(Display Feature Testing): Fix typo.

[gnu-emacs] / lispref / frames.texi

@c -*-texinfo-*-
@c This is part of the GNU Emacs Lisp Reference Manual.
@c Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995, 1998, 1999, 2002
@c   Free Software Foundation, Inc. 
@c See the file elisp.texi for copying conditions.
@setfilename ../info/frames
@node Frames, Positions, Windows, Top
@chapter Frames
@cindex frame

  A @dfn{frame} is a rectangle on the screen that contains one or more
Emacs windows.  A frame initially contains a single main window (plus
perhaps a minibuffer window), which you can subdivide vertically or
horizontally into smaller windows.

@cindex terminal frame
  When Emacs runs on a text-only terminal, it starts with one
@dfn{terminal frame}.  If you create additional ones, Emacs displays
one and only one at any given time---on the terminal screen, of course.

@cindex window frame
  When Emacs communicates directly with a supported window system, such
as X, it does not have a terminal frame; instead, it starts with
a single @dfn{window frame}, but you can create more, and Emacs can
display several such frames at once as is usual for window systems.

@defun framep object
This predicate returns a non-@code{nil} value if @var{object} is a
frame, and @code{nil} otherwise.  For a frame, the value indicates which
kind of display the frame uses:

@table @code
@item x
The frame is displayed in an X window.
@item t
A terminal frame on a character display.
@item mac
The frame is displayed on a Macintosh.
@item w32
The frame is displayed on MS-Windows 9X/NT.
@item pc
The frame is displayed on an MS-DOS terminal.
@end table
@end defun

@menu
* Creating Frames::             Creating additional frames.
* Multiple Displays::           Creating frames on other displays.
* Frame Parameters::            Controlling frame size, position, font, etc.
* Frame Titles::                Automatic updating of frame titles.
* Deleting Frames::             Frames last until explicitly deleted.
* Finding All Frames::          How to examine all existing frames.
* Frames and Windows::          A frame contains windows;
                                  display of text always works through windows.
* Minibuffers and Frames::      How a frame finds the minibuffer to use.
* Input Focus::                 Specifying the selected frame.
* Visibility of Frames::        Frames may be visible or invisible, or icons.
* Raising and Lowering::        Raising a frame makes it hide other windows;
                                  lowering it makes the others hide them.
* Frame Configurations::        Saving the state of all frames.
* Mouse Tracking::              Getting events that say when the mouse moves.
* Mouse Position::              Asking where the mouse is, or moving it.
* Pop-Up Menus::                Displaying a menu for the user to select from.
* Dialog Boxes::                Displaying a box to ask yes or no.
* Pointer Shapes::              Specifying the shape of the mouse pointer.
* Window System Selections::    Transferring text to and from other X clients.
* Color Names::                 Getting the definitions of color names.
* Text Terminal Colors::        Defining colors for text-only terminals.
* Resources::                   Getting resource values from the server.
* Display Feature Testing::     Determining the features of a terminal.
@end menu

  @xref{Display}, for information about the related topic of 
controlling Emacs redisplay.

@node Creating Frames
@section Creating Frames

To create a new frame, call the function @code{make-frame}.

@defun make-frame &optional alist
This function creates a new frame.  If you are using a supported window
system, it makes a window frame; otherwise, it makes a terminal frame.

The argument is an alist specifying frame parameters.  Any parameters
not mentioned in @var{alist} default according to the value of the
variable @code{default-frame-alist}; parameters not specified even there
default from the standard X resources or whatever is used instead on
your system.

The set of possible parameters depends in principle on what kind of
window system Emacs uses to display its frames.  @xref{Window Frame
Parameters}, for documentation of individual parameters you can specify.
@end defun

@defvar before-make-frame-hook
A normal hook run by @code{make-frame} before it actually creates the
frame.
@end defvar

@defvar after-make-frame-functions
@tindex after-make-frame-functions
An abnormal hook run by @code{make-frame} after it creates the frame.
Each function in @code{after-make-frame-functions} receives one argument, the
frame just created.
@end defvar

@node Multiple Displays
@section Multiple Displays
@cindex multiple X displays
@cindex displays, multiple

  A single Emacs can talk to more than one X display.
Initially, Emacs uses just one display---the one chosen with the
@code{DISPLAY} environment variable or with the @samp{--display} option
(@pxref{Initial Options,,, emacs, The GNU Emacs Manual}).  To connect to
another display, use the command @code{make-frame-on-display} or specify
the @code{display} frame parameter when you create the frame.

  Emacs treats each X server as a separate terminal, giving each one its
own selected frame and its own minibuffer windows.  However, only one of
those frames is ``@emph{the} selected frame'' at any given moment, see
@ref{Input Focus}.

  A few Lisp variables are @dfn{terminal-local}; that is, they have a
separate binding for each terminal.  The binding in effect at any time
is the one for the terminal that the currently selected frame belongs
to.  These variables include @code{default-minibuffer-frame},
@code{defining-kbd-macro}, @code{last-kbd-macro}, and
@code{system-key-alist}.  They are always terminal-local, and can never
be buffer-local (@pxref{Buffer-Local Variables}) or frame-local.

  A single X server can handle more than one screen.  A display name
@samp{@var{host}:@var{server}.@var{screen}} has three parts; the last
part specifies the screen number for a given server.  When you use two
screens belonging to one server, Emacs knows by the similarity in their
names that they share a single keyboard, and it treats them as a single
terminal.

@deffn Command make-frame-on-display display &optional parameters
This creates a new frame on display @var{display}, taking the other
frame parameters from @var{parameters}.  Aside from the @var{display}
argument, it is like @code{make-frame} (@pxref{Creating Frames}).
@end deffn

@defun x-display-list
This returns a list that indicates which X displays Emacs has a
connection to.  The elements of the list are strings, and each one is
a display name.
@end defun

@defun x-open-connection display &optional xrm-string must-succeed
This function opens a connection to the X display @var{display}.  It
does not create a frame on that display, but it permits you to check
that communication can be established with that display.

The optional argument @var{xrm-string}, if not @code{nil}, is a
string of resource names and values, in the same format used in the
@file{.Xresources} file.  The values you specify override the resource
values recorded in the X server itself; they apply to all Emacs frames
created on this display.  Here's an example of what this string might
look like:

@example
"*BorderWidth: 3\n*InternalBorder: 2\n"
@end example

@xref{Resources}.

If @var{must-succeed} is non-@code{nil}, failure to open the connection
terminates Emacs.  Otherwise, it is an ordinary Lisp error.
@end defun

@defun x-close-connection display
This function closes the connection to display @var{display}.  Before
you can do this, you must first delete all the frames that were open on
that display (@pxref{Deleting Frames}).
@end defun

@node Frame Parameters
@section Frame Parameters

  A frame has many parameters that control its appearance and behavior.
Just what parameters a frame has depends on what display mechanism it
uses.

  Frame parameters exist mostly for the sake of window systems.  A
terminal frame has a few parameters, mostly for compatibility's sake;
only the @code{height}, @code{width}, @code{name}, @code{title},
@code{menu-bar-lines}, @code{buffer-list} and @code{buffer-predicate}
parameters do something special.  If the terminal supports colors, the
parameters @code{foreground-color}, @code{background-color},
@code{background-mode} and @code{display-type} are also meaningful.

@menu
* Parameter Access::       How to change a frame's parameters.
* Initial Parameters::     Specifying frame parameters when you make a frame.
* Window Frame Parameters:: List of frame parameters for window systems.
* Size and Position::      Changing the size and position of a frame.
@end menu

@node Parameter Access
@subsection Access to Frame Parameters

These functions let you read and change the parameter values of a
frame.

@defun frame-parameter frame parameter
@tindex frame-parameter
This function returns the value of the parameter named @var{parameter}
of @var{frame}.  If @var{frame} is @code{nil}, it returns the
selected  frame's parameter.
@end defun

@defun frame-parameters frame
The function @code{frame-parameters} returns an alist listing all the
parameters of @var{frame} and their values.
@end defun

@defun modify-frame-parameters frame alist
This function alters the parameters of frame @var{frame} based on the
elements of @var{alist}.  Each element of @var{alist} has the form
@code{(@var{parm} . @var{value})}, where @var{parm} is a symbol naming a
parameter.  If you don't mention a parameter in @var{alist}, its value
doesn't change.
@end defun

@node Initial Parameters
@subsection Initial Frame Parameters

You can specify the parameters for the initial startup frame
by setting @code{initial-frame-alist} in your init file (@pxref{Init File}).

@defvar initial-frame-alist
This variable's value is an alist of parameter values used when creating
the initial window frame.  You can set this variable to specify the
appearance of the initial frame without altering subsequent frames.
Each element has the form:

@example
(@var{parameter} . @var{value})
@end example

Emacs creates the initial frame before it reads your init
file.  After reading that file, Emacs checks @code{initial-frame-alist},
and applies the parameter settings in the altered value to the already
created initial frame.

If these settings affect the frame geometry and appearance, you'll see
the frame appear with the wrong ones and then change to the specified
ones.  If that bothers you, you can specify the same geometry and
appearance with X resources; those do take effect before the frame is
created.  @xref{X Resources,, X Resources, emacs, The GNU Emacs Manual}.

X resource settings typically apply to all frames.  If you want to
specify some X resources solely for the sake of the initial frame, and
you don't want them to apply to subsequent frames, here's how to achieve
this.  Specify parameters in @code{default-frame-alist} to override the
X resources for subsequent frames; then, to prevent these from affecting
the initial frame, specify the same parameters in
@code{initial-frame-alist} with values that match the X resources.
@end defvar

If these parameters specify a separate minibuffer-only frame with
@code{(minibuffer . nil)}, and you have not created one, Emacs creates
one for you.

@defvar minibuffer-frame-alist
This variable's value is an alist of parameter values used when creating
an initial minibuffer-only frame---if such a frame is needed, according
to the parameters for the main initial frame.
@end defvar

@defvar default-frame-alist
This is an alist specifying default values of frame parameters for all
Emacs frames---the first frame, and subsequent frames.  When using the X
Window System, you can get the same results by means of X resources
in many cases.
@end defvar

See also @code{special-display-frame-alist}, in @ref{Choosing Window}.

If you use options that specify window appearance when you invoke Emacs,
they take effect by adding elements to @code{default-frame-alist}.  One
exception is @samp{-geometry}, which adds the specified position to
@code{initial-frame-alist} instead.  @xref{Command Arguments,,, emacs,
The GNU Emacs Manual}.

@node Window Frame Parameters
@subsection Window Frame Parameters

Just what parameters a frame has depends on what display mechanism it
uses.  Here is a table of the parameters that have special meanings in a
window frame; of these, @code{name}, @code{title}, @code{height},
@code{width}, @code{buffer-list} and @code{buffer-predicate} provide
meaningful information in terminal frames, and @code{tty-color-mode}
is meaningful @emph{only} in terminal frames.

@table @code
@item display
The display on which to open this frame.  It should be a string of the
form @code{"@var{host}:@var{dpy}.@var{screen}"}, just like the
@code{DISPLAY} environment variable.

@item title
If a frame has a non-@code{nil} title, it appears in the window system's
border for the frame, and also in the mode line of windows in that frame
if @code{mode-line-frame-identification} uses @samp{%F}
(@pxref{%-Constructs}).  This is normally the case when Emacs is not
using a window system, and can only display one frame at a time.
@xref{Frame Titles}.

@item name
The name of the frame.  The frame name serves as a default for the frame
title, if the @code{title} parameter is unspecified or @code{nil}.  If
you don't specify a name, Emacs sets the frame name automatically
(@pxref{Frame Titles}).

If you specify the frame name explicitly when you create the frame, the
name is also used (instead of the name of the Emacs executable) when
looking up X resources for the frame.

@item left
The screen position of the left edge, in pixels, with respect to the
left edge of the screen.  The value may be a positive number @var{pos},
or a list of the form @code{(+ @var{pos})} which permits specifying a
negative @var{pos} value.

A negative number @minus{}@var{pos}, or a list of the form @code{(-
@var{pos})}, actually specifies the position of the right edge of the
window with respect to the right edge of the screen.  A positive value
of @var{pos} counts toward the left.  @strong{Reminder:} if the
parameter is a negative integer @minus{}@var{pos}, then @var{pos} is
positive.

Some window managers ignore program-specified positions.  If you want to
be sure the position you specify is not ignored, specify a
non-@code{nil} value for the @code{user-position} parameter as well.

@item top
The screen position of the top edge, in pixels, with respect to the
top edge of the screen.  The value may be a positive number @var{pos},
or a list of the form @code{(+ @var{pos})} which permits specifying a
negative @var{pos} value.

A negative number @minus{}@var{pos}, or a list of the form @code{(-
@var{pos})}, actually specifies the position of the bottom edge of the
window with respect to the bottom edge of the screen.  A positive value
of @var{pos} counts toward the top.  @strong{Reminder:} if the
parameter is a negative integer @minus{}@var{pos}, then @var{pos} is
positive.

Some window managers ignore program-specified positions.  If you want to
be sure the position you specify is not ignored, specify a
non-@code{nil} value for the @code{user-position} parameter as well.

@item icon-left
The screen position of the left edge @emph{of the frame's icon}, in
pixels, counting from the left edge of the screen.  This takes effect if
and when the frame is iconified.

@item icon-top
The screen position of the top edge @emph{of the frame's icon}, in
pixels, counting from the top edge of the screen.  This takes effect if
and when the frame is iconified.

@item user-position
When you create a frame and specify its screen position with the
@code{left} and @code{top} parameters, use this parameter to say whether
the specified position was user-specified (explicitly requested in some
way by a human user) or merely program-specified (chosen by a program).
A non-@code{nil} value says the position was user-specified.

Window managers generally heed user-specified positions, and some heed
program-specified positions too.  But many ignore program-specified
positions, placing the window in a default fashion or letting the user
place it with the mouse.  Some window managers, including @code{twm},
let the user specify whether to obey program-specified positions or
ignore them.

When you call @code{make-frame}, you should specify a non-@code{nil}
value for this parameter if the values of the @code{left} and @code{top}
parameters represent the user's stated preference; otherwise, use
@code{nil}.

@item height
The height of the frame contents, in characters.  (To get the height in
pixels, call @code{frame-pixel-height}; see @ref{Size and Position}.)

@item width
The width of the frame contents, in characters.  (To get the height in
pixels, call @code{frame-pixel-width}; see @ref{Size and Position}.)

@item fullscreen
Specify that width, height or both shall be set to the size of the screen.
The value @code{fullwidth} specifies that width shall be the size of the
screen.  The value @code{fullheight} specifies that height shall be the
size of the screen.  The value @code{fullboth} specifies that both the
width and the height shall be set to the size of the screen.

@item window-id
The number of the window-system window used by the frame
to contain the actual Emacs windows.

@item outer-window-id
The number of the outermost window-system window used for the whole frame.

@item minibuffer
Whether this frame has its own minibuffer.  The value @code{t} means
yes, @code{nil} means no, @code{only} means this frame is just a
minibuffer.  If the value is a minibuffer window (in some other frame),
the new frame uses that minibuffer.

@item buffer-predicate
The buffer-predicate function for this frame.  The function
@code{other-buffer} uses this predicate (from the selected frame) to
decide which buffers it should consider, if the predicate is not
@code{nil}.  It calls the predicate with one argument, a buffer, once for
each buffer; if the predicate returns a non-@code{nil} value, it
considers that buffer.

@item buffer-list
A list of buffers that have been selected in this frame,
ordered most-recently-selected first.

@item font
The name of the font for displaying text in the frame.  This is a
string, either a valid font name for your system or the name of an Emacs
fontset (@pxref{Fontsets}).  Changing this frame parameter on a frame
also changes the font-related attributes of the default face on that
frame.

@item auto-raise
Whether selecting the frame raises it (non-@code{nil} means yes).

@item auto-lower
Whether deselecting the frame lowers it (non-@code{nil} means yes).

@item vertical-scroll-bars
Whether the frame has scroll bars for vertical scrolling, and which side
of the frame they should be on.  The possible values are @code{left},
@code{right}, and @code{nil} for no scroll bars.

@item horizontal-scroll-bars
Whether the frame has scroll bars for horizontal scrolling
(non-@code{nil} means yes).  (Horizontal scroll bars are not currently
implemented.)

@item scroll-bar-width
The width of the vertical scroll bar, in pixels.

@item icon-type
The type of icon to use for this frame when it is iconified.  If the
value is a string, that specifies a file containing a bitmap to use.
Any other non-@code{nil} value specifies the default bitmap icon (a
picture of a gnu); @code{nil} specifies a text icon.

@item icon-name
The name to use in the icon for this frame, when and if the icon
appears.  If this is @code{nil}, the frame's title is used.

@item foreground-color
The color to use for the image of a character.  This is a string; the
window system defines the meaningful color names.  Changing this
parameter is equivalent to changing the foreground color of the face
@code{default} on the frame in question.

@item background-color
The color to use for the background of characters.  Changing this
parameter is equivalent to changing the foreground color of the face
@code{default} on the frame in question.

@item background-mode
This parameter is either @code{dark} or @code{light}, according
to whether the background color is a light one or a dark one.

@item mouse-color
The color for the mouse pointer.  Changing this parameter is equivalent
to changing the background color of face @code{mouse}.

@item cursor-color
The color for the cursor that shows point.  Changing this parameter is
equivalent to changing the background color of face @code{cursor}.

@item border-color
The color for the border of the frame.  Changing this parameter is
equivalent to changing the background color of face @code{border}.

@item tty-color-mode
@cindex standard colors for character terminals
This parameter overrides the terminal's color support as given by the
system's terminal capabilities database in that this parameter's value
specifies the color mode to use in terminal frames.  The value can be
either a symbol or a number.  A number specifies the number of colors
to use (and, indirectly, what commands to issue to produce each
color).  For example, @code{(tty-color-mode . 8)} forces Emacs to use
the ANSI escape sequences for 8 standard text colors; and a value of
-1 means Emacs should turn off color support.  If the parameter's
value is a symbol, that symbol is looked up in the alist
@code{tty-color-mode-alist}, and if found, the associated number is
used as the color support mode.

@item scroll-bar-foreground
If non-@code{nil}, the color for the foreground of scroll bars.
Changing this parameter is equivalent to setting the foreground color of
face @code{scroll-bar}.

@item scroll-bar-background
If non-@code{nil}, the color for the background of scroll bars.
Changing this parameter is equivalent to setting the background color of
face @code{scroll-bar}.

@item display-type
This parameter describes the range of possible colors that can be used
in this frame.  Its value is @code{color}, @code{grayscale} or
@code{mono}.

@item cursor-type
The way to display the cursor.  The legitimate values are @code{bar},
@code{box}, and @code{(bar . @var{width})}.  The symbol @code{box}
specifies an ordinary black box overlaying the character after point;
that is the default.  The symbol @code{bar} specifies a vertical bar
between characters as the cursor.  @code{(bar . @var{width})}
specifies a bar @var{width} pixels wide.  The symbol @code{hbar}
specifies a horizontal bar, an underscore-like cursor.  @code{(hbar .
@var{width})} specifiles a horizontal bar @var{width} pixels high.

@vindex cursor-type
The buffer-local variable @code{cursor-type} overrides the value of
the @code{cursor-type} frame parameter, and can in addition have
values @code{t} (use the cursor specified for the frame) and
@code{nil} (don't display a cursor).

@item border-width
The width in pixels of the window border.

@item internal-border-width
The distance in pixels between text and border.

@item unsplittable
If non-@code{nil}, this frame's window is never split automatically.

@item visibility
The state of visibility of the frame.  There are three possibilities:
@code{nil} for invisible, @code{t} for visible, and @code{icon} for
iconified.  @xref{Visibility of Frames}.

@item menu-bar-lines
The number of lines to allocate at the top of the frame for a menu bar.
The default is 1.  @xref{Menu Bar}.  (In Emacs versions that use the X
toolkit, there is only one menu bar line; all that matters about the
number you specify is whether it is greater than zero.)

@item screen-gamma
@cindex gamma correction
If this is a number, Emacs performs ``gamma correction'' which adjusts
the brightness of all colors.  The value should be the screen gamma of
your display, a floating point number.

Usual PC monitors have a screen gamma of 2.2, so color values in
Emacs, and in X windows generally, are calibrated to display properly
on a monitor with that gamma value.  If you specify 2.2 for
@code{screen-gamma}, that means no correction is needed.  Other values
request correction, designed to make the corrected colors appear on
your screen they way they would have appeared without correction on an
ordinary monitor with a gamma value of 2.2.

If your monitor displays colors too light, you should specify a
@code{screen-gamma} value smaller than 2.2.  This requests correction
that makes colors darker.  A screen gamma value of 1.5 may give good
results for LCD color displays.

@item tool-bar-lines
The number of lines to use for the toolbar.  A value of @code{nil} means
don't display a tool bar.

@item line-spacing
Additional space put below text lines in pixels (a positive integer).

@ignore
@item parent-id
@c ??? Not yet working.
The X window number of the window that should be the parent of this one.
Specifying this lets you create an Emacs window inside some other
application's window.  (It is not certain this will be implemented; try
it and see if it works.)
@end ignore
@end table

@node Size and Position
@subsection Frame Size And Position
@cindex size of frame
@cindex screen size
@cindex frame size
@cindex resize frame

  You can read or change the size and position of a frame using the
frame parameters @code{left}, @code{top}, @code{height}, and
@code{width}.  Whatever geometry parameters you don't specify are chosen
by the window manager in its usual fashion.

  Here are some special features for working with sizes and positions.
(For the precise meaning of ``selected frame'' used by these functions,
see @ref{Input Focus}.)

@defun set-frame-position frame left top
This function sets the position of the top left corner of @var{frame} to
@var{left} and @var{top}.  These arguments are measured in pixels, and
normally count from the top left corner of the screen.

Negative parameter values position the bottom edge of the window up from
the bottom edge of the screen, or the right window edge to the left of
the right edge of the screen.  It would probably be better if the values
were always counted from the left and top, so that negative arguments
would position the frame partly off the top or left edge of the screen,
but it seems inadvisable to change that now.
@end defun

@defun frame-height &optional frame
@defunx frame-width &optional frame
These functions return the height and width of @var{frame}, measured in
lines and columns.  If you don't supply @var{frame}, they use the
selected frame.
@end defun

@defun screen-height
@defunx screen-width
These functions are old aliases for @code{frame-height} and
@code{frame-width}.  When you are using a non-window terminal, the size
of the frame is normally the same as the size of the terminal screen.
@end defun

@defun frame-pixel-height &optional frame
@defunx frame-pixel-width &optional frame
These functions return the height and width of @var{frame}, measured in
pixels.  If you don't supply @var{frame}, they use the selected frame.
@end defun

@defun frame-char-height &optional frame
@defunx frame-char-width &optional frame
These functions return the height and width of a character in
@var{frame}, measured in pixels.  The values depend on the choice of
font.  If you don't supply @var{frame}, these functions use the selected
frame.
@end defun

@defun set-frame-size frame cols rows
This function sets the size of @var{frame}, measured in characters;
@var{cols} and @var{rows} specify the new width and height.

To set the size based on values measured in pixels, use
@code{frame-char-height} and @code{frame-char-width} to convert
them to units of characters.
@end defun

@defun set-frame-height frame lines &optional pretend
This function resizes @var{frame} to a height of @var{lines} lines.  The
sizes of existing windows in @var{frame} are altered proportionally to
fit.

If @var{pretend} is non-@code{nil}, then Emacs displays @var{lines}
lines of output in @var{frame}, but does not change its value for the
actual height of the frame.  This is only useful for a terminal frame.
Using a smaller height than the terminal actually implements may be
useful to reproduce behavior observed on a smaller screen, or if the
terminal malfunctions when using its whole screen.  Setting the frame
height ``for real'' does not always work, because knowing the correct
actual size may be necessary for correct cursor positioning on a
terminal frame.
@end defun

@defun set-frame-width frame width &optional pretend
This function sets the width of @var{frame}, measured in characters.
The argument @var{pretend} has the same meaning as in
@code{set-frame-height}.
@end defun

@findex set-screen-height
@findex set-screen-width
  The older functions @code{set-screen-height} and
@code{set-screen-width} were used to specify the height and width of the
screen, in Emacs versions that did not support multiple frames.  They
are semi-obsolete, but still work; they apply to the selected frame.

@defun x-parse-geometry geom
@cindex geometry specification
The function @code{x-parse-geometry} converts a standard X window
geometry string to an alist that you can use as part of the argument to
@code{make-frame}.

The alist describes which parameters were specified in @var{geom}, and
gives the values specified for them.  Each element looks like
@code{(@var{parameter} . @var{value})}.  The possible @var{parameter}
values are @code{left}, @code{top}, @code{width}, and @code{height}.

For the size parameters, the value must be an integer.  The position
parameter names @code{left} and @code{top} are not totally accurate,
because some values indicate the position of the right or bottom edges
instead.  These are the @var{value} possibilities for the position
parameters:

@table @asis
@item an integer
A positive integer relates the left edge or top edge of the window to
the left or top edge of the screen.  A negative integer relates the
right or bottom edge of the window to the right or bottom edge of the
screen.

@item @code{(+ @var{position})}
This specifies the position of the left or top edge of the window
relative to the left or top edge of the screen.  The integer
@var{position} may be positive or negative; a negative value specifies a
position outside the screen.

@item @code{(- @var{position})}
This specifies the position of the right or bottom edge of the window
relative to the right or bottom edge of the screen.  The integer
@var{position} may be positive or negative; a negative value specifies a
position outside the screen.
@end table

Here is an example:

@example
(x-parse-geometry "35x70+0-0")
     @result{} ((height . 70) (width . 35)
         (top - 0) (left . 0))
@end example
@end defun

@node Frame Titles
@section Frame Titles

  Every frame has a @code{name} parameter; this serves as the default
for the frame title which window systems typically display at the top of
the frame.  You can specify a name explicitly by setting the @code{name}
frame property.

  Normally you don't specify the name explicitly, and Emacs computes the
frame name automatically based on a template stored in the variable
@code{frame-title-format}.  Emacs recomputes the name each time the
frame is redisplayed.

@defvar frame-title-format
This variable specifies how to compute a name for a frame when you have
not explicitly specified one.  The variable's value is actually a mode
line construct, just like @code{mode-line-format}.  @xref{Mode Line
Data}.
@end defvar

@defvar icon-title-format
This variable specifies how to compute the name for an iconified frame,
when you have not explicitly specified the frame title.  This title
appears in the icon itself.
@end defvar

@defvar multiple-frames
This variable is set automatically by Emacs.  Its value is @code{t} when
there are two or more frames (not counting minibuffer-only frames or
invisible frames).  The default value of @code{frame-title-format} uses
@code{multiple-frames} so as to put the buffer name in the frame title
only when there is more than one frame.
@end defvar

@node Deleting Frames
@section Deleting Frames
@cindex deletion of frames

Frames remain potentially visible until you explicitly @dfn{delete}
them.  A deleted frame cannot appear on the screen, but continues to
exist as a Lisp object until there are no references to it.  There is no
way to cancel the deletion of a frame aside from restoring a saved frame
configuration (@pxref{Frame Configurations}); this is similar to the
way windows behave.

@deffn Command delete-frame &optional frame force
@vindex delete-frame-hook
This function deletes the frame @var{frame} after running the hook
@code{delete-frame-hook}.  By default, @var{frame} is the selected
frame.

A frame cannot be deleted if its minibuffer is used by other frames.
Normally, you cannot delete a frame if all other frames are invisible,
but if the @var{force} is non-@code{nil}, then you are allowed to do so.
@end deffn

@defun frame-live-p frame
The function @code{frame-live-p} returns non-@code{nil} if the frame
@var{frame} has not been deleted.
@end defun

  Some window managers provide a command to delete a window.  These work
by sending a special message to the program that operates the window.
When Emacs gets one of these commands, it generates a
@code{delete-frame} event, whose normal definition is a command that
calls the function @code{delete-frame}.  @xref{Misc Events}.

@node Finding All Frames
@section Finding All Frames

@defun frame-list
The function @code{frame-list} returns a list of all the frames that
have not been deleted.  It is analogous to @code{buffer-list} for
buffers, and includes frames on all terminals.  The list that you get is
newly created, so modifying the list doesn't have any effect on the
internals of Emacs.
@end defun

@defun visible-frame-list
This function returns a list of just the currently visible frames.
@xref{Visibility of Frames}.  (Terminal frames always count as
``visible'', even though only the selected one is actually displayed.)
@end defun

@defun next-frame &optional frame minibuf
The function @code{next-frame} lets you cycle conveniently through all
the frames on the current display from an arbitrary starting point.  It
returns the ``next'' frame after @var{frame} in the cycle.  If
@var{frame} is omitted or @code{nil}, it defaults to the selected frame
(@pxref{Input Focus}).

The second argument, @var{minibuf}, says which frames to consider:

@table @asis
@item @code{nil}
Exclude minibuffer-only frames.
@item @code{visible}
Consider all visible frames.
@item 0
Consider all visible or iconified frames.
@item a window
Consider only the frames using that particular window as their
minibuffer.
@item anything else
Consider all frames.
@end table
@end defun

@defun previous-frame &optional frame minibuf
Like @code{next-frame}, but cycles through all frames in the opposite
direction.
@end defun

  See also @code{next-window} and @code{previous-window}, in @ref{Cyclic
Window Ordering}.

@node Frames and Windows
@section Frames and Windows

  Each window is part of one and only one frame; you can get the frame
with @code{window-frame}.

@defun window-frame window
This function returns the frame that @var{window} is on.
@end defun

  All the non-minibuffer windows in a frame are arranged in a cyclic
order.  The order runs from the frame's top window, which is at the
upper left corner, down and to the right, until it reaches the window at
the lower right corner (always the minibuffer window, if the frame has
one), and then it moves back to the top.  @xref{Cyclic Window Ordering}.

@defun frame-first-window frame
This returns the topmost, leftmost window of frame @var{frame}.
@end defun

At any time, exactly one window on any frame is @dfn{selected within the
frame}.  The significance of this designation is that selecting the
frame also selects this window.  You can get the frame's current
selected window with @code{frame-selected-window}.

@defun frame-selected-window frame
This function returns the window on @var{frame} that is selected within
@var{frame}.
@end defun

  Conversely, selecting a window for Emacs with @code{select-window} also
makes that window selected within its frame.  @xref{Selecting Windows}.

  Another function that (usually) returns one of the windows in a given
frame is @code{minibuffer-window}.  @xref{Minibuffer Misc}.

@node Minibuffers and Frames
@section Minibuffers and Frames

Normally, each frame has its own minibuffer window at the bottom, which
is used whenever that frame is selected.  If the frame has a minibuffer,
you can get it with @code{minibuffer-window} (@pxref{Minibuffer Misc}).

However, you can also create a frame with no minibuffer.  Such a frame
must use the minibuffer window of some other frame.  When you create the
frame, you can specify explicitly the minibuffer window to use (in some
other frame).  If you don't, then the minibuffer is found in the frame
which is the value of the variable @code{default-minibuffer-frame}.  Its
value should be a frame that does have a minibuffer.

If you use a minibuffer-only frame, you might want that frame to raise
when you enter the minibuffer.  If so, set the variable
@code{minibuffer-auto-raise} to @code{t}.  @xref{Raising and Lowering}.

@defvar default-minibuffer-frame
This variable specifies the frame to use for the minibuffer window, by
default.  It is always local to the current terminal and cannot be
buffer-local.  @xref{Multiple Displays}.
@end defvar

@node Input Focus
@section Input Focus
@cindex input focus
@cindex selected frame

At any time, one frame in Emacs is the @dfn{selected frame}.  The selected
window always resides on the selected frame.

When Emacs displays its frames on several terminals (@pxref{Multiple
Displays}), each terminal has its own selected frame.  But only one of
these is ``@emph{the} selected frame'': it's the frame that belongs to
the terminal from which the most recent input came.  That is, when Emacs
runs a command that came from a certain terminal, the selected frame is
the one of that terminal.  Since Emacs runs only a single command at any
given time, it needs to consider only one selected frame at a time; this
frame is what we call @dfn{the selected frame} in this manual.  The
display on which the selected frame is displayed is the @dfn{selected
frame's display}.

@defun selected-frame
This function returns the selected frame.
@end defun

Some window systems and window managers direct keyboard input to the
window object that the mouse is in; others require explicit clicks or
commands to @dfn{shift the focus} to various window objects.  Either
way, Emacs automatically keeps track of which frame has the focus.

Lisp programs can also switch frames ``temporarily'' by calling the
function @code{select-frame}.  This does not alter the window system's
concept of focus; rather, it escapes from the window manager's control
until that control is somehow reasserted.

When using a text-only terminal, only the selected terminal frame is
actually displayed on the terminal.  @code{switch-frame} is the only way
to switch frames, and the change lasts until overridden by a subsequent
call to @code{switch-frame}.  Each terminal screen except for the
initial one has a number, and the number of the selected frame appears
in the mode line before the buffer name (@pxref{Mode Line Variables}).

@c ??? This is not yet implemented properly.
@defun select-frame frame
This function selects frame @var{frame}, temporarily disregarding the
focus of the X server if any.  The selection of @var{frame} lasts until
the next time the user does something to select a different frame, or
until the next time this function is called.  The specified @var{frame}
becomes the selected frame, as explained above, and the terminal that
@var{frame} is on becomes the selected terminal.

In general, you should never use @code{select-frame} in a way that could
switch to a different terminal without switching back when you're done.
@end defun

Emacs cooperates with the window system by arranging to select frames as
the server and window manager request.  It does so by generating a
special kind of input event, called a @dfn{focus} event, when
appropriate.  The command loop handles a focus event by calling
@code{handle-switch-frame}.  @xref{Focus Events}.

@deffn Command handle-switch-frame frame
This function handles a focus event by selecting frame @var{frame}.

Focus events normally do their job by invoking this command.
Don't call it for any other reason.
@end deffn

@defun redirect-frame-focus frame focus-frame
This function redirects focus from @var{frame} to @var{focus-frame}.
This means that @var{focus-frame} will receive subsequent keystrokes and
events intended for @var{frame}.  After such an event, the value of
@code{last-event-frame} will be @var{focus-frame}.  Also, switch-frame
events specifying @var{frame} will instead select @var{focus-frame}.

If @var{focus-frame} is @code{nil}, that cancels any existing
redirection for @var{frame}, which therefore once again receives its own
events.

One use of focus redirection is for frames that don't have minibuffers.
These frames use minibuffers on other frames.  Activating a minibuffer
on another frame redirects focus to that frame.  This puts the focus on
the minibuffer's frame, where it belongs, even though the mouse remains
in the frame that activated the minibuffer.

Selecting a frame can also change focus redirections.  Selecting frame
@code{bar}, when @code{foo} had been selected, changes any redirections
pointing to @code{foo} so that they point to @code{bar} instead.  This
allows focus redirection to work properly when the user switches from
one frame to another using @code{select-window}.

This means that a frame whose focus is redirected to itself is treated
differently from a frame whose focus is not redirected.
@code{select-frame} affects the former but not the latter.

The redirection lasts until @code{redirect-frame-focus} is called to
change it.
@end defun

@defopt focus-follows-mouse
This option is how you inform Emacs whether the window manager transfers
focus when the user moves the mouse.  Non-@code{nil} says that it does.
When this is so, the command @code{other-frame} moves the mouse to a
position consistent with the new selected frame.
@end defopt

@node Visibility of Frames
@section Visibility of Frames
@cindex visible frame
@cindex invisible frame
@cindex iconified frame
@cindex frame visibility

A window frame may be @dfn{visible}, @dfn{invisible}, or
@dfn{iconified}.  If it is visible, you can see its contents.  If it is
iconified, the frame's contents do not appear on the screen, but an icon
does.  If the frame is invisible, it doesn't show on the screen, not
even as an icon.

Visibility is meaningless for terminal frames, since only the selected
one is actually displayed in any case.

@deffn Command make-frame-visible &optional frame
This function makes frame @var{frame} visible.  If you omit @var{frame},
it makes the selected frame visible.
@end deffn

@deffn Command make-frame-invisible &optional frame
This function makes frame @var{frame} invisible.  If you omit
@var{frame}, it makes the selected frame invisible.
@end deffn

@deffn Command iconify-frame &optional frame
This function iconifies frame @var{frame}.  If you omit @var{frame}, it
iconifies the selected frame.
@end deffn

@defun frame-visible-p frame
This returns the visibility status of frame @var{frame}.  The value is
@code{t} if @var{frame} is visible, @code{nil} if it is invisible, and
@code{icon} if it is iconified.
@end defun

  The visibility status of a frame is also available as a frame
parameter.  You can read or change it as such.  @xref{Window Frame
Parameters}.

  The user can iconify and deiconify frames with the window manager.
This happens below the level at which Emacs can exert any control, but
Emacs does provide events that you can use to keep track of such
changes.  @xref{Misc Events}.

@node Raising and Lowering
@section Raising and Lowering Frames

  Most window systems use a desktop metaphor.  Part of this metaphor is
the idea that windows are stacked in a notional third dimension
perpendicular to the screen surface, and thus ordered from ``highest''
to ``lowest''.  Where two windows overlap, the one higher up covers
the one underneath.  Even a window at the bottom of the stack can be
seen if no other window overlaps it.

@cindex raising a frame
@cindex lowering a frame
  A window's place in this ordering is not fixed; in fact, users tend
to change the order frequently.  @dfn{Raising} a window means moving
it ``up'', to the top of the stack.  @dfn{Lowering} a window means
moving it to the bottom of the stack.  This motion is in the notional
third dimension only, and does not change the position of the window
on the screen.

  You can raise and lower Emacs frame Windows with these functions:

@deffn Command raise-frame &optional frame
This function raises frame @var{frame} (default, the selected frame).
@end deffn

@deffn Command lower-frame &optional frame
This function lowers frame @var{frame} (default, the selected frame).
@end deffn

@defopt minibuffer-auto-raise
If this is non-@code{nil}, activation of the minibuffer raises the frame
that the minibuffer window is in.
@end defopt

You can also enable auto-raise (raising automatically when a frame is
selected) or auto-lower (lowering automatically when it is deselected)
for any frame using frame parameters.  @xref{Window Frame Parameters}.

@node Frame Configurations
@section Frame Configurations
@cindex frame configuration

  A @dfn{frame configuration} records the current arrangement of frames,
all their properties, and the window configuration of each one.
(@xref{Window Configurations}.)

@defun current-frame-configuration
This function returns a frame configuration list that describes
the current arrangement of frames and their contents.
@end defun

@defun set-frame-configuration configuration &optional nodelete
This function restores the state of frames described in
@var{configuration}.

Ordinarily, this function deletes all existing frames not listed in
@var{configuration}.  But if @var{nodelete} is non-@code{nil}, the
unwanted frames are iconified instead.
@end defun

@node Mouse Tracking
@section Mouse Tracking
@cindex mouse tracking
@cindex tracking the mouse

Sometimes it is useful to @dfn{track} the mouse, which means to display
something to indicate where the mouse is and move the indicator as the
mouse moves.  For efficient mouse tracking, you need a way to wait until
the mouse actually moves.

The convenient way to track the mouse is to ask for events to represent
mouse motion.  Then you can wait for motion by waiting for an event.  In
addition, you can easily handle any other sorts of events that may
occur.  That is useful, because normally you don't want to track the
mouse forever---only until some other event, such as the release of a
button.

@defspec track-mouse body@dots{}
This special form executes @var{body}, with generation of mouse motion
events enabled.  Typically @var{body} would use @code{read-event} to
read the motion events and modify the display accordingly.  @xref{Motion
Events}, for the format of mouse motion events.

The value of @code{track-mouse} is that of the last form in @var{body}.
You should design @var{body} to return when it sees the up-event that
indicates the release of the button, or whatever kind of event means
it is time to stop tracking.
@end defspec

The usual purpose of tracking mouse motion is to indicate on the screen
the consequences of pushing or releasing a button at the current
position.

In many cases, you can avoid the need to track the mouse by using
the @code{mouse-face} text property (@pxref{Special Properties}).
That works at a much lower level and runs more smoothly than
Lisp-level mouse tracking.

@ignore
@c These are not implemented yet.

These functions change the screen appearance instantaneously.  The
effect is transient, only until the next ordinary Emacs redisplay.  That
is OK for mouse tracking, since it doesn't make sense for mouse tracking
to change the text, and the body of @code{track-mouse} normally reads
the events itself and does not do redisplay.

@defun x-contour-region window beg end
This function draws lines to make a box around the text from @var{beg}
to @var{end}, in window @var{window}.
@end defun

@defun x-uncontour-region window beg end
This function erases the lines that would make a box around the text
from @var{beg} to @var{end}, in window @var{window}.  Use it to remove
a contour that you previously made by calling @code{x-contour-region}.
@end defun

@defun x-draw-rectangle frame left top right bottom
This function draws a hollow rectangle on frame @var{frame} with the
specified edge coordinates, all measured in pixels from the inside top
left corner.  It uses the cursor color, the one used for indicating the
location of point.
@end defun

@defun x-erase-rectangle frame left top right bottom
This function erases a hollow rectangle on frame @var{frame} with the
specified edge coordinates, all measured in pixels from the inside top
left corner.  Erasure means redrawing the text and background that
normally belong in the specified rectangle.
@end defun
@end ignore

@node Mouse Position
@section Mouse Position
@cindex mouse position
@cindex position of mouse

  The functions @code{mouse-position} and @code{set-mouse-position}
give access to the current position of the mouse.

@defun mouse-position
This function returns a description of the position of the mouse.  The
value looks like @code{(@var{frame} @var{x} . @var{y})}, where @var{x}
and @var{y} are integers giving the position in characters relative to
the top left corner of the inside of @var{frame}.
@end defun

@defvar mouse-position-function
If non-@code{nil}, the value of this variable is a function for
@code{mouse-position} to call.  @code{mouse-position} calls this
function just before returning, with its normal return value as the
sole argument, and it returns whatever this function returns to it.

This abnormal hook exists for the benefit of packages like
@file{xt-mouse.el} that need to do mouse handling at the Lisp level.
@end defvar

@defun set-mouse-position frame x y
This function @dfn{warps the mouse} to position @var{x}, @var{y} in
frame @var{frame}.  The arguments @var{x} and @var{y} are integers,
giving the position in characters relative to the top left corner of the
inside of @var{frame}.  If @var{frame} is not visible, this function
does nothing.  The return value is not significant.
@end defun

@defun mouse-pixel-position
This function is like @code{mouse-position} except that it returns
coordinates in units of pixels rather than units of characters.
@end defun

@defun set-mouse-pixel-position frame x y
This function warps the mouse like @code{set-mouse-position} except that
@var{x} and @var{y} are in units of pixels rather than units of
characters.  These coordinates are not required to be within the frame.

If @var{frame} is not visible, this function does nothing.  The return
value is not significant.
@end defun

@need 3000

@node Pop-Up Menus
@section Pop-Up Menus

  When using a window system, a Lisp program can pop up a menu so that
the user can choose an alternative with the mouse.

@defun x-popup-menu position menu
This function displays a pop-up menu and returns an indication of
what selection the user makes.

The argument @var{position} specifies where on the screen to put the
menu.  It can be either a mouse button event (which says to put the menu
where the user actuated the button) or a list of this form:

@example
((@var{xoffset} @var{yoffset}) @var{window})
@end example

@noindent
where @var{xoffset} and @var{yoffset} are coordinates, measured in
pixels, counting from the top left corner of @var{window}'s frame.

If @var{position} is @code{t}, it means to use the current mouse
position.  If @var{position} is @code{nil}, it means to precompute the
key binding equivalents for the keymaps specified in @var{menu},
without actually displaying or popping up the menu.

The argument @var{menu} says what to display in the menu.  It can be a
keymap or a list of keymaps (@pxref{Menu Keymaps}).  Alternatively, it
can have the following form:

@example
(@var{title} @var{pane1} @var{pane2}...)
@end example

@noindent
where each pane is a list of form

@example
(@var{title} (@var{line} . @var{item})...)
@end example

Each @var{line} should be a string, and each @var{item} should be the
value to return if that @var{line} is chosen.
@end defun

  @strong{Usage note:} Don't use @code{x-popup-menu} to display a menu
if you could do the job with a prefix key defined with a menu keymap.
If you use a menu keymap to implement a menu, @kbd{C-h c} and @kbd{C-h
a} can see the individual items in that menu and provide help for them.
If instead you implement the menu by defining a command that calls
@code{x-popup-menu}, the help facilities cannot know what happens inside
that command, so they cannot give any help for the menu's items.

  The menu bar mechanism, which lets you switch between submenus by
moving the mouse, cannot look within the definition of a command to see
that it calls @code{x-popup-menu}.  Therefore, if you try to implement a
submenu using @code{x-popup-menu}, it cannot work with the menu bar in
an integrated fashion.  This is why all menu bar submenus are
implemented with menu keymaps within the parent menu, and never with
@code{x-popup-menu}.  @xref{Menu Bar},

  If you want a menu bar submenu to have contents that vary, you should
still use a menu keymap to implement it.  To make the contents vary, add
a hook function to @code{menu-bar-update-hook} to update the contents of
the menu keymap as necessary.

@node Dialog Boxes
@section Dialog Boxes
@cindex dialog boxes

  A dialog box is a variant of a pop-up menu---it looks a little
different, it always appears in the center of a frame, and it has just
one level and one pane.  The main use of dialog boxes is for asking
questions that the user can answer with ``yes'', ``no'', and a few other
alternatives.  The functions @code{y-or-n-p} and @code{yes-or-no-p} use
dialog boxes instead of the keyboard, when called from commands invoked
by mouse clicks.

@defun x-popup-dialog position contents
This function displays a pop-up dialog box and returns an indication of
what selection the user makes.  The argument @var{contents} specifies
the alternatives to offer; it has this format:

@example
(@var{title} (@var{string} . @var{value})@dots{})
@end example

@noindent
which looks like the list that specifies a single pane for
@code{x-popup-menu}.

The return value is @var{value} from the chosen alternative.

An element of the list may be just a string instead of a cons cell
@code{(@var{string} . @var{value})}.  That makes a box that cannot
be selected.

If @code{nil} appears in the list, it separates the left-hand items from
the right-hand items; items that precede the @code{nil} appear on the
left, and items that follow the @code{nil} appear on the right.  If you
don't include a @code{nil} in the list, then approximately half the
items appear on each side.

Dialog boxes always appear in the center of a frame; the argument
@var{position} specifies which frame.  The possible values are as in
@code{x-popup-menu}, but the precise coordinates don't matter; only the
frame matters.

In some configurations, Emacs cannot display a real dialog box; so
instead it displays the same items in a pop-up menu in the center of the
frame.
@end defun

@node Pointer Shapes
@section Pointer Shapes
@cindex pointer shape
@cindex mouse pointer shape

  These variables specify which shape to use for the mouse pointer in
various situations, when using the X Window System:

@table @code
@item x-pointer-shape
@vindex x-pointer-shape
This variable specifies the pointer shape to use ordinarily in the Emacs
frame.

@item x-sensitive-text-pointer-shape
@vindex x-sensitive-text-pointer-shape
This variable specifies the pointer shape to use when the mouse
is over mouse-sensitive text.
@end table

  These variables affect newly created frames.  They do not normally
affect existing frames; however, if you set the mouse color of a frame,
that also updates its pointer shapes based on the current values of
these variables.  @xref{Window Frame Parameters}.

  The values you can use, to specify either of these pointer shapes, are
defined in the file @file{lisp/term/x-win.el}.  Use @kbd{M-x apropos
@key{RET} x-pointer @key{RET}} to see a list of them.

@node Window System Selections
@section Window System Selections
@cindex selection (for window systems)

The X server records a set of @dfn{selections} which permit transfer of
data between application programs.  The various selections are
distinguished by @dfn{selection types}, represented in Emacs by
symbols.  X clients including Emacs can read or set the selection for
any given type.

@defun x-set-selection type data
This function sets a ``selection'' in the X server.  It takes two
arguments: a selection type @var{type}, and the value to assign to it,
@var{data}.  If @var{data} is @code{nil}, it means to clear out the
selection.  Otherwise, @var{data} may be a string, a symbol, an integer
(or a cons of two integers or list of two integers), an overlay, or a
cons of two markers pointing to the same buffer.  An overlay or a pair
of markers stands for text in the overlay or between the markers.

The argument @var{data} may also be a vector of valid non-vector
selection values.

Each possible @var{type} has its own selection value, which changes
independently.  The usual values of @var{type} are @code{PRIMARY} and
@code{SECONDARY}; these are symbols with upper-case names, in accord
with X Window System conventions.  The default is @code{PRIMARY}.
@end defun

@defun x-get-selection &optional type data-type
This function accesses selections set up by Emacs or by other X
clients.  It takes two optional arguments, @var{type} and
@var{data-type}.  The default for @var{type}, the selection type, is
@code{PRIMARY}.

The @var{data-type} argument specifies the form of data conversion to
use, to convert the raw data obtained from another X client into Lisp
data.  Meaningful values include @code{TEXT}, @code{STRING},
@code{TARGETS}, @code{LENGTH}, @code{DELETE}, @code{FILE_NAME},
@code{CHARACTER_POSITION}, @code{LINE_NUMBER}, @code{COLUMN_NUMBER},
@code{OWNER_OS}, @code{HOST_NAME}, @code{USER}, @code{CLASS},
@code{NAME}, @code{ATOM}, and @code{INTEGER}.  (These are symbols with
upper-case names in accord with X conventions.)  The default for
@var{data-type} is @code{STRING}.
@end defun

@cindex cut buffer
The X server also has a set of numbered @dfn{cut buffers} which can
store text or other data being moved between applications.  Cut buffers
are considered obsolete, but Emacs supports them for the sake of X
clients that still use them.

@defun x-get-cut-buffer n
This function returns the contents of cut buffer number @var{n}.
@end defun

@defun x-set-cut-buffer string &optional push
This function stores @var{string} into the first cut buffer (cut buffer
0).  If @var{push} is @code{nil}, only the first cut buffer is changed.
If @var{push} is non-@code{nil}, that says to move the values down
through the series of cut buffers, much like the way successive kills in
Emacs move down the kill ring.  In other words, the previous value of
the first cut buffer moves into the second cut buffer, and the second to
the third, and so on through all eight cut buffers.
@end defun

@defvar selection-coding-system
This variable specifies the coding system to use when reading and
writing selections, the clipboard, or a cut buffer.  @xref{Coding
Systems}.  The default is @code{compound-text-with-extensions}, which
converts to the text representation that X11 normally uses.
@end defvar

@cindex clipboard support (for MS-Windows)
When Emacs runs on MS-Windows, it does not implement X selections in
general, but it does support the clipboard.  @code{x-get-selection}
and @code{x-set-selection} on MS-Windows support the text data type
only; if the clipboard holds other types of data, Emacs treats the
clipboard as empty.

@defopt x-select-enable-clipboard
If this is non-@code{nil}, the Emacs yank functions consult the
clipboard before the primary selection, and the kill functions store in
the clipboard as well as the primary selection.  Otherwise they do not
access the clipboard at all.  The default is @code{nil} on most systems,
but @code{t} on MS-Windows.
@end defopt

@node Color Names
@section Color Names

  These functions provide a way to determine which color names are
valid, and what they look like.  In some cases, the value depends on the
@dfn{selected frame}, as described below; see @ref{Input Focus}, for the
meaning of the term ``selected frame''.

@defun color-defined-p color &optional frame
@tindex color-defined-p
This function reports whether a color name is meaningful.  It returns
@code{t} if so; otherwise, @code{nil}.  The argument @var{frame} says
which frame's display to ask about; if @var{frame} is omitted or
@code{nil}, the selected frame is used.

Note that this does not tell you whether the display you are using
really supports that color.  When using X, you can ask for any defined
color on any kind of display, and you will get some result---typically,
the closest it can do.  To determine whether a frame can really display
a certain color, use @code{color-supported-p} (see below).

@findex x-color-defined-p
This function used to be called @code{x-color-defined-p},
and that name is still supported as an alias.
@end defun

@defun defined-colors &optional frame
@tindex defined-colors
This function returns a list of the color names that are defined
and supported on frame @var{frame} (default, the selected frame).

@findex x-defined-colors
This function used to be called @code{x-defined-colors},
and that name is still supported as an alias.
@end defun

@defun color-supported-p color &optional frame background-p
@tindex color-supported-p
This returns @code{t} if @var{frame} can really display the color
@var{color} (or at least something close to it).  If @var{frame} is
omitted or @code{nil}, the question applies to the selected frame.

Some terminals support a different set of colors for foreground and
background.  If @var{background-p} is non-@code{nil}, that means you are
asking whether @var{color} can be used as a background; otherwise you
are asking whether it can be used as a foreground.

The argument @var{color} must be a valid color name.
@end defun

@defun color-gray-p color &optional frame
@tindex color-gray-p
This returns @code{t} if @var{color} is a shade of gray, as defined on
@var{frame}'s display.  If @var{frame} is omitted or @code{nil}, the
question applies to the selected frame.  The argument @var{color} must
be a valid color name.
@end defun

@defun color-values color &optional frame
@tindex color-values
This function returns a value that describes what @var{color} should
ideally look like.  If @var{color} is defined, the value is a list of
three integers, which give the amount of red, the amount of green, and
the amount of blue.  Each integer ranges in principle from 0 to 65535,
but in practice no value seems to be above 65280.  This kind
of three-element list is called an @dfn{rgb value}.

If @var{color} is not defined, the value is @code{nil}.

@example
(color-values "black")
     @result{} (0 0 0)
(color-values "white")
     @result{} (65280 65280 65280)
(color-values "red")
     @result{} (65280 0 0)
(color-values "pink")
     @result{} (65280 49152 51968)
(color-values "hungry")
     @result{} nil
@end example

The color values are returned for @var{frame}'s display.  If @var{frame}
is omitted or @code{nil}, the information is returned for the selected
frame's display.

@findex x-color-values
This function used to be called @code{x-color-values},
and that name is still supported as an alias.
@end defun

@node Text Terminal Colors
@section Text Terminal Colors
@cindex colors on text-only terminals

  Emacs can display color on text-only terminals, starting with version
21.  These terminals usually support only a small number of colors, and
the computer uses small integers to select colors on the terminal.  This
means that the computer cannot reliably tell what the selected color
looks like; instead, you have to inform your application which small
integers correspond to which colors.  However, Emacs does know the
standard set of colors and will try to use them automatically.

  The functions described in this section control how terminal colors
are used by Emacs.

@cindex rgb value
  Several of these functions use or return @dfn{rgb values}.  An rgb
value is a list of three integers, which give the amount of red, the
amount of green, and the amount of blue.  Each integer ranges in
principle from 0 to 65535, but in practice the largest value used is
65280.

  These functions accept a display (either a frame or the name of a
terminal) as an optional argument.  We hope in the future to make Emacs
support more than one text-only terminal at one time; then this argument
will specify which terminal to operate on (the default being the
selected frame's terminal; @pxref{Input Focus}).  At present, though,
the @var{display} argument has no effect.

@defun tty-color-define name number &optional rgb display
@tindex tty-color-define
This function associates the color name @var{name} with
color number @var{number} on the terminal.

The optional argument @var{rgb}, if specified, is an rgb value; it says
what the color actually looks like.  If you do not specify @var{rgb},
then this color cannot be used by @code{tty-color-approximate} to
approximate other colors, because Emacs does not know what it looks
like.
@end defun

@defun tty-color-clear &optional display
@tindex tty-color-clear
This function clears the table of defined colors for a text-only terminal.
@end defun

@defun tty-color-alist &optional display
@tindex tty-color-alist
This function returns an alist recording the known colors supported by a
text-only terminal.

Each element has the form @code{(@var{name} @var{number} . @var{rgb})}
or @code{(@var{name} @var{number})}.  Here, @var{name} is the color
name, @var{number} is the number used to specify it to the terminal.
If present, @var{rgb} is an rgb value that says what the color
actually looks like.
@end defun

@defun tty-color-approximate rgb &optional display
@tindex tty-color-approximate
This function finds the closest color, among the known colors supported
for @var{display}, to that described by the rgb value @var{rgb}.
@end defun

@defun tty-color-translate color &optional display
@tindex tty-color-translate
This function finds the closest color to @var{color} among the known
colors supported for @var{display}.  If the name @var{color} is not
defined, the value is @code{nil}.

@var{color} can be an X-style @code{"#@var{xxxyyyzzz}"} specification
instead of an actual name.  The format
@code{"RGB:@var{xx}/@var{yy}/@var{zz}"} is also supported.
@end defun

@node Resources
@section X Resources

@defun x-get-resource attribute class &optional component subclass
The function @code{x-get-resource} retrieves a resource value from the X
Windows defaults database.

Resources are indexed by a combination of a @dfn{key} and a @dfn{class}.
This function searches using a key of the form
@samp{@var{instance}.@var{attribute}} (where @var{instance} is the name
under which Emacs was invoked), and using @samp{Emacs.@var{class}} as
the class.

The optional arguments @var{component} and @var{subclass} add to the key
and the class, respectively.  You must specify both of them or neither.
If you specify them, the key is
@samp{@var{instance}.@var{component}.@var{attribute}}, and the class is
@samp{Emacs.@var{class}.@var{subclass}}.
@end defun

@defvar x-resource-class
This variable specifies the application name that @code{x-get-resource}
should look up.  The default value is @code{"Emacs"}.  You can examine X
resources for application names other than ``Emacs'' by binding this
variable to some other string, around a call to @code{x-get-resource}.
@end defvar

  @xref{X Resources,, X Resources, emacs, The GNU Emacs Manual}.

@node Display Feature Testing
@section Display Feature Testing
@cindex display feature testing

  The functions in this section describe the basic capabilities of a
particular display.  Lisp programs can use them to adapt their behavior
to what the display can do.  For example, a program that ordinarly uses
a popup menu could use the minibuffer if popup menus are not supported.

  The optional argument @var{display} in these functions specifies which
display to ask the question about.  It can be a display name, a frame
(which designates the display that frame is on), or @code{nil} (which
refers to the selected frame's display, @pxref{Input Focus}).

  @xref{Color Names}, @ref{Text Terminal Colors}, for other functions to
obtain information about displays.

@defun display-popup-menus-p &optional display
@tindex display-popup-menus-p
This function returns @code{t} if popup menus are supported on
@var{display}, @code{nil} if not.  Support for popup menus requires that
the mouse be available, since the user cannot choose menu items without
a mouse.
@end defun

@defun display-graphic-p &optional display
@tindex display-graphic-p
@cindex frames, more than one on display
@cindex fonts, more than one on display
This function returns @code{t} if @var{display} is a graphic display
capable of displaying several frames and several different fonts at
once.  This is true for displays that use a window system such as X, and
false for text-only terminals.
@end defun

@defun display-mouse-p &optional display
@tindex display-mouse-p
@cindex mouse, availability
This function returns @code{t} if @var{display} has a mouse available,
@code{nil} if not.
@end defun

@defun display-color-p &optional display
@tindex display-color-p
@findex x-display-color-p
This function returns @code{t} if the screen is a color screen.
It used to be called @code{x-display-color-p}, and that name
is still supported as an alias.
@end defun

@defun display-grayscale-p &optional display
@tindex display-grayscale-p
This function returns @code{t} if the screen can display shades of gray.
(All color displays can do this.)
@end defun

@anchor{Display Face Attribute Testing}
@defun display-supports-face-attributes-p attributes &optional display
@tindex display-supports-face-attributes-p
This function returns non-@code{nil} if all the face attributes in
@var{attributes} are supported (@pxref{Face Attributes}).

The definition of `supported' is somewhat heuristic, but basically
means that a face containing all the attributes in @var{attributes},
when merged with the default face for display, can be represented in a
way that's

@enumerate
@item
different in appearance than the default face, and

@item
`close in spirit' to what the attributes specify, if not exact.
@end enumerate

Point (2) implies that a @code{:weight black} attribute will be
satisfied by any display that can display bold, as will
@code{:foreground "yellow"} as long as some yellowish color can be
displayed, but @code{:slant italic} will @emph{not} be satisfied by
the tty display code's automatic substitution of a `dim' face for
italic.
@end defun

@defun display-selections-p &optional display
@tindex display-selections-p
This function returns @code{t} if @var{display} supports selections.
Windowed displays normally support selections, but they may also be
supported in some other cases.
@end defun

@defun display-images-p &optional display
This function returns @code{t} if @var{display} can display images.
Windowed displays ought in principle to handle images, but some
systems lack the support for that.  On a display that does not support
images, Emacs cannot display a tool bar.
@end defun

@defun display-screens &optional display
@tindex display-screens
This function returns the number of screens associated with the display.
@end defun

@defun display-pixel-height &optional display
@tindex display-pixel-height
This function returns the height of the screen in pixels.
@end defun

@defun display-mm-height &optional display
@tindex display-mm-height
This function returns the height of the screen in millimeters,
or @code{nil} if Emacs cannot get that information.
@end defun

@defun display-pixel-width &optional display
@tindex display-pixel-width
This function returns the width of the screen in pixels.
@end defun

@defun display-mm-width &optional display
@tindex display-mm-width
This function returns the width of the screen in millimeters,
or @code{nil} if Emacs cannot get that information.
@end defun

@defun display-backing-store &optional display
@tindex display-backing-store
This function returns the backing store capability of the display.
Backing store means recording the pixels of windows (and parts of
windows) that are not exposed, so that when exposed they can be
displayed very quickly.

Values can be the symbols @code{always}, @code{when-mapped}, or
@code{not-useful}.  The function can also return @code{nil}
when the question is inapplicable to a certain kind of display.
@end defun

@defun display-save-under &optional display
@tindex display-save-under
This function returns non-@code{nil} if the display supports the
SaveUnder feature.  That feature is used by pop-up windows
to save the pixels they obscure, so that they can pop down
quickly.
@end defun

@defun display-planes &optional display
@tindex display-planes
This function returns the number of planes the display supports.
This is typically the number of bits per pixel.
For a tty display, it is log to base two of the number of colours supported.
@end defun

@defun display-visual-class &optional display
@tindex display-visual-class
This function returns the visual class for the screen.  The value is one
of the symbols @code{static-gray}, @code{gray-scale},
@code{static-color}, @code{pseudo-color}, @code{true-color}, and
@code{direct-color}.
@end defun

@defun display-color-cells &optional display
@tindex display-color-cells
This function returns the number of color cells the screen supports.
@end defun

  These functions obtain additional information specifically
about X displays.

@defun x-server-version &optional display
This function returns the list of version numbers of the X server
running the display.
@end defun

@defun x-server-vendor &optional display
This function returns the vendor that provided the X server software.
@end defun

@ignore
@defvar x-no-window-manager
This variable's value is @code{t} if no X window manager is in use.
@end defvar
@end ignore

@ignore
@item
The functions @code{x-pixel-width} and @code{x-pixel-height} return the
width and height of an X Window frame, measured in pixels.
@end ignore