 This variable specifies which kinds of @code{invisible} properties
867 actually make a character invisible. Setting this variable makes it
872 A character is invisible if its @code{invisible} property is
873 non-@code{nil}. This is the default.
876 Each element of the list specifies a criterion for invisibility; if a
877 character's @code{invisible} property fits any one of these criteria,
878 the character is invisible. The list can have two kinds of elements:
882 A character is invisible if its @code{invisible} property value is
883 @var{atom} or if it is a list with @var{atom} as a member; comparison
884 is done with @code{eq}.
886 @item (@var{atom} . t)
887 A character is invisible if its @code{invisible} property value is
888 @var{atom} or if it is a list with @var{atom} as a member; comparison
889 is done with @code{eq}. Moreover, a sequence of such characters
890 displays as an ellipsis.
895 Two functions are specifically provided for adding elements to
896 @code{buffer-invisibility-spec} and removing elements from it.
898 @defun add-to-invisibility-spec element
899 This function adds the element @var{element} to
900 @code{buffer-invisibility-spec}. If @code{buffer-invisibility-spec}
901 was @code{t}, it changes to a list, @code{(t)}, so that text whose
902 @code{invisible} property is @code{t} remains invisible.
905 @defun remove-from-invisibility-spec element
906 This removes the element @var{element} from
907 @code{buffer-invisibility-spec}. This does nothing if @var{element}
911 A convention for use of @code{buffer-invisibility-spec} is that a
912 major mode should use the mode's own name as an element of
913 @code{buffer-invisibility-spec} and as the value of the
914 @code{invisible} property:
917 ;; @r{If you want to display an ellipsis:}
918 (add-to-invisibility-spec '(my-symbol . t))
919 ;; @r{If you don't want ellipsis:}
920 (add-to-invisibility-spec 'my-symbol)
922 (overlay-put (make-overlay beginning end)
923 'invisible 'my-symbol)
925 ;; @r{When done with the invisibility:}
926 (remove-from-invisibility-spec '(my-symbol . t))
927 ;; @r{Or respectively:}
928 (remove-from-invisibility-spec 'my-symbol)
931 You can check for invisibility using the following function:
933 @defun invisible-p pos-or-prop
934 If @var{pos-or-prop} is a marker or number, this function returns a
935 non-@code{nil} value if the text at that position is invisible.
937 If @var{pos-or-prop} is any other kind of Lisp object, that is taken
938 to mean a possible value of the @code{invisible} text or overlay
939 property. In that case, this function returns a non-@code{nil} value
940 if that value would cause text to become invisible, based on the
941 current value of @code{buffer-invisibility-spec}.
944 @vindex line-move-ignore-invisible
945 Ordinarily, functions that operate on text or move point do not care
946 whether the text is invisible, they process invisible characters and
947 visible characters alike. The user-level line motion commands,
948 such as @code{next-line}, @code{previous-line}, ignore invisible
949 newlines if @code{line-move-ignore-invisible} is non-@code{nil} (the
950 default), i.e., behave like these invisible newlines didn't exist in
951 the buffer, but only because they are explicitly programmed to do so.
953 If a command ends with point inside or at the boundary of
954 invisible text, the main editing loop relocates point to one of the
955 two ends of the invisible text. Emacs chooses the direction of
956 relocation so that it is the same as the overall movement direction of
957 the command; if in doubt, it prefers a position where an inserted char
958 would not inherit the @code{invisible} property. Additionally, if the
959 text is not replaced by an ellipsis and the command only moved within
960 the invisible text, then point is moved one extra character so as to
961 try and reflect the command's movement by a visible movement of the
964 Thus, if the command moved point back to an invisible range (with the usual
965 stickiness), Emacs moves point back to the beginning of that range. If the
966 command moved point forward into an invisible range, Emacs moves point forward
967 to the first visible character that follows the invisible text and then forward
970 These @dfn{adjustments} of point that ended up in the middle of
971 invisible text can be disabled by setting @code{disable-point-adjustment}
972 to a non-@code{nil} value. @xref{Adjusting Point}.
974 Incremental search can make invisible overlays visible temporarily
975 and/or permanently when a match includes invisible text. To enable
976 this, the overlay should have a non-@code{nil}
977 @code{isearch-open-invisible} property. The property value should be a
978 function to be called with the overlay as an argument. This function
979 should make the overlay visible permanently; it is used when the match
980 overlaps the overlay on exit from the search.
982 During the search, such overlays are made temporarily visible by
983 temporarily modifying their invisible and intangible properties. If you
984 want this to be done differently for a certain overlay, give it an
985 @code{isearch-open-invisible-temporary} property which is a function.
986 The function is called with two arguments: the first is the overlay, and
987 the second is @code{nil} to make the overlay visible, or @code{t} to
988 make it invisible again.
990 @node Selective Display
991 @section Selective Display
992 @c @cindex selective display Duplicates selective-display
994 @dfn{Selective display} refers to a pair of related features for
995 hiding certain lines on the screen.
997 @cindex explicit selective display
998 The first variant, explicit selective display, was designed for use in a Lisp
999 program: it controls which lines are hidden by altering the text. This kind of
1000 hiding is now obsolete; instead you can get the same effect with the
1001 @code{invisible} property (@pxref{Invisible Text}).
1003 In the second variant, the choice of lines to hide is made
1004 automatically based on indentation. This variant is designed to be a
1007 The way you control explicit selective display is by replacing a
1008 newline (control-j) with a carriage return (control-m). The text that
1009 was formerly a line following that newline is now hidden. Strictly
1010 speaking, it is temporarily no longer a line at all, since only
1011 newlines can separate lines; it is now part of the previous line.
1013 Selective display does not directly affect editing commands. For
1014 example, @kbd{C-f} (@code{forward-char}) moves point unhesitatingly
1015 into hidden text. However, the replacement of newline characters with
1016 carriage return characters affects some editing commands. For
1017 example, @code{next-line} skips hidden lines, since it searches only
1018 for newlines. Modes that use selective display can also define
1019 commands that take account of the newlines, or that control which
1020 parts of the text are hidden.
1022 When you write a selectively displayed buffer into a file, all the
1023 control-m's are output as newlines. This means that when you next read
1024 in the file, it looks OK, with nothing hidden. The selective display
1025 effect is seen only within Emacs.
1027 @defvar selective-display
1028 This buffer-local variable enables selective display. This means that
1029 lines, or portions of lines, may be made hidden.
1033 If the value of @code{selective-display} is @code{t}, then the character
1034 control-m marks the start of hidden text; the control-m, and the rest
1035 of the line following it, are not displayed. This is explicit selective
1039 If the value of @code{selective-display} is a positive integer, then
1040 lines that start with more than that many columns of indentation are not
1044 When some portion of a buffer is hidden, the vertical movement
1045 commands operate as if that portion did not exist, allowing a single
1046 @code{next-line} command to skip any number of hidden lines.
1047 However, character movement commands (such as @code{forward-char}) do
1048 not skip the hidden portion, and it is possible (if tricky) to insert
1049 or delete text in an hidden portion.
1051 In the examples below, we show the @emph{display appearance} of the
1052 buffer @code{foo}, which changes with the value of
1053 @code{selective-display}. The @emph{contents} of the buffer do not
1058 (setq selective-display nil)
1061 ---------- Buffer: foo ----------
1068 ---------- Buffer: foo ----------
1072 (setq selective-display 2)
1075 ---------- Buffer: foo ----------
1080 ---------- Buffer: foo ----------
1085 @defopt selective-display-ellipses
1086 If this buffer-local variable is non-@code{nil}, then Emacs displays
1087 @samp{@dots{}} at the end of a line that is followed by hidden text.
1088 This example is a continuation of the previous one.
1092 (setq selective-display-ellipses t)
1095 ---------- Buffer: foo ----------
1100 ---------- Buffer: foo ----------
1104 You can use a display table to substitute other text for the ellipsis
1105 (@samp{@dots{}}). @xref{Display Tables}.
1108 @node Temporary Displays
1109 @section Temporary Displays
1110 @cindex temporary display
1111 @cindex temporary buffer display
1113 Temporary displays are used by Lisp programs to put output into a
1114 buffer and then present it to the user for perusal rather than for
1115 editing. Many help commands use this feature.
1117 @defmac with-output-to-temp-buffer buffer-name body@dots{}
1118 This function executes the forms in @var{body} while arranging to insert
1119 any output they print into the buffer named @var{buffer-name}, which is
1120 first created if necessary, and put into Help mode. (See the similar
1121 form @code{with-temp-buffer-window} below.) Finally, the buffer is
1122 displayed in some window, but that window is not selected.
1124 If the forms in @var{body} do not change the major mode in the output
1125 buffer, so that it is still Help mode at the end of their execution,
1126 then @code{with-output-to-temp-buffer} makes this buffer read-only at
1127 the end, and also scans it for function and variable names to make them
1128 into clickable cross-references. @xref{Docstring hyperlinks, , Tips for
1129 Documentation Strings}, in particular the item on hyperlinks in
1130 documentation strings, for more details.
1132 The string @var{buffer-name} specifies the temporary buffer, which need
1133 not already exist. The argument must be a string, not a buffer. The
1134 buffer is erased initially (with no questions asked), and it is marked
1135 as unmodified after @code{with-output-to-temp-buffer} exits.
1137 @code{with-output-to-temp-buffer} binds @code{standard-output} to the
1138 temporary buffer, then it evaluates the forms in @var{body}. Output
1139 using the Lisp output functions within @var{body} goes by default to
1140 that buffer (but screen display and messages in the echo area, although
1141 they are ``output'' in the general sense of the word, are not affected).
1142 @xref{Output Functions}.
1144 Several hooks are available for customizing the behavior
1145 of this construct; they are listed below.
1147 The value of the last form in @var{body} is returned.
1151 ---------- Buffer: foo ----------
1152 This is the contents of foo.
1153 ---------- Buffer: foo ----------
1157 (with-output-to-temp-buffer "foo"
1159 (print standard-output))
1160 @result{} #<buffer foo>
1162 ---------- Buffer: foo ----------
1168 ---------- Buffer: foo ----------
1173 @defopt temp-buffer-show-function
1174 If this variable is non-@code{nil}, @code{with-output-to-temp-buffer}
1175 calls it as a function to do the job of displaying a help buffer. The
1176 function gets one argument, which is the buffer it should display.
1178 It is a good idea for this function to run @code{temp-buffer-show-hook}
1179 just as @code{with-output-to-temp-buffer} normally would, inside of
1180 @code{save-selected-window} and with the chosen window and buffer
1184 @defvar temp-buffer-setup-hook
1185 This normal hook is run by @code{with-output-to-temp-buffer} before
1186 evaluating @var{body}. When the hook runs, the temporary buffer is
1187 current. This hook is normally set up with a function to put the
1188 buffer in Help mode.
1191 @defvar temp-buffer-show-hook
1192 This normal hook is run by @code{with-output-to-temp-buffer} after
1193 displaying the temporary buffer. When the hook runs, the temporary buffer
1194 is current, and the window it was displayed in is selected.
1197 @defmac with-temp-buffer-window buffer-or-name action quit-function body@dots{}
1198 This macro is similar to @code{with-output-to-temp-buffer}. Like that
1199 construct, it executes @var{body} while arranging to insert any output
1200 it prints into the buffer named @var{buffer-or-name} and displays that
1201 buffer in some window. Unlike @code{with-output-to-temp-buffer},
1202 however, it does not automatically switch that buffer to Help mode.
1204 The argument @var{buffer-or-name} specifies the temporary buffer. It
1205 can be either a buffer, which must already exist, or a string, in which
1206 case a buffer of that name is created, if necessary. The buffer is
1207 marked as unmodified and read-only when @code{with-temp-buffer-window}
1210 This macro does not call @code{temp-buffer-show-function}. Rather, it
1211 passes the @var{action} argument to @code{display-buffer}
1212 (@pxref{Choosing Window}) in order to display the buffer.
1214 The value of the last form in @var{body} is returned, unless the
1215 argument @var{quit-function} is specified. In that case, it is called
1216 with two arguments: the window showing the buffer and the result of
1217 @var{body}. The final return value is then whatever @var{quit-function}
1220 @vindex temp-buffer-window-setup-hook
1221 @vindex temp-buffer-window-show-hook
1222 This macro uses the normal hooks @code{temp-buffer-window-setup-hook}
1223 and @code{temp-buffer-window-show-hook} in place of the analogous hooks
1224 run by @code{with-output-to-temp-buffer}.
1227 The two constructs described next are mostly identical to
1228 @code{with-temp-buffer-window} but differ from it as specified:
1230 @defmac with-current-buffer-window buffer-or-name action quit-function &rest body
1231 This macro is like @code{with-temp-buffer-window} but unlike that makes
1232 the buffer specified by @var{buffer-or-name} current for running
1236 @defmac with-displayed-buffer-window buffer-or-name action quit-function &rest body
1237 This macro is like @code{with-current-buffer-window} but unlike that
1238 displays the buffer specified by @var{buffer-or-name} @emph{before}
1242 A window showing a temporary buffer can be fit to the size of that
1243 buffer using the following mode:
1245 @defopt temp-buffer-resize-mode
1246 When this minor mode is enabled, windows showing a temporary buffer are
1247 automatically resized to fit their buffer's contents.
1249 A window is resized if and only if it has been specially created for the
1250 buffer. In particular, windows that have shown another buffer before
1251 are not resized. By default, this mode uses @code{fit-window-to-buffer}
1252 (@pxref{Resizing Windows}) for resizing. You can specify a different
1253 function by customizing the options @code{temp-buffer-max-height} and
1254 @code{temp-buffer-max-width} below.
1257 @defopt temp-buffer-max-height
1258 This option specifies the maximum height (in lines) of a window
1259 displaying a temporary buffer when @code{temp-buffer-resize-mode} is
1260 enabled. It can also be a function to be called to choose the height
1261 for such a buffer. It gets one argument, the buffer, and should return
1262 a positive integer. At the time the function is called, the window to
1263 be resized is selected.
1266 @defopt temp-buffer-max-width
1267 This option specifies the maximum width of a window (in columns)
1268 displaying a temporary buffer when @code{temp-buffer-resize-mode} is
1269 enabled. It can also be a function to be called to choose the width for
1270 such a buffer. It gets one argument, the buffer, and should return a
1271 positive integer. At the time the function is called, the window to be
1272 resized is selected.
1275 The following function uses the current buffer for temporal display:
1277 @defun momentary-string-display string position &optional char message
1278 This function momentarily displays @var{string} in the current buffer at
1279 @var{position}. It has no effect on the undo list or on the buffer's
1280 modification status.
1282 The momentary display remains until the next input event. If the next
1283 input event is @var{char}, @code{momentary-string-display} ignores it
1284 and returns. Otherwise, that event remains buffered for subsequent use
1285 as input. Thus, typing @var{char} will simply remove the string from
1286 the display, while typing (say) @kbd{C-f} will remove the string from
1287 the display and later (presumably) move point forward. The argument
1288 @var{char} is a space by default.
1290 The return value of @code{momentary-string-display} is not meaningful.
1292 If the string @var{string} does not contain control characters, you can
1293 do the same job in a more general way by creating (and then subsequently
1294 deleting) an overlay with a @code{before-string} property.
1295 @xref{Overlay Properties}.
1297 If @var{message} is non-@code{nil}, it is displayed in the echo area
1298 while @var{string} is displayed in the buffer. If it is @code{nil}, a
1299 default message says to type @var{char} to continue.
1301 In this example, point is initially located at the beginning of the
1306 ---------- Buffer: foo ----------
1307 This is the contents of foo.
1308 @point{}Second line.
1309 ---------- Buffer: foo ----------
1313 (momentary-string-display
1314 "**** Important Message! ****"
1316 "Type RET when done reading")
1321 ---------- Buffer: foo ----------
1322 This is the contents of foo.
1323 **** Important Message! ****Second line.
1324 ---------- Buffer: foo ----------
1326 ---------- Echo Area ----------
1327 Type RET when done reading
1328 ---------- Echo Area ----------
1336 @c FIXME: mention intervals in this section?
1338 You can use @dfn{overlays} to alter the appearance of a buffer's text on
1339 the screen, for the sake of presentation features. An overlay is an
1340 object that belongs to a particular buffer, and has a specified
1341 beginning and end. It also has properties that you can examine and set;
1342 these affect the display of the text within the overlay.
1344 @cindex scalability of overlays
1345 @cindex overlays, scalability
1346 The visual effect of an overlay is the same as of the corresponding
1347 text property (@pxref{Text Properties}). However, due to a different
1348 implementation, overlays generally don't scale well (many operations
1349 take a time that is proportional to the number of overlays in the
1350 buffer). If you need to affect the visual appearance of many portions
1351 in the buffer, we recommend using text properties.
1353 An overlay uses markers to record its beginning and end; thus,
1354 editing the text of the buffer adjusts the beginning and end of each
1355 overlay so that it stays with the text. When you create the overlay,
1356 you can specify whether text inserted at the beginning should be
1357 inside the overlay or outside, and likewise for the end of the overlay.
1360 * Managing Overlays:: Creating and moving overlays.
1361 * Overlay Properties:: How to read and set properties.
1362 What properties do to the screen display.
1363 * Finding Overlays:: Searching for overlays.
1366 @node Managing Overlays
1367 @subsection Managing Overlays
1368 @cindex managing overlays
1369 @cindex overlays, managing
1371 This section describes the functions to create, delete and move
1372 overlays, and to examine their contents. Overlay changes are not
1373 recorded in the buffer's undo list, since the overlays are not
1374 part of the buffer's contents.
1376 @defun overlayp object
1377 This function returns @code{t} if @var{object} is an overlay.
1380 @defun make-overlay start end &optional buffer front-advance rear-advance
1381 This function creates and returns an overlay that belongs to
1382 @var{buffer} and ranges from @var{start} to @var{end}. Both @var{start}
1383 and @var{end} must specify buffer positions; they may be integers or
1384 markers. If @var{buffer} is omitted, the overlay is created in the
1387 @cindex empty overlay
1388 @cindex overlay, empty
1389 An overlay whose @var{start} and @var{end} specify the same buffer
1390 position is known as @dfn{empty}. A non-empty overlay can become
1391 empty if the text between its @var{start} and @var{end} is deleted.
1392 When that happens, the overlay is by default not deleted, but you can
1393 cause it to be deleted by giving it the @samp{evaporate} property
1394 (@pxref{Overlay Properties, evaporate property}).
1396 The arguments @var{front-advance} and @var{rear-advance} specify the
1397 marker insertion type for the start of the overlay and for the end of
1398 the overlay, respectively. @xref{Marker Insertion Types}. If they
1399 are both @code{nil}, the default, then the overlay extends to include
1400 any text inserted at the beginning, but not text inserted at the end.
1401 If @var{front-advance} is non-@code{nil}, text inserted at the
1402 beginning of the overlay is excluded from the overlay. If
1403 @var{rear-advance} is non-@code{nil}, text inserted at the end of the
1404 overlay is included in the overlay.
1407 @defun overlay-start overlay
1408 This function returns the position at which @var{overlay} starts,
1412 @defun overlay-end overlay
1413 This function returns the position at which @var{overlay} ends,
1417 @defun overlay-buffer overlay
1418 This function returns the buffer that @var{overlay} belongs to. It
1419 returns @code{nil} if @var{overlay} has been deleted.
1422 @defun delete-overlay overlay
1423 This function deletes @var{overlay}. The overlay continues to exist as
1424 a Lisp object, and its property list is unchanged, but it ceases to be
1425 attached to the buffer it belonged to, and ceases to have any effect on
1428 A deleted overlay is not permanently disconnected. You can give it a
1429 position in a buffer again by calling @code{move-overlay}.
1432 @defun move-overlay overlay start end &optional buffer
1433 This function moves @var{overlay} to @var{buffer}, and places its bounds
1434 at @var{start} and @var{end}. Both arguments @var{start} and @var{end}
1435 must specify buffer positions; they may be integers or markers.
1437 If @var{buffer} is omitted, @var{overlay} stays in the same buffer it
1438 was already associated with; if @var{overlay} was deleted, it goes into
1441 The return value is @var{overlay}.
1443 This is the only valid way to change the endpoints of an overlay. Do
1444 not try modifying the markers in the overlay by hand, as that fails to
1445 update other vital data structures and can cause some overlays to be
1449 @defun remove-overlays &optional start end name value
1450 This function removes all the overlays between @var{start} and
1451 @var{end} whose property @var{name} has the value @var{value}. It can
1452 move the endpoints of the overlays in the region, or split them.
1454 If @var{name} is omitted or @code{nil}, it means to delete all overlays in
1455 the specified region. If @var{start} and/or @var{end} are omitted or
1456 @code{nil}, that means the beginning and end of the buffer respectively.
1457 Therefore, @code{(remove-overlays)} removes all the overlays in the
1461 @defun copy-overlay overlay
1462 This function returns a copy of @var{overlay}. The copy has the same
1463 endpoints and properties as @var{overlay}. However, the marker
1464 insertion type for the start of the overlay and for the end of the
1465 overlay are set to their default values (@pxref{Marker Insertion
1469 Here are some examples:
1472 ;; @r{Create an overlay.}
1473 (setq foo (make-overlay 1 10))
1474 @result{} #<overlay from 1 to 10 in display.texi>
1479 (overlay-buffer foo)
1480 @result{} #<buffer display.texi>
1481 ;; @r{Give it a property we can check later.}
1482 (overlay-put foo 'happy t)
1484 ;; @r{Verify the property is present.}
1485 (overlay-get foo 'happy)
1487 ;; @r{Move the overlay.}
1488 (move-overlay foo 5 20)
1489 @result{} #<overlay from 5 to 20 in display.texi>
1494 ;; @r{Delete the overlay.}
1495 (delete-overlay foo)
1497 ;; @r{Verify it is deleted.}
1499 @result{} #<overlay in no buffer>
1500 ;; @r{A deleted overlay has no position.}
1505 (overlay-buffer foo)
1507 ;; @r{Undelete the overlay.}
1508 (move-overlay foo 1 20)
1509 @result{} #<overlay from 1 to 20 in display.texi>
1510 ;; @r{Verify the results.}
1515 (overlay-buffer foo)
1516 @result{} #<buffer display.texi>
1517 ;; @r{Moving and deleting the overlay does not change its properties.}
1518 (overlay-get foo 'happy)
1522 Emacs stores the overlays of each buffer in two lists, divided
1523 around an arbitrary center position. One list extends backwards
1524 through the buffer from that center position, and the other extends
1525 forwards from that center position. The center position can be anywhere
1528 @defun overlay-recenter pos
1529 This function recenters the overlays of the current buffer around
1530 position @var{pos}. That makes overlay lookup faster for positions
1531 near @var{pos}, but slower for positions far away from @var{pos}.
1534 A loop that scans the buffer forwards, creating overlays, can run
1535 faster if you do @code{(overlay-recenter (point-max))} first.
1537 @node Overlay Properties
1538 @subsection Overlay Properties
1539 @cindex overlay properties
1541 Overlay properties are like text properties in that the properties that
1542 alter how a character is displayed can come from either source. But in
1543 most respects they are different. @xref{Text Properties}, for comparison.
1545 Text properties are considered a part of the text; overlays and
1546 their properties are specifically considered not to be part of the
1547 text. Thus, copying text between various buffers and strings
1548 preserves text properties, but does not try to preserve overlays.
1549 Changing a buffer's text properties marks the buffer as modified,
1550 while moving an overlay or changing its properties does not. Unlike
1551 text property changes, overlay property changes are not recorded in
1552 the buffer's undo list.
1554 Since more than one overlay can specify a property value for the
1555 same character, Emacs lets you specify a priority value of each
1556 overlay. In case two overlays have the same priority value, and one
1557 is nested in the other, then the inner one will have priority over the
1558 outer one. If neither is nested in the other then you should not make
1559 assumptions about which overlay will prevail.
1561 These functions read and set the properties of an overlay:
1563 @defun overlay-get overlay prop
1564 This function returns the value of property @var{prop} recorded in
1565 @var{overlay}, if any. If @var{overlay} does not record any value for
1566 that property, but it does have a @code{category} property which is a
1567 symbol, that symbol's @var{prop} property is used. Otherwise, the value
1571 @defun overlay-put overlay prop value
1572 This function sets the value of property @var{prop} recorded in
1573 @var{overlay} to @var{value}. It returns @var{value}.
1576 @defun overlay-properties overlay
1577 This returns a copy of the property list of @var{overlay}.
1580 See also the function @code{get-char-property} which checks both
1581 overlay properties and text properties for a given character.
1582 @xref{Examining Properties}.
1584 Many overlay properties have special meanings; here is a table
1589 @kindex priority @r{(overlay property)}
1590 This property's value determines the priority of the overlay.
1591 If you want to specify a priority value, use either @code{nil}
1592 (or zero), or a positive integer. Any other value has undefined behavior.
1594 The priority matters when two or more overlays cover the same
1595 character and both specify the same property; the one whose
1596 @code{priority} value is larger overrides the other. For the
1597 @code{face} property, the higher priority overlay's value does not
1598 completely override the other value; instead, its face attributes
1599 override the face attributes of the lower priority @code{face}
1602 Currently, all overlays take priority over text properties.
1604 Note that Emacs sometimes uses non-numeric priority values for some of
1605 its internal overlays, so do not try to do arithmetic on the
1606 priority of an overlay (unless it is one that you created). If you
1607 need to put overlays in priority order, use the @var{sorted} argument
1608 of @code{overlays-at}. @xref{Finding Overlays}.
1611 @kindex window @r{(overlay property)}
1612 If the @code{window} property is non-@code{nil}, then the overlay
1613 applies only on that window.
1616 @kindex category @r{(overlay property)}
1617 If an overlay has a @code{category} property, we call it the
1618 @dfn{category} of the overlay. It should be a symbol. The properties
1619 of the symbol serve as defaults for the properties of the overlay.
1622 @kindex face @r{(overlay property)}
1623 This property controls the appearance of the text (@pxref{Faces}).
1624 The value of the property can be the following:
1628 A face name (a symbol or string).
1631 An anonymous face: a property list of the form @code{(@var{keyword}
1632 @var{value} @dots{})}, where each @var{keyword} is a face attribute
1633 name and @var{value} is a value for that attribute.
1636 A list of faces. Each list element should be either a face name or an
1637 anonymous face. This specifies a face which is an aggregate of the
1638 attributes of each of the listed faces. Faces occurring earlier in
1639 the list have higher priority.
1642 A cons cell of the form @code{(foreground-color . @var{color-name})}
1643 or @code{(background-color . @var{color-name})}. This specifies the
1644 foreground or background color, similar to @code{(:foreground
1645 @var{color-name})} or @code{(:background @var{color-name})}. This
1646 form is supported for backward compatibility only, and should be
1651 @kindex mouse-face @r{(overlay property)}
1652 This property is used instead of @code{face} when the mouse is within
1653 the range of the overlay. However, Emacs ignores all face attributes
1654 from this property that alter the text size (e.g., @code{:height},
1655 @code{:weight}, and @code{:slant}). Those attributes are always the
1656 same as in the unhighlighted text.
1659 @kindex display @r{(overlay property)}
1660 This property activates various features that change the
1661 way text is displayed. For example, it can make text appear taller
1662 or shorter, higher or lower, wider or narrower, or replaced with an image.
1663 @xref{Display Property}.
1666 @kindex help-echo @r{(overlay property)}
1667 If an overlay has a @code{help-echo} property, then when you move the
1668 mouse onto the text in the overlay, Emacs displays a help string in the
1669 echo area, or in the tooltip window. For details see @ref{Text
1673 @kindex field @r{(overlay property)}
1674 @c Copied from Special Properties.
1675 Consecutive characters with the same @code{field} property constitute a
1676 @emph{field}. Some motion functions including @code{forward-word} and
1677 @code{beginning-of-line} stop moving at a field boundary.
1680 @item modification-hooks
1681 @kindex modification-hooks @r{(overlay property)}
1682 This property's value is a list of functions to be called if any
1683 character within the overlay is changed or if text is inserted strictly
1686 The hook functions are called both before and after each change.
1687 If the functions save the information they receive, and compare notes
1688 between calls, they can determine exactly what change has been made
1691 When called before a change, each function receives four arguments: the
1692 overlay, @code{nil}, and the beginning and end of the text range to be
1695 When called after a change, each function receives five arguments: the
1696 overlay, @code{t}, the beginning and end of the text range just
1697 modified, and the length of the pre-change text replaced by that range.
1698 (For an insertion, the pre-change length is zero; for a deletion, that
1699 length is the number of characters deleted, and the post-change
1700 beginning and end are equal.)
1702 If these functions modify the buffer, they should bind
1703 @code{inhibit-modification-hooks} to @code{t} around doing so, to
1704 avoid confusing the internal mechanism that calls these hooks.
1706 Text properties also support the @code{modification-hooks} property,
1707 but the details are somewhat different (@pxref{Special Properties}).
1709 @item insert-in-front-hooks
1710 @kindex insert-in-front-hooks @r{(overlay property)}
1711 This property's value is a list of functions to be called before and
1712 after inserting text right at the beginning of the overlay. The calling
1713 conventions are the same as for the @code{modification-hooks} functions.
1715 @item insert-behind-hooks
1716 @kindex insert-behind-hooks @r{(overlay property)}
1717 This property's value is a list of functions to be called before and
1718 after inserting text right at the end of the overlay. The calling
1719 conventions are the same as for the @code{modification-hooks} functions.
1722 @kindex invisible @r{(overlay property)}
1723 The @code{invisible} property can make the text in the overlay
1724 invisible, which means that it does not appear on the screen.
1725 @xref{Invisible Text}, for details.
1728 @kindex intangible @r{(overlay property)}
1729 The @code{intangible} property on an overlay works just like the
1730 @code{intangible} text property. It is obsolete. @xref{Special
1731 Properties}, for details.
1733 @item isearch-open-invisible
1734 This property tells incremental search how to make an invisible overlay
1735 visible, permanently, if the final match overlaps it. @xref{Invisible
1738 @item isearch-open-invisible-temporary
1739 This property tells incremental search how to make an invisible overlay
1740 visible, temporarily, during the search. @xref{Invisible Text}.
1743 @kindex before-string @r{(overlay property)}
1744 This property's value is a string to add to the display at the beginning
1745 of the overlay. The string does not appear in the buffer in any
1746 sense---only on the screen.
1749 @kindex after-string @r{(overlay property)}
1750 This property's value is a string to add to the display at the end of
1751 the overlay. The string does not appear in the buffer in any
1752 sense---only on the screen.
1755 This property specifies a display spec to prepend to each
1756 non-continuation line at display-time. @xref{Truncation}.
1759 This property specifies a display spec to prepend to each continuation
1760 line at display-time. @xref{Truncation}.
1763 @kindex evaporate @r{(overlay property)}
1764 If this property is non-@code{nil}, the overlay is deleted automatically
1765 if it becomes empty (i.e., if its length becomes zero). If you give
1766 an empty overlay (@pxref{Managing Overlays, empty overlay}) a
1767 non-@code{nil} @code{evaporate} property, that deletes it immediately.
1768 Note that, unless an overlay has this property, it will not be deleted
1769 when the text between its starting and ending positions is deleted
1773 @cindex keymap of character (and overlays)
1774 @kindex keymap @r{(overlay property)}
1775 If this property is non-@code{nil}, it specifies a keymap for a portion of the
1776 text. This keymap is used when the character after point is within the
1777 overlay, and takes precedence over most other keymaps. @xref{Active Keymaps}.
1780 @kindex local-map @r{(overlay property)}
1781 The @code{local-map} property is similar to @code{keymap} but replaces the
1782 buffer's local map rather than augmenting existing keymaps. This also means it
1783 has lower precedence than minor mode keymaps.
1786 The @code{keymap} and @code{local-map} properties do not affect a
1787 string displayed by the @code{before-string}, @code{after-string}, or
1788 @code{display} properties. This is only relevant for mouse clicks and
1789 other mouse events that fall on the string, since point is never on
1790 the string. To bind special mouse events for the string, assign it a
1791 @code{keymap} or @code{local-map} text property. @xref{Special
1794 @node Finding Overlays
1795 @subsection Searching for Overlays
1796 @cindex searching for overlays
1797 @cindex overlays, searching for
1799 @defun overlays-at pos &optional sorted
1800 This function returns a list of all the overlays that cover the character at
1801 position @var{pos} in the current buffer. If @var{sorted} is non-@code{nil},
1802 the list is in decreasing order of priority, otherwise it is in no particular
1803 order. An overlay contains position @var{pos} if it begins at or before
1804 @var{pos}, and ends after @var{pos}.
1806 To illustrate usage, here is a Lisp function that returns a list of the
1807 overlays that specify property @var{prop} for the character at point:
1810 (defun find-overlays-specifying (prop)
1811 (let ((overlays (overlays-at (point)))
1814 (let ((overlay (car overlays)))
1815 (if (overlay-get overlay prop)
1816 (setq found (cons overlay found))))
1817 (setq overlays (cdr overlays)))
1822 @defun overlays-in beg end
1823 This function returns a list of the overlays that overlap the region
1824 @var{beg} through @var{end}. An overlay overlaps with a region if it
1825 contains one or more characters in the region; empty overlays
1826 (@pxref{Managing Overlays, empty overlay}) overlap if they are at
1827 @var{beg}, strictly between @var{beg} and @var{end}, or at @var{end}
1828 when @var{end} denotes the position at the end of the buffer.
1831 @defun next-overlay-change pos
1832 This function returns the buffer position of the next beginning or end
1833 of an overlay, after @var{pos}. If there is none, it returns
1837 @defun previous-overlay-change pos
1838 This function returns the buffer position of the previous beginning or
1839 end of an overlay, before @var{pos}. If there is none, it returns
1843 As an example, here's a simplified (and inefficient) version of the
1844 primitive function @code{next-single-char-property-change}
1845 (@pxref{Property Search}). It searches forward from position
1846 @var{pos} for the next position where the value of a given property
1847 @code{prop}, as obtained from either overlays or text properties,
1851 (defun next-single-char-property-change (position prop)
1853 (goto-char position)
1854 (let ((propval (get-char-property (point) prop)))
1855 (while (and (not (eobp))
1856 (eq (get-char-property (point) prop) propval))
1857 (goto-char (min (next-overlay-change (point))
1858 (next-single-property-change (point) prop)))))
1862 @node Size of Displayed Text
1863 @section Size of Displayed Text
1864 @cindex size of text on display
1865 @cindex character width on display
1867 Since not all characters have the same width, these functions let you
1868 check the width of a character. @xref{Primitive Indent}, and
1869 @ref{Screen Lines}, for related functions.
1871 @defun char-width char
1872 This function returns the width in columns of the character
1873 @var{char}, if it were displayed in the current buffer (i.e., taking
1874 into account the buffer's display table, if any; @pxref{Display
1875 Tables}). The width of a tab character is usually @code{tab-width}
1876 (@pxref{Usual Display}).
1879 @defun string-width string
1880 This function returns the width in columns of the string @var{string},
1881 if it were displayed in the current buffer and the selected window.
1884 @defun truncate-string-to-width string width &optional start-column padding ellipsis
1885 This function returns the part of @var{string} that fits within
1886 @var{width} columns, as a new string.
1888 If @var{string} does not reach @var{width}, then the result ends where
1889 @var{string} ends. If one multi-column character in @var{string}
1890 extends across the column @var{width}, that character is not included in
1891 the result. Thus, the result can fall short of @var{width} but cannot
1894 The optional argument @var{start-column} specifies the starting column.
1895 If this is non-@code{nil}, then the first @var{start-column} columns of
1896 the string are omitted from the value. If one multi-column character in
1897 @var{string} extends across the column @var{start-column}, that
1898 character is not included.
1900 The optional argument @var{padding}, if non-@code{nil}, is a padding
1901 character added at the beginning and end of the result string, to extend
1902 it to exactly @var{width} columns. The padding character is used at the
1903 end of the result if it falls short of @var{width}. It is also used at
1904 the beginning of the result if one multi-column character in
1905 @var{string} extends across the column @var{start-column}.
1907 @vindex truncate-string-ellipsis
1908 If @var{ellipsis} is non-@code{nil}, it should be a string which will
1909 replace the end of @var{string} (including any padding) if it extends
1910 beyond @var{width}, unless the display width of @var{string} is equal
1911 to or less than the display width of @var{ellipsis}. If
1912 @var{ellipsis} is non-@code{nil} and not a string, it stands for
1913 the value of the variable @code{truncate-string-ellipsis}.
1916 (truncate-string-to-width "\tab\t" 12 4)
1918 (truncate-string-to-width "\tab\t" 12 4 ?\s)
1923 The following function returns the size in pixels of text as if it were
1924 displayed in a given window. This function is used by
1925 @code{fit-window-to-buffer} and @code{fit-frame-to-buffer}
1926 (@pxref{Resizing Windows}) to make a window exactly as large as the text
1929 @defun window-text-pixel-size &optional window from to x-limit y-limit mode-and-header-line
1930 This function returns the size of the text of @var{window}'s buffer in
1931 pixels. @var{window} must be a live window and defaults to the selected
1932 one. The return value is a cons of the maximum pixel-width of any text
1933 line and the maximum pixel-height of all text lines.
1935 The optional argument @var{from}, if non-@code{nil}, specifies the first
1936 text position to consider and defaults to the minimum accessible
1937 position of the buffer. If @var{from} is @code{t}, it uses the minimum
1938 accessible position that is not a newline character. The optional
1939 argument @var{to}, if non-@code{nil}, specifies the last text position
1940 to consider and defaults to the maximum accessible position of the
1941 buffer. If @var{to} is @code{t}, it uses the maximum accessible
1942 position that is not a newline character.
1944 The optional argument @var{x-limit}, if non-@code{nil}, specifies the
1945 maximum pixel-width that can be returned. @var{x-limit} @code{nil} or
1946 omitted, means to use the pixel-width of @var{window}'s body
1947 (@pxref{Window Sizes}); this is useful when the caller does not intend
1948 to change the width of @var{window}. Otherwise, the caller should
1949 specify here the maximum width @var{window}'s body may assume. Text
1950 whose x-coordinate is beyond @var{x-limit} is ignored. Since
1951 calculating the width of long lines can take some time, it's always a
1952 good idea to make this argument as small as needed; in particular, if
1953 the buffer might contain long lines that will be truncated anyway.
1955 The optional argument @var{y-limit}, if non-@code{nil}, specifies the
1956 maximum pixel-height that can be returned. Text lines whose
1957 y-coordinate is beyond @var{y-limit} are ignored. Since calculating the
1958 pixel-height of a large buffer can take some time, it makes sense to
1959 specify this argument; in particular, if the caller does not know the
1962 The optional argument @var{mode-and-header-line} @code{nil} or omitted
1963 means to not include the height of the mode- or header-line of
1964 @var{window} in the return value. If it is either the symbol
1965 @code{mode-line} or @code{header-line}, include only the height of that
1966 line, if present, in the return value. If it is @code{t}, include the
1967 height of both, if present, in the return value.
1972 @section Line Height
1974 @cindex height of a line
1976 The total height of each display line consists of the height of the
1977 contents of the line, plus optional additional vertical line spacing
1978 above or below the display line.
1980 The height of the line contents is the maximum height of any character
1981 or image on that display line, including the final newline if there is
1982 one. (A display line that is continued doesn't include a final
1983 newline.) That is the default line height, if you do nothing to specify
1984 a greater height. (In the most common case, this equals the height of
1985 the corresponding frame's default font, see @ref{Frame Font}.)
1987 There are several ways to explicitly specify a larger line height,
1988 either by specifying an absolute height for the display line, or by
1989 specifying vertical space. However, no matter what you specify, the
1990 actual line height can never be less than the default.
1992 @kindex line-height @r{(text property)}
1993 A newline can have a @code{line-height} text or overlay property
1994 that controls the total height of the display line ending in that
1997 If the property value is @code{t}, the newline character has no
1998 effect on the displayed height of the line---the visible contents
1999 alone determine the height. The @code{line-spacing} property,
2000 described below, is also ignored in this case. This is useful for
2001 tiling small images (or image slices) without adding blank areas
2004 If the property value is a list of the form @code{(@var{height}
2005 @var{total})}, that adds extra space @emph{below} the display line.
2006 First Emacs uses @var{height} as a height spec to control extra space
2007 @emph{above} the line; then it adds enough space @emph{below} the line
2008 to bring the total line height up to @var{total}. In this case, any
2009 value of @code{line-spacing} property for the newline is ignored.
2012 Any other kind of property value is a height spec, which translates
2013 into a number---the specified line height. There are several ways to
2014 write a height spec; here's how each of them translates into a number:
2018 If the height spec is a positive integer, the height value is that integer.
2020 If the height spec is a float, @var{float}, the numeric height value
2021 is @var{float} times the frame's default line height.
2022 @item (@var{face} . @var{ratio})
2023 If the height spec is a cons of the format shown, the numeric height
2024 is @var{ratio} times the height of face @var{face}. @var{ratio} can
2025 be any type of number, or @code{nil} which means a ratio of 1.
2026 If @var{face} is @code{t}, it refers to the current face.
2027 @item (nil . @var{ratio})
2028 If the height spec is a cons of the format shown, the numeric height
2029 is @var{ratio} times the height of the contents of the line.
2032 Thus, any valid height spec determines the height in pixels, one way
2033 or another. If the line contents' height is less than that, Emacs
2034 adds extra vertical space above the line to achieve the specified
2037 If you don't specify the @code{line-height} property, the line's
2038 height consists of the contents' height plus the line spacing.
2039 There are several ways to specify the line spacing for different
2040 parts of Emacs text.
2042 On graphical terminals, you can specify the line spacing for all
2043 lines in a frame, using the @code{line-spacing} frame parameter
2044 (@pxref{Layout Parameters}). However, if the default value of
2045 @code{line-spacing} is non-@code{nil}, it overrides the
2046 frame's @code{line-spacing} parameter. An integer specifies the
2047 number of pixels put below lines. A floating-point number specifies
2048 the spacing relative to the frame's default line height.
2050 @vindex line-spacing
2051 You can specify the line spacing for all lines in a buffer via the
2052 buffer-local @code{line-spacing} variable. An integer specifies
2053 the number of pixels put below lines. A floating-point number
2054 specifies the spacing relative to the default frame line height. This
2055 overrides line spacings specified for the frame.
2057 @kindex line-spacing @r{(text property)}
2058 Finally, a newline can have a @code{line-spacing} text or overlay
2059 property that can enlarge the default frame line spacing and the
2060 buffer local @code{line-spacing} variable: if its value is larger than
2061 the buffer or frame defaults, that larger value is used instead, for
2062 the display line ending in that newline.
2064 One way or another, these mechanisms specify a Lisp value for the
2065 spacing of each line. The value is a height spec, and it translates
2066 into a Lisp value as described above. However, in this case the
2067 numeric height value specifies the line spacing, rather than the line
2070 On text terminals, the line spacing cannot be altered.
2076 A @dfn{face} is a collection of graphical attributes for displaying
2077 text: font, foreground color, background color, optional underlining,
2078 etc. Faces control how Emacs displays text in buffers, as well as
2079 other parts of the frame such as the mode line.
2081 @cindex anonymous face
2082 One way to represent a face is as a property list of attributes,
2083 like @code{(:foreground "red" :weight bold)}. Such a list is called
2084 an @dfn{anonymous face}. For example, you can assign an anonymous
2085 face as the value of the @code{face} text property, and Emacs will
2086 display the underlying text with the specified attributes.
2087 @xref{Special Properties}.
2090 More commonly, a face is referred to via a @dfn{face name}: a Lisp
2091 symbol associated with a set of face attributes@footnote{For backward
2092 compatibility, you can also use a string to specify a face name; that
2093 is equivalent to a Lisp symbol with the same name.}. Named faces are
2094 defined using the @code{defface} macro (@pxref{Defining Faces}).
2095 Emacs comes with several standard named faces (@pxref{Basic Faces}).
2097 Many parts of Emacs required named faces, and do not accept
2098 anonymous faces. These include the functions documented in
2099 @ref{Attribute Functions}, and the variable @code{font-lock-keywords}
2100 (@pxref{Search-based Fontification}). Unless otherwise stated, we
2101 will use the term @dfn{face} to refer only to named faces.
2104 This function returns a non-@code{nil} value if @var{object} is a
2105 named face: a Lisp symbol or string which serves as a face name.
2106 Otherwise, it returns @code{nil}.
2110 * Face Attributes:: What is in a face?
2111 * Defining Faces:: How to define a face.
2112 * Attribute Functions:: Functions to examine and set face attributes.
2113 * Displaying Faces:: How Emacs combines the faces specified for a character.
2114 * Face Remapping:: Remapping faces to alternative definitions.
2115 * Face Functions:: How to define and examine faces.
2116 * Auto Faces:: Hook for automatic face assignment.
2117 * Basic Faces:: Faces that are defined by default.
2118 * Font Selection:: Finding the best available font for a face.
2119 * Font Lookup:: Looking up the names of available fonts
2120 and information about them.
2121 * Fontsets:: A fontset is a collection of fonts
2122 that handle a range of character sets.
2123 * Low-Level Font:: Lisp representation for character display fonts.
2126 @node Face Attributes
2127 @subsection Face Attributes
2128 @cindex face attributes
2130 @dfn{Face attributes} determine the visual appearance of a face.
2131 The following table lists all the face attributes, their possible
2132 values, and their effects.
2134 Apart from the values given below, each face attribute can have the
2135 value @code{unspecified}. This special value means that the face
2136 doesn't specify that attribute directly. An @code{unspecified}
2137 attribute tells Emacs to refer instead to a parent face (see the
2138 description @code{:inherit} attribute below); or, failing that, to an
2139 underlying face (@pxref{Displaying Faces}). The @code{default} face
2140 must specify all attributes.
2142 Some of these attributes are meaningful only on certain kinds of
2143 displays. If your display cannot handle a certain attribute, the
2144 attribute is ignored.
2148 Font family or fontset (a string). @xref{Fonts,,, emacs, The GNU
2149 Emacs Manual}, for more information about font families. The function
2150 @code{font-family-list} (see below) returns a list of available family
2151 names. @xref{Fontsets}, for information about fontsets.
2154 The name of the @dfn{font foundry} for the font family specified by
2155 the @code{:family} attribute (a string). @xref{Fonts,,, emacs, The
2159 Relative character width. This should be one of the symbols
2160 @code{ultra-condensed}, @code{extra-condensed}, @code{condensed},
2161 @code{semi-condensed}, @code{normal}, @code{semi-expanded},
2162 @code{expanded}, @code{extra-expanded}, or @code{ultra-expanded}.
2165 The height of the font. In the simplest case, this is an integer in
2166 units of 1/10 point.
2168 The value can also be floating point or a function, which
2169 specifies the height relative to an @dfn{underlying face}
2170 (@pxref{Displaying Faces}). A floating-point value
2171 specifies the amount by which to scale the height of the
2172 underlying face. A function value is called
2173 with one argument, the height of the underlying face, and returns the
2174 height of the new face. If the function is passed an integer
2175 argument, it must return an integer.
2177 The height of the default face must be specified using an integer;
2178 floating point and function values are not allowed.
2181 Font weight---one of the symbols (from densest to faintest)
2182 @code{ultra-bold}, @code{extra-bold}, @code{bold}, @code{semi-bold},
2183 @code{normal}, @code{semi-light}, @code{light}, @code{extra-light}, or
2184 @code{ultra-light}. On text terminals which support
2185 variable-brightness text, any weight greater than normal is displayed
2186 as extra bright, and any weight less than normal is displayed as
2191 Font slant---one of the symbols @code{italic}, @code{oblique},
2192 @code{normal}, @code{reverse-italic}, or @code{reverse-oblique}. On
2193 text terminals that support variable-brightness text, slanted text is
2194 displayed as half-bright.
2197 Foreground color, a string. The value can be a system-defined color
2198 name, or a hexadecimal color specification. @xref{Color Names}. On
2199 black-and-white displays, certain shades of gray are implemented by
2202 @item :distant-foreground
2203 Alternative foreground color, a string. This is like @code{:foreground}
2204 but the color is only used as a foreground when the background color is
2205 near to the foreground that would have been used. This is useful for
2206 example when marking text (i.e., the region face). If the text has a foreground
2207 that is visible with the region face, that foreground is used.
2208 If the foreground is near the region face background,
2209 @code{:distant-foreground} is used instead so the text is readable.
2212 Background color, a string. The value can be a system-defined color
2213 name, or a hexadecimal color specification. @xref{Color Names}.
2215 @cindex underlined text
2217 Whether or not characters should be underlined, and in what
2218 way. The possible values of the @code{:underline} attribute are:
2225 Underline with the foreground color of the face.
2228 Underline in color @var{color}, a string specifying a color.
2230 @item @code{(:color @var{color} :style @var{style})}
2231 @var{color} is either a string, or the symbol @code{foreground-color},
2232 meaning the foreground color of the face. Omitting the attribute
2233 @code{:color} means to use the foreground color of the face.
2234 @var{style} should be a symbol @code{line} or @code{wave}, meaning to
2235 use a straight or wavy line. Omitting the attribute @code{:style}
2236 means to use a straight line.
2239 @cindex overlined text
2241 Whether or not characters should be overlined, and in what color.
2242 If the value is @code{t}, overlining uses the foreground color of the
2243 face. If the value is a string, overlining uses that color. The
2244 value @code{nil} means do not overline.
2246 @cindex strike-through text
2247 @item :strike-through
2248 Whether or not characters should be strike-through, and in what
2249 color. The value is used like that of @code{:overline}.
2254 Whether or not a box should be drawn around characters, its color, the
2255 width of the box lines, and 3D appearance. Here are the possible
2256 values of the @code{:box} attribute, and what they mean:
2263 Draw a box with lines of width 1, in the foreground color.
2266 Draw a box with lines of width 1, in color @var{color}.
2268 @item @code{(:line-width @var{width} :color @var{color} :style @var{style})}
2269 This way you can explicitly specify all aspects of the box. The value
2270 @var{width} specifies the width of the lines to draw; it defaults to
2271 1. A negative width @var{-n} means to draw a line of width @var{n}
2272 that occupies the space of the underlying text, thus avoiding any
2273 increase in the character height or width.
2275 The value @var{color} specifies the color to draw with. The default is
2276 the foreground color of the face for simple boxes, and the background
2277 color of the face for 3D boxes.
2279 The value @var{style} specifies whether to draw a 3D box. If it is
2280 @code{released-button}, the box looks like a 3D button that is not being
2281 pressed. If it is @code{pressed-button}, the box looks like a 3D button
2282 that is being pressed. If it is @code{nil} or omitted, a plain 2D box
2286 @item :inverse-video
2287 Whether or not characters should be displayed in inverse video. The
2288 value should be @code{t} (yes) or @code{nil} (no).
2291 The background stipple, a bitmap.
2293 The value can be a string; that should be the name of a file containing
2294 external-format X bitmap data. The file is found in the directories
2295 listed in the variable @code{x-bitmap-file-path}.
2297 Alternatively, the value can specify the bitmap directly, with a list
2298 of the form @code{(@var{width} @var{height} @var{data})}. Here,
2299 @var{width} and @var{height} specify the size in pixels, and
2300 @var{data} is a string containing the raw bits of the bitmap, row by
2301 row. Each row occupies @math{(@var{width} + 7) / 8} consecutive bytes
2302 in the string (which should be a unibyte string for best results).
2303 This means that each row always occupies at least one whole byte.
2305 If the value is @code{nil}, that means use no stipple pattern.
2307 Normally you do not need to set the stipple attribute, because it is
2308 used automatically to handle certain shades of gray.
2311 The font used to display the face. Its value should be a font object.
2312 @xref{Low-Level Font}, for information about font objects, font specs,
2315 When specifying this attribute using @code{set-face-attribute}
2316 (@pxref{Attribute Functions}), you may also supply a font spec, a font
2317 entity, or a string. Emacs converts such values to an appropriate
2318 font object, and stores that font object as the actual attribute
2319 value. If you specify a string, the contents of the string should be
2320 a font name (@pxref{Fonts,,, emacs, The GNU Emacs Manual}); if the
2321 font name is an XLFD containing wildcards, Emacs chooses the first
2322 font matching those wildcards. Specifying this attribute also changes
2323 the values of the @code{:family}, @code{:foundry}, @code{:width},
2324 @code{:height}, @code{:weight}, and @code{:slant} attributes.
2326 @cindex inheritance, for faces
2328 The name of a face from which to inherit attributes, or a list of face
2329 names. Attributes from inherited faces are merged into the face like
2330 an underlying face would be, with higher priority than underlying
2331 faces (@pxref{Displaying Faces}). If a list of faces is used,
2332 attributes from faces earlier in the list override those from later
2336 @defun font-family-list &optional frame
2337 This function returns a list of available font family names. The
2338 optional argument @var{frame} specifies the frame on which the text is
2339 to be displayed; if it is @code{nil}, the selected frame is used.
2342 @defopt underline-minimum-offset
2343 This variable specifies the minimum distance between the baseline and
2344 the underline, in pixels, when displaying underlined text.
2347 @defopt x-bitmap-file-path
2348 This variable specifies a list of directories for searching
2349 for bitmap files, for the @code{:stipple} attribute.
2352 @defun bitmap-spec-p object
2353 This returns @code{t} if @var{object} is a valid bitmap specification,
2354 suitable for use with @code{:stipple} (see above). It returns
2355 @code{nil} otherwise.
2358 @node Defining Faces
2359 @subsection Defining Faces
2360 @cindex defining faces
2363 The usual way to define a face is through the @code{defface} macro.
2364 This macro associates a face name (a symbol) with a default @dfn{face
2365 spec}. A face spec is a construct which specifies what attributes a
2366 face should have on any given terminal; for example, a face spec might
2367 specify one foreground color on high-color terminals, and a different
2368 foreground color on low-color terminals.
2370 People are sometimes tempted to create a variable whose value is a
2371 face name. In the vast majority of cases, this is not necessary; the
2372 usual procedure is to define a face with @code{defface}, and then use
2375 @defmac defface face spec doc [keyword value]@dots{}
2376 This macro declares @var{face} as a named face whose default face spec
2377 is given by @var{spec}. You should not quote the symbol @var{face},
2378 and it should not end in @samp{-face} (that would be redundant). The
2379 argument @var{doc} is a documentation string for the face. The
2380 additional @var{keyword} arguments have the same meanings as in
2381 @code{defgroup} and @code{defcustom} (@pxref{Common Keywords}).
2383 If @var{face} already has a default face spec, this macro does
2386 The default face spec determines @var{face}'s appearance when no
2387 customizations are in effect (@pxref{Customization}). If @var{face}
2388 has already been customized (via Custom themes or via customizations
2389 read from the init file), its appearance is determined by the custom
2390 face spec(s), which override the default face spec @var{spec}.
2391 However, if the customizations are subsequently removed, the
2392 appearance of @var{face} will again be determined by its default face
2395 As an exception, if you evaluate a @code{defface} form with
2396 @kbd{C-M-x} in Emacs Lisp mode (@code{eval-defun}), a special feature
2397 of @code{eval-defun} overrides any custom face specs on the face,
2398 causing the face to reflect exactly what the @code{defface} says.
2400 The @var{spec} argument is a @dfn{face spec}, which states how the
2401 face should appear on different kinds of terminals. It should be an
2402 alist whose elements each have the form
2405 (@var{display} . @var{plist})
2409 @var{display} specifies a class of terminals (see below). @var{plist}
2410 is a property list of face attributes and their values, specifying how
2411 the face appears on such terminals. For backward compatibility, you
2412 can also write an element as @code{(@var{display} @var{plist})}.
2414 The @var{display} part of an element of @var{spec} determines which
2415 terminals the element matches. If more than one element of @var{spec}
2416 matches a given terminal, the first element that matches is the one
2417 used for that terminal. There are three possibilities for
2421 @item @code{default}
2422 This element of @var{spec} doesn't match any terminal; instead, it
2423 specifies defaults that apply to all terminals. This element, if
2424 used, must be the first element of @var{spec}. Each of the following
2425 elements can override any or all of these defaults.
2428 This element of @var{spec} matches all terminals. Therefore, any
2429 subsequent elements of @var{spec} are never used. Normally @code{t}
2430 is used in the last (or only) element of @var{spec}.
2433 If @var{display} is a list, each element should have the form
2434 @code{(@var{characteristic} @var{value}@dots{})}. Here
2435 @var{characteristic} specifies a way of classifying terminals, and the
2436 @var{value}s are possible classifications which @var{display} should
2437 apply to. Here are the possible values of @var{characteristic}:
2441 The kind of window system the terminal uses---either @code{graphic}
2442 (any graphics-capable display), @code{x}, @code{pc} (for the MS-DOS
2443 console), @code{w32} (for MS Windows 9X/NT/2K/XP), or @code{tty} (a
2444 non-graphics-capable display). @xref{Window Systems, window-system}.
2447 What kinds of colors the terminal supports---either @code{color},
2448 @code{grayscale}, or @code{mono}.
2451 The kind of background---either @code{light} or @code{dark}.
2454 An integer that represents the minimum number of colors the terminal
2455 should support. This matches a terminal if its
2456 @code{display-color-cells} value is at least the specified integer.
2459 Whether or not the terminal can display the face attributes given in
2460 @var{value}@dots{} (@pxref{Face Attributes}). @xref{Display Face
2461 Attribute Testing}, for more information on exactly how this testing
2465 If an element of @var{display} specifies more than one @var{value} for
2466 a given @var{characteristic}, any of those values is acceptable. If
2467 @var{display} has more than one element, each element should specify a
2468 different @var{characteristic}; then @emph{each} characteristic of the
2469 terminal must match one of the @var{value}s specified for it in
2474 For example, here's the definition of the standard face
2479 '((((class color) (min-colors 88) (background light))
2480 :background "darkseagreen2")
2481 (((class color) (min-colors 88) (background dark))
2482 :background "darkolivegreen")
2483 (((class color) (min-colors 16) (background light))
2484 :background "darkseagreen2")
2485 (((class color) (min-colors 16) (background dark))
2486 :background "darkolivegreen")
2487 (((class color) (min-colors 8))
2488 :background "green" :foreground "black")
2489 (t :inverse-video t))
2490 "Basic face for highlighting."
2491 :group 'basic-faces)
2494 Internally, Emacs stores each face's default spec in its
2495 @code{face-defface-spec} symbol property (@pxref{Symbol Properties}).
2496 The @code{saved-face} property stores any face spec saved by the user
2497 using the customization buffer; the @code{customized-face} property
2498 stores the face spec customized for the current session, but not
2499 saved; and the @code{theme-face} property stores an alist associating
2500 the active customization settings and Custom themes with the face
2501 specs for that face. The face's documentation string is stored in the
2502 @code{face-documentation} property.
2504 Normally, a face is declared just once, using @code{defface}, and
2505 any further changes to its appearance are applied using the Customize
2506 framework (e.g., via the Customize user interface or via the
2507 @code{custom-set-faces} function; @pxref{Applying Customizations}), or
2508 by face remapping (@pxref{Face Remapping}). In the rare event that
2509 you need to change a face spec directly from Lisp, you can use the
2510 @code{face-spec-set} function.
2512 @defun face-spec-set face spec &optional spec-type
2513 This function applies @var{spec} as a face spec for @code{face}.
2514 @var{spec} should be a face spec, as described in the above
2515 documentation for @code{defface}.
2517 This function also defines @var{face} as a valid face name if it is
2518 not already one, and (re)calculates its attributes on existing frames.
2520 @cindex override spec @r{(for a face)}
2521 The argument @var{spec-type} determines which spec to set. If it is
2522 @code{nil} or @code{face-override-spec}, this function sets the
2523 @dfn{override spec}, which overrides over all other face specs on
2524 @var{face}. If it is @code{customized-face} or @code{saved-face},
2525 this function sets the customized spec or the saved custom spec. If
2526 it is @code{face-defface-spec}, this function sets the default face
2527 spec (the same one set by @code{defface}). If it is @code{reset},
2528 this function clears out all customization specs and override specs
2529 from @var{face} (in this case, the value of @var{spec} is ignored).
2530 Any other value of @var{spec-type} is reserved for internal use.
2533 @node Attribute Functions
2534 @subsection Face Attribute Functions
2535 @cindex face attributes, access and modification
2537 This section describes functions for directly accessing and
2538 modifying the attributes of a named face.
2540 @defun face-attribute face attribute &optional frame inherit
2541 This function returns the value of the @var{attribute} attribute for
2542 @var{face} on @var{frame}.
2544 If @var{frame} is @code{nil}, that means the selected frame
2545 (@pxref{Input Focus}). If @var{frame} is @code{t}, this function
2546 returns the value of the specified attribute for newly-created frames
2547 (this is normally @code{unspecified}, unless you have specified some
2548 value using @code{set-face-attribute}; see below).
2550 If @var{inherit} is @code{nil}, only attributes directly defined by
2551 @var{face} are considered, so the return value may be
2552 @code{unspecified}, or a relative value. If @var{inherit} is
2553 non-@code{nil}, @var{face}'s definition of @var{attribute} is merged
2554 with the faces specified by its @code{:inherit} attribute; however the
2555 return value may still be @code{unspecified} or relative. If
2556 @var{inherit} is a face or a list of faces, then the result is further
2557 merged with that face (or faces), until it becomes specified and
2560 To ensure that the return value is always specified and absolute, use
2561 a value of @code{default} for @var{inherit}; this will resolve any
2562 unspecified or relative values by merging with the @code{default} face
2563 (which is always completely specified).
2568 (face-attribute 'bold :weight)
2573 @c FIXME: Add an index for "relative face attribute", maybe here? --xfq
2574 @defun face-attribute-relative-p attribute value
2575 This function returns non-@code{nil} if @var{value}, when used as the
2576 value of the face attribute @var{attribute}, is relative. This means
2577 it would modify, rather than completely override, any value that comes
2578 from a subsequent face in the face list or that is inherited from
2581 @code{unspecified} is a relative value for all attributes. For
2582 @code{:height}, floating point and function values are also relative.
2587 (face-attribute-relative-p :height 2.0)
2592 @defun face-all-attributes face &optional frame
2593 This function returns an alist of attributes of @var{face}. The
2594 elements of the result are name-value pairs of the form
2595 @w{@code{(@var{attr-name} . @var{attr-value})}}. Optional argument
2596 @var{frame} specifies the frame whose definition of @var{face} to
2597 return; if omitted or @code{nil}, the returned value describes the
2598 default attributes of @var{face} for newly created frames.
2601 @defun merge-face-attribute attribute value1 value2
2602 If @var{value1} is a relative value for the face attribute
2603 @var{attribute}, returns it merged with the underlying value
2604 @var{value2}; otherwise, if @var{value1} is an absolute value for the
2605 face attribute @var{attribute}, returns @var{value1} unchanged.
2608 Normally, Emacs uses the face specs of each face to automatically
2609 calculate its attributes on each frame (@pxref{Defining Faces}). The
2610 function @code{set-face-attribute} can override this calculation by
2611 directly assigning attributes to a face, either on a specific frame or
2612 for all frames. This function is mostly intended for internal usage.
2614 @defun set-face-attribute face frame &rest arguments
2615 This function sets one or more attributes of @var{face} for
2616 @var{frame}. The attributes specifies in this way override the face
2617 spec(s) belonging to @var{face}.
2619 The extra arguments @var{arguments} specify the attributes to set, and
2620 the values for them. They should consist of alternating attribute
2621 names (such as @code{:family} or @code{:underline}) and values. Thus,
2624 (set-face-attribute 'foo nil :weight 'bold :slant 'italic)
2628 sets the attribute @code{:weight} to @code{bold} and the attribute
2629 @code{:slant} to @code{italic}.
2632 If @var{frame} is @code{t}, this function sets the default attributes
2633 for newly created frames. If @var{frame} is @code{nil}, this function
2634 sets the attributes for all existing frames, as well as for newly
2638 The following commands and functions mostly provide compatibility
2639 with old versions of Emacs. They work by calling
2640 @code{set-face-attribute}. Values of @code{t} and @code{nil} for
2641 their @var{frame} argument are handled just like
2642 @code{set-face-attribute} and @code{face-attribute}. The commands
2643 read their arguments using the minibuffer, if called interactively.
2645 @deffn Command set-face-foreground face color &optional frame
2646 @deffnx Command set-face-background face color &optional frame
2647 These set the @code{:foreground} attribute (or @code{:background}
2648 attribute, respectively) of @var{face} to @var{color}.
2651 @deffn Command set-face-stipple face pattern &optional frame
2652 This sets the @code{:stipple} attribute of @var{face} to
2656 @deffn Command set-face-font face font &optional frame
2657 This sets the @code{:font} attribute of @var{face} to @var{font}.
2660 @defun set-face-bold face bold-p &optional frame
2661 This sets the @code{:weight} attribute of @var{face} to @var{normal}
2662 if @var{bold-p} is @code{nil}, and to @var{bold} otherwise.
2665 @defun set-face-italic face italic-p &optional frame
2666 This sets the @code{:slant} attribute of @var{face} to @var{normal} if
2667 @var{italic-p} is @code{nil}, and to @var{italic} otherwise.
2670 @defun set-face-underline face underline &optional frame
2671 This sets the @code{:underline} attribute of @var{face} to
2675 @defun set-face-inverse-video face inverse-video-p &optional frame
2676 This sets the @code{:inverse-video} attribute of @var{face} to
2677 @var{inverse-video-p}.
2680 @deffn Command invert-face face &optional frame
2681 This swaps the foreground and background colors of face @var{face}.
2684 The following functions examine the attributes of a face. They
2685 mostly provide compatibility with old versions of Emacs. If you don't
2686 specify @var{frame}, they refer to the selected frame; @code{t} refers
2687 to the default data for new frames. They return @code{unspecified} if
2688 the face doesn't define any value for that attribute. If
2689 @var{inherit} is @code{nil}, only an attribute directly defined by the
2690 face is returned. If @var{inherit} is non-@code{nil}, any faces
2691 specified by its @code{:inherit} attribute are considered as well, and
2692 if @var{inherit} is a face or a list of faces, then they are also
2693 considered, until a specified attribute is found. To ensure that the
2694 return value is always specified, use a value of @code{default} for
2697 @defun face-font face &optional frame character
2698 This function returns the name of the font of face @var{face}.
2700 If the optional argument @var{frame} is specified, it returns the name
2701 of the font of @var{face} for that frame. If @var{frame} is omitted or
2702 @code{nil}, the selected frame is used. And, in this case, if the
2703 optional third argument @var{character} is supplied, it returns the font
2704 name used for @var{character}.
2707 @defun face-foreground face &optional frame inherit
2708 @defunx face-background face &optional frame inherit
2709 These functions return the foreground color (or background color,
2710 respectively) of face @var{face}, as a string.
2713 @defun face-stipple face &optional frame inherit
2714 This function returns the name of the background stipple pattern of face
2715 @var{face}, or @code{nil} if it doesn't have one.
2718 @defun face-bold-p face &optional frame inherit
2719 This function returns a non-@code{nil} value if the @code{:weight}
2720 attribute of @var{face} is bolder than normal (i.e., one of
2721 @code{semi-bold}, @code{bold}, @code{extra-bold}, or
2722 @code{ultra-bold}). Otherwise, it returns @code{nil}.
2725 @defun face-italic-p face &optional frame inherit
2726 This function returns a non-@code{nil} value if the @code{:slant}
2727 attribute of @var{face} is @code{italic} or @code{oblique}, and
2728 @code{nil} otherwise.
2731 @defun face-underline-p face &optional frame inherit
2732 This function returns non-@code{nil} if face @var{face} specifies
2733 a non-@code{nil} @code{:underline} attribute.
2736 @defun face-inverse-video-p face &optional frame inherit
2737 This function returns non-@code{nil} if face @var{face} specifies
2738 a non-@code{nil} @code{:inverse-video} attribute.
2741 @node Displaying Faces
2742 @subsection Displaying Faces
2743 @cindex displaying faces
2744 @cindex face merging
2746 When Emacs displays a given piece of text, the visual appearance of
2747 the text may be determined by faces drawn from different sources. If
2748 these various sources together specify more than one face for a
2749 particular character, Emacs merges the attributes of the various
2750 faces. Here is the order in which Emacs merges the faces, from
2751 highest to lowest priority:
2755 If the text consists of a special glyph, the glyph can specify a
2756 particular face. @xref{Glyphs}.
2759 If the text lies within an active region, Emacs highlights it using
2760 the @code{region} face. @xref{Standard Faces,,, emacs, The GNU Emacs
2764 If the text lies within an overlay with a non-@code{nil} @code{face}
2765 property, Emacs applies the face(s) specified by that property. If
2766 the overlay has a @code{mouse-face} property and the mouse is near
2767 enough to the overlay, Emacs applies the face or face attributes
2768 specified by the @code{mouse-face} property instead. @xref{Overlay
2771 When multiple overlays cover one character, an overlay with higher
2772 priority overrides those with lower priority. @xref{Overlays}.
2775 If the text contains a @code{face} or @code{mouse-face} property,
2776 Emacs applies the specified faces and face attributes. @xref{Special
2777 Properties}. (This is how Font Lock mode faces are applied.
2778 @xref{Font Lock Mode}.)
2781 If the text lies within the mode line of the selected window, Emacs
2782 applies the @code{mode-line} face. For the mode line of a
2783 non-selected window, Emacs applies the @code{mode-line-inactive} face.
2784 For a header line, Emacs applies the @code{header-line} face.
2787 If any given attribute has not been specified during the preceding
2788 steps, Emacs applies the attribute of the @code{default} face.
2791 At each stage, if a face has a valid @code{:inherit} attribute,
2792 Emacs treats any attribute with an @code{unspecified} value as having
2793 the corresponding value drawn from the parent face(s). @pxref{Face
2794 Attributes}. Note that the parent face(s) may also leave the
2795 attribute unspecified; in that case, the attribute remains unspecified
2796 at the next level of face merging.
2798 @node Face Remapping
2799 @subsection Face Remapping
2800 @cindex face remapping
2802 The variable @code{face-remapping-alist} is used for buffer-local or
2803 global changes in the appearance of a face. For instance, it is used
2804 to implement the @code{text-scale-adjust} command (@pxref{Text
2805 Scale,,, emacs, The GNU Emacs Manual}).
2807 @defvar face-remapping-alist
2808 The value of this variable is an alist whose elements have the form
2809 @code{(@var{face} . @var{remapping})}. This causes Emacs to display
2810 any text having the face @var{face} with @var{remapping}, rather than
2811 the ordinary definition of @var{face}.
2813 @var{remapping} may be any face spec suitable for a @code{face} text
2814 property: either a face (i.e., a face name or a property list of
2815 attribute/value pairs), or a list of faces. For details, see the
2816 description of the @code{face} text property in @ref{Special
2817 Properties}. @var{remapping} serves as the complete specification for
2818 the remapped face---it replaces the normal definition of @var{face},
2819 instead of modifying it.
2821 If @code{face-remapping-alist} is buffer-local, its local value takes
2822 effect only within that buffer.
2824 Note: face remapping is non-recursive. If @var{remapping} references
2825 the same face name @var{face}, either directly or via the
2826 @code{:inherit} attribute of some other face in @var{remapping}, that
2827 reference uses the normal definition of @var{face}. For instance, if
2828 the @code{mode-line} face is remapped using this entry in
2829 @code{face-remapping-alist}:
2832 (mode-line italic mode-line)
2836 then the new definition of the @code{mode-line} face inherits from the
2837 @code{italic} face, and the @emph{normal} (non-remapped) definition of
2838 @code{mode-line} face.
2841 @cindex relative remapping, faces
2842 @cindex base remapping, faces
2843 The following functions implement a higher-level interface to
2844 @code{face-remapping-alist}. Most Lisp code should use these
2845 functions instead of setting @code{face-remapping-alist} directly, to
2846 avoid trampling on remappings applied elsewhere. These functions are
2847 intended for buffer-local remappings, so they all make
2848 @code{face-remapping-alist} buffer-local as a side-effect. They manage
2849 @code{face-remapping-alist} entries of the form
2852 (@var{face} @var{relative-spec-1} @var{relative-spec-2} @var{...} @var{base-spec})
2856 where, as explained above, each of the @var{relative-spec-N} and
2857 @var{base-spec} is either a face name, or a property list of
2858 attribute/value pairs. Each of the @dfn{relative remapping} entries,
2859 @var{relative-spec-N}, is managed by the
2860 @code{face-remap-add-relative} and @code{face-remap-remove-relative}
2861 functions; these are intended for simple modifications like changing
2862 the text size. The @dfn{base remapping} entry, @var{base-spec}, has
2863 the lowest priority and is managed by the @code{face-remap-set-base}
2864 and @code{face-remap-reset-base} functions; it is intended for major
2865 modes to remap faces in the buffers they control.
2867 @defun face-remap-add-relative face &rest specs
2868 This function adds the face spec in @var{specs} as relative
2869 remappings for face @var{face} in the current buffer. The remaining
2870 arguments, @var{specs}, should form either a list of face names, or a
2871 property list of attribute/value pairs.
2873 The return value is a Lisp object that serves as a cookie; you can
2874 pass this object as an argument to @code{face-remap-remove-relative}
2875 if you need to remove the remapping later.
2878 ;; Remap the 'escape-glyph' face into a combination
2879 ;; of the 'highlight' and 'italic' faces:
2880 (face-remap-add-relative 'escape-glyph 'highlight 'italic)
2882 ;; Increase the size of the 'default' face by 50%:
2883 (face-remap-add-relative 'default :height 1.5)
2887 @defun face-remap-remove-relative cookie
2888 This function removes a relative remapping previously added by
2889 @code{face-remap-add-relative}. @var{cookie} should be the Lisp
2890 object returned by @code{face-remap-add-relative} when the remapping
2894 @defun face-remap-set-base face &rest specs
2895 This function sets the base remapping of @var{face} in the current
2896 buffer to @var{specs}. If @var{specs} is empty, the default base
2897 remapping is restored, similar to calling @code{face-remap-reset-base}
2898 (see below); note that this is different from @var{specs} containing a
2899 single value @code{nil}, which has the opposite result (the global
2900 definition of @var{face} is ignored).
2902 This overwrites the default @var{base-spec}, which inherits the global
2903 face definition, so it is up to the caller to add such inheritance if
2907 @defun face-remap-reset-base face
2908 This function sets the base remapping of @var{face} to its default
2909 value, which inherits from @var{face}'s global definition.
2912 @node Face Functions
2913 @subsection Functions for Working with Faces
2915 Here are additional functions for creating and working with faces.
2918 This function returns a list of all defined face names.
2922 This function returns the @dfn{face number} of face @var{face}. This
2923 is a number that uniquely identifies a face at low levels within
2924 Emacs. It is seldom necessary to refer to a face by its face number.
2927 @defun face-documentation face
2928 This function returns the documentation string of face @var{face}, or
2929 @code{nil} if none was specified for it.
2932 @defun face-equal face1 face2 &optional frame
2933 This returns @code{t} if the faces @var{face1} and @var{face2} have the
2934 same attributes for display.
2937 @defun face-differs-from-default-p face &optional frame
2938 This returns non-@code{nil} if the face @var{face} displays
2939 differently from the default face.
2943 @cindex alias, for faces
2944 A @dfn{face alias} provides an equivalent name for a face. You can
2945 define a face alias by giving the alias symbol the @code{face-alias}
2946 property, with a value of the target face name. The following example
2947 makes @code{modeline} an alias for the @code{mode-line} face.
2950 (put 'modeline 'face-alias 'mode-line)
2953 @defmac define-obsolete-face-alias obsolete-face current-face when
2954 This macro defines @code{obsolete-face} as an alias for
2955 @var{current-face}, and also marks it as obsolete, indicating that it
2956 may be removed in future. @var{when} should be a string indicating
2957 when @code{obsolete-face} was made obsolete (usually a version number
2962 @subsection Automatic Face Assignment
2963 @cindex automatic face assignment
2964 @cindex faces, automatic choice
2966 This hook is used for automatically assigning faces to text in the
2967 buffer. It is part of the implementation of Jit-Lock mode, used by
2970 @defvar fontification-functions
2971 This variable holds a list of functions that are called by Emacs
2972 redisplay as needed, just before doing redisplay. They are called even
2973 when Font Lock Mode isn't enabled. When Font Lock Mode is enabled, this
2974 variable usually holds just one function, @code{jit-lock-function}.
2976 The functions are called in the order listed, with one argument, a
2977 buffer position @var{pos}. Collectively they should attempt to assign
2978 faces to the text in the current buffer starting at @var{pos}.
2980 The functions should record the faces they assign by setting the
2981 @code{face} property. They should also add a non-@code{nil}
2982 @code{fontified} property to all the text they have assigned faces to.
2983 That property tells redisplay that faces have been assigned to that text
2986 It is probably a good idea for the functions to do nothing if the
2987 character after @var{pos} already has a non-@code{nil} @code{fontified}
2988 property, but this is not required. If one function overrides the
2989 assignments made by a previous one, the properties after the last
2990 function finishes are the ones that really matter.
2992 For efficiency, we recommend writing these functions so that they
2993 usually assign faces to around 400 to 600 characters at each call.
2997 @subsection Basic Faces
3000 If your Emacs Lisp program needs to assign some faces to text, it is
3001 often a good idea to use certain existing faces or inherit from them,
3002 rather than defining entirely new faces. This way, if other users
3003 have customized the basic faces to give Emacs a certain look, your
3004 program will fit in without additional customization.
3006 Some of the basic faces defined in Emacs are listed below. In
3007 addition to these, you might want to make use of the Font Lock faces
3008 for syntactic highlighting, if highlighting is not already handled by
3009 Font Lock mode, or if some Font Lock faces are not in use.
3010 @xref{Faces for Font Lock}.
3014 The default face, whose attributes are all specified. All other faces
3015 implicitly inherit from it: any unspecified attribute defaults to the
3016 attribute on this face (@pxref{Face Attributes}).
3023 @itemx fixed-pitch-serif
3024 @itemx variable-pitch
3025 These have the attributes indicated by their names (e.g., @code{bold}
3026 has a bold @code{:weight} attribute), with all other attributes
3027 unspecified (and so given by @code{default}).
3030 For dimmed-out text. For example, it is used for the ignored
3031 part of a filename in the minibuffer (@pxref{Minibuffer File,,
3032 Minibuffers for File Names, emacs, The GNU Emacs Manual}).
3036 For clickable text buttons that send the user to a different
3040 For stretches of text that should temporarily stand out. For example,
3041 it is commonly assigned to the @code{mouse-face} property for cursor
3042 highlighting (@pxref{Special Properties}).
3046 @itemx lazy-highlight
3047 For text matching (respectively) permanent search matches, interactive
3048 search matches, and lazy highlighting other matches than the current
3054 For text concerning errors, warnings, or successes. For example,
3055 these are used for messages in @file{*Compilation*} buffers.
3058 @node Font Selection
3059 @subsection Font Selection
3060 @cindex font selection
3061 @cindex selecting a font
3063 Before Emacs can draw a character on a graphical display, it must
3064 select a @dfn{font} for that character@footnote{In this context, the
3065 term @dfn{font} has nothing to do with Font Lock (@pxref{Font Lock
3066 Mode}).}. @xref{Fonts,,, emacs, The GNU Emacs Manual}. Normally,
3067 Emacs automatically chooses a font based on the faces assigned to that
3068 character---specifically, the face attributes @code{:family},
3069 @code{:weight}, @code{:slant}, and @code{:width} (@pxref{Face
3070 Attributes}). The choice of font also depends on the character to be
3071 displayed; some fonts can only display a limited set of characters.
3072 If no available font exactly fits the requirements, Emacs looks for
3073 the @dfn{closest matching font}. The variables in this section
3074 control how Emacs makes this selection.
3076 @defopt face-font-family-alternatives
3077 If a given family is specified but does not exist, this variable
3078 specifies alternative font families to try. Each element should have
3082 (@var{family} @var{alternate-families}@dots{})
3085 If @var{family} is specified but not available, Emacs will try the other
3086 families given in @var{alternate-families}, one by one, until it finds a
3087 family that does exist.
3090 @defopt face-font-selection-order
3091 If there is no font that exactly matches all desired face attributes
3092 (@code{:width}, @code{:height}, @code{:weight}, and @code{:slant}),
3093 this variable specifies the order in which these attributes should be
3094 considered when selecting the closest matching font. The value should
3095 be a list containing those four attribute symbols, in order of
3096 decreasing importance. The default is @code{(:width :height :weight
3099 Font selection first finds the best available matches for the first
3100 attribute in the list; then, among the fonts which are best in that
3101 way, it searches for the best matches in the second attribute, and so
3104 The attributes @code{:weight} and @code{:width} have symbolic values in
3105 a range centered around @code{normal}. Matches that are more extreme
3106 (farther from @code{normal}) are somewhat preferred to matches that are
3107 less extreme (closer to @code{normal}); this is designed to ensure that
3108 non-normal faces contrast with normal ones, whenever possible.
3110 One example of a case where this variable makes a difference is when the
3111 default font has no italic equivalent. With the default ordering, the
3112 @code{italic} face will use a non-italic font that is similar to the
3113 default one. But if you put @code{:slant} before @code{:height}, the
3114 @code{italic} face will use an italic font, even if its height is not
3118 @defopt face-font-registry-alternatives
3119 This variable lets you specify alternative font registries to try, if a
3120 given registry is specified and doesn't exist. Each element should have
3124 (@var{registry} @var{alternate-registries}@dots{})
3127 If @var{registry} is specified but not available, Emacs will try the
3128 other registries given in @var{alternate-registries}, one by one,
3129 until it finds a registry that does exist.
3132 @cindex scalable fonts
3133 Emacs can make use of scalable fonts, but by default it does not use
3136 @defopt scalable-fonts-allowed
3137 This variable controls which scalable fonts to use. A value of
3138 @code{nil}, the default, means do not use scalable fonts. @code{t}
3139 means to use any scalable font that seems appropriate for the text.
3141 Otherwise, the value must be a list of regular expressions. Then a
3142 scalable font is enabled for use if its name matches any regular
3143 expression in the list. For example,
3146 (setq scalable-fonts-allowed '("iso10646-1$"))
3150 allows the use of scalable fonts with registry @code{iso10646-1}.
3153 @defvar face-font-rescale-alist
3154 This variable specifies scaling for certain faces. Its value should
3155 be a list of elements of the form
3158 (@var{fontname-regexp} . @var{scale-factor})
3161 If @var{fontname-regexp} matches the font name that is about to be
3162 used, this says to choose a larger similar font according to the
3163 factor @var{scale-factor}. You would use this feature to normalize
3164 the font size if certain fonts are bigger or smaller than their
3165 nominal heights and widths would suggest.
3169 @subsection Looking Up Fonts
3171 @cindex looking up fonts
3173 @defun x-list-fonts name &optional reference-face frame maximum width
3174 This function returns a list of available font names that match
3175 @var{name}. @var{name} should be a string containing a font name in
3176 either the Fontconfig, GTK, or XLFD format (@pxref{Fonts,,, emacs, The
3177 GNU Emacs Manual}). Within an XLFD string, wildcard characters may be
3178 used: the @samp{*} character matches any substring, and the @samp{?}
3179 character matches any single character. Case is ignored when matching
3182 If the optional arguments @var{reference-face} and @var{frame} are
3183 specified, the returned list includes only fonts that are the same
3184 size as @var{reference-face} (a face name) currently is on the frame
3187 The optional argument @var{maximum} sets a limit on how many fonts to
3188 return. If it is non-@code{nil}, then the return value is truncated
3189 after the first @var{maximum} matching fonts. Specifying a small
3190 value for @var{maximum} can make this function much faster, in cases
3191 where many fonts match the pattern.
3193 The optional argument @var{width} specifies a desired font width. If
3194 it is non-@code{nil}, the function only returns those fonts whose
3195 characters are (on average) @var{width} times as wide as
3196 @var{reference-face}.
3199 @defun x-family-fonts &optional family frame
3200 This function returns a list describing the available fonts for family
3201 @var{family} on @var{frame}. If @var{family} is omitted or @code{nil},
3202 this list applies to all families, and therefore, it contains all
3203 available fonts. Otherwise, @var{family} must be a string; it may
3204 contain the wildcards @samp{?} and @samp{*}.
3206 The list describes the display that @var{frame} is on; if @var{frame} is
3207 omitted or @code{nil}, it applies to the selected frame's display
3208 (@pxref{Input Focus}).
3210 Each element in the list is a vector of the following form:
3213 [@var{family} @var{width} @var{point-size} @var{weight} @var{slant}
3214 @var{fixed-p} @var{full} @var{registry-and-encoding}]
3217 The first five elements correspond to face attributes; if you
3218 specify these attributes for a face, it will use this font.
3220 The last three elements give additional information about the font.
3221 @var{fixed-p} is non-@code{nil} if the font is fixed-pitch.
3222 @var{full} is the full name of the font, and
3223 @var{registry-and-encoding} is a string giving the registry and
3224 encoding of the font.
3228 @subsection Fontsets
3231 A @dfn{fontset} is a list of fonts, each assigned to a range of
3232 character codes. An individual font cannot display the whole range of
3233 characters that Emacs supports, but a fontset can. Fontsets have names,
3234 just as fonts do, and you can use a fontset name in place of a font name
3235 when you specify the font for a frame or a face. Here is
3236 information about defining a fontset under Lisp program control.
3238 @defun create-fontset-from-fontset-spec fontset-spec &optional style-variant-p noerror
3239 This function defines a new fontset according to the specification
3240 string @var{fontset-spec}. The string should have this format:
3243 @var{fontpattern}, @r{[}@var{charset}:@var{font}@r{]@dots{}}
3247 Whitespace characters before and after the commas are ignored.
3249 The first part of the string, @var{fontpattern}, should have the form of
3250 a standard X font name, except that the last two fields should be
3251 @samp{fontset-@var{alias}}.
3253 The new fontset has two names, one long and one short. The long name is
3254 @var{fontpattern} in its entirety. The short name is
3255 @samp{fontset-@var{alias}}. You can refer to the fontset by either
3256 name. If a fontset with the same name already exists, an error is
3257 signaled, unless @var{noerror} is non-@code{nil}, in which case this
3258 function does nothing.
3260 If optional argument @var{style-variant-p} is non-@code{nil}, that says
3261 to create bold, italic and bold-italic variants of the fontset as well.
3262 These variant fontsets do not have a short name, only a long one, which
3263 is made by altering @var{fontpattern} to indicate the bold and/or italic
3266 The specification string also says which fonts to use in the fontset.
3267 See below for the details.
3270 The construct @samp{@var{charset}:@var{font}} specifies which font to
3271 use (in this fontset) for one particular character set. Here,
3272 @var{charset} is the name of a character set, and @var{font} is the font
3273 to use for that character set. You can use this construct any number of
3274 times in the specification string.
3276 For the remaining character sets, those that you don't specify
3277 explicitly, Emacs chooses a font based on @var{fontpattern}: it replaces
3278 @samp{fontset-@var{alias}} with a value that names one character set.
3279 For the @acronym{ASCII} character set, @samp{fontset-@var{alias}} is replaced
3280 with @samp{ISO8859-1}.
3282 In addition, when several consecutive fields are wildcards, Emacs
3283 collapses them into a single wildcard. This is to prevent use of
3284 auto-scaled fonts. Fonts made by scaling larger fonts are not usable
3285 for editing, and scaling a smaller font is not useful because it is
3286 better to use the smaller font in its own size, which Emacs does.
3288 Thus if @var{fontpattern} is this,
3291 -*-fixed-medium-r-normal-*-24-*-*-*-*-*-fontset-24
3295 the font specification for @acronym{ASCII} characters would be this:
3298 -*-fixed-medium-r-normal-*-24-*-ISO8859-1
3302 and the font specification for Chinese GB2312 characters would be this:
3305 -*-fixed-medium-r-normal-*-24-*-gb2312*-*
3308 You may not have any Chinese font matching the above font
3309 specification. Most X distributions include only Chinese fonts that
3310 have @samp{song ti} or @samp{fangsong ti} in the @var{family} field. In
3311 such a case, @samp{Fontset-@var{n}} can be specified as below:
3314 Emacs.Fontset-0: -*-fixed-medium-r-normal-*-24-*-*-*-*-*-fontset-24,\
3315 chinese-gb2312:-*-*-medium-r-normal-*-24-*-gb2312*-*
3319 Then, the font specifications for all but Chinese GB2312 characters have
3320 @samp{fixed} in the @var{family} field, and the font specification for
3321 Chinese GB2312 characters has a wild card @samp{*} in the @var{family}
3324 @defun set-fontset-font name character font-spec &optional frame add
3325 This function modifies the existing fontset @var{name} to use the font
3326 matching with @var{font-spec} for the specified @var{character}.
3328 If @var{name} is @code{nil}, this function modifies the fontset of the
3329 selected frame or that of @var{frame} if @var{frame} is not
3332 If @var{name} is @code{t}, this function modifies the default
3333 fontset, whose short name is @samp{fontset-default}.
3335 In addition to specifying a single codepoint, @var{character} may be a
3336 cons @code{(@var{from} . @var{to})}, where @var{from} and @var{to} are
3337 character codepoints. In that case, use @var{font-spec} for all the
3338 characters in the range @var{from} and @var{to} (inclusive).
3340 @var{character} may be a charset. In that case, use
3341 @var{font-spec} for all character in the charsets.
3343 @var{character} may be a script name. In that case, use
3344 @var{font-spec} for all character in the charsets.
3346 @var{font-spec} may be a font-spec object created by the function
3347 @code{font-spec} (@pxref{Low-Level Font}).
3349 @var{font-spec} may be a cons; @code{(@var{family} . @var{registry})},
3350 where @var{family} is a family name of a font (possibly including a
3351 foundry name at the head), @var{registry} is a registry name of a font
3352 (possibly including an encoding name at the tail).
3354 @var{font-spec} may be a font name string.
3356 @var{font-spec} may be @code{nil}, which explicitly specifies that
3357 there's no font for the specified @var{character}. This is useful,
3358 for example, to avoid expensive system-wide search for fonts for
3359 characters that have no glyphs, like those from the Unicode Private
3362 The optional argument @var{add}, if non-@code{nil}, specifies how to
3363 add @var{font-spec} to the font specifications previously set. If it
3364 is @code{prepend}, @var{font-spec} is prepended. If it is
3365 @code{append}, @var{font-spec} is appended. By default,
3366 @var{font-spec} overrides the previous settings.
3368 For instance, this changes the default fontset to use a font of which
3369 family name is @samp{Kochi Gothic} for all characters belonging to
3370 the charset @code{japanese-jisx0208}.
3373 (set-fontset-font t 'japanese-jisx0208
3374 (font-spec :family "Kochi Gothic"))
3378 @defun char-displayable-p char
3379 This function returns @code{t} if Emacs ought to be able to display
3380 @var{char}. More precisely, if the selected frame's fontset has a
3381 font to display the character set that @var{char} belongs to.
3383 Fontsets can specify a font on a per-character basis; when the fontset
3384 does that, this function's value may not be accurate.
3387 @node Low-Level Font
3388 @subsection Low-Level Font Representation
3389 @cindex font property
3391 Normally, it is not necessary to manipulate fonts directly. In case
3392 you need to do so, this section explains how.
3394 In Emacs Lisp, fonts are represented using three different Lisp
3395 object types: @dfn{font objects}, @dfn{font specs}, and @dfn{font
3398 @defun fontp object &optional type
3399 Return @code{t} if @var{object} is a font object, font spec, or font
3400 entity. Otherwise, return @code{nil}.
3402 The optional argument @var{type}, if non-@code{nil}, determines the
3403 exact type of Lisp object to check for. In that case, @var{type}
3404 should be one of @code{font-object}, @code{font-spec}, or
3409 A font object is a Lisp object that represents a font that Emacs has
3410 @dfn{opened}. Font objects cannot be modified in Lisp, but they can
3413 @defun font-at position &optional window string
3414 Return the font object that is being used to display the character at
3415 position @var{position} in the window @var{window}. If @var{window}
3416 is @code{nil}, it defaults to the selected window. If @var{string} is
3417 @code{nil}, @var{position} specifies a position in the current buffer;
3418 otherwise, @var{string} should be a string, and @var{position}
3419 specifies a position in that string.
3423 A font spec is a Lisp object that contains a set of specifications
3424 that can be used to find a font. More than one font may match the
3425 specifications in a font spec.
3427 @defun font-spec &rest arguments
3428 Return a new font spec using the specifications in @var{arguments},
3429 which should come in @code{property}-@code{value} pairs. The possible
3430 specifications are as follows:
3434 The font name (a string), in either XLFD, Fontconfig, or GTK format.
3435 @xref{Fonts,,, emacs, The GNU Emacs Manual}.
3442 These have the same meanings as the face attributes of the same name.
3443 @xref{Face Attributes}.
3446 The font size---either a non-negative integer that specifies the pixel
3447 size, or a floating-point number that specifies the point size.
3450 Additional typographic style information for the font, such as
3451 @samp{sans}. The value should be a string or a symbol.
3453 @cindex font registry
3455 The charset registry and encoding of the font, such as
3456 @samp{iso8859-1}. The value should be a string or a symbol.
3459 The script that the font must support (a symbol).
3462 The language that the font should support. The value should be a
3463 symbol whose name is a two-letter ISO-639 language name. On X, the
3464 value is matched against the ``Additional Style'' field of the XLFD
3465 name of a font, if it is non-empty. On MS-Windows, fonts matching the
3466 spec are required to support codepages needed for the language.
3467 Currently, only a small set of CJK languages is supported with this
3468 property: @samp{ja}, @samp{ko}, and @samp{zh}.
3471 @cindex OpenType font
3472 The font must be an OpenType font that supports these OpenType
3473 features, provided Emacs is compiled with a library, such as
3474 @samp{libotf} on GNU/Linux, that supports complex text layout for
3475 scripts which need that. The value must be a list of the form
3478 @code{(@var{script-tag} @var{langsys-tag} @var{gsub} @var{gpos})}
3481 where @var{script-tag} is the OpenType script tag symbol;
3482 @var{langsys-tag} is the OpenType language system tag symbol, or
3483 @code{nil} to use the default language system; @code{gsub} is a list
3484 of OpenType GSUB feature tag symbols, or @code{nil} if none is
3485 required; and @code{gpos} is a list of OpenType GPOS feature tag
3486 symbols, or @code{nil} if none is required. If @code{gsub} or
3487 @code{gpos} is a list, a @code{nil} element in that list means that
3488 the font must not match any of the remaining tag symbols. The
3489 @code{gpos} element may be omitted.
3493 @defun font-put font-spec property value
3494 Set the font property @var{property} in the font-spec @var{font-spec}
3499 A font entity is a reference to a font that need not be open. Its
3500 properties are intermediate between a font object and a font spec:
3501 like a font object, and unlike a font spec, it refers to a single,
3502 specific font. Unlike a font object, creating a font entity does not
3503 load the contents of that font into computer memory. Emacs may open
3504 multiple font objects of different sizes from a single font entity
3505 referring to a scalable font.
3507 @defun find-font font-spec &optional frame
3508 This function returns a font entity that best matches the font spec
3509 @var{font-spec} on frame @var{frame}. If @var{frame} is @code{nil},
3510 it defaults to the selected frame.
3513 @defun list-fonts font-spec &optional frame num prefer
3514 This function returns a list of all font entities that match the font
3515 spec @var{font-spec}.
3517 The optional argument @var{frame}, if non-@code{nil}, specifies the
3518 frame on which the fonts are to be displayed. The optional argument
3519 @var{num}, if non-@code{nil}, should be an integer that specifies the
3520 maximum length of the returned list. The optional argument
3521 @var{prefer}, if non-@code{nil}, should be another font spec, which is
3522 used to control the order of the returned list; the returned font
3523 entities are sorted in order of decreasing closeness to that font
3527 If you call @code{set-face-attribute} and pass a font spec, font
3528 entity, or font name string as the value of the @code{:font}
3529 attribute, Emacs opens the best matching font that is available
3530 for display. It then stores the corresponding font object as the
3531 actual value of the @code{:font} attribute for that face.
3533 The following functions can be used to obtain information about a
3534 font. For these functions, the @var{font} argument can be a font
3535 object, a font entity, or a font spec.
3537 @defun font-get font property
3538 This function returns the value of the font property @var{property}
3541 If @var{font} is a font spec and the font spec does not specify
3542 @var{property}, the return value is @code{nil}. If @var{font} is a
3543 font object or font entity, the value for the @var{:script} property
3544 may be a list of scripts supported by the font.
3547 @defun font-face-attributes font &optional frame
3548 This function returns a list of face attributes corresponding to
3549 @var{font}. The optional argument @var{frame} specifies the frame on
3550 which the font is to be displayed. If it is @code{nil}, the selected
3551 frame is used. The return value has the form
3554 (:family @var{family} :height @var{height} :weight @var{weight}
3555 :slant @var{slant} :width @var{width})
3558 where the values of @var{family}, @var{height}, @var{weight},
3559 @var{slant}, and @var{width} are face attribute values. Some of these
3560 key-attribute pairs may be omitted from the list if they are not
3561 specified by @var{font}.
3564 @defun font-xlfd-name font &optional fold-wildcards
3565 This function returns the XLFD (X Logical Font Descriptor), a string,
3566 matching @var{font}. @xref{Fonts,,, emacs, The GNU Emacs Manual}, for
3567 information about XLFDs. If the name is too long for an XLFD (which
3568 can contain at most 255 characters), the function returns @code{nil}.
3570 If the optional argument @var{fold-wildcards} is non-@code{nil},
3571 consecutive wildcards in the XLFD are folded into one.
3574 The following two functions return important information about a font.
3576 @defun font-info name &optional frame
3577 This function returns information about a font specified by its
3578 @var{name}, a string, as it is used on @var{frame}. If @var{frame} is
3579 omitted or @code{nil}, it defaults to the selected frame.
3581 The value returned by the function is a vector of the form
3582 @code{[@var{opened-name} @var{full-name} @var{size} @var{height}
3583 @var{baseline-offset} @var{relative-compose} @var{default-ascent}
3584 @var{max-width} @var{ascent} @var{descent} @var{space-width}
3585 @var{average-width} @var{filename} @var{capability}]}. Here's the
3586 description of each components of this vector:
3590 The name used to open the font, a string.
3593 The full name of the font, a string.
3596 The pixel size of the font.
3599 The height of the font in pixels.
3601 @item baseline-offset
3602 The offset in pixels from the @acronym{ASCII} baseline, positive
3605 @item relative-compose
3606 @itemx default-ascent
3607 Numbers controlling how to compose characters.
3611 The ascent and descent of this font. The sum of these two numbers
3612 should be equal to the value of @var{height} above.
3615 The width, in pixels, of the font's space character.
3618 The average width of the font characters. If this is zero, Emacs uses
3619 the value of @var{space-width} instead, when it calculates text layout
3623 The file name of the font as a string. This can be @code{nil} if the
3624 font back-end does not provide a way to find out the font's file name.
3627 A list whose first element is a symbol representing the font type, one
3628 of @code{x}, @code{opentype}, @code{truetype}, @code{type1},
3629 @code{pcf}, or @code{bdf}. For OpenType fonts, the list includes 2
3630 additional elements describing the @sc{gsub} and @sc{gpos} features
3631 supported by the font. Each of these elements is a list of the form
3632 @code{((@var{script} (@var{langsys} @var{feature} @dots{}) @dots{})
3633 @dots{})}, where @var{script} is a symbol representing an OpenType
3634 script tag, @var{langsys} is a symbol representing an OpenType langsys
3635 tag (or @code{nil}, which stands for the default langsys), and each
3636 @var{feature} is a symbol representing an OpenType feature tag.
3640 @defun query-font font-object
3641 This function returns information about a @var{font-object}. (This is
3642 in contrast to @code{font-info}, which takes the font name, a string,
3645 The value returned by the function is a vector of the form
3646 @code{[@var{name} @var{filename} @var{pixel-size} @var{max-width}
3647 @var{ascent} @var{descent} @var{space-width} @var{average-width}
3648 @var{capability}]}. Here's the description of each components of this
3653 The font name, a string.
3656 The file name of the font as a string. This can be @code{nil} if the
3657 font back-end does not provide a way to find out the font's file name.
3660 The pixel size of the font used to open the font.
3663 The maximum advance width of the font.
3667 The ascent and descent of this font. The sum of these two numbers
3668 gives the font height.
3671 The width, in pixels, of the font's space character.
3674 The average width of the font characters. If this is zero, Emacs uses
3675 the value of @var{space-width} instead, when it calculates text layout
3679 A list whose first element is a symbol representing the font type, one
3680 of @code{x}, @code{opentype}, @code{truetype}, @code{type1},
3681 @code{pcf}, or @code{bdf}. For OpenType fonts, the list includes 2
3682 additional elements describing the @sc{gsub} and @sc{gpos} features
3683 supported by the font. Each of these elements is a list of the form
3684 @code{((@var{script} (@var{langsys} @var{feature} @dots{}) @dots{})
3685 @dots{})}, where @var{script} is a symbol representing an OpenType
3686 script tag, @var{langsys} is a symbol representing an OpenType langsys
3687 tag (or @code{nil}, which stands for the default langsys), and each
3688 @var{feature} is a symbol representing an OpenType feature tag.
3692 @cindex font information for layout
3693 The following four functions return size information about fonts used
3694 by various faces, allowing various layout considerations in Lisp
3695 programs. These functions take face remapping into consideration,
3696 returning information about the remapped face, if the face in question
3697 was remapped. @xref{Face Remapping}.
3699 @defun default-font-width
3700 This function returns the average width in pixels of the font used by
3701 the current buffer's default face.
3704 @defun default-font-height
3705 This function returns the height in pixels of the font used by the
3706 current buffer's default face.
3709 @defun window-font-width &optional window face
3710 This function returns the average width in pixels for the font used by
3711 @var{face} in @var{window}. The specified @var{window} must be a live
3712 window. If @code{nil} or omitted, @var{window} defaults to the
3713 selected window, and @var{face} defaults to the default face in
3717 @defun window-font-height &optional window face
3718 This function returns the height in pixels for the font used by
3719 @var{face} in @var{window}. The specified @var{window} must be a live
3720 window. If @code{nil} or omitted, @var{window} defaults to the
3721 selected window, and @var{face} defaults to the default face in
3729 On graphical displays, Emacs draws @dfn{fringes} next to each
3730 window: thin vertical strips down the sides which can display bitmaps
3731 indicating truncation, continuation, horizontal scrolling, and so on.
3734 * Fringe Size/Pos:: Specifying where to put the window fringes.
3735 * Fringe Indicators:: Displaying indicator icons in the window fringes.
3736 * Fringe Cursors:: Displaying cursors in the right fringe.
3737 * Fringe Bitmaps:: Specifying bitmaps for fringe indicators.
3738 * Customizing Bitmaps:: Specifying your own bitmaps to use in the fringes.
3739 * Overlay Arrow:: Display of an arrow to indicate position.
3742 @node Fringe Size/Pos
3743 @subsection Fringe Size and Position
3745 The following buffer-local variables control the position and width
3746 of fringes in windows showing that buffer.
3748 @defvar fringes-outside-margins
3749 The fringes normally appear between the display margins and the window
3750 text. If the value is non-@code{nil}, they appear outside the display
3751 margins. @xref{Display Margins}.
3754 @defvar left-fringe-width
3755 This variable, if non-@code{nil}, specifies the width of the left
3756 fringe in pixels. A value of @code{nil} means to use the left fringe
3757 width from the window's frame.
3760 @defvar right-fringe-width
3761 This variable, if non-@code{nil}, specifies the width of the right
3762 fringe in pixels. A value of @code{nil} means to use the right fringe
3763 width from the window's frame.
3766 Any buffer which does not specify values for these variables uses
3767 the values specified by the @code{left-fringe} and @code{right-fringe}
3768 frame parameters (@pxref{Layout Parameters}).
3770 The above variables actually take effect via the function
3771 @code{set-window-buffer} (@pxref{Buffers and Windows}), which calls
3772 @code{set-window-fringes} as a subroutine. If you change one of these
3773 variables, the fringe display is not updated in existing windows
3774 showing the buffer, unless you call @code{set-window-buffer} again in
3775 each affected window. You can also use @code{set-window-fringes} to
3776 control the fringe display in individual windows.
3778 @defun set-window-fringes window left &optional right outside-margins
3779 This function sets the fringe widths of window @var{window}.
3780 If @var{window} is @code{nil}, the selected window is used.
3782 The argument @var{left} specifies the width in pixels of the left
3783 fringe, and likewise @var{right} for the right fringe. A value of
3784 @code{nil} for either one stands for the default width. If
3785 @var{outside-margins} is non-@code{nil}, that specifies that fringes
3786 should appear outside of the display margins.
3789 @defun window-fringes &optional window
3790 This function returns information about the fringes of a window
3791 @var{window}. If @var{window} is omitted or @code{nil}, the selected
3792 window is used. The value has the form @code{(@var{left-width}
3793 @var{right-width} @var{outside-margins})}.
3797 @node Fringe Indicators
3798 @subsection Fringe Indicators
3799 @cindex fringe indicators
3800 @cindex indicators, fringe
3802 @dfn{Fringe indicators} are tiny icons displayed in the window
3803 fringe to indicate truncated or continued lines, buffer boundaries,
3806 @defopt indicate-empty-lines
3807 @cindex fringes, and empty line indication
3808 @cindex empty lines, indicating
3809 When this is non-@code{nil}, Emacs displays a special glyph in the
3810 fringe of each empty line at the end of the buffer, on graphical
3811 displays. @xref{Fringes}. This variable is automatically
3812 buffer-local in every buffer.
3815 @defopt indicate-buffer-boundaries
3816 @cindex buffer boundaries, indicating
3817 This buffer-local variable controls how the buffer boundaries and
3818 window scrolling are indicated in the window fringes.
3820 Emacs can indicate the buffer boundaries---that is, the first and last
3821 line in the buffer---with angle icons when they appear on the screen.
3822 In addition, Emacs can display an up-arrow in the fringe to show
3823 that there is text above the screen, and a down-arrow to show
3824 there is text below the screen.
3826 There are three kinds of basic values:
3830 Don't display any of these fringe icons.
3832 Display the angle icons and arrows in the left fringe.
3834 Display the angle icons and arrows in the right fringe.
3836 Display the angle icons in the left fringe
3837 and don't display the arrows.
3840 Otherwise the value should be an alist that specifies which fringe
3841 indicators to display and where. Each element of the alist should
3842 have the form @code{(@var{indicator} . @var{position})}. Here,
3843 @var{indicator} is one of @code{top}, @code{bottom}, @code{up},
3844 @code{down}, and @code{t} (which covers all the icons not yet
3845 specified), while @var{position} is one of @code{left}, @code{right}
3848 For example, @code{((top . left) (t . right))} places the top angle
3849 bitmap in left fringe, and the bottom angle bitmap as well as both
3850 arrow bitmaps in right fringe. To show the angle bitmaps in the left
3851 fringe, and no arrow bitmaps, use @code{((top . left) (bottom . left))}.
3854 @defvar fringe-indicator-alist
3855 This buffer-local variable specifies the mapping from logical fringe
3856 indicators to the actual bitmaps displayed in the window fringes. The
3857 value is an alist of elements @code{(@var{indicator}
3858 . @var{bitmaps})}, where @var{indicator} specifies a logical indicator
3859 type and @var{bitmaps} specifies the fringe bitmaps to use for that
3862 Each @var{indicator} should be one of the following symbols:
3865 @item @code{truncation}, @code{continuation}.
3866 Used for truncation and continuation lines.
3868 @item @code{up}, @code{down}, @code{top}, @code{bottom}, @code{top-bottom}
3869 Used when @code{indicate-buffer-boundaries} is non-@code{nil}:
3870 @code{up} and @code{down} indicate a buffer boundary lying above or
3871 below the window edge; @code{top} and @code{bottom} indicate the
3872 topmost and bottommost buffer text line; and @code{top-bottom}
3873 indicates where there is just one line of text in the buffer.
3875 @item @code{empty-line}
3876 Used to indicate empty lines when @code{indicate-empty-lines} is
3879 @item @code{overlay-arrow}
3880 Used for overlay arrows (@pxref{Overlay Arrow}).
3881 @c Is this used anywhere?
3882 @c @item Unknown bitmap indicator:
3886 Each @var{bitmaps} value may be a list of symbols @code{(@var{left}
3887 @var{right} [@var{left1} @var{right1}])}. The @var{left} and
3888 @var{right} symbols specify the bitmaps shown in the left and/or right
3889 fringe, for the specific indicator. @var{left1} and @var{right1} are
3890 specific to the @code{bottom} and @code{top-bottom} indicators, and
3891 are used to indicate that the last text line has no final newline.
3892 Alternatively, @var{bitmaps} may be a single symbol which is used in
3893 both left and right fringes.
3895 @xref{Fringe Bitmaps}, for a list of standard bitmap symbols and how
3896 to define your own. In addition, @code{nil} represents the empty
3897 bitmap (i.e., an indicator that is not shown).
3899 When @code{fringe-indicator-alist} has a buffer-local value, and
3900 there is no bitmap defined for a logical indicator, or the bitmap is
3901 @code{t}, the corresponding value from the default value of
3902 @code{fringe-indicator-alist} is used.
3905 @node Fringe Cursors
3906 @subsection Fringe Cursors
3907 @cindex fringe cursors
3908 @cindex cursor, fringe
3910 When a line is exactly as wide as the window, Emacs displays the
3911 cursor in the right fringe instead of using two lines. Different
3912 bitmaps are used to represent the cursor in the fringe depending on
3913 the current buffer's cursor type.
3915 @defopt overflow-newline-into-fringe
3916 If this is non-@code{nil}, lines exactly as wide as the window (not
3917 counting the final newline character) are not continued. Instead,
3918 when point is at the end of the line, the cursor appears in the right
3922 @defvar fringe-cursor-alist
3923 This variable specifies the mapping from logical cursor type to the
3924 actual fringe bitmaps displayed in the right fringe. The value is an
3925 alist where each element has the form @code{(@var{cursor-type}
3926 . @var{bitmap})}, which means to use the fringe bitmap @var{bitmap} to
3927 display cursors of type @var{cursor-type}.
3929 Each @var{cursor-type} should be one of @code{box}, @code{hollow},
3930 @code{bar}, @code{hbar}, or @code{hollow-small}. The first four have
3931 the same meanings as in the @code{cursor-type} frame parameter
3932 (@pxref{Cursor Parameters}). The @code{hollow-small} type is used
3933 instead of @code{hollow} when the normal @code{hollow-rectangle}
3934 bitmap is too tall to fit on a specific display line.
3936 Each @var{bitmap} should be a symbol specifying the fringe bitmap to
3937 be displayed for that logical cursor type.
3939 See the next subsection for details.
3942 @xref{Fringe Bitmaps}.
3945 @c FIXME: I can't find the fringes-indicator-alist variable. Maybe
3946 @c it should be fringe-indicator-alist or fringe-cursor-alist? --xfq
3947 When @code{fringe-cursor-alist} has a buffer-local value, and there is
3948 no bitmap defined for a cursor type, the corresponding value from the
3949 default value of @code{fringes-indicator-alist} is used.
3952 @node Fringe Bitmaps
3953 @subsection Fringe Bitmaps
3954 @cindex fringe bitmaps
3955 @cindex bitmaps, fringe
3957 The @dfn{fringe bitmaps} are the actual bitmaps which represent the
3958 logical fringe indicators for truncated or continued lines, buffer
3959 boundaries, overlay arrows, etc. Each bitmap is represented by a
3962 These symbols are referred to by the variables
3963 @code{fringe-indicator-alist} and @code{fringe-cursor-alist},
3964 described in the previous subsections.
3967 These symbols are referred to by the variable
3968 @code{fringe-indicator-alist}, which maps fringe indicators to bitmaps
3969 (@pxref{Fringe Indicators}), and the variable
3970 @code{fringe-cursor-alist}, which maps fringe cursors to bitmaps
3971 (@pxref{Fringe Cursors}).
3974 Lisp programs can also directly display a bitmap in the left or
3975 right fringe, by using a @code{display} property for one of the
3976 characters appearing in the line (@pxref{Other Display Specs}). Such
3977 a display specification has the form
3980 (@var{fringe} @var{bitmap} [@var{face}])
3984 @var{fringe} is either the symbol @code{left-fringe} or
3985 @code{right-fringe}. @var{bitmap} is a symbol identifying the bitmap
3986 to display. The optional @var{face} names a face whose foreground
3987 color is used to display the bitmap; this face is automatically merged
3988 with the @code{fringe} face.
3990 Here is a list of the standard fringe bitmaps defined in Emacs, and
3991 how they are currently used in Emacs (via
3992 @code{fringe-indicator-alist} and @code{fringe-cursor-alist}):
3995 @item @code{left-arrow}, @code{right-arrow}
3996 Used to indicate truncated lines.
3998 @item @code{left-curly-arrow}, @code{right-curly-arrow}
3999 Used to indicate continued lines.
4001 @item @code{right-triangle}, @code{left-triangle}
4002 The former is used by overlay arrows. The latter is unused.
4004 @item @code{up-arrow}, @code{down-arrow}, @code{top-left-angle} @code{top-right-angle}
4005 @itemx @code{bottom-left-angle}, @code{bottom-right-angle}
4006 @itemx @code{top-right-angle}, @code{top-left-angle}
4007 @itemx @code{left-bracket}, @code{right-bracket}, @code{top-right-angle}, @code{top-left-angle}
4008 Used to indicate buffer boundaries.
4010 @item @code{filled-rectangle}, @code{hollow-rectangle}
4011 @itemx @code{filled-square}, @code{hollow-square}
4012 @itemx @code{vertical-bar}, @code{horizontal-bar}
4013 Used for different types of fringe cursors.
4015 @item @code{empty-line}, @code{exclamation-mark}, @code{question-mark}, @code{exclamation-mark}
4016 Not used by core Emacs features.
4020 The next subsection describes how to define your own fringe bitmaps.
4022 @defun fringe-bitmaps-at-pos &optional pos window
4023 This function returns the fringe bitmaps of the display line
4024 containing position @var{pos} in window @var{window}. The return
4025 value has the form @code{(@var{left} @var{right} @var{ov})}, where @var{left}
4026 is the symbol for the fringe bitmap in the left fringe (or @code{nil}
4027 if no bitmap), @var{right} is similar for the right fringe, and @var{ov}
4028 is non-@code{nil} if there is an overlay arrow in the left fringe.
4030 The value is @code{nil} if @var{pos} is not visible in @var{window}.
4031 If @var{window} is @code{nil}, that stands for the selected window.
4032 If @var{pos} is @code{nil}, that stands for the value of point in
4036 @node Customizing Bitmaps
4037 @subsection Customizing Fringe Bitmaps
4038 @cindex fringe bitmaps, customizing
4040 @defun define-fringe-bitmap bitmap bits &optional height width align
4041 This function defines the symbol @var{bitmap} as a new fringe bitmap,
4042 or replaces an existing bitmap with that name.
4044 The argument @var{bits} specifies the image to use. It should be
4045 either a string or a vector of integers, where each element (an
4046 integer) corresponds to one row of the bitmap. Each bit of an integer
4047 corresponds to one pixel of the bitmap, where the low bit corresponds
4048 to the rightmost pixel of the bitmap.
4050 The height is normally the length of @var{bits}. However, you
4051 can specify a different height with non-@code{nil} @var{height}. The width
4052 is normally 8, but you can specify a different width with non-@code{nil}
4053 @var{width}. The width must be an integer between 1 and 16.
4055 The argument @var{align} specifies the positioning of the bitmap
4056 relative to the range of rows where it is used; the default is to
4057 center the bitmap. The allowed values are @code{top}, @code{center},
4060 The @var{align} argument may also be a list @code{(@var{align}
4061 @var{periodic})} where @var{align} is interpreted as described above.
4062 If @var{periodic} is non-@code{nil}, it specifies that the rows in
4063 @code{bits} should be repeated enough times to reach the specified
4067 @defun destroy-fringe-bitmap bitmap
4068 This function destroy the fringe bitmap identified by @var{bitmap}.
4069 If @var{bitmap} identifies a standard fringe bitmap, it actually
4070 restores the standard definition of that bitmap, instead of
4071 eliminating it entirely.
4074 @defun set-fringe-bitmap-face bitmap &optional face
4075 This sets the face for the fringe bitmap @var{bitmap} to @var{face}.
4076 If @var{face} is @code{nil}, it selects the @code{fringe} face. The
4077 bitmap's face controls the color to draw it in.
4079 @var{face} is merged with the @code{fringe} face, so normally
4080 @var{face} should specify only the foreground color.
4084 @subsection The Overlay Arrow
4085 @c @cindex overlay arrow Duplicates variable names
4087 The @dfn{overlay arrow} is useful for directing the user's attention
4088 to a particular line in a buffer. For example, in the modes used for
4089 interface to debuggers, the overlay arrow indicates the line of code
4090 about to be executed. This feature has nothing to do with
4091 @dfn{overlays} (@pxref{Overlays}).
4093 @defvar overlay-arrow-string
4094 This variable holds the string to display to call attention to a
4095 particular line, or @code{nil} if the arrow feature is not in use.
4096 On a graphical display the contents of the string are ignored; instead a
4097 glyph is displayed in the fringe area to the left of the display area.
4100 @defvar overlay-arrow-position
4101 This variable holds a marker that indicates where to display the overlay
4102 arrow. It should point at the beginning of a line. On a non-graphical
4103 display the arrow text
4104 appears at the beginning of that line, overlaying any text that would
4105 otherwise appear. Since the arrow is usually short, and the line
4106 usually begins with indentation, normally nothing significant is
4109 The overlay-arrow string is displayed in any given buffer if the value
4110 of @code{overlay-arrow-position} in that buffer points into that
4111 buffer. Thus, it is possible to display multiple overlay arrow strings
4112 by creating buffer-local bindings of @code{overlay-arrow-position}.
4113 However, it is usually cleaner to use
4114 @code{overlay-arrow-variable-list} to achieve this result.
4115 @c !!! overlay-arrow-position: but the overlay string may remain in the display
4116 @c of some other buffer until an update is required. This should be fixed
4120 You can do a similar job by creating an overlay with a
4121 @code{before-string} property. @xref{Overlay Properties}.
4123 You can define multiple overlay arrows via the variable
4124 @code{overlay-arrow-variable-list}.
4126 @defvar overlay-arrow-variable-list
4127 This variable's value is a list of variables, each of which specifies
4128 the position of an overlay arrow. The variable
4129 @code{overlay-arrow-position} has its normal meaning because it is on
4133 Each variable on this list can have properties
4134 @code{overlay-arrow-string} and @code{overlay-arrow-bitmap} that
4135 specify an overlay arrow string (for text terminals) or fringe bitmap
4136 (for graphical terminals) to display at the corresponding overlay
4137 arrow position. If either property is not set, the default
4138 @code{overlay-arrow-string} or @code{overlay-arrow} fringe indicator
4143 @section Scroll Bars
4146 Normally the frame parameter @code{vertical-scroll-bars} controls
4147 whether the windows in the frame have vertical scroll bars, and whether
4148 they are on the left or right. The frame parameter
4149 @code{scroll-bar-width} specifies how wide they are (@code{nil} meaning
4152 The frame parameter @code{horizontal-scroll-bars} controls whether
4153 the windows in the frame have horizontal scroll bars. The frame
4154 parameter @code{scroll-bar-height} specifies how high they are
4155 (@code{nil} meaning the default). @xref{Layout Parameters}.
4157 @vindex horizontal-scroll-bars-available-p
4158 Horizontal scroll bars are not available on all platforms. The
4159 function @code{horizontal-scroll-bars-available-p} which takes no
4160 argument returns non-@code{nil} if they are available on your system.
4162 The following three functions take as argument a live frame which
4163 defaults to the selected one.
4165 @defun frame-current-scroll-bars &optional frame
4166 This function reports the scroll bar types for frame @var{frame}. The
4167 value is a cons cell @code{(@var{vertical-type} .@:
4168 @var{horizontal-type})}, where @var{vertical-type} is either
4169 @code{left}, @code{right}, or @code{nil} (which means no vertical scroll
4170 bar.) @var{horizontal-type} is either @code{bottom} or @code{nil}
4171 (which means no horizontal scroll bar).
4174 @defun frame-scroll-bar-width &optional Lisp_Object &optional frame
4175 This function returns the width of vertical scroll bars of @var{frame}
4179 @defun frame-scroll-bar-height &optional Lisp_Object &optional frame
4180 This function returns the height of horizontal scroll bars of
4181 @var{frame} in pixels.
4184 You can override the frame specific settings for individual windows by
4185 using the following function:
4187 @defun set-window-scroll-bars window &optional width vertical-type height horizontal-type
4188 This function sets the width and/or height and the types of scroll bars
4189 for window @var{window}.
4191 @var{width} specifies the width of the vertical scroll bar in pixels
4192 (@code{nil} means use the width specified for the frame).
4193 @var{vertical-type} specifies whether to have a vertical scroll bar and,
4194 if so, where. The possible values are @code{left}, @code{right},
4195 @code{t}, which means to use the frame's default, and @code{nil} for no
4196 vertical scroll bar.
4198 @var{height} specifies the height of the horizontal scroll bar in pixels
4199 (@code{nil} means use the height specified for the frame).
4200 @var{horizontal-type} specifies whether to have a horizontal scroll bar.
4201 The possible values are @code{bottom}, @code{t}, which means to use the
4202 frame's default, and @code{nil} for no horizontal scroll bar.
4204 If @var{window} is @code{nil}, the selected window is used.
4207 The following four functions take as argument a live window which
4208 defaults to the selected one.
4210 @defun window-scroll-bars &optional window
4211 This function returns a list of the form @code{(@var{width}
4212 @var{columns} @var{vertical-type} @var{height} @var{lines}
4213 @var{horizontal-type})}.
4215 The value @var{width} is the value that was specified for the width of
4216 the vertical scroll bar (which may be @code{nil}); @var{columns} is the
4217 (possibly rounded) number of columns that the vertical scroll bar
4220 The value @var{height} is the value that was specified for the height of
4221 the horizontal scroll bar (which may be @code{nil}); @var{lines} is the
4222 (possibly rounded) number of lines that the horizontally scroll bar
4226 @defun window-current-scroll-bars &optional window
4227 This function reports the scroll bar type for window @var{window}. The
4228 value is a cons cell @code{(@var{vertical-type} .@:
4229 @var{horizontal-type})}. Unlike @code{window-scroll-bars}, this reports
4230 the scroll bar type actually used, once frame defaults and
4231 @code{scroll-bar-mode} are taken into account.
4234 @defun window-scroll-bar-width &optional window
4235 This function returns the width in pixels of @var{window}'s vertical
4239 @defun window-scroll-bar-height &optional window
4240 This function returns the height in pixels of @var{window}'s horizontal
4244 If you don't specify these values for a window with
4245 @code{set-window-scroll-bars}, the buffer-local variables
4246 @code{vertical-scroll-bar}, @code{horizontal-scroll-bar},
4247 @code{scroll-bar-width} and @code{scroll-bar-height} in the buffer being
4248 displayed control the window's scroll bars. The function
4249 @code{set-window-buffer} examines these variables. If you change them
4250 in a buffer that is already visible in a window, you can make the window
4251 take note of the new values by calling @code{set-window-buffer}
4252 specifying the same buffer that is already displayed.
4254 You can control the appearance of scroll bars for a particular buffer by
4255 setting the following variables which automatically become buffer-local
4258 @defvar vertical-scroll-bar
4259 This variable specifies the location of the vertical scroll bar. The
4260 possible values are @code{left}, @code{right}, @code{t}, which means to
4261 use the frame's default, and @code{nil} for no scroll bar.
4264 @defvar horizontal-scroll-bar
4265 This variable specifies the location of the horizontal scroll bar. The
4266 possible values are @code{bottom}, @code{t}, which means to use the
4267 frame's default, and @code{nil} for no scroll bar.
4270 @defvar scroll-bar-width
4271 This variable specifies the width of the buffer's vertical scroll bars,
4272 measured in pixels. A value of @code{nil} means to use the value
4273 specified by the frame.
4276 @defvar scroll-bar-height
4277 This variable specifies the height of the buffer's horizontal scroll
4278 bar, measured in pixels. A value of @code{nil} means to use the value
4279 specified by the frame.
4282 Finally you can toggle the display of scroll bars on all frames by
4283 customizing the variables @code{scroll-bar-mode} and
4284 @code{horizontal-scroll-bar-mode}.
4286 @defopt scroll-bar-mode
4287 This variable controls whether and where to put vertical scroll bars in
4288 all frames. The possible values are @code{nil} for no scroll bars,
4289 @code{left} to put scroll bars on the left and @code{right} to put
4290 scroll bars on the right.
4293 @defopt horizontal-scroll-bar-mode
4294 This variable controls whether to display horizontal scroll bars on all
4299 @node Window Dividers
4300 @section Window Dividers
4301 @cindex window dividers
4302 @cindex right dividers
4303 @cindex bottom dividers
4305 Window dividers are bars drawn between a frame's windows. A right
4306 divider is drawn between a window and any adjacent windows on the right.
4307 Its width (thickness) is specified by the frame parameter
4308 @code{right-divider-width}. A bottom divider is drawn between a
4309 window and adjacent windows on the bottom or the echo area. Its width
4310 is specified by the frame parameter @code{bottom-divider-width}. In
4311 either case, specifying a width of zero means to not draw such dividers.
4312 @xref{Layout Parameters}.
4314 Technically, a right divider belongs to the window on its left,
4315 which means that its width contributes to the total width of that
4316 window. A bottom divider belongs to the window above it, which
4317 means that its width contributes to the total height of that window.
4318 @xref{Window Sizes}. When a window has both, a right and a bottom
4319 divider, the bottom divider prevails. This means that a bottom
4320 divider is drawn over the full total width of its window while the right
4321 divider ends above the bottom divider.
4323 Dividers can be dragged with the mouse and are therefore useful for
4324 adjusting the sizes of adjacent windows with the mouse. They also serve
4325 to visually set apart adjacent windows when no scroll bars or mode lines
4326 are present. The following three faces allow the customization of the
4327 appearance of dividers:
4330 @item window-divider
4331 When a divider is less than three pixels wide, it is drawn solidly with
4332 the foreground of this face. For larger dividers this face is used for
4333 the inner part only, excluding the first and last pixel.
4335 @item window-divider-first-pixel
4336 This is the face used for drawing the first pixel of a divider that is
4337 at least three pixels wide. To obtain a solid appearance, set this to
4338 the same value used for the @code{window-divider} face.
4340 @item window-divider-last-pixel
4341 This is the face used for drawing the last pixel of a divider that is at
4342 least three pixels wide. To obtain a solid appearance, set this to the
4343 same value used for the @code{window-divider} face.
4346 You can get the sizes of the dividers of a specific window with the
4347 following two functions.
4349 @defun window-right-divider-width &optional window
4350 Return the width (thickness) in pixels of @var{window}'s right divider.
4351 @var{window} must be a live window and defaults to the selected one.
4352 The return value is always zero for a rightmost window.
4355 @defun window-bottom-divider-width &optional window
4356 Return the width (thickness) in pixels of @var{window}'s bottom divider.
4357 @var{window} must be a live window and defaults to the selected one.
4358 The return value is zero for the minibuffer window or a bottommost
4359 window on a minibuffer-less frame.
4363 @node Display Property
4364 @section The @code{display} Property
4365 @cindex display specification
4366 @kindex display @r{(text property)}
4368 The @code{display} text property (or overlay property) is used to
4369 insert images into text, and to control other aspects of how text
4370 displays. The value of the @code{display} property should be a
4371 display specification, or a list or vector containing several display
4372 specifications. Display specifications in the same @code{display}
4373 property value generally apply in parallel to the text they cover.
4375 If several sources (overlays and/or a text property) specify values
4376 for the @code{display} property, only one of the values takes effect,
4377 following the rules of @code{get-char-property}. @xref{Examining
4380 The rest of this section describes several kinds of
4381 display specifications and what they mean.
4384 * Replacing Specs:: Display specs that replace the text.
4385 * Specified Space:: Displaying one space with a specified width.
4386 * Pixel Specification:: Specifying space width or height in pixels.
4387 * Other Display Specs:: Displaying an image; adjusting the height,
4388 spacing, and other properties of text.
4389 * Display Margins:: Displaying text or images to the side of the main text.
4392 @node Replacing Specs
4393 @subsection Display Specs That Replace The Text
4394 @cindex replacing display specs
4396 Some kinds of display specifications specify something to display
4397 instead of the text that has the property. These are called
4398 @dfn{replacing} display specifications. Emacs does not allow the user
4399 to interactively move point into the middle of buffer text that is
4400 replaced in this way.
4402 If a list of display specifications includes more than one replacing
4403 display specification, the first overrides the rest. Replacing
4404 display specifications make most other display specifications
4405 irrelevant, since those don't apply to the replacement.
4407 For replacing display specifications, @dfn{the text that has the
4408 property} means all the consecutive characters that have the same
4409 Lisp object as their @code{display} property; these characters are
4410 replaced as a single unit. If two characters have different Lisp
4411 objects as their @code{display} properties (i.e., objects which are
4412 not @code{eq}), they are handled separately.
4414 Here is an example which illustrates this point. A string serves as
4415 a replacing display specification, which replaces the text that has
4416 the property with the specified string (@pxref{Other Display Specs}).
4417 Consider the following function:
4422 (let ((string (concat "A"))
4423 (start (+ i i (point-min))))
4424 (put-text-property start (1+ start) 'display string)
4425 (put-text-property start (+ 2 start) 'display string))))
4429 This function gives each of the first ten characters in the buffer a
4430 @code{display} property which is a string @code{"A"}, but they don't
4431 all get the same string object. The first two characters get the same
4432 string object, so they are replaced with one @samp{A}; the fact that
4433 the display property was assigned in two separate calls to
4434 @code{put-text-property} is irrelevant. Similarly, the next two
4435 characters get a second string (@code{concat} creates a new string
4436 object), so they are replaced with one @samp{A}; and so on. Thus, the
4437 ten characters appear as five A's.
4439 @node Specified Space
4440 @subsection Specified Spaces
4441 @cindex spaces, specified height or width
4442 @cindex variable-width spaces
4444 To display a space of specified width and/or height, use a display
4445 specification of the form @code{(space . @var{props})}, where
4446 @var{props} is a property list (a list of alternating properties and
4447 values). You can put this property on one or more consecutive
4448 characters; a space of the specified height and width is displayed in
4449 place of @emph{all} of those characters. These are the properties you
4450 can use in @var{props} to specify the weight of the space:
4453 @item :width @var{width}
4454 If @var{width} is a number, it specifies
4455 that the space width should be @var{width} times the normal character
4456 width. @var{width} can also be a @dfn{pixel width} specification
4457 (@pxref{Pixel Specification}).
4459 @item :relative-width @var{factor}
4460 Specifies that the width of the stretch should be computed from the
4461 first character in the group of consecutive characters that have the
4462 same @code{display} property. The space width is the pixel width of
4463 that character, multiplied by @var{factor}. (On text-mode terminals,
4464 the ``pixel width'' of a character is usually 1, but it could be more
4465 for TABs and double-width CJK characters.)
4467 @item :align-to @var{hpos}
4468 Specifies that the space should be wide enough to reach @var{hpos}.
4469 If @var{hpos} is a number, it is measured in units of the normal
4470 character width. @var{hpos} can also be a @dfn{pixel width}
4471 specification (@pxref{Pixel Specification}).
4474 You should use one and only one of the above properties. You can
4475 also specify the height of the space, with these properties:
4478 @item :height @var{height}
4479 Specifies the height of the space.
4480 If @var{height} is a number, it specifies
4481 that the space height should be @var{height} times the normal character
4482 height. The @var{height} may also be a @dfn{pixel height} specification
4483 (@pxref{Pixel Specification}).
4485 @item :relative-height @var{factor}
4486 Specifies the height of the space, multiplying the ordinary height
4487 of the text having this display specification by @var{factor}.
4489 @item :ascent @var{ascent}
4490 If the value of @var{ascent} is a non-negative number no greater than
4491 100, it specifies that @var{ascent} percent of the height of the space
4492 should be considered as the ascent of the space---that is, the part
4493 above the baseline. The ascent may also be specified in pixel units
4494 with a @dfn{pixel ascent} specification (@pxref{Pixel Specification}).
4498 Don't use both @code{:height} and @code{:relative-height} together.
4500 The @code{:width} and @code{:align-to} properties are supported on
4501 non-graphic terminals, but the other space properties in this section
4504 Note that space properties are treated as paragraph separators for
4505 the purposes of reordering bidirectional text for display.
4506 @xref{Bidirectional Display}, for the details.
4508 @node Pixel Specification
4509 @subsection Pixel Specification for Spaces
4510 @cindex spaces, pixel specification
4512 The value of the @code{:width}, @code{:align-to}, @code{:height},
4513 and @code{:ascent} properties can be a special kind of expression that
4514 is evaluated during redisplay. The result of the evaluation is used
4515 as an absolute number of pixels.
4517 The following expressions are supported:
4521 @var{expr} ::= @var{num} | (@var{num}) | @var{unit} | @var{elem} | @var{pos} | @var{image} | @var{form}
4522 @var{num} ::= @var{integer} | @var{float} | @var{symbol}
4523 @var{unit} ::= in | mm | cm | width | height
4526 @var{elem} ::= left-fringe | right-fringe | left-margin | right-margin
4528 @var{pos} ::= left | center | right
4529 @var{form} ::= (@var{num} . @var{expr}) | (@var{op} @var{expr} ...)
4534 The form @var{num} specifies a fraction of the default frame font
4535 height or width. The form @code{(@var{num})} specifies an absolute
4536 number of pixels. If @var{num} is a symbol, @var{symbol}, its
4537 buffer-local variable binding is used.
4539 The @code{in}, @code{mm}, and @code{cm} units specify the number of
4540 pixels per inch, millimeter, and centimeter, respectively. The
4541 @code{width} and @code{height} units correspond to the default width
4542 and height of the current face. An image specification @code{image}
4543 corresponds to the width or height of the image.
4545 The elements @code{left-fringe}, @code{right-fringe},
4546 @code{left-margin}, @code{right-margin}, @code{scroll-bar}, and
4547 @code{text} specify to the width of the corresponding area of the
4550 The @code{left}, @code{center}, and @code{right} positions can be
4551 used with @code{:align-to} to specify a position relative to the left
4552 edge, center, or right edge of the text area.
4554 Any of the above window elements (except @code{text}) can also be
4555 used with @code{:align-to} to specify that the position is relative to
4556 the left edge of the given area. Once the base offset for a relative
4557 position has been set (by the first occurrence of one of these
4558 symbols), further occurrences of these symbols are interpreted as the
4559 width of the specified area. For example, to align to the center of
4560 the left-margin, use
4563 :align-to (+ left-margin (0.5 . left-margin))
4566 If no specific base offset is set for alignment, it is always relative
4567 to the left edge of the text area. For example, @samp{:align-to 0} in a
4568 header-line aligns with the first text column in the text area.
4570 A value of the form @code{(@var{num} . @var{expr})} stands for the
4571 product of the values of @var{num} and @var{expr}. For example,
4572 @code{(2 . in)} specifies a width of 2 inches, while @code{(0.5 .
4573 @var{image})} specifies half the width (or height) of the specified
4576 The form @code{(+ @var{expr} ...)} adds up the value of the
4577 expressions. The form @code{(- @var{expr} ...)} negates or subtracts
4578 the value of the expressions.
4580 @node Other Display Specs
4581 @subsection Other Display Specifications
4583 Here are the other sorts of display specifications that you can use
4584 in the @code{display} text property.
4588 Display @var{string} instead of the text that has this property.
4590 Recursive display specifications are not supported---@var{string}'s
4591 @code{display} properties, if any, are not used.
4593 @item (image . @var{image-props})
4594 This kind of display specification is an image descriptor (@pxref{Images}).
4595 When used as a display specification, it means to display the image
4596 instead of the text that has the display specification.
4598 @item (slice @var{x} @var{y} @var{width} @var{height})
4599 This specification together with @code{image} specifies a @dfn{slice}
4600 (a partial area) of the image to display. The elements @var{y} and
4601 @var{x} specify the top left corner of the slice, within the image;
4602 @var{width} and @var{height} specify the width and height of the
4603 slice. Integers are numbers of pixels. A floating-point number
4604 in the range 0.0--1.0 stands for that fraction of the width or height
4605 of the entire image.
4607 @item ((margin nil) @var{string})
4608 A display specification of this form means to display @var{string}
4609 instead of the text that has the display specification, at the same
4610 position as that text. It is equivalent to using just @var{string},
4611 but it is done as a special case of marginal display (@pxref{Display
4614 @item (left-fringe @var{bitmap} @r{[}@var{face}@r{]})
4615 @itemx (right-fringe @var{bitmap} @r{[}@var{face}@r{]})
4616 This display specification on any character of a line of text causes
4617 the specified @var{bitmap} be displayed in the left or right fringes
4618 for that line, instead of the characters that have the display
4619 specification. The optional @var{face} specifies the colors to be
4620 used for the bitmap. @xref{Fringe Bitmaps}, for the details.
4622 @item (space-width @var{factor})
4623 This display specification affects all the space characters within the
4624 text that has the specification. It displays all of these spaces
4625 @var{factor} times as wide as normal. The element @var{factor} should
4626 be an integer or float. Characters other than spaces are not affected
4627 at all; in particular, this has no effect on tab characters.
4629 @item (height @var{height})
4630 This display specification makes the text taller or shorter.
4631 Here are the possibilities for @var{height}:
4634 @item @code{(+ @var{n})}
4635 @c FIXME: Add an index for "step"? --xfq
4636 This means to use a font that is @var{n} steps larger. A @dfn{step} is
4637 defined by the set of available fonts---specifically, those that match
4638 what was otherwise specified for this text, in all attributes except
4639 height. Each size for which a suitable font is available counts as
4640 another step. @var{n} should be an integer.
4642 @item @code{(- @var{n})}
4643 This means to use a font that is @var{n} steps smaller.
4645 @item a number, @var{factor}
4646 A number, @var{factor}, means to use a font that is @var{factor} times
4647 as tall as the default font.
4649 @item a symbol, @var{function}
4650 A symbol is a function to compute the height. It is called with the
4651 current height as argument, and should return the new height to use.
4653 @item anything else, @var{form}
4654 If the @var{height} value doesn't fit the previous possibilities, it is
4655 a form. Emacs evaluates it to get the new height, with the symbol
4656 @code{height} bound to the current specified font height.
4659 @item (raise @var{factor})
4660 This kind of display specification raises or lowers the text
4661 it applies to, relative to the baseline of the line.
4663 @var{factor} must be a number, which is interpreted as a multiple of the
4664 height of the affected text. If it is positive, that means to display
4665 the characters raised. If it is negative, that means to display them
4668 If the text also has a @code{height} display specification, that does
4669 not affect the amount of raising or lowering, which is based on the
4670 faces used for the text.
4673 @c We put all the '@code{(when ...)}' on one line to encourage
4674 @c makeinfo's end-of-sentence heuristics to DTRT. Previously, the dot
4675 @c was at eol; the info file ended up w/ two spaces rendered after it.
4676 You can make any display specification conditional. To do that,
4677 package it in another list of the form
4678 @code{(when @var{condition} . @var{spec})}.
4679 Then the specification @var{spec} applies only when
4680 @var{condition} evaluates to a non-@code{nil} value. During the
4681 evaluation, @code{object} is bound to the string or buffer having the
4682 conditional @code{display} property. @code{position} and
4683 @code{buffer-position} are bound to the position within @code{object}
4684 and the buffer position where the @code{display} property was found,
4685 respectively. Both positions can be different when @code{object} is a
4688 @node Display Margins
4689 @subsection Displaying in the Margins
4690 @cindex display margins
4691 @cindex margins, display
4693 A buffer can have blank areas called @dfn{display margins} on the
4694 left and on the right. Ordinary text never appears in these areas,
4695 but you can put things into the display margins using the
4696 @code{display} property. There is currently no way to make text or
4697 images in the margin mouse-sensitive.
4699 The way to display something in the margins is to specify it in a
4700 margin display specification in the @code{display} property of some
4701 text. This is a replacing display specification, meaning that the
4702 text you put it on does not get displayed; the margin display appears,
4703 but that text does not.
4705 A margin display specification looks like @code{((margin
4706 right-margin) @var{spec})} or @code{((margin left-margin) @var{spec})}.
4707 Here, @var{spec} is another display specification that says what to
4708 display in the margin. Typically it is a string of text to display,
4709 or an image descriptor.
4711 To display something in the margin @emph{in association with}
4712 certain buffer text, without altering or preventing the display of
4713 that text, put a @code{before-string} property on the text and put the
4714 margin display specification on the contents of the before-string.
4716 Before the display margins can display anything, you must give
4717 them a nonzero width. The usual way to do that is to set these
4720 @defvar left-margin-width
4721 This variable specifies the width of the left margin, in character
4722 cell (a.k.a.@: ``column'') units. It is buffer-local in all buffers.
4723 A value of @code{nil} means no left marginal area.
4726 @defvar right-margin-width
4727 This variable specifies the width of the right margin, in character
4728 cell units. It is buffer-local in all buffers. A value of @code{nil}
4729 means no right marginal area.
4732 Setting these variables does not immediately affect the window. These
4733 variables are checked when a new buffer is displayed in the window.
4734 Thus, you can make changes take effect by calling
4735 @code{set-window-buffer}.
4737 You can also set the margin widths immediately.
4739 @defun set-window-margins window left &optional right
4740 This function specifies the margin widths for window @var{window}, in
4741 character cell units. The argument @var{left} controls the left
4742 margin, and @var{right} controls the right margin (default @code{0}).
4745 @defun window-margins &optional window
4746 This function returns the width of the left and right margins of
4747 @var{window} as a cons cell of the form @w{@code{(@var{left}
4748 . @var{right})}}. If one of the two marginal areas does not exist,
4749 its width is returned as @code{nil}; if neither of the two margins exist,
4750 the function returns @code{(nil)}. If @var{window} is @code{nil}, the
4751 selected window is used.
4756 @cindex images in buffers
4758 To display an image in an Emacs buffer, you must first create an image
4759 descriptor, then use it as a display specifier in the @code{display}
4760 property of text that is displayed (@pxref{Display Property}).
4762 Emacs is usually able to display images when it is run on a
4763 graphical terminal. Images cannot be displayed in a text terminal, on
4764 certain graphical terminals that lack the support for this, or if
4765 Emacs is compiled without image support. You can use the function
4766 @code{display-images-p} to determine if images can in principle be
4767 displayed (@pxref{Display Feature Testing}).
4770 * Image Formats:: Supported image formats.
4771 * Image Descriptors:: How to specify an image for use in @code{:display}.
4772 * XBM Images:: Special features for XBM format.
4773 * XPM Images:: Special features for XPM format.
4774 * PostScript Images:: Special features for PostScript format.
4775 * ImageMagick Images:: Special features available through ImageMagick.
4776 * SVG Images:: Creating and manipulating SVG images.
4777 * Other Image Types:: Various other formats are supported.
4778 * Defining Images:: Convenient ways to define an image for later use.
4779 * Showing Images:: Convenient ways to display an image once it is defined.
4780 * Multi-Frame Images:: Some images contain more than one frame.
4781 * Image Cache:: Internal mechanisms of image display.
4785 @subsection Image Formats
4786 @cindex image formats
4789 Emacs can display a number of different image formats. Some of
4790 these image formats are supported only if particular support libraries
4791 are installed. On some platforms, Emacs can load support libraries on
4792 demand; if so, the variable @code{dynamic-library-alist} can be used
4793 to modify the set of known names for these dynamic libraries.
4794 @xref{Dynamic Libraries}.
4796 Supported image formats (and the required support libraries) include
4797 PBM and XBM (which do not depend on support libraries and are always
4798 available), XPM (@code{libXpm}), GIF (@code{libgif} or
4799 @code{libungif}), PostScript (@code{gs}), JPEG (@code{libjpeg}), TIFF
4800 (@code{libtiff}), PNG (@code{libpng}), and SVG (@code{librsvg}).
4802 Each of these image formats is associated with an @dfn{image type
4803 symbol}. The symbols for the above formats are, respectively,
4804 @code{pbm}, @code{xbm}, @code{xpm}, @code{gif}, @code{postscript},
4805 @code{jpeg}, @code{tiff}, @code{png}, and @code{svg}.
4807 Furthermore, if you build Emacs with ImageMagick
4808 (@code{libMagickWand}) support, Emacs can display any image format
4809 that ImageMagick can. @xref{ImageMagick Images}. All images
4810 displayed via ImageMagick have type symbol @code{imagemagick}.
4813 This variable contains a list of type symbols for image formats which
4814 are potentially supported in the current configuration.
4816 ``Potentially'' means that Emacs knows about the image types, not
4817 necessarily that they can be used (for example, they could depend on
4818 unavailable dynamic libraries). To know which image types are really
4819 available, use @code{image-type-available-p}.
4822 @defun image-type-available-p type
4823 This function returns non-@code{nil} if images of type @var{type} can
4824 be loaded and displayed. @var{type} must be an image type symbol.
4826 For image types whose support libraries are statically linked, this
4827 function always returns @code{t}. For image types whose support
4828 libraries are dynamically loaded, it returns @code{t} if the library
4829 could be loaded and @code{nil} otherwise.
4832 @node Image Descriptors
4833 @subsection Image Descriptors
4834 @cindex image descriptor
4836 An @dfn{image descriptor} is a list which specifies the underlying
4837 data for an image, and how to display it. It is typically used as the
4838 value of a @code{display} overlay or text property (@pxref{Other
4839 Display Specs}); but @xref{Showing Images}, for convenient helper
4840 functions to insert images into buffers.
4842 Each image descriptor has the form @code{(image . @var{props})},
4843 where @var{props} is a property list of alternating keyword symbols
4844 and values, including at least the pair @code{:type @var{type}} that
4845 specifies the image type.
4847 The following is a list of properties that are meaningful for all
4848 image types (there are also properties which are meaningful only for
4849 certain image types, as documented in the following subsections):
4852 @item :type @var{type}
4855 @xref{Image Formats}.
4857 Every image descriptor must include this property.
4859 @item :file @var{file}
4860 This says to load the image from file @var{file}. If @var{file} is
4861 not an absolute file name, it is expanded in @code{data-directory}.
4863 @item :data @var{data}
4864 This specifies the raw image data. Each image descriptor must have
4865 either @code{:data} or @code{:file}, but not both.
4867 For most image types, the value of a @code{:data} property should be a
4868 string containing the image data. Some image types do not support
4869 @code{:data}; for some others, @code{:data} alone is not enough, so
4870 you need to use other image properties along with @code{:data}. See
4871 the following subsections for details.
4873 @item :margin @var{margin}
4874 This specifies how many pixels to add as an extra margin around the
4875 image. The value, @var{margin}, must be a non-negative number, or a
4876 pair @code{(@var{x} . @var{y})} of such numbers. If it is a pair,
4877 @var{x} specifies how many pixels to add horizontally, and @var{y}
4878 specifies how many pixels to add vertically. If @code{:margin} is not
4879 specified, the default is zero.
4881 @item :ascent @var{ascent}
4882 This specifies the amount of the image's height to use for its
4883 ascent---that is, the part above the baseline. The value,
4884 @var{ascent}, must be a number in the range 0 to 100, or the symbol
4887 If @var{ascent} is a number, that percentage of the image's height is
4888 used for its ascent.
4890 If @var{ascent} is @code{center}, the image is vertically centered
4891 around a centerline which would be the vertical centerline of text drawn
4892 at the position of the image, in the manner specified by the text
4893 properties and overlays that apply to the image.
4895 If this property is omitted, it defaults to 50.
4897 @item :relief @var{relief}
4898 This adds a shadow rectangle around the image. The value,
4899 @var{relief}, specifies the width of the shadow lines, in pixels. If
4900 @var{relief} is negative, shadows are drawn so that the image appears
4901 as a pressed button; otherwise, it appears as an unpressed button.
4903 @item :conversion @var{algorithm}
4904 This specifies a conversion algorithm that should be applied to the
4905 image before it is displayed; the value, @var{algorithm}, specifies
4911 Specifies the Laplace edge detection algorithm, which blurs out small
4912 differences in color while highlighting larger differences. People
4913 sometimes consider this useful for displaying the image for a
4916 @item (edge-detection :matrix @var{matrix} :color-adjust @var{adjust})
4917 @cindex edge detection, images
4918 Specifies a general edge-detection algorithm. @var{matrix} must be
4919 either a nine-element list or a nine-element vector of numbers. A pixel
4920 at position @math{x/y} in the transformed image is computed from
4921 original pixels around that position. @var{matrix} specifies, for each
4922 pixel in the neighborhood of @math{x/y}, a factor with which that pixel
4923 will influence the transformed pixel; element @math{0} specifies the
4924 factor for the pixel at @math{x-1/y-1}, element @math{1} the factor for
4925 the pixel at @math{x/y-1} etc., as shown below:
4928 $$\pmatrix{x-1/y-1 & x/y-1 & x+1/y-1 \cr
4929 x-1/y & x/y & x+1/y \cr
4930 x-1/y+1& x/y+1 & x+1/y+1 \cr}$$
4935 (x-1/y-1 x/y-1 x+1/y-1
4937 x-1/y+1 x/y+1 x+1/y+1)
4941 The resulting pixel is computed from the color intensity of the color
4942 resulting from summing up the RGB values of surrounding pixels,
4943 multiplied by the specified factors, and dividing that sum by the sum
4944 of the factors' absolute values.
4946 Laplace edge-detection currently uses a matrix of
4949 $$\pmatrix{1 & 0 & 0 \cr
4962 Emboss edge-detection uses a matrix of
4965 $$\pmatrix{ 2 & -1 & 0 \cr
4979 Specifies transforming the image so that it looks disabled.
4982 @item :mask @var{mask}
4983 If @var{mask} is @code{heuristic} or @code{(heuristic @var{bg})}, build
4984 a clipping mask for the image, so that the background of a frame is
4985 visible behind the image. If @var{bg} is not specified, or if @var{bg}
4986 is @code{t}, determine the background color of the image by looking at
4987 the four corners of the image, assuming the most frequently occurring
4988 color from the corners is the background color of the image. Otherwise,
4989 @var{bg} must be a list @code{(@var{red} @var{green} @var{blue})}
4990 specifying the color to assume for the background of the image.
4992 If @var{mask} is @code{nil}, remove a mask from the image, if it has
4993 one. Images in some formats include a mask which can be removed by
4994 specifying @code{:mask nil}.
4996 @item :pointer @var{shape}
4997 This specifies the pointer shape when the mouse pointer is over this
4998 image. @xref{Pointer Shape}, for available pointer shapes.
5000 @item :map @var{map}
5002 This associates an image map of @dfn{hot spots} with this image.
5004 An image map is an alist where each element has the format
5005 @code{(@var{area} @var{id} @var{plist})}. An @var{area} is specified
5006 as either a rectangle, a circle, or a polygon.
5008 A rectangle is a cons
5009 @code{(rect . ((@var{x0} . @var{y0}) . (@var{x1} . @var{y1})))}
5010 which specifies the pixel coordinates of the upper left and bottom right
5011 corners of the rectangle area.
5014 @code{(circle . ((@var{x0} . @var{y0}) . @var{r}))}
5015 which specifies the center and the radius of the circle; @var{r} may
5016 be a float or integer.
5019 @code{(poly . [@var{x0} @var{y0} @var{x1} @var{y1} ...])}
5020 where each pair in the vector describes one corner in the polygon.
5022 When the mouse pointer lies on a hot-spot area of an image, the
5023 @var{plist} of that hot-spot is consulted; if it contains a @code{help-echo}
5024 property, that defines a tool-tip for the hot-spot, and if it contains
5025 a @code{pointer} property, that defines the shape of the mouse cursor when
5026 it is on the hot-spot.
5027 @xref{Pointer Shape}, for available pointer shapes.
5029 When you click the mouse when the mouse pointer is over a hot-spot, an
5030 event is composed by combining the @var{id} of the hot-spot with the
5031 mouse event; for instance, @code{[area4 mouse-1]} if the hot-spot's
5032 @var{id} is @code{area4}.
5035 @defun image-mask-p spec &optional frame
5036 This function returns @code{t} if image @var{spec} has a mask bitmap.
5037 @var{frame} is the frame on which the image will be displayed.
5038 @var{frame} @code{nil} or omitted means to use the selected frame
5039 (@pxref{Input Focus}).
5043 @subsection XBM Images
5046 To use XBM format, specify @code{xbm} as the image type. This image
5047 format doesn't require an external library, so images of this type are
5050 Additional image properties supported for the @code{xbm} image type are:
5053 @item :foreground @var{foreground}
5054 The value, @var{foreground}, should be a string specifying the image
5055 foreground color, or @code{nil} for the default color. This color is
5056 used for each pixel in the XBM that is 1. The default is the frame's
5059 @item :background @var{background}
5060 The value, @var{background}, should be a string specifying the image
5061 background color, or @code{nil} for the default color. This color is
5062 used for each pixel in the XBM that is 0. The default is the frame's
5066 If you specify an XBM image using data within Emacs instead of an
5067 external file, use the following three properties:
5070 @item :data @var{data}
5071 The value, @var{data}, specifies the contents of the image.
5072 There are three formats you can use for @var{data}:
5076 A vector of strings or bool-vectors, each specifying one line of the
5077 image. Do specify @code{:height} and @code{:width}.
5080 A string containing the same byte sequence as an XBM file would contain.
5081 You must not specify @code{:height} and @code{:width} in this case,
5082 because omitting them is what indicates the data has the format of an
5083 XBM file. The file contents specify the height and width of the image.
5086 A string or a bool-vector containing the bits of the image (plus perhaps
5087 some extra bits at the end that will not be used). It should contain at
5088 least @var{width} * @code{height} bits. In this case, you must specify
5089 @code{:height} and @code{:width}, both to indicate that the string
5090 contains just the bits rather than a whole XBM file, and to specify the
5094 @item :width @var{width}
5095 The value, @var{width}, specifies the width of the image, in pixels.
5097 @item :height @var{height}
5098 The value, @var{height}, specifies the height of the image, in pixels.
5102 @subsection XPM Images
5105 To use XPM format, specify @code{xpm} as the image type. The
5106 additional image property @code{:color-symbols} is also meaningful with
5107 the @code{xpm} image type:
5110 @item :color-symbols @var{symbols}
5111 The value, @var{symbols}, should be an alist whose elements have the
5112 form @code{(@var{name} . @var{color})}. In each element, @var{name} is
5113 the name of a color as it appears in the image file, and @var{color}
5114 specifies the actual color to use for displaying that name.
5117 @node PostScript Images
5118 @subsection PostScript Images
5119 @cindex postscript images
5121 To use PostScript for an image, specify image type @code{postscript}.
5122 This works only if you have Ghostscript installed. You must always use
5123 these three properties:
5126 @item :pt-width @var{width}
5127 The value, @var{width}, specifies the width of the image measured in
5128 points (1/72 inch). @var{width} must be an integer.
5130 @item :pt-height @var{height}
5131 The value, @var{height}, specifies the height of the image in points
5132 (1/72 inch). @var{height} must be an integer.
5134 @item :bounding-box @var{box}
5135 The value, @var{box}, must be a list or vector of four integers, which
5136 specifying the bounding box of the PostScript image, analogous to the
5137 @samp{BoundingBox} comment found in PostScript files.
5140 %%BoundingBox: 22 171 567 738
5144 @node ImageMagick Images
5145 @subsection ImageMagick Images
5146 @cindex ImageMagick images
5147 @cindex images, support for more formats
5149 If your Emacs build has ImageMagick support, you can use the
5150 ImageMagick library to load many image formats (@pxref{File
5151 Conveniences,,, emacs, The GNU Emacs Manual}). The image type symbol
5152 for images loaded via ImageMagick is @code{imagemagick}, regardless of
5153 the actual underlying image format.
5155 To check for ImageMagick support, use the following:
5158 (image-type-available-p 'imagemagick)
5161 @defun imagemagick-types
5162 This function returns a list of image file extensions supported by the
5163 current ImageMagick installation. Each list element is a symbol
5164 representing an internal ImageMagick name for an image type, such as
5165 @code{BMP} for @file{.bmp} images.
5168 @defopt imagemagick-enabled-types
5169 The value of this variable is a list of ImageMagick image types which
5170 Emacs may attempt to render using ImageMagick. Each list element
5171 should be one of the symbols in the list returned by
5172 @code{imagemagick-types}, or an equivalent string. Alternatively, a
5173 value of @code{t} enables ImageMagick for all possible image types.
5174 Regardless of the value of this variable,
5175 @code{imagemagick-types-inhibit} (see below) takes precedence.
5178 @defopt imagemagick-types-inhibit
5179 The value of this variable lists the ImageMagick image types which
5180 should never be rendered using ImageMagick, regardless of the value of
5181 @code{imagemagick-enabled-types}. A value of @code{t} disables
5182 ImageMagick entirely.
5185 @defvar image-format-suffixes
5186 This variable is an alist mapping image types to file name extensions.
5187 Emacs uses this in conjunction with the @code{:format} image property
5188 (see below) to give a hint to the ImageMagick library as to the type
5189 of an image. Each element has the form @code{(@var{type}
5190 @var{extension})}, where @var{type} is a symbol specifying an image
5191 content-type, and @var{extension} is a string that specifies the
5192 associated file name extension.
5195 Images loaded with ImageMagick support the following additional
5196 image descriptor properties:
5199 @item :background @var{background}
5200 @var{background}, if non-@code{nil}, should be a string specifying a
5201 color, which is used as the image's background color if the image
5202 supports transparency. If the value is @code{nil}, it defaults to the
5203 frame's background color.
5205 @item :width @var{width}, :height @var{height}
5206 The @code{:width} and @code{:height} keywords are used for scaling the
5207 image. If only one of them is specified, the other one will be
5208 calculated so as to preserve the aspect ratio. If both are specified,
5209 aspect ratio may not be preserved.
5211 @item :max-width @var{max-width}, :max-height @var{max-height}
5212 The @code{:max-width} and @code{:max-height} keywords are used for
5213 scaling if the size of the image of the image exceeds these values.
5214 If @code{:width} is set it will have precedence over @code{max-width},
5215 and if @code{:height} is set it will have precedence over
5216 @code{max-height}, but you can otherwise mix these keywords as you
5217 wish. @code{:max-width} and @code{:max-height} will always preserve
5220 @item :scale @var{scale}
5221 This should be a number, where values higher than 1 means to increase
5222 the size, and lower means to decrease the size. For instance, a value
5223 of 0.25 will make the image a quarter size of what it originally was.
5224 If the scaling makes the image larger than specified by
5225 @code{:max-width} or @code{:max-height}, the resulting size will not
5226 exceed those two values. If both @code{:scale} and
5227 @code{:height}/@code{:width} are specified, the height/width will be
5228 adjusted by the specified scaling factor.
5230 @item :format @var{type}
5231 The value, @var{type}, should be a symbol specifying the type of the
5232 image data, as found in @code{image-format-suffixes}. This is used
5233 when the image does not have an associated file name, to provide a
5234 hint to ImageMagick to help it detect the image type.
5236 @item :rotation @var{angle}
5237 Specifies a rotation angle in degrees.
5239 @item :index @var{frame}
5240 @c Doesn't work: http://debbugs.gnu.org/7978
5241 @xref{Multi-Frame Images}.
5245 @subsection SVG Images
5248 SVG (Scalable Vector Graphics) is an XML format for specifying images.
5249 If your Emacs build has with SVG support, you can create and manipulate
5250 these images with the following commands.
5252 @defun svg-create width height &rest args
5253 Create a new, empty SVG image with the specified dimensions.
5254 @var{args} is an argument plist with you can specify following:
5258 The default width (in pixels) of any lines created.
5261 The default stroke color on any lines created.
5264 This function returns an SVG structure, and all the following commands
5265 work on that structure.
5268 @defun svg-gradient svg id type stops
5269 Create a gradient in @var{svg} with identifier @var{id}. @var{type}
5270 specifies the gradient type, and can be either @code{linear} or
5271 @code{radial}. @var{stops} is a list of percentage/color pairs.
5273 The following will create a linear gradient that goes from red at the
5274 start, to green 25% of the way, to blue at the end:
5277 (svg-gradient svg "gradient1" 'linear
5278 '((0 . "red") (25 . "green") (100 . "blue")))
5281 The gradient created (and inserted into the SVG object) can later be
5282 used by all functions that create shapes.
5285 All the following functions take an optional list of keyword
5286 parameters that alter the various attributes from their default
5287 values. Valid attributes include:
5291 The width (in pixels) of lines drawn, and outlines around solid
5295 The color of lines drawn, and outlines around solid shapes.
5298 The color used for solid shapes.
5301 The identified of the shape.
5304 If given, this should be the identifier of a previously defined
5308 @defun svg-rectangle svg x y width height &rest args
5309 Add a rectangle to @var{svg} where the upper left corner is at
5310 position @var{x}/@var{y} and is of size @var{width}/@var{height}.
5313 (svg-rectangle svg 100 100 500 500 :gradient "gradient1")
5317 @defun svg-circle svg x y radius &rest args
5318 Add a circle to @var{svg} where the center is at @var{x}/@var{y}
5319 and the radius is @var{radius}.
5322 @defun svg-ellipse svg x y x-radius y-radius &rest args
5323 Add a circle to @var{svg} where the center is at @var{x}/@var{y} and
5324 the horizontal radius is @var{x-radius} and the vertical radius is
5328 @defun svg-line svg x1 y1 x2 y2 &rest args
5329 Add a line to @var{svg} that starts at @var{x1}/@var{y1} and extends
5330 to @var{x2}/@var{y2}.
5333 @defun svg-polyline svg points &rest args
5334 Add a multiple segment line to @var{svg} that goes through
5335 @var{points}, which is a list of X/Y position pairs.
5338 (svg-polyline svg '((200 . 100) (500 . 450) (80 . 100))
5339 :stroke-color "green")
5343 @defun svg-polygon svg points &rest args
5344 Add a polygon to @var{svg} where @var{points} is a list of X/Y pairs
5345 that describe the outer circumference of the polygon.
5348 (svg-polygon svg '((100 . 100) (200 . 150) (150 . 90))
5349 :stroke-color "blue" :fill-color "red"")
5353 Finally, the @code{svg-image} takes an SVG object as its parameter and
5354 returns an image object suitable for use in functions like
5355 @code{insert-image}. Here's a complete example that creates and
5356 inserts an image with a circle:
5359 (let ((svg (svg-create 400 400 :stroke-width 10)))
5360 (svg-gradient svg "gradient1" 'linear '((0 . "red") (100 . "blue")))
5361 (svg-circle svg 200 200 100 :gradient "gradient1" :stroke-color "green")
5362 (insert-image (svg-image svg)))
5366 @node Other Image Types
5367 @subsection Other Image Types
5370 For PBM images, specify image type @code{pbm}. Color, gray-scale and
5371 monochromatic images are supported. For mono PBM images, two additional
5372 image properties are supported.
5375 @item :foreground @var{foreground}
5376 The value, @var{foreground}, should be a string specifying the image
5377 foreground color, or @code{nil} for the default color. This color is
5378 used for each pixel in the PBM that is 1. The default is the frame's
5381 @item :background @var{background}
5382 The value, @var{background}, should be a string specifying the image
5383 background color, or @code{nil} for the default color. This color is
5384 used for each pixel in the PBM that is 0. The default is the frame's
5389 The remaining image types that Emacs can support are:
5393 Image type @code{gif}.
5394 Supports the @code{:index} property. @xref{Multi-Frame Images}.
5397 Image type @code{jpeg}.
5400 Image type @code{png}.
5403 Image type @code{tiff}.
5404 Supports the @code{:index} property. @xref{Multi-Frame Images}.
5407 @node Defining Images
5408 @subsection Defining Images
5409 @cindex define image
5411 The functions @code{create-image}, @code{defimage} and
5412 @code{find-image} provide convenient ways to create image descriptors.
5414 @defun create-image file-or-data &optional type data-p &rest props
5415 This function creates and returns an image descriptor which uses the
5416 data in @var{file-or-data}. @var{file-or-data} can be a file name or
5417 a string containing the image data; @var{data-p} should be @code{nil}
5418 for the former case, non-@code{nil} for the latter case.
5420 The optional argument @var{type} is a symbol specifying the image type.
5421 If @var{type} is omitted or @code{nil}, @code{create-image} tries to
5422 determine the image type from the file's first few bytes, or else
5423 from the file's name.
5425 The remaining arguments, @var{props}, specify additional image
5426 properties---for example,
5428 @c ':heuristic-mask' is not documented?
5430 (create-image "foo.xpm" 'xpm nil :heuristic-mask t)
5433 The function returns @code{nil} if images of this type are not
5434 supported. Otherwise it returns an image descriptor.
5437 @defmac defimage symbol specs &optional doc
5438 This macro defines @var{symbol} as an image name. The arguments
5439 @var{specs} is a list which specifies how to display the image.
5440 The third argument, @var{doc}, is an optional documentation string.
5442 Each argument in @var{specs} has the form of a property list, and each
5443 one should specify at least the @code{:type} property and either the
5444 @code{:file} or the @code{:data} property. The value of @code{:type}
5445 should be a symbol specifying the image type, the value of
5446 @code{:file} is the file to load the image from, and the value of
5447 @code{:data} is a string containing the actual image data. Here is an
5451 (defimage test-image
5452 ((:type xpm :file "~/test1.xpm")
5453 (:type xbm :file "~/test1.xbm")))
5456 @code{defimage} tests each argument, one by one, to see if it is
5457 usable---that is, if the type is supported and the file exists. The
5458 first usable argument is used to make an image descriptor which is
5459 stored in @var{symbol}.
5461 If none of the alternatives will work, then @var{symbol} is defined
5465 @defun image-property image property
5466 Return the value of @var{property} in @var{image}. Properties can be
5467 set by using @code{setf}. Setting a property to @code{nil} will
5468 remove the property from the image.
5471 @defun find-image specs
5472 This function provides a convenient way to find an image satisfying one
5473 of a list of image specifications @var{specs}.
5475 Each specification in @var{specs} is a property list with contents
5476 depending on image type. All specifications must at least contain the
5477 properties @code{:type @var{type}} and either @w{@code{:file @var{file}}}
5478 or @w{@code{:data @var{data}}}, where @var{type} is a symbol specifying
5479 the image type, e.g., @code{xbm}, @var{file} is the file to load the
5480 image from, and @var{data} is a string containing the actual image data.
5481 The first specification in the list whose @var{type} is supported, and
5482 @var{file} exists, is used to construct the image specification to be
5483 returned. If no specification is satisfied, @code{nil} is returned.
5485 The image is looked for in @code{image-load-path}.
5488 @defopt image-load-path
5489 This variable's value is a list of locations in which to search for
5490 image files. If an element is a string or a variable symbol whose
5491 value is a string, the string is taken to be the name of a directory
5492 to search. If an element is a variable symbol whose value is a list,
5493 that is taken to be a list of directory names to search.
5495 The default is to search in the @file{images} subdirectory of the
5496 directory specified by @code{data-directory}, then the directory
5497 specified by @code{data-directory}, and finally in the directories in
5498 @code{load-path}. Subdirectories are not automatically included in
5499 the search, so if you put an image file in a subdirectory, you have to
5500 supply the subdirectory name explicitly. For example, to find the
5501 image @file{images/foo/bar.xpm} within @code{data-directory}, you
5502 should specify the image as follows:
5505 (defimage foo-image '((:type xpm :file "foo/bar.xpm")))
5509 @defun image-load-path-for-library library image &optional path no-error
5510 This function returns a suitable search path for images used by the
5511 Lisp package @var{library}.
5513 The function searches for @var{image} first using @code{image-load-path},
5514 excluding @file{@code{data-directory}/images}, and then in
5515 @code{load-path}, followed by a path suitable for @var{library}, which
5516 includes @file{../../etc/images} and @file{../etc/images} relative to
5517 the library file itself, and finally in
5518 @file{@code{data-directory}/images}.
5520 Then this function returns a list of directories which contains first
5521 the directory in which @var{image} was found, followed by the value of
5522 @code{load-path}. If @var{path} is given, it is used instead of
5525 If @var{no-error} is non-@code{nil} and a suitable path can't be
5526 found, don't signal an error. Instead, return a list of directories as
5527 before, except that @code{nil} appears in place of the image directory.
5529 Here is an example of using @code{image-load-path-for-library}:
5532 (defvar image-load-path) ; shush compiler
5533 (let* ((load-path (image-load-path-for-library
5534 "mh-e" "mh-logo.xpm"))
5535 (image-load-path (cons (car load-path)
5537 (mh-tool-bar-folder-buttons-init))
5541 @vindex image-scaling-factor
5542 Images are automatically scaled when created based on the
5543 @code{image-scaling-factor} variable. The value is either a floating
5544 point number (where numbers higher than 1 means to increase the size
5545 and lower means to shrink the size), or the symbol @code{auto}, which
5546 will compute a scaling factor based on the font pixel size.
5548 @node Showing Images
5549 @subsection Showing Images
5552 You can use an image descriptor by setting up the @code{display}
5553 property yourself, but it is easier to use the functions in this
5556 @defun insert-image image &optional string area slice
5557 This function inserts @var{image} in the current buffer at point. The
5558 value @var{image} should be an image descriptor; it could be a value
5559 returned by @code{create-image}, or the value of a symbol defined with
5560 @code{defimage}. The argument @var{string} specifies the text to put
5561 in the buffer to hold the image. If it is omitted or @code{nil},
5562 @code{insert-image} uses @code{" "} by default.
5564 The argument @var{area} specifies whether to put the image in a margin.
5565 If it is @code{left-margin}, the image appears in the left margin;
5566 @code{right-margin} specifies the right margin. If @var{area} is
5567 @code{nil} or omitted, the image is displayed at point within the
5570 The argument @var{slice} specifies a slice of the image to insert. If
5571 @var{slice} is @code{nil} or omitted the whole image is inserted.
5572 Otherwise, @var{slice} is a list @code{(@var{x} @var{y} @var{width}
5573 @var{height})} which specifies the @var{x} and @var{y} positions and
5574 @var{width} and @var{height} of the image area to insert. Integer
5575 values are in units of pixels. A floating-point number in the range
5576 0.0--1.0 stands for that fraction of the width or height of the entire
5579 Internally, this function inserts @var{string} in the buffer, and gives
5580 it a @code{display} property which specifies @var{image}. @xref{Display
5584 @cindex slice, image
5586 @defun insert-sliced-image image &optional string area rows cols
5587 This function inserts @var{image} in the current buffer at point, like
5588 @code{insert-image}, but splits the image into @var{rows}x@var{cols}
5589 equally sized slices.
5591 Emacs displays each slice as a
5592 separate image, and allows more intuitive scrolling up/down, instead of
5593 jumping up/down the entire image when paging through a buffer that
5594 displays (large) images.
5597 @defun put-image image pos &optional string area
5598 This function puts image @var{image} in front of @var{pos} in the
5599 current buffer. The argument @var{pos} should be an integer or a
5600 marker. It specifies the buffer position where the image should appear.
5601 The argument @var{string} specifies the text that should hold the image
5602 as an alternative to the default.
5604 The argument @var{image} must be an image descriptor, perhaps returned
5605 by @code{create-image} or stored by @code{defimage}.
5607 The argument @var{area} specifies whether to put the image in a margin.
5608 If it is @code{left-margin}, the image appears in the left margin;
5609 @code{right-margin} specifies the right margin. If @var{area} is
5610 @code{nil} or omitted, the image is displayed at point within the
5613 Internally, this function creates an overlay, and gives it a
5614 @code{before-string} property containing text that has a @code{display}
5615 property whose value is the image. (Whew!)
5618 @defun remove-images start end &optional buffer
5619 This function removes images in @var{buffer} between positions
5620 @var{start} and @var{end}. If @var{buffer} is omitted or @code{nil},
5621 images are removed from the current buffer.
5623 This removes only images that were put into @var{buffer} the way
5624 @code{put-image} does it, not images that were inserted with
5625 @code{insert-image} or in other ways.
5628 @defun image-size spec &optional pixels frame
5629 @cindex size of image
5630 This function returns the size of an image as a pair
5631 @w{@code{(@var{width} . @var{height})}}. @var{spec} is an image
5632 specification. @var{pixels} non-@code{nil} means return sizes measured
5633 in pixels, otherwise return sizes measured in the default character size
5634 of @var{frame} (@pxref{Frame Font}). @var{frame} is the frame on which
5635 the image will be displayed. @var{frame} null or omitted means use the
5636 selected frame (@pxref{Input Focus}).
5639 @defvar max-image-size
5640 This variable is used to define the maximum size of image that Emacs
5641 will load. Emacs will refuse to load (and display) any image that is
5642 larger than this limit.
5644 If the value is an integer, it directly specifies the maximum
5645 image height and width, measured in pixels. If it is floating
5646 point, it specifies the maximum image height and width
5647 as a ratio to the frame height and width. If the value is
5648 non-numeric, there is no explicit limit on the size of images.
5650 The purpose of this variable is to prevent unreasonably large images
5651 from accidentally being loaded into Emacs. It only takes effect the
5652 first time an image is loaded. Once an image is placed in the image
5653 cache, it can always be displayed, even if the value of
5654 @code{max-image-size} is subsequently changed (@pxref{Image Cache}).
5657 Images inserted with the insertion functions above also get a local
5658 keymap installed in the text properties (or overlays) that span the
5659 displayed image. This keymap defines the following commands:
5663 Increase the image size (@code{image-increase-size}). A prefix value
5664 of @samp{4} means to increase the size by 40%. The default is 20%.
5667 Decrease the image size (@code{image-increase-size}). A prefix value
5668 of @samp{4} means to decrease the size by 40%. The default is 20%.
5671 Rotate the image by 90 degrees (@code{image-rotate}).
5674 Save the image to a file (@code{image-save}).
5677 @node Multi-Frame Images
5678 @subsection Multi-Frame Images
5679 @cindex multi-frame images
5682 @cindex image animation
5683 @cindex image frames
5684 Some image files can contain more than one image. We say that there
5685 are multiple ``frames'' in the image. At present, Emacs supports
5686 multiple frames for GIF, TIFF, and certain ImageMagick formats such as
5689 The frames can be used either to represent multiple pages (this is
5690 usually the case with multi-frame TIFF files, for example), or to
5691 create animation (usually the case with multi-frame GIF files).
5693 A multi-frame image has a property @code{:index}, whose value is an
5694 integer (counting from 0) that specifies which frame is being displayed.
5696 @defun image-multi-frame-p image
5697 This function returns non-@code{nil} if @var{image} contains more than
5698 one frame. The actual return value is a cons @code{(@var{nimages}
5699 . @var{delay})}, where @var{nimages} is the number of frames and
5700 @var{delay} is the delay in seconds between them, or @code{nil}
5701 if the image does not specify a delay. Images that are intended to be
5702 animated usually specify a frame delay, whereas ones that are intended
5703 to be treated as multiple pages do not.
5706 @defun image-current-frame image
5707 This function returns the index of the current frame number for
5708 @var{image}, counting from 0.
5711 @defun image-show-frame image n &optional nocheck
5712 This function switches @var{image} to frame number @var{n}. It
5713 replaces a frame number outside the valid range with that of the end
5714 of the range, unless @var{nocheck} is non-@code{nil}. If @var{image}
5715 does not contain a frame with the specified number, the image displays
5719 @defun image-animate image &optional index limit
5720 This function animates @var{image}. The optional integer @var{index}
5721 specifies the frame from which to start (default 0). The optional
5722 argument @var{limit} controls the length of the animation. If omitted
5723 or @code{nil}, the image animates once only; if @code{t} it loops
5724 forever; if a number animation stops after that many seconds.
5727 @vindex image-minimum-frame-delay
5728 @vindex image-default-frame-delay
5729 @noindent Animation operates by means of a timer. Note that Emacs imposes a
5730 minimum frame delay of 0.01 (@code{image-minimum-frame-delay}) seconds.
5731 If the image itself does not specify a delay, Emacs uses
5732 @code{image-default-frame-delay}.
5734 @defun image-animate-timer image
5735 This function returns the timer responsible for animating @var{image},
5741 @subsection Image Cache
5744 Emacs caches images so that it can display them again more
5745 efficiently. When Emacs displays an image, it searches the image
5746 cache for an existing image specification @code{equal} to the desired
5747 specification. If a match is found, the image is displayed from the
5748 cache. Otherwise, Emacs loads the image normally.
5750 @defun image-flush spec &optional frame
5751 This function removes the image with specification @var{spec} from the
5752 image cache of frame @var{frame}. Image specifications are compared
5753 using @code{equal}. If @var{frame} is @code{nil}, it defaults to the
5754 selected frame. If @var{frame} is @code{t}, the image is flushed on
5755 all existing frames.
5757 In Emacs's current implementation, each graphical terminal possesses an
5758 image cache, which is shared by all the frames on that terminal
5759 (@pxref{Multiple Terminals}). Thus, refreshing an image in one frame
5760 also refreshes it in all other frames on the same terminal.
5763 One use for @code{image-flush} is to tell Emacs about a change in an
5764 image file. If an image specification contains a @code{:file}
5765 property, the image is cached based on the file's contents when the
5766 image is first displayed. Even if the file subsequently changes,
5767 Emacs continues displaying the old version of the image. Calling
5768 @code{image-flush} flushes the image from the cache, forcing Emacs to
5769 re-read the file the next time it needs to display that image.
5771 Another use for @code{image-flush} is for memory conservation. If
5772 your Lisp program creates a large number of temporary images over a
5773 period much shorter than @code{image-cache-eviction-delay} (see
5774 below), you can opt to flush unused images yourself, instead of
5775 waiting for Emacs to do it automatically.
5777 @defun clear-image-cache &optional filter
5778 This function clears an image cache, removing all the images stored in
5779 it. If @var{filter} is omitted or @code{nil}, it clears the cache for
5780 the selected frame. If @var{filter} is a frame, it clears the cache
5781 for that frame. If @var{filter} is @code{t}, all image caches are
5782 cleared. Otherwise, @var{filter} is taken to be a file name, and all
5783 images associated with that file name are removed from all image
5787 If an image in the image cache has not been displayed for a specified
5788 period of time, Emacs removes it from the cache and frees the
5791 @defvar image-cache-eviction-delay
5792 This variable specifies the number of seconds an image can remain in
5793 the cache without being displayed. When an image is not displayed for
5794 this length of time, Emacs removes it from the image cache.
5796 Under some circumstances, if the number of images in the cache grows
5797 too large, the actual eviction delay may be shorter than this.
5799 If the value is @code{nil}, Emacs does not remove images from the cache
5800 except when you explicitly clear it. This mode can be useful for
5805 @section Embedded Native Widgets
5807 @cindex embedded widgets
5808 @cindex webkit browser widget
5810 Emacs is able to display native widgets, such as GTK WebKit widgets,
5811 in Emacs buffers when it was built with the necessary support
5812 libraries and is running on a graphical terminal. To test whether
5813 Emacs supports display of embedded widgets, check that the
5814 @code{xwidget-internal} feature is available (@pxref{Named Features}).
5816 To display an embedded widget in a buffer, you must first create an
5817 xwidget object, and then use that object as the display specifier
5818 in a @code{display} text or overlay property (@pxref{Display
5821 @defun make-xwidget type title width height arguments &optional buffer
5822 This creates and returns an xwidget object. If
5823 @var{buffer} is omitted or @code{nil}, it defaults to the current
5824 buffer. If @var{buffer} names a buffer that doesn't exist, it will be
5825 created. The @var{type} identifies the type of the xwidget component,
5826 it can be one of the following:
5830 The WebKit component.
5833 The @var{width} and @var{height} arguments specify the widget size in
5834 pixels, and @var{title}, a string, specifies its title.
5837 @defun xwidgetp object
5838 This function returns @code{t} if @var{object} is an xwidget,
5839 @code{nil} otherwise.
5842 @defun xwidget-plist xwidget
5843 This function returns the property list of @var{xwidget}.
5846 @defun set-xwidget-plist xwidget plist
5847 This function replaces the property list of @var{xwidget} with a new
5848 property list given by @var{plist}.
5851 @defun xwidget-buffer xwidget
5852 This function returns the buffer of @var{xwidget}.
5855 @defun get-buffer-xwidgets buffer
5856 This function returns a list of xwidget objects associated with the
5857 @var{buffer}, which can be specified as a buffer object or a name of
5858 an existing buffer, a string. The value is @code{nil} if @var{buffer}
5859 contains no xwidgets.
5862 @defun xwidget-webkit-goto-uri xwidget uri
5863 This function browses the specified @var{uri} in the given
5864 @var{xwidget}. The @var{uri} is a string that specifies the name of a
5865 file or a URL. @c FIXME: What else can a URI specify in this context?
5868 @defun xwidget-webkit-execute-script xwidget script
5869 This function causes the browser widget specified by @var{xwidget} to
5870 execute the specified JavaScript @code{script}.
5873 @defun xwidget-webkit-execute-script-rv xwidget script &optional default
5874 This function executes the specified @var{script} like
5875 @code{xwidget-webkit-execute-script} does, but it also returns the
5876 script's return value as a string. If @var{script} doesn't return a
5877 value, this function returns @var{default}, or @code{nil} if
5878 @var{default} was omitted.
5881 @defun xwidget-webkit-get-title xwidget
5882 This function returns the title of @var{xwidget} as a string.
5885 @defun xwidget-resize xwidget width height
5886 This function resizes the specified @var{xwidget} to the size
5887 @var{width}x@var{height} pixels.
5890 @defun xwidget-size-request xwidget
5891 This function returns the desired size of @var{xwidget} as a list of
5892 the form @code{(@var{width} @var{height})}. The dimensions are in
5896 @defun xwidget-info xwidget
5897 This function returns the attributes of @var{xwidget} as a vector of
5898 the form @code{[@var{type} @var{title} @var{width} @var{height}]}.
5899 The attributes are usually determined by @code{make-xwidget} when the
5903 @defun set-xwidget-query-on-exit-flag xwidget flag
5904 This function allows you to arrange that Emacs will ask the user for
5905 confirmation before exiting or before killing a buffer that has
5906 @var{xwidget} associated with it. If @var{flag} is non-@code{nil},
5907 Emacs will query the user, otherwise it will not.
5910 @defun xwidget-query-on-exit-flag xwidget
5911 This function returns the current setting of @var{xwidget}s
5912 query-on-exit flag, either @code{t} or @code{nil}.
5917 @cindex buttons in buffers
5918 @cindex clickable buttons in buffers
5920 The Button package defines functions for inserting and manipulating
5921 @dfn{buttons} that can be activated with the mouse or via keyboard
5922 commands. These buttons are typically used for various kinds of
5925 A button is essentially a set of text or overlay properties,
5926 attached to a stretch of text in a buffer. These properties are
5927 called @dfn{button properties}. One of these properties, the
5928 @dfn{action property}, specifies a function which is called when the
5929 user invokes the button using the keyboard or the mouse. The action
5930 function may examine the button and use its other properties as
5933 In some ways, the Button package duplicates the functionality in the
5934 Widget package. @xref{Top, , Introduction, widget, The Emacs Widget
5935 Library}. The advantage of the Button package is that it is faster,
5936 smaller, and simpler to program. From the point of view of the user,
5937 the interfaces produced by the two packages are very similar.
5940 * Button Properties:: Button properties with special meanings.
5941 * Button Types:: Defining common properties for classes of buttons.
5942 * Making Buttons:: Adding buttons to Emacs buffers.
5943 * Manipulating Buttons:: Getting and setting properties of buttons.
5944 * Button Buffer Commands:: Buffer-wide commands and bindings for buttons.
5947 @node Button Properties
5948 @subsection Button Properties
5949 @cindex button properties
5951 Each button has an associated list of properties defining its
5952 appearance and behavior, and other arbitrary properties may be used
5953 for application specific purposes. The following properties have
5954 special meaning to the Button package:
5958 @kindex action @r{(button property)}
5959 The function to call when the user invokes the button, which is passed
5960 the single argument @var{button}. By default this is @code{ignore},
5964 @kindex mouse-action @r{(button property)}
5965 This is similar to @code{action}, and when present, will be used
5966 instead of @code{action} for button invocations resulting from
5967 mouse-clicks (instead of the user hitting @key{RET}). If not
5968 present, mouse-clicks use @code{action} instead.
5971 @kindex face @r{(button property)}
5972 This is an Emacs face controlling how buttons of this type are
5973 displayed; by default this is the @code{button} face.
5976 @kindex mouse-face @r{(button property)}
5977 This is an additional face which controls appearance during
5978 mouse-overs (merged with the usual button face); by default this is
5979 the usual Emacs @code{highlight} face.
5982 @kindex keymap @r{(button property)}
5983 The button's keymap, defining bindings active within the button
5984 region. By default this is the usual button region keymap, stored
5985 in the variable @code{button-map}, which defines @key{RET} and
5986 @key{mouse-2} to invoke the button.
5989 @kindex type @r{(button property)}
5990 The button type. @xref{Button Types}.
5993 @kindex help-index @r{(button property)}
5994 A string displayed by the Emacs tool-tip help system; by default,
5995 @code{"mouse-2, RET: Push this button"}.
5998 @kindex follow-link @r{(button property)}
5999 The follow-link property, defining how a @key{mouse-1} click behaves
6000 on this button, @xref{Clickable Text}.
6003 @kindex button @r{(button property)}
6004 All buttons have a non-@code{nil} @code{button} property, which may be useful
6005 in finding regions of text that comprise buttons (which is what the
6006 standard button functions do).
6009 There are other properties defined for the regions of text in a
6010 button, but these are not generally interesting for typical uses.
6013 @subsection Button Types
6014 @cindex button types
6016 Every button has a @dfn{button type}, which defines default values
6017 for the button's properties. Button types are arranged in a
6018 hierarchy, with specialized types inheriting from more general types,
6019 so that it's easy to define special-purpose types of buttons for
6022 @defun define-button-type name &rest properties
6023 Define a button type called @var{name} (a symbol).
6024 The remaining arguments
6025 form a sequence of @var{property value} pairs, specifying default
6026 property values for buttons with this type (a button's type may be set
6027 by giving it a @code{type} property when creating the button, using
6028 the @code{:type} keyword argument).
6030 In addition, the keyword argument @code{:supertype} may be used to
6031 specify a button-type from which @var{name} inherits its default
6032 property values. Note that this inheritance happens only when
6033 @var{name} is defined; subsequent changes to a supertype are not
6034 reflected in its subtypes.
6037 Using @code{define-button-type} to define default properties for
6038 buttons is not necessary---buttons without any specified type use the
6039 built-in button-type @code{button}---but it is encouraged, since
6040 doing so usually makes the resulting code clearer and more efficient.
6042 @node Making Buttons
6043 @subsection Making Buttons
6044 @cindex making buttons
6046 Buttons are associated with a region of text, using an overlay or
6047 text properties to hold button-specific information, all of which are
6048 initialized from the button's type (which defaults to the built-in
6049 button type @code{button}). Like all Emacs text, the appearance of
6050 the button is governed by the @code{face} property; by default (via
6051 the @code{face} property inherited from the @code{button} button-type)
6052 this is a simple underline, like a typical web-page link.
6054 For convenience, there are two sorts of button-creation functions,
6055 those that add button properties to an existing region of a buffer,
6056 called @code{make-...button}, and those that also insert the button
6057 text, called @code{insert-...button}.
6059 The button-creation functions all take the @code{&rest} argument
6060 @var{properties}, which should be a sequence of @var{property value}
6061 pairs, specifying properties to add to the button; see @ref{Button
6062 Properties}. In addition, the keyword argument @code{:type} may be
6063 used to specify a button-type from which to inherit other properties;
6064 see @ref{Button Types}. Any properties not explicitly specified
6065 during creation will be inherited from the button's type (if the type
6066 defines such a property).
6068 The following functions add a button using an overlay
6069 (@pxref{Overlays}) to hold the button properties:
6071 @defun make-button beg end &rest properties
6072 This makes a button from @var{beg} to @var{end} in the
6073 current buffer, and returns it.
6076 @defun insert-button label &rest properties
6077 This insert a button with the label @var{label} at point,
6081 The following functions are similar, but using text properties
6082 (@pxref{Text Properties}) to hold the button properties. Such buttons
6083 do not add markers to the buffer, so editing in the buffer does not
6084 slow down if there is an extremely large numbers of buttons. However,
6085 if there is an existing face text property on the text (e.g., a face
6086 assigned by Font Lock mode), the button face may not be visible. Both
6087 of these functions return the starting position of the new button.
6089 @defun make-text-button beg end &rest properties
6090 This makes a button from @var{beg} to @var{end} in the current buffer,
6091 using text properties.
6094 @defun insert-text-button label &rest properties
6095 This inserts a button with the label @var{label} at point, using text
6099 @node Manipulating Buttons
6100 @subsection Manipulating Buttons
6101 @cindex manipulating buttons
6103 These are functions for getting and setting properties of buttons.
6104 Often these are used by a button's invocation function to determine
6107 Where a @var{button} parameter is specified, it means an object
6108 referring to a specific button, either an overlay (for overlay
6109 buttons), or a buffer-position or marker (for text property buttons).
6110 Such an object is passed as the first argument to a button's
6111 invocation function when it is invoked.
6113 @defun button-start button
6114 Return the position at which @var{button} starts.
6117 @defun button-end button
6118 Return the position at which @var{button} ends.
6121 @defun button-get button prop
6122 Get the property of button @var{button} named @var{prop}.
6125 @defun button-put button prop val
6126 Set @var{button}'s @var{prop} property to @var{val}.
6129 @defun button-activate button &optional use-mouse-action
6130 Call @var{button}'s @code{action} property (i.e., invoke the function
6131 that is the value of that property, passing it the single argument
6132 @var{button}). If @var{use-mouse-action} is non-@code{nil}, try to
6133 invoke the button's @code{mouse-action} property instead of
6134 @code{action}; if the button has no @code{mouse-action} property, use
6135 @code{action} as normal.
6138 @defun button-label button
6139 Return @var{button}'s text label.
6142 @defun button-type button
6143 Return @var{button}'s button-type.
6146 @defun button-has-type-p button type
6147 Return @code{t} if @var{button} has button-type @var{type}, or one of
6148 @var{type}'s subtypes.
6151 @defun button-at pos
6152 Return the button at position @var{pos} in the current buffer, or
6153 @code{nil}. If the button at @var{pos} is a text property button, the
6154 return value is a marker pointing to @var{pos}.
6157 @defun button-type-put type prop val
6158 Set the button-type @var{type}'s @var{prop} property to @var{val}.
6161 @defun button-type-get type prop
6162 Get the property of button-type @var{type} named @var{prop}.
6165 @defun button-type-subtype-p type supertype
6166 Return @code{t} if button-type @var{type} is a subtype of @var{supertype}.
6169 @node Button Buffer Commands
6170 @subsection Button Buffer Commands
6171 @cindex button buffer commands
6173 These are commands and functions for locating and operating on
6174 buttons in an Emacs buffer.
6176 @code{push-button} is the command that a user uses to actually push
6177 a button, and is bound by default in the button itself to @key{RET}
6178 and to @key{mouse-2} using a local keymap in the button's overlay or
6179 text properties. Commands that are useful outside the buttons itself,
6180 such as @code{forward-button} and @code{backward-button} are
6181 additionally available in the keymap stored in
6182 @code{button-buffer-map}; a mode which uses buttons may want to use
6183 @code{button-buffer-map} as a parent keymap for its keymap.
6185 If the button has a non-@code{nil} @code{follow-link} property, and
6186 @code{mouse-1-click-follows-link} is set, a quick @key{mouse-1} click
6187 will also activate the @code{push-button} command.
6188 @xref{Clickable Text}.
6190 @deffn Command push-button &optional pos use-mouse-action
6191 Perform the action specified by a button at location @var{pos}.
6192 @var{pos} may be either a buffer position or a mouse-event. If
6193 @var{use-mouse-action} is non-@code{nil}, or @var{pos} is a
6194 mouse-event (@pxref{Mouse Events}), try to invoke the button's
6195 @code{mouse-action} property instead of @code{action}; if the button
6196 has no @code{mouse-action} property, use @code{action} as normal.
6197 @var{pos} defaults to point, except when @code{push-button} is invoked
6198 interactively as the result of a mouse-event, in which case, the mouse
6199 event's position is used. If there's no button at @var{pos}, do
6200 nothing and return @code{nil}, otherwise return @code{t}.
6203 @deffn Command forward-button n &optional wrap display-message
6204 Move to the @var{n}th next button, or @var{n}th previous button if
6205 @var{n} is negative. If @var{n} is zero, move to the start of any
6206 button at point. If @var{wrap} is non-@code{nil}, moving past either
6207 end of the buffer continues from the other end. If
6208 @var{display-message} is non-@code{nil}, the button's help-echo string
6209 is displayed. Any button with a non-@code{nil} @code{skip} property
6210 is skipped over. Returns the button found.
6213 @deffn Command backward-button n &optional wrap display-message
6214 Move to the @var{n}th previous button, or @var{n}th next button if
6215 @var{n} is negative. If @var{n} is zero, move to the start of any
6216 button at point. If @var{wrap} is non-@code{nil}, moving past either
6217 end of the buffer continues from the other end. If
6218 @var{display-message} is non-@code{nil}, the button's help-echo string
6219 is displayed. Any button with a non-@code{nil} @code{skip} property
6220 is skipped over. Returns the button found.
6223 @defun next-button pos &optional count-current
6224 @defunx previous-button pos &optional count-current
6225 Return the next button after (for @code{next-button}) or before (for
6226 @code{previous-button}) position @var{pos} in the current buffer. If
6227 @var{count-current} is non-@code{nil}, count any button at @var{pos}
6228 in the search, instead of starting at the next button.
6231 @node Abstract Display
6232 @section Abstract Display
6234 @cindex display, abstract
6235 @cindex display, arbitrary objects
6236 @cindex model/view/controller
6237 @cindex view part, model/view/controller
6239 The Ewoc package constructs buffer text that represents a structure
6240 of Lisp objects, and updates the text to follow changes in that
6241 structure. This is like the ``view'' component in the
6242 ``model--view--controller'' design paradigm. Ewoc means ``Emacs's
6243 Widget for Object Collections''.
6245 An @dfn{ewoc} is a structure that organizes information required to
6246 construct buffer text that represents certain Lisp data. The buffer
6247 text of the ewoc has three parts, in order: first, fixed @dfn{header}
6248 text; next, textual descriptions of a series of data elements (Lisp
6249 objects that you specify); and last, fixed @dfn{footer} text.
6250 Specifically, an ewoc contains information on:
6254 The buffer which its text is generated in.
6257 The text's start position in the buffer.
6260 The header and footer strings.
6264 @c or "@cindex node, abstract display"?
6265 A doubly-linked chain of @dfn{nodes}, each of which contains:
6269 A @dfn{data element}, a single Lisp object.
6272 Links to the preceding and following nodes in the chain.
6276 A @dfn{pretty-printer} function which is responsible for
6277 inserting the textual representation of a data
6278 element value into the current buffer.
6281 Typically, you define an ewoc with @code{ewoc-create}, and then pass
6282 the resulting ewoc structure to other functions in the Ewoc package to
6283 build nodes within it, and display it in the buffer. Once it is
6284 displayed in the buffer, other functions determine the correspondence
6285 between buffer positions and nodes, move point from one node's textual
6286 representation to another, and so forth. @xref{Abstract Display
6289 @cindex encapsulation, ewoc
6290 @c or "@cindex encapsulation, abstract display"?
6291 A node @dfn{encapsulates} a data element much the way a variable
6292 holds a value. Normally, encapsulation occurs as a part of adding a
6293 node to the ewoc. You can retrieve the data element value and place a
6294 new value in its place, like so:
6297 (ewoc-data @var{node})
6300 (ewoc-set-data @var{node} @var{new-value})
6301 @result{} @var{new-value}
6305 You can also use, as the data element value, a Lisp object (list or
6306 vector) that is a container for the real value, or an index into
6307 some other structure. The example (@pxref{Abstract Display Example})
6308 uses the latter approach.
6310 When the data changes, you will want to update the text in the
6311 buffer. You can update all nodes by calling @code{ewoc-refresh}, or
6312 just specific nodes using @code{ewoc-invalidate}, or all nodes
6313 satisfying a predicate using @code{ewoc-map}. Alternatively, you can
6314 delete invalid nodes using @code{ewoc-delete} or @code{ewoc-filter},
6315 and add new nodes in their place. Deleting a node from an ewoc deletes
6316 its associated textual description from buffer, as well.
6319 * Abstract Display Functions:: Functions in the Ewoc package.
6320 * Abstract Display Example:: Example of using Ewoc.
6323 @node Abstract Display Functions
6324 @subsection Abstract Display Functions
6326 In this subsection, @var{ewoc} and @var{node} stand for the
6327 structures described above (@pxref{Abstract Display}), while
6328 @var{data} stands for an arbitrary Lisp object used as a data element.
6330 @defun ewoc-create pretty-printer &optional header footer nosep
6331 This constructs and returns a new ewoc, with no nodes (and thus no data
6332 elements). @var{pretty-printer} should be a function that takes one
6333 argument, a data element of the sort you plan to use in this ewoc, and
6334 inserts its textual description at point using @code{insert} (and never
6335 @code{insert-before-markers}, because that would interfere with the
6336 Ewoc package's internal mechanisms).
6338 Normally, a newline is automatically inserted after the header,
6339 the footer and every node's textual description. If @var{nosep}
6340 is non-@code{nil}, no newline is inserted. This may be useful for
6341 displaying an entire ewoc on a single line, for example, or for
6342 making nodes invisible by arranging for @var{pretty-printer}
6343 to do nothing for those nodes.
6345 An ewoc maintains its text in the buffer that is current when
6346 you create it, so switch to the intended buffer before calling
6350 @defun ewoc-buffer ewoc
6351 This returns the buffer where @var{ewoc} maintains its text.
6354 @defun ewoc-get-hf ewoc
6355 This returns a cons cell @code{(@var{header} . @var{footer})}
6356 made from @var{ewoc}'s header and footer.
6359 @defun ewoc-set-hf ewoc header footer
6360 This sets the header and footer of @var{ewoc} to the strings
6361 @var{header} and @var{footer}, respectively.
6364 @defun ewoc-enter-first ewoc data
6365 @defunx ewoc-enter-last ewoc data
6366 These add a new node encapsulating @var{data}, putting it, respectively,
6367 at the beginning or end of @var{ewoc}'s chain of nodes.
6370 @defun ewoc-enter-before ewoc node data
6371 @defunx ewoc-enter-after ewoc node data
6372 These add a new node encapsulating @var{data}, adding it to
6373 @var{ewoc} before or after @var{node}, respectively.
6376 @defun ewoc-prev ewoc node
6377 @defunx ewoc-next ewoc node
6378 These return, respectively, the previous node and the next node of @var{node}
6382 @defun ewoc-nth ewoc n
6383 This returns the node in @var{ewoc} found at zero-based index @var{n}.
6384 A negative @var{n} means count from the end. @code{ewoc-nth} returns
6385 @code{nil} if @var{n} is out of range.
6388 @defun ewoc-data node
6389 This extracts the data encapsulated by @var{node} and returns it.
6392 @defun ewoc-set-data node data
6393 This sets the data encapsulated by @var{node} to @var{data}.
6396 @defun ewoc-locate ewoc &optional pos guess
6397 This determines the node in @var{ewoc} which contains point (or
6398 @var{pos} if specified), and returns that node. If @var{ewoc} has no
6399 nodes, it returns @code{nil}. If @var{pos} is before the first node,
6400 it returns the first node; if @var{pos} is after the last node, it returns
6401 the last node. The optional third arg @var{guess}
6402 should be a node that is likely to be near @var{pos}; this doesn't
6403 alter the result, but makes the function run faster.
6406 @defun ewoc-location node
6407 This returns the start position of @var{node}.
6410 @defun ewoc-goto-prev ewoc arg
6411 @defunx ewoc-goto-next ewoc arg
6412 These move point to the previous or next, respectively, @var{arg}th node
6413 in @var{ewoc}. @code{ewoc-goto-prev} does not move if it is already at
6414 the first node or if @var{ewoc} is empty, whereas @code{ewoc-goto-next}
6415 moves past the last node, returning @code{nil}. Excepting this special
6416 case, these functions return the node moved to.
6419 @defun ewoc-goto-node ewoc node
6420 This moves point to the start of @var{node} in @var{ewoc}.
6423 @defun ewoc-refresh ewoc
6424 This function regenerates the text of @var{ewoc}. It works by
6425 deleting the text between the header and the footer, i.e., all the
6426 data elements' representations, and then calling the pretty-printer
6427 function for each node, one by one, in order.
6430 @defun ewoc-invalidate ewoc &rest nodes
6431 This is similar to @code{ewoc-refresh}, except that only @var{nodes} in
6432 @var{ewoc} are updated instead of the entire set.
6435 @defun ewoc-delete ewoc &rest nodes
6436 This deletes each node in @var{nodes} from @var{ewoc}.
6439 @defun ewoc-filter ewoc predicate &rest args
6440 This calls @var{predicate} for each data element in @var{ewoc} and
6441 deletes those nodes for which @var{predicate} returns @code{nil}.
6442 Any @var{args} are passed to @var{predicate}.
6445 @defun ewoc-collect ewoc predicate &rest args
6446 This calls @var{predicate} for each data element in @var{ewoc}
6447 and returns a list of those elements for which @var{predicate}
6448 returns non-@code{nil}. The elements in the list are ordered
6449 as in the buffer. Any @var{args} are passed to @var{predicate}.
6452 @defun ewoc-map map-function ewoc &rest args
6453 This calls @var{map-function} for each data element in @var{ewoc} and
6454 updates those nodes for which @var{map-function} returns non-@code{nil}.
6455 Any @var{args} are passed to @var{map-function}.
6458 @node Abstract Display Example
6459 @subsection Abstract Display Example
6461 Here is a simple example using functions of the ewoc package to
6462 implement a @dfn{color components} display, an area in a buffer that
6463 represents a vector of three integers (itself representing a 24-bit RGB
6464 value) in various ways.
6467 (setq colorcomp-ewoc nil
6469 colorcomp-mode-map nil
6470 colorcomp-labels ["Red" "Green" "Blue"])
6472 (defun colorcomp-pp (data)
6474 (let ((comp (aref colorcomp-data data)))
6475 (insert (aref colorcomp-labels data) "\t: #x"
6476 (format "%02X" comp) " "
6477 (make-string (ash comp -2) ?#) "\n"))
6478 (let ((cstr (format "#%02X%02X%02X"
6479 (aref colorcomp-data 0)
6480 (aref colorcomp-data 1)
6481 (aref colorcomp-data 2)))
6482 (samp " (sample text) "))
6484 (propertize samp 'face
6485 `(foreground-color . ,cstr))
6486 (propertize samp 'face
6487 `(background-color . ,cstr))
6490 (defun colorcomp (color)
6491 "Allow fiddling with COLOR in a new buffer.
6492 The buffer is in Color Components mode."
6493 (interactive "sColor (name or #RGB or #RRGGBB): ")
6494 (when (string= "" color)
6495 (setq color "green"))
6496 (unless (color-values color)
6497 (error "No such color: %S" color))
6499 (generate-new-buffer (format "originally: %s" color)))
6500 (kill-all-local-variables)
6501 (setq major-mode 'colorcomp-mode
6502 mode-name "Color Components")
6503 (use-local-map colorcomp-mode-map)
6505 (buffer-disable-undo)
6506 (let ((data (apply 'vector (mapcar (lambda (n) (ash n -8))
6507 (color-values color))))
6508 (ewoc (ewoc-create 'colorcomp-pp
6509 "\nColor Components\n\n"
6510 (substitute-command-keys
6511 "\n\\@{colorcomp-mode-map@}"))))
6512 (set (make-local-variable 'colorcomp-data) data)
6513 (set (make-local-variable 'colorcomp-ewoc) ewoc)
6514 (ewoc-enter-last ewoc 0)
6515 (ewoc-enter-last ewoc 1)
6516 (ewoc-enter-last ewoc 2)
6517 (ewoc-enter-last ewoc nil)))
6520 @cindex controller part, model/view/controller
6521 This example can be extended to be a color selection widget (in
6522 other words, the ``controller'' part of the ``model--view--controller''
6523 design paradigm) by defining commands to modify @code{colorcomp-data}
6524 and to finish the selection process, and a keymap to tie it all
6525 together conveniently.
6528 (defun colorcomp-mod (index limit delta)
6529 (let ((cur (aref colorcomp-data index)))
6530 (unless (= limit cur)
6531 (aset colorcomp-data index (+ cur delta)))
6534 (ewoc-nth colorcomp-ewoc index)
6535 (ewoc-nth colorcomp-ewoc -1))))
6537 (defun colorcomp-R-more () (interactive) (colorcomp-mod 0 255 1))
6538 (defun colorcomp-G-more () (interactive) (colorcomp-mod 1 255 1))
6539 (defun colorcomp-B-more () (interactive) (colorcomp-mod 2 255 1))
6540 (defun colorcomp-R-less () (interactive) (colorcomp-mod 0 0 -1))
6541 (defun colorcomp-G-less () (interactive) (colorcomp-mod 1 0 -1))
6542 (defun colorcomp-B-less () (interactive) (colorcomp-mod 2 0 -1))
6544 (defun colorcomp-copy-as-kill-and-exit ()
6545 "Copy the color components into the kill ring and kill the buffer.
6546 The string is formatted #RRGGBB (hash followed by six hex digits)."
6548 (kill-new (format "#%02X%02X%02X"
6549 (aref colorcomp-data 0)
6550 (aref colorcomp-data 1)
6551 (aref colorcomp-data 2)))
6554 (setq colorcomp-mode-map
6555 (let ((m (make-sparse-keymap)))
6557 (define-key m "i" 'colorcomp-R-less)
6558 (define-key m "o" 'colorcomp-R-more)
6559 (define-key m "k" 'colorcomp-G-less)
6560 (define-key m "l" 'colorcomp-G-more)
6561 (define-key m "," 'colorcomp-B-less)
6562 (define-key m "." 'colorcomp-B-more)
6563 (define-key m " " 'colorcomp-copy-as-kill-and-exit)
6567 Note that we never modify the data in each node, which is fixed when the
6568 ewoc is created to be either @code{nil} or an index into the vector
6569 @code{colorcomp-data}, the actual color components.
6572 @section Blinking Parentheses
6573 @cindex parenthesis matching
6574 @cindex blinking parentheses
6575 @cindex balancing parentheses
6577 This section describes the mechanism by which Emacs shows a matching
6578 open parenthesis when the user inserts a close parenthesis.
6580 @defvar blink-paren-function
6581 The value of this variable should be a function (of no arguments) to
6582 be called whenever a character with close parenthesis syntax is inserted.
6583 The value of @code{blink-paren-function} may be @code{nil}, in which
6584 case nothing is done.
6587 @defopt blink-matching-paren
6588 If this variable is @code{nil}, then @code{blink-matching-open} does
6592 @defopt blink-matching-paren-distance
6593 This variable specifies the maximum distance to scan for a matching
6594 parenthesis before giving up.
6597 @defopt blink-matching-delay
6598 This variable specifies the number of seconds to keep indicating the
6599 matching parenthesis. A fraction of a second often gives good
6600 results, but the default is 1, which works on all systems.
6603 @deffn Command blink-matching-open
6604 This function is the default value of @code{blink-paren-function}. It
6605 assumes that point follows a character with close parenthesis syntax
6606 and applies the appropriate effect momentarily to the matching opening
6607 character. If that character is not already on the screen, it
6608 displays the character's context in the echo area. To avoid long
6609 delays, this function does not search farther than
6610 @code{blink-matching-paren-distance} characters.
6612 Here is an example of calling this function explicitly.
6616 (defun interactive-blink-matching-open ()
6617 "Indicate momentarily the start of parenthesized sexp before point."
6621 (let ((blink-matching-paren-distance
6623 (blink-matching-paren t))
6624 (blink-matching-open)))
6629 @node Character Display
6630 @section Character Display
6632 This section describes how characters are actually displayed by
6633 Emacs. Typically, a character is displayed as a @dfn{glyph} (a
6634 graphical symbol which occupies one character position on the screen),
6635 whose appearance corresponds to the character itself. For example,
6636 the character @samp{a} (character code 97) is displayed as @samp{a}.
6637 Some characters, however, are displayed specially. For example, the
6638 formfeed character (character code 12) is usually displayed as a
6639 sequence of two glyphs, @samp{^L}, while the newline character
6640 (character code 10) starts a new screen line.
6642 You can modify how each character is displayed by defining a
6643 @dfn{display table}, which maps each character code into a sequence of
6644 glyphs. @xref{Display Tables}.
6647 * Usual Display:: The usual conventions for displaying characters.
6648 * Display Tables:: What a display table consists of.
6649 * Active Display Table:: How Emacs selects a display table to use.
6650 * Glyphs:: How to define a glyph, and what glyphs mean.
6651 * Glyphless Chars:: How glyphless characters are drawn.
6655 @subsection Usual Display Conventions
6657 Here are the conventions for displaying each character code (in the
6658 absence of a display table, which can override these
6663 conventions; @pxref{Display Tables}).
6666 @cindex printable ASCII characters
6669 The @dfn{printable @acronym{ASCII} characters}, character codes 32
6670 through 126 (consisting of numerals, English letters, and symbols like
6671 @samp{#}) are displayed literally.
6674 The tab character (character code 9) displays as whitespace stretching
6675 up to the next tab stop column. @xref{Text Display,,, emacs, The GNU
6676 Emacs Manual}. The variable @code{tab-width} controls the number of
6677 spaces per tab stop (see below).
6680 The newline character (character code 10) has a special effect: it
6681 ends the preceding line and starts a new line.
6683 @cindex ASCII control characters
6685 The non-printable @dfn{@acronym{ASCII} control characters}---character
6686 codes 0 through 31, as well as the @key{DEL} character (character code
6687 127)---display in one of two ways according to the variable
6688 @code{ctl-arrow}. If this variable is non-@code{nil} (the default),
6689 these characters are displayed as sequences of two glyphs, where the
6690 first glyph is @samp{^} (a display table can specify a glyph to use
6691 instead of @samp{^}); e.g., the @key{DEL} character is displayed as
6694 If @code{ctl-arrow} is @code{nil}, these characters are displayed as
6695 octal escapes (see below).
6697 This rule also applies to carriage return (character code 13), if that
6698 character appears in the buffer. But carriage returns usually do not
6699 appear in buffer text; they are eliminated as part of end-of-line
6700 conversion (@pxref{Coding System Basics}).
6702 @cindex octal escapes
6704 @dfn{Raw bytes} are non-@acronym{ASCII} characters with codes 128
6705 through 255 (@pxref{Text Representations}). These characters display
6706 as @dfn{octal escapes}: sequences of four glyphs, where the first
6707 glyph is the @acronym{ASCII} code for @samp{\}, and the others are
6708 digit characters representing the character code in octal. (A display
6709 table can specify a glyph to use instead of @samp{\}.)
6712 Each non-@acronym{ASCII} character with code above 255 is displayed
6713 literally, if the terminal supports it. If the terminal does not
6714 support it, the character is said to be @dfn{glyphless}, and it is
6715 usually displayed using a placeholder glyph. For example, if a
6716 graphical terminal has no font for a character, Emacs usually displays
6717 a box containing the character code in hexadecimal. @xref{Glyphless
6721 The above display conventions apply even when there is a display
6722 table, for any character whose entry in the active display table is
6723 @code{nil}. Thus, when you set up a display table, you need only
6724 specify the characters for which you want special behavior.
6726 The following variables affect how certain characters are displayed
6727 on the screen. Since they change the number of columns the characters
6728 occupy, they also affect the indentation functions. They also affect
6729 how the mode line is displayed; if you want to force redisplay of the
6730 mode line using the new values, call the function
6731 @code{force-mode-line-update} (@pxref{Mode Line Format}).
6734 @cindex control characters in display
6735 This buffer-local variable controls how control characters are
6736 displayed. If it is non-@code{nil}, they are displayed as a caret
6737 followed by the character: @samp{^A}. If it is @code{nil}, they are
6738 displayed as octal escapes: a backslash followed by three octal
6739 digits, as in @samp{\001}.
6743 The value of this buffer-local variable is the spacing between tab
6744 stops used for displaying tab characters in Emacs buffers. The value
6745 is in units of columns, and the default is 8. Note that this feature
6746 is completely independent of the user-settable tab stops used by the
6747 command @code{tab-to-tab-stop}. @xref{Indent Tabs}.
6750 @node Display Tables
6751 @subsection Display Tables
6753 @cindex display table
6754 A display table is a special-purpose char-table
6755 (@pxref{Char-Tables}), with @code{display-table} as its subtype, which
6756 is used to override the usual character display conventions. This
6757 section describes how to make, inspect, and assign elements to a
6758 display table object.
6760 @defun make-display-table
6761 This creates and returns a display table. The table initially has
6762 @code{nil} in all elements.
6765 The ordinary elements of the display table are indexed by character
6766 codes; the element at index @var{c} says how to display the character
6767 code @var{c}. The value should be @code{nil} (which means to display
6768 the character @var{c} according to the usual display conventions;
6769 @pxref{Usual Display}), or a vector of glyph codes (which means to
6770 display the character @var{c} as those glyphs; @pxref{Glyphs}).
6772 @strong{Warning:} if you use the display table to change the display
6773 of newline characters, the whole buffer will be displayed as one long
6776 The display table also has six @dfn{extra slots} which serve special
6777 purposes. Here is a table of their meanings; @code{nil} in any slot
6778 means to use the default for that slot, as stated below.
6782 The glyph for the end of a truncated screen line (the default for this
6783 is @samp{$}). @xref{Glyphs}. On graphical terminals, Emacs uses
6784 arrows in the fringes to indicate truncation, so the display table has
6788 The glyph for the end of a continued line (the default is @samp{\}).
6789 On graphical terminals, Emacs uses curved arrows in the fringes to
6790 indicate continuation, so the display table has no effect.
6793 The glyph for indicating a character displayed as an octal character
6794 code (the default is @samp{\}).
6797 The glyph for indicating a control character (the default is @samp{^}).
6800 A vector of glyphs for indicating the presence of invisible lines (the
6801 default is @samp{...}). @xref{Selective Display}.
6804 The glyph used to draw the border between side-by-side windows (the
6805 default is @samp{|}). @xref{Splitting Windows}. This takes effect only
6806 when there are no scroll bars; if scroll bars are supported and in use,
6807 a scroll bar separates the two windows.
6810 For example, here is how to construct a display table that mimics
6811 the effect of setting @code{ctl-arrow} to a non-@code{nil} value
6812 (@pxref{Glyphs}, for the function @code{make-glyph-code}):
6815 (setq disptab (make-display-table))
6820 (vector (make-glyph-code ?^ 'escape-glyph)
6821 (make-glyph-code (+ i 64) 'escape-glyph)))))
6823 (vector (make-glyph-code ?^ 'escape-glyph)
6824 (make-glyph-code ?? 'escape-glyph)))))
6827 @defun display-table-slot display-table slot
6828 This function returns the value of the extra slot @var{slot} of
6829 @var{display-table}. The argument @var{slot} may be a number from 0 to
6830 5 inclusive, or a slot name (symbol). Valid symbols are
6831 @code{truncation}, @code{wrap}, @code{escape}, @code{control},
6832 @code{selective-display}, and @code{vertical-border}.
6835 @defun set-display-table-slot display-table slot value
6836 This function stores @var{value} in the extra slot @var{slot} of
6837 @var{display-table}. The argument @var{slot} may be a number from 0 to
6838 5 inclusive, or a slot name (symbol). Valid symbols are
6839 @code{truncation}, @code{wrap}, @code{escape}, @code{control},
6840 @code{selective-display}, and @code{vertical-border}.
6843 @defun describe-display-table display-table
6844 This function displays a description of the display table
6845 @var{display-table} in a help buffer.
6848 @deffn Command describe-current-display-table
6849 This command displays a description of the current display table in a
6853 @node Active Display Table
6854 @subsection Active Display Table
6855 @cindex active display table
6857 Each window can specify a display table, and so can each buffer.
6858 The window's display table, if there is one, takes precedence over the
6859 buffer's display table. If neither exists, Emacs tries to use the
6860 standard display table; if that is @code{nil}, Emacs uses the usual
6861 character display conventions (@pxref{Usual Display}).
6863 Note that display tables affect how the mode line is displayed, so
6864 if you want to force redisplay of the mode line using a new display
6865 table, call @code{force-mode-line-update} (@pxref{Mode Line Format}).
6867 @defun window-display-table &optional window
6868 This function returns @var{window}'s display table, or @code{nil} if
6869 there is none. The default for @var{window} is the selected window.
6872 @defun set-window-display-table window table
6873 This function sets the display table of @var{window} to @var{table}.
6874 The argument @var{table} should be either a display table or
6878 @defvar buffer-display-table
6879 This variable is automatically buffer-local in all buffers; its value
6880 specifies the buffer's display table. If it is @code{nil}, there is
6881 no buffer display table.
6884 @defvar standard-display-table
6885 The value of this variable is the standard display table, which is
6886 used when Emacs is displaying a buffer in a window with neither a
6887 window display table nor a buffer display table defined, or when Emacs
6888 is outputting text to the standard output or error streams. Although its
6889 default is typically @code{nil}, in an interactive session if the
6890 terminal cannot display curved quotes, its default maps curved quotes
6891 to ASCII approximations. @xref{Keys in Documentation}.
6894 The @file{disp-table} library defines several functions for changing
6895 the standard display table.
6902 A @dfn{glyph} is a graphical symbol which occupies a single
6903 character position on the screen. Each glyph is represented in Lisp
6904 as a @dfn{glyph code}, which specifies a character and optionally a
6905 face to display it in (@pxref{Faces}). The main use of glyph codes is
6906 as the entries of display tables (@pxref{Display Tables}). The
6907 following functions are used to manipulate glyph codes:
6909 @defun make-glyph-code char &optional face
6910 This function returns a glyph code representing char @var{char} with
6911 face @var{face}. If @var{face} is omitted or @code{nil}, the glyph
6912 uses the default face; in that case, the glyph code is an integer. If
6913 @var{face} is non-@code{nil}, the glyph code is not necessarily an
6917 @defun glyph-char glyph
6918 This function returns the character of glyph code @var{glyph}.
6921 @defun glyph-face glyph
6922 This function returns face of glyph code @var{glyph}, or @code{nil} if
6923 @var{glyph} uses the default face.
6927 You can set up a @dfn{glyph table} to change how glyph codes are
6928 actually displayed on text terminals. This feature is semi-obsolete;
6929 use @code{glyphless-char-display} instead (@pxref{Glyphless Chars}).
6932 The value of this variable, if non-@code{nil}, is the current glyph
6933 table. It takes effect only on character terminals; on graphical
6934 displays, all glyphs are displayed literally. The glyph table should
6935 be a vector whose @var{g}th element specifies how to display glyph
6936 code @var{g}, where @var{g} is the glyph code for a glyph whose face
6937 is unspecified. Each element should be one of the following:
6941 Display this glyph literally.
6944 Display this glyph by sending the specified string to the terminal.
6947 Display the specified glyph code instead.
6950 Any integer glyph code greater than or equal to the length of the
6951 glyph table is displayed literally.
6955 @node Glyphless Chars
6956 @subsection Glyphless Character Display
6957 @cindex glyphless characters
6959 @dfn{Glyphless characters} are characters which are displayed in a
6960 special way, e.g., as a box containing a hexadecimal code, instead of
6961 being displayed literally. These include characters which are
6962 explicitly defined to be glyphless, as well as characters for which
6963 there is no available font (on a graphical display), and characters
6964 which cannot be encoded by the terminal's coding system (on a text
6967 @defvar glyphless-char-display
6968 The value of this variable is a char-table which defines glyphless
6969 characters and how they are displayed. Each entry must be one of the
6970 following display methods:
6974 Display the character in the usual way.
6976 @item @code{zero-width}
6977 Don't display the character.
6979 @item @code{thin-space}
6980 Display a thin space, 1-pixel wide on graphical displays, or
6981 1-character wide on text terminals.
6983 @item @code{empty-box}
6984 Display an empty box.
6986 @item @code{hex-code}
6987 Display a box containing the Unicode codepoint of the character, in
6988 hexadecimal notation.
6990 @item an @acronym{ASCII} string
6991 Display a box containing that string. The string should contain at
6992 most 6 @acronym{ASCII} characters.
6994 @item a cons cell @code{(@var{graphical} . @var{text})}
6995 Display with @var{graphical} on graphical displays, and with
6996 @var{text} on text terminals. Both @var{graphical} and @var{text}
6997 must be one of the display methods described above.
7001 The @code{thin-space}, @code{empty-box}, @code{hex-code}, and
7002 @acronym{ASCII} string display methods are drawn with the
7003 @code{glyphless-char} face. On text terminals, a box is emulated by
7004 square brackets, @samp{[]}.
7006 The char-table has one extra slot, which determines how to display any
7007 character that cannot be displayed with any available font, or cannot
7008 be encoded by the terminal's coding system. Its value should be one
7009 of the above display methods, except @code{zero-width} or a cons cell.
7011 If a character has a non-@code{nil} entry in an active display table,
7012 the display table takes effect; in this case, Emacs does not consult
7013 @code{glyphless-char-display} at all.
7016 @defopt glyphless-char-display-control
7017 This user option provides a convenient way to set
7018 @code{glyphless-char-display} for groups of similar characters. Do
7019 not set its value directly from Lisp code; the value takes effect only
7020 via a custom @code{:set} function (@pxref{Variable Definitions}),
7021 which updates @code{glyphless-char-display}.
7023 Its value should be an alist of elements @code{(@var{group}
7024 . @var{method})}, where @var{group} is a symbol specifying a group of
7025 characters, and @var{method} is a symbol specifying how to display
7028 @var{group} should be one of the following:
7032 @acronym{ASCII} control characters @code{U+0000} to @code{U+001F},
7033 excluding the newline and tab characters (normally displayed as escape
7034 sequences like @samp{^A}; @pxref{Text Display,, How Text Is Displayed,
7035 emacs, The GNU Emacs Manual}).
7038 Non-@acronym{ASCII}, non-printing characters @code{U+0080} to
7039 @code{U+009F} (normally displayed as octal escape sequences like
7042 @item format-control
7043 Characters of Unicode General Category [Cf], such as @samp{U+200E}
7044 (Left-to-Right Mark), but excluding characters that have graphic
7045 images, such as @samp{U+00AD} (Soft Hyphen).
7048 Characters for there is no suitable font, or which cannot be encoded
7049 by the terminal's coding system.
7052 @c FIXME: this can also be 'acronym', but that's not currently
7053 @c completely implemented; it applies only to the format-control
7054 @c group, and only works if the acronym is in 'char-acronym-table'.
7055 The @var{method} symbol should be one of @code{zero-width},
7056 @code{thin-space}, @code{empty-box}, or @code{hex-code}. These have
7057 the same meanings as in @code{glyphless-char-display}, above.
7064 This section describes how to make Emacs ring the bell (or blink the
7065 screen) to attract the user's attention. Be conservative about how
7066 often you do this; frequent bells can become irritating. Also be
7067 careful not to use just beeping when signaling an error is more
7068 appropriate (@pxref{Errors}).
7070 @defun ding &optional do-not-terminate
7071 @cindex keyboard macro termination
7072 This function beeps, or flashes the screen (see @code{visible-bell} below).
7073 It also terminates any keyboard macro currently executing unless
7074 @var{do-not-terminate} is non-@code{nil}.
7077 @defun beep &optional do-not-terminate
7078 This is a synonym for @code{ding}.
7081 @defopt visible-bell
7082 This variable determines whether Emacs should flash the screen to
7083 represent a bell. Non-@code{nil} means yes, @code{nil} means no.
7084 This is effective on graphical displays, and on text terminals
7085 provided the terminal's Termcap entry defines the visible bell
7086 capability (@samp{vb}).
7089 @defopt ring-bell-function
7090 If this is non-@code{nil}, it specifies how Emacs should ring the
7091 bell. Its value should be a function of no arguments. If this is
7092 non-@code{nil}, it takes precedence over the @code{visible-bell}
7096 @node Window Systems
7097 @section Window Systems
7099 Emacs works with several window systems, most notably the X Window
7100 System. Both Emacs and X use the term ``window'', but use it
7101 differently. An Emacs frame is a single window as far as X is
7102 concerned; the individual Emacs windows are not known to X at all.
7104 @defvar window-system
7105 This terminal-local variable tells Lisp programs what window system
7106 Emacs is using for displaying the frame. The possible values are
7110 @cindex X Window System
7111 Emacs is displaying the frame using X.
7113 Emacs is displaying the frame using native MS-Windows GUI.
7115 Emacs is displaying the frame using the Nextstep interface (used on
7116 GNUstep and Mac OS X).
7118 Emacs is displaying the frame using MS-DOS direct screen writes.
7120 Emacs is displaying the frame on a character-based terminal.
7124 @defvar initial-window-system
7125 This variable holds the value of @code{window-system} used for the
7126 first frame created by Emacs during startup. (When Emacs is invoked
7127 with the @option{--daemon} option, it does not create any initial
7128 frames, so @code{initial-window-system} is @code{nil}, except on
7129 MS-Windows, where it is still @code{w32}. @xref{Initial Options,
7130 daemon,, emacs, The GNU Emacs Manual}.)
7133 @defun window-system &optional frame
7134 This function returns a symbol whose name tells what window system is
7135 used for displaying @var{frame} (which defaults to the currently
7136 selected frame). The list of possible symbols it returns is the same
7137 one documented for the variable @code{window-system} above.
7140 Do @emph{not} use @code{window-system} and
7141 @code{initial-window-system} as predicates or boolean flag variables,
7142 if you want to write code that works differently on text terminals and
7143 graphic displays. That is because @code{window-system} is not a good
7144 indicator of Emacs capabilities on a given display type. Instead, use
7145 @code{display-graphic-p} or any of the other @code{display-*-p}
7146 predicates described in @ref{Display Feature Testing}.
7151 @dfn{Tooltips} are special frames (@pxref{Frames}) that are used to
7152 display helpful hints (a.k.a.@: ``tips'') related to the current
7153 position of the mouse pointer. Emacs uses tooltips to display help
7154 strings about active portions of text (@pxref{Special Properties}) and
7155 about various UI elements, such as menu items (@pxref{Extended Menu
7156 Items}) and tool-bar buttons (@pxref{Tool Bar}).
7159 Tooltip Mode is a minor mode that enables display of tooltips.
7160 Turning off this mode causes the tooltips be displayed in the echo
7161 area. On text-mode (a.k.a.@: ``TTY'') frames, tooltips are always
7162 displayed in the echo area.
7165 @vindex x-gtk-use-system-tooltips
7166 When Emacs is built with GTK+ support, it by default displays tooltips
7167 using GTK+ functions, and the appearance of the tooltips is then
7168 controlled by GTK+ settings. GTK+ tooltips can be disabled by
7169 changing the value of the variable @code{x-gtk-use-system-tooltips} to
7170 @code{nil}. The rest of this subsection describes how to control
7171 non-GTK+ tooltips, which are presented by Emacs itself.
7173 Since tooltips are special frames, they have their frame parameters
7174 (@pxref{Frame Parameters}). Unlike other frames, the frame parameters
7175 for tooltips are stored in a special variable.
7177 @defvar tooltip-frame-parameters
7178 This customizable option holds the frame parameters used for
7179 displaying tooltips. Any font and color parameters are ignored, and
7180 the corresponding attributes of the @code{tooltip} face are used
7181 instead. If @code{left} or @code{top} parameters are included, they
7182 are used as absolute frame-relative coordinates where the tooltip
7183 should be shown. (Mouse-relative position of the tooltip can be
7184 customized using the variables described in @ref{Tooltips,,, emacs,
7185 The GNU Emacs Manual}.) Note that the @code{left} and @code{top}
7186 parameters, if present, override the values of mouse-relative offsets.
7189 @vindex tooltip@r{ face}
7190 The @code{tooltip} face determines the appearance of text shown in
7191 tooltips. It should generally use a variable-pitch font of size that
7192 is preferably smaller than the default frame font.
7194 @findex tooltip-help-tips
7195 @defvar tooltip-functions
7196 This abnormal hook is a list of functions to call when Emacs needs to
7197 display a tooltip. Each function is called with a single argument
7198 @var{event} which is a copy of the last mouse movement event. If a
7199 function on this list actually displays the tooltip, it should return
7200 non-@code{nil}, and then the rest of the functions will not be
7201 called. The default value of this variable is a single function
7202 @code{tooltip-help-tips}.
7205 If you write your own function to be put on the
7206 @code{tooltip-functions} list, you may need to know the buffer of the
7207 mouse event that triggered the tooltip display. The following
7208 function provides that information.
7210 @defun tooltip-event-buffer event
7211 This function returns the buffer over which @var{event} occurred.
7212 Call it with the argument of the function from
7213 @code{tooltip-functions} to obtain the buffer whose text triggered the
7214 tooltip. Note that the event might occur not over a buffer (e.g.,
7215 over the tool bar), in which case this function will return
7219 Other aspects of tooltip display are controlled by several
7220 customizable settings; see @ref{Tooltips,,, emacs, The GNU Emacs
7223 @node Bidirectional Display
7224 @section Bidirectional Display
7225 @cindex bidirectional display
7226 @cindex right-to-left text
7228 Emacs can display text written in scripts, such as Arabic, Farsi,
7229 and Hebrew, whose natural ordering for horizontal text display runs
7230 from right to left. Furthermore, segments of Latin script and digits
7231 embedded in right-to-left text are displayed left-to-right, while
7232 segments of right-to-left script embedded in left-to-right text
7233 (e.g., Arabic or Hebrew text in comments or strings in a program
7234 source file) are appropriately displayed right-to-left. We call such
7235 mixtures of left-to-right and right-to-left text @dfn{bidirectional
7236 text}. This section describes the facilities and options for editing
7237 and displaying bidirectional text.
7239 @cindex logical order
7240 @cindex reading order
7241 @cindex visual order
7242 @cindex unicode bidirectional algorithm
7244 @cindex bidirectional reordering
7245 @cindex reordering, of bidirectional text
7246 Text is stored in Emacs buffers and strings in @dfn{logical} (or
7247 @dfn{reading}) order, i.e., the order in which a human would read
7248 each character. In right-to-left and bidirectional text, the order in
7249 which characters are displayed on the screen (called @dfn{visual
7250 order}) is not the same as logical order; the characters' screen
7251 positions do not increase monotonically with string or buffer
7252 position. In performing this @dfn{bidirectional reordering}, Emacs
7253 follows the Unicode Bidirectional Algorithm (a.k.a.@: @acronym{UBA}),
7254 which is described in Annex #9 of the Unicode standard
7255 (@url{http://www.unicode.org/reports/tr9/}). Emacs provides a ``Full
7256 Bidirectionality'' class implementation of the @acronym{UBA},
7257 consistent with the requirements of the Unicode Standard v8.0.
7259 @defvar bidi-display-reordering
7260 If the value of this buffer-local variable is non-@code{nil} (the
7261 default), Emacs performs bidirectional reordering for display. The
7262 reordering affects buffer text, as well as display strings and overlay
7263 strings from text and overlay properties in the buffer (@pxref{Overlay
7264 Properties}, and @pxref{Display Property}). If the value is
7265 @code{nil}, Emacs does not perform bidirectional reordering in the
7268 The default value of @code{bidi-display-reordering} controls the
7269 reordering of strings which are not directly supplied by a buffer,
7270 including the text displayed in mode lines (@pxref{Mode Line Format})
7271 and header lines (@pxref{Header Lines}).
7274 @cindex unibyte buffers, and bidi reordering
7275 Emacs never reorders the text of a unibyte buffer, even if
7276 @code{bidi-display-reordering} is non-@code{nil} in the buffer. This
7277 is because unibyte buffers contain raw bytes, not characters, and thus
7278 lack the directionality properties required for reordering.
7279 Therefore, to test whether text in a buffer will be reordered for
7280 display, it is not enough to test the value of
7281 @code{bidi-display-reordering} alone. The correct test is this:
7284 (if (and enable-multibyte-characters
7285 bidi-display-reordering)
7286 ;; Buffer is being reordered for display
7290 However, unibyte display and overlay strings @emph{are} reordered if
7291 their parent buffer is reordered. This is because plain-@sc{ascii}
7292 strings are stored by Emacs as unibyte strings. If a unibyte display
7293 or overlay string includes non-@sc{ascii} characters, these characters
7294 are assumed to have left-to-right direction.
7296 @cindex display properties, and bidi reordering of text
7297 Text covered by @code{display} text properties, by overlays with
7298 @code{display} properties whose value is a string, and by any other
7299 properties that replace buffer text, is treated as a single unit when
7300 it is reordered for display. That is, the entire chunk of text
7301 covered by these properties is reordered together. Moreover, the
7302 bidirectional properties of the characters in such a chunk of text are
7303 ignored, and Emacs reorders them as if they were replaced with a
7304 single character @code{U+FFFC}, known as the @dfn{Object Replacement
7305 Character}. This means that placing a display property over a portion
7306 of text may change the way that the surrounding text is reordered for
7307 display. To prevent this unexpected effect, always place such
7308 properties on text whose directionality is identical with text that
7311 @cindex base direction of a paragraph
7312 Each paragraph of bidirectional text has a @dfn{base direction},
7313 either right-to-left or left-to-right. Left-to-right paragraphs are
7314 displayed beginning at the left margin of the window, and are
7315 truncated or continued when the text reaches the right margin.
7316 Right-to-left paragraphs are displayed beginning at the right margin,
7317 and are continued or truncated at the left margin.
7319 By default, Emacs determines the base direction of each paragraph by
7320 looking at the text at its beginning. The precise method of
7321 determining the base direction is specified by the @acronym{UBA}; in a
7322 nutshell, the first character in a paragraph that has an explicit
7323 directionality determines the base direction of the paragraph.
7324 However, sometimes a buffer may need to force a certain base direction
7325 for its paragraphs. For example, buffers containing program source
7326 code should force all paragraphs to be displayed left-to-right. You
7327 can use following variable to do this:
7329 @defvar bidi-paragraph-direction
7330 If the value of this buffer-local variable is the symbol
7331 @code{right-to-left} or @code{left-to-right}, all paragraphs in the
7332 buffer are assumed to have that specified direction. Any other value
7333 is equivalent to @code{nil} (the default), which means to determine
7334 the base direction of each paragraph from its contents.
7336 @cindex @code{prog-mode}, and @code{bidi-paragraph-direction}
7337 Modes for program source code should set this to @code{left-to-right}.
7338 Prog mode does this by default, so modes derived from Prog mode do not
7339 need to set this explicitly (@pxref{Basic Major Modes}).
7342 @defun current-bidi-paragraph-direction &optional buffer
7343 This function returns the paragraph direction at point in the named
7344 @var{buffer}. The returned value is a symbol, either
7345 @code{left-to-right} or @code{right-to-left}. If @var{buffer} is
7346 omitted or @code{nil}, it defaults to the current buffer. If the
7347 buffer-local value of the variable @code{bidi-paragraph-direction} is
7348 non-@code{nil}, the returned value will be identical to that value;
7349 otherwise, the returned value reflects the paragraph direction
7350 determined dynamically by Emacs. For buffers whose value of
7351 @code{bidi-display-reordering} is @code{nil} as well as unibyte
7352 buffers, this function always returns @code{left-to-right}.
7355 @cindex visual-order cursor motion
7356 Sometimes there's a need to move point in strict visual order,
7357 either to the left or to the right of its current screen position.
7358 Emacs provides a primitive to do that.
7360 @defun move-point-visually direction
7361 This function moves point of the currently selected window to the
7362 buffer position that appears immediately to the right or to the left
7363 of point on the screen. If @var{direction} is positive, point will
7364 move one screen position to the right, otherwise it will move one
7365 screen position to the left. Note that, depending on the surrounding
7366 bidirectional context, this could potentially move point many buffer
7367 positions away. If invoked at the end of a screen line, the function
7368 moves point to the rightmost or leftmost screen position of the next
7369 or previous screen line, as appropriate for the value of
7372 The function returns the new buffer position as its value.
7375 @cindex layout on display, and bidirectional text
7376 @cindex jumbled display of bidirectional text
7377 @cindex concatenating bidirectional strings
7378 Bidirectional reordering can have surprising and unpleasant effects
7379 when two strings with bidirectional content are juxtaposed in a
7380 buffer, or otherwise programmatically concatenated into a string of
7381 text. A typical problematic case is when a buffer consists of
7382 sequences of text fields separated by whitespace or punctuation
7383 characters, like Buffer Menu mode or Rmail Summary Mode. Because the
7384 punctuation characters used as separators have @dfn{weak
7385 directionality}, they take on the directionality of surrounding text.
7386 As result, a numeric field that follows a field with bidirectional
7387 content can be displayed @emph{to the left} of the preceding field,
7388 messing up the expected layout. There are several ways to avoid this
7393 Append the special character @code{U+200E}, LEFT-TO-RIGHT MARK, or
7394 @acronym{LRM}, to the end of each field that may have bidirectional
7395 content, or prepend it to the beginning of the following field. The
7396 function @code{bidi-string-mark-left-to-right}, described below, comes
7397 in handy for this purpose. (In a right-to-left paragraph, use
7398 @code{U+200F}, RIGHT-TO-LEFT MARK, or @acronym{RLM}, instead.) This
7399 is one of the solutions recommended by the UBA.
7402 Include the tab character in the field separator. The tab character
7403 plays the role of @dfn{segment separator} in bidirectional reordering,
7404 causing the text on either side to be reordered separately.
7406 @cindex @code{space} display spec, and bidirectional text
7408 Separate fields with a @code{display} property or overlay with a
7409 property value of the form @code{(space . PROPS)} (@pxref{Specified
7410 Space}). Emacs treats this display specification as a @dfn{paragraph
7411 separator}, and reorders the text on either side separately.
7414 @defun bidi-string-mark-left-to-right string
7415 This function returns its argument @var{string}, possibly modified,
7416 such that the result can be safely concatenated with another string,
7417 or juxtaposed with another string in a buffer, without disrupting the
7418 relative layout of this string and the next one on display. If the
7419 string returned by this function is displayed as part of a
7420 left-to-right paragraph, it will always appear on display to the left
7421 of the text that follows it. The function works by examining the
7422 characters of its argument, and if any of those characters could cause
7423 reordering on display, the function appends the @acronym{LRM}
7424 character to the string. The appended @acronym{LRM} character is made
7425 invisible by giving it an @code{invisible} text property of @code{t}
7426 (@pxref{Invisible Text}).
7429 The reordering algorithm uses the bidirectional properties of the
7430 characters stored as their @code{bidi-class} property
7431 (@pxref{Character Properties}). Lisp programs can change these
7432 properties by calling the @code{put-char-code-property} function.
7433 However, doing this requires a thorough understanding of the
7434 @acronym{UBA}, and is therefore not recommended. Any changes to the
7435 bidirectional properties of a character have global effect: they
7436 affect all Emacs frames and windows.
7438 Similarly, the @code{mirroring} property is used to display the
7439 appropriate mirrored character in the reordered text. Lisp programs
7440 can affect the mirrored display by changing this property. Again, any
7441 such changes affect all of Emacs display.
7443 @cindex overriding bidirectional properties
7444 @cindex directional overrides
7447 The bidirectional properties of characters can be overridden by
7448 inserting into the text special directional control characters,
7449 LEFT-TO-RIGHT OVERRIDE (@acronym{LRO}) and RIGHT-TO-LEFT OVERRIDE
7450 (@acronym{RLO}). Any characters between a @acronym{RLO} and the
7451 following newline or POP DIRECTIONAL FORMATTING (@acronym{PDF})
7452 control character, whichever comes first, will be displayed as if they
7453 were strong right-to-left characters, i.e.@: they will be reversed on
7454 display. Similarly, any characters between @acronym{LRO} and
7455 @acronym{PDF} or newline will display as if they were strong
7456 left-to-right, and will @emph{not} be reversed even if they are strong
7457 right-to-left characters.
7459 @cindex phishing using directional overrides
7460 @cindex malicious use of directional overrides
7461 These overrides are useful when you want to make some text
7462 unaffected by the reordering algorithm, and instead directly control
7463 the display order. But they can also be used for malicious purposes,
7464 known as @dfn{phishing}. Specifically, a URL on a Web page or a link
7465 in an email message can be manipulated to make its visual appearance
7466 unrecognizable, or similar to some popular benign location, while the
7467 real location, interpreted by a browser in the logical order, is very
7470 Emacs provides a primitive that applications can use to detect
7471 instances of text whose bidirectional properties were overridden so as
7472 to make a left-to-right character display as if it were a
7473 right-to-left character, or vise versa.
7475 @defun bidi-find-overridden-directionality from to &optional object
7476 This function looks at the text of the specified @var{object} between
7477 positions @var{from} (inclusive) and @var{to} (exclusive), and returns
7478 the first position where it finds a strong left-to-right character
7479 whose directional properties were forced to display the character as
7480 right-to-left, or for a strong right-to-left character that was forced
7481 to display as left-to-right. If it finds no such characters in the
7482 specified region of text, it returns @code{nil}.
7484 The optional argument @var{object} specifies which text to search, and
7485 defaults to the current buffer. If @var{object} is non-@code{nil}, it
7486 can be some other buffer, or it can be a string or a window. If it is
7487 a string, the function searches that string. If it is a window, the
7488 function searches the buffer displayed in that window. If a buffer
7489 whose text you want to examine is displayed in some window, we
7490 recommend to specify it by that window, rather than pass the buffer to
7491 the function. This is because telling the function about the window
7492 allows it to correctly account for window-specific overlays, which
7493 might change the result of the function if some text in the buffer is
7494 covered by overlays.
7497 @cindex copying bidirectional text, preserve visual order
7498 @cindex visual order, preserve when copying bidirectional text
7499 When text that includes mixed right-to-left and left-to-right
7500 characters and bidirectional controls is copied into a different
7501 location, it can change its visual appearance, and also can affect the
7502 visual appearance of the surrounding text at destination. This is
7503 because reordering of bidirectional text specified by the
7504 @acronym{UBA} has non-trivial context-dependent effects both on the
7505 copied text and on the text at copy destination that will surround it.
7507 Sometimes, a Lisp program may need to preserve the exact visual
7508 appearance of the copied text at destination, and of the text that
7509 surrounds the copy. Lisp programs can use the following function to
7510 achieve that effect.
7512 @defun buffer-substring-with-bidi-context start end &optional no-properties
7513 This function works similar to @code{buffer-substring} (@pxref{Buffer
7514 Contents}), but it prepends and appends to the copied text bidi
7515 directional control characters necessary to preserve the visual
7516 appearance of the text when it is inserted at another place. Optional
7517 argument @var{no-properties}, if non-@code{nil}, means remove the text
7518 properties from the copy of the text.