;;; follow.el --- synchronize windows showing the same buffer
-;; Copyright (C) 1995-1997, 1999, 2001-2015 Free Software Foundation,
+;; Copyright (C) 1995-1997, 1999, 2001-2016 Free Software Foundation,
;; Inc.
-;; Author: Anders Lindgren <andersl@andersl.com>
-;; Maintainer: emacs-devel@gnu.org (Anders' email bounces, Sep 2005)
+;; Author: Anders Lindgren
+;; Maintainer: emacs-devel@gnu.org
;; Created: 1995-05-25
;; Keywords: display, window, minor-mode, convenience
(defvar follow-windows-start-end-cache nil
"Cache used by `follow-window-start-end'.")
+(defvar follow-fixed-window nil
+ "If non-nil, the current window must not be scrolled.
+This is typically set by explicit scrolling commands.")
;;; Debug messages
;; This inline function must be as small as possible!
makes it possible to walk between windows using normal cursor
movement commands.
-Follow mode comes to its prime when used on a large screen and two
-side-by-side windows are used. The user can, with the help of Follow
-mode, use two full-height windows as though they would have been
-one. Imagine yourself editing a large function, or section of text,
-and being able to use 144 lines instead of the normal 72... (your
+Follow mode comes to its prime when used on a large screen and two or
+more side-by-side windows are used. The user can, with the help of
+Follow mode, use these full-height windows as though they were one.
+Imagine yourself editing a large function, or section of text, and
+being able to use 144 or 216 lines instead of the normal 72... (your
mileage may vary).
To split one large window into two side-by-side windows, the commands
(progn
(add-hook 'compilation-filter-hook 'follow-align-compilation-windows t t)
(add-hook 'post-command-hook 'follow-post-command-hook t)
- (add-hook 'window-size-change-functions 'follow-window-size-change t))
+ (add-hook 'window-size-change-functions 'follow-window-size-change t)
+ (add-hook 'after-change-functions 'follow-after-change nil t)
+ (add-hook 'isearch-update-post-hook 'follow-post-command-hook nil t)
+ (add-hook 'replace-update-post-hook 'follow-post-command-hook nil t)
+ (add-hook 'ispell-update-post-hook 'follow-post-command-hook nil t)
+
+ (setq window-group-start-function 'follow-window-start)
+ (setq window-group-end-function 'follow-window-end)
+ (setq set-window-group-start-function 'follow-set-window-start)
+ (setq recenter-window-group-function 'follow-recenter)
+ (setq pos-visible-in-window-group-p-function
+ 'follow-pos-visible-in-window-p)
+ (setq selected-window-group-function 'follow-all-followers)
+ (setq move-to-window-group-line-function 'follow-move-to-window-line))
+
;; Remove globally-installed hook functions only if there is no
;; other Follow mode buffer.
(let ((buffers (buffer-list))
(unless following
(remove-hook 'post-command-hook 'follow-post-command-hook)
(remove-hook 'window-size-change-functions 'follow-window-size-change)))
+
+ (kill-local-variable 'move-to-window-group-line-function)
+ (kill-local-variable 'selected-window-group-function)
+ (kill-local-variable 'pos-visible-in-window-group-p-function)
+ (kill-local-variable 'recenter-window-group-function)
+ (kill-local-variable 'set-window-group-start-function)
+ (kill-local-variable 'window-group-end-function)
+ (kill-local-variable 'window-group-start-function)
+
+ (remove-hook 'ispell-update-post-hook 'follow-post-command-hook t)
+ (remove-hook 'replace-update-post-hook 'follow-post-command-hook t)
+ (remove-hook 'isearch-update-post-hook 'follow-post-command-hook t)
+ (remove-hook 'after-change-functions 'follow-after-change t)
(remove-hook 'compilation-filter-hook 'follow-align-compilation-windows t)))
(defun follow-find-file-hook ()
;;; Scroll
+(defun follow-get-scrolled-point (dest windows)
+ "Calculate the correct value for point after a scrolling operation.
+
+DEST is our default position, typically where point was before the scroll.
+If `scroll-preserve-screen-position' is non-nil and active, DEST will be
+in the same screen position as before the scroll. WINDOWS is the list of
+windows in the follow chain.
+
+This function attempts to duplicate the point placing from
+`window_scroll_line_based' in the Emacs core source window.c.
+
+Return the new position."
+ (if (and scroll-preserve-screen-position
+ (get this-command 'scroll-command))
+ dest
+ (let ((dest-column
+ (save-excursion
+ (goto-char dest)
+ (- (current-column)
+ (progn (vertical-motion 0) (current-column)))))
+ (limit0
+ (with-selected-window (car windows)
+ (save-excursion
+ (goto-char (window-start))
+ (vertical-motion 0)
+ (point))))
+ (limitn
+ (with-selected-window (car (reverse windows))
+ (save-excursion
+ (goto-char (window-end nil t))
+ (if (pos-visible-in-window-p)
+ (point) ; i.e. (point-max)
+ (1- (point)))))))
+ (cond
+ ((< dest limit0)
+ (with-selected-window (car windows)
+ (save-excursion
+ (goto-char limit0)
+ (vertical-motion (cons dest-column 0))
+ (point))))
+ ((> dest limitn)
+ (with-selected-window (car (reverse windows))
+ (save-excursion
+ (goto-char limitn)
+ (vertical-motion (cons dest-column 0))
+ (point))))
+ (t dest)))))
+
;; `scroll-up' and `-down', but for windows in Follow mode.
;;
;; Almost like the real thing, except when the cursor ends up outside
;; position... (This would also be corrected if we would have had a
;; good redisplay abstraction.)
+(defun follow-scroll-up-arg (arg)
+ "Scroll the text in a follow mode window chain up by ARG lines.
+If ARG is nil, scroll the size of the current window.
+
+This is an internal function for `follow-scroll-up' and
+`follow-scroll-up-window'."
+ (let ((opoint (point)) (owin (selected-window)))
+ (while
+ ;; If we are too near EOB, try scrolling the previous window.
+ (condition-case nil (progn (scroll-up arg) nil)
+ (end-of-buffer
+ (condition-case nil (progn (follow-previous-window) t)
+ (error
+ (select-window owin)
+ (goto-char opoint)
+ (signal 'end-of-buffer nil))))))
+ (unless (and scroll-preserve-screen-position
+ (get this-command 'scroll-command))
+ (goto-char opoint))
+ (setq follow-fixed-window t)))
+
+(defun follow-scroll-down-arg (arg)
+ "Scroll the text in a follow mode window chain down by ARG lines.
+If ARG is nil, scroll the size of the current window.
+
+This is an internal function for `follow-scroll-down' and
+`follow-scroll-down-window'."
+ (let ((opoint (point)))
+ (scroll-down arg)
+ (unless (and scroll-preserve-screen-position
+ (get this-command 'scroll-command))
+ (goto-char opoint))
+ (setq follow-fixed-window t)))
+
+;;;###autoload
+(defun follow-scroll-up-window (&optional arg)
+ "Scroll text in a Follow mode window up by that window's size.
+The other windows in the window chain will scroll synchronously.
+
+If called with no ARG, the `next-screen-context-lines' last lines of
+the window will be visible after the scroll.
+
+If called with an argument, scroll ARG lines up.
+Negative ARG means scroll downward.
+
+Works like `scroll-up' when not in Follow mode."
+ (interactive "P")
+ (cond ((not follow-mode)
+ (scroll-up arg))
+ ((eq arg '-)
+ (follow-scroll-down-window))
+ (t (follow-scroll-up-arg arg))))
+(put 'follow-scroll-up-window 'scroll-command t)
+
+;;;###autoload
+(defun follow-scroll-down-window (&optional arg)
+ "Scroll text in a Follow mode window down by that window's size.
+The other windows in the window chain will scroll synchronously.
+
+If called with no ARG, the `next-screen-context-lines' top lines of
+the window in the chain will be visible after the scroll.
+
+If called with an argument, scroll ARG lines down.
+Negative ARG means scroll upward.
+
+Works like `scroll-down' when not in Follow mode."
+ (interactive "P")
+ (cond ((not follow-mode)
+ (scroll-down arg))
+ ((eq arg '-)
+ (follow-scroll-up-window))
+ (t (follow-scroll-down-arg arg))))
+(put 'follow-scroll-down-window 'scroll-command t)
+
+;;;###autoload
(defun follow-scroll-up (&optional arg)
"Scroll text in a Follow mode window chain up.
(interactive "P")
(cond ((not follow-mode)
(scroll-up arg))
- (arg
- (save-excursion (scroll-up arg))
- (setq follow-internal-force-redisplay t))
- (t
+ (arg (follow-scroll-up-arg arg))
+ (t
(let* ((windows (follow-all-followers))
(end (window-end (car (reverse windows)))))
(if (eq end (point-max))
(goto-char end))
(vertical-motion (- next-screen-context-lines))
(set-window-start (car windows) (point)))))))
+(put 'follow-scroll-up 'scroll-command t)
-
+;;;###autoload
(defun follow-scroll-down (&optional arg)
"Scroll text in a Follow mode window chain down.
If called with an argument, scroll ARG lines down.
Negative ARG means scroll upward.
-Works like `scroll-up' when not in Follow mode."
+Works like `scroll-down' when not in Follow mode."
(interactive "P")
(cond ((not follow-mode)
- (scroll-up arg))
- (arg
- (save-excursion (scroll-down arg)))
- (t
+ (scroll-down arg))
+ (arg (follow-scroll-down-arg arg))
+ (t
(let* ((windows (follow-all-followers))
(win (car (reverse windows)))
(start (window-start (car windows))))
(goto-char start)
(vertical-motion (- next-screen-context-lines 1))
(setq follow-internal-force-redisplay t))))))
+(put 'follow-scroll-down 'scroll-command t)
(declare-function comint-adjust-point "comint" (window))
(defvar comint-scroll-show-maximum-output)
Return (END-POS END-OF-BUFFER).
Actually, the position returned is the start of the line after
-the last fully-visible line in WIN. If WIN is nil, the selected
-window is used."
+the last fully-visible line in WIN. END-OF-BUFFER is t when EOB
+is fully-visible in WIN. If WIN is nil, the selected window is
+used."
(let* ((win (or win (selected-window)))
(edges (window-inside-pixel-edges win))
(ht (- (nth 3 edges) (nth 1 edges)))
(last-line-pos (posn-point (posn-at-x-y 0 (1- ht) win))))
(if (pos-visible-in-window-p last-line-pos win)
(let ((end (window-end win t)))
- (list end (= end (point-max))))
+ (list end (pos-visible-in-window-p (point-max) win)))
(list last-line-pos nil))))
(defun follow-calc-win-start (windows pos win)
(let ((orig-win (selected-window))
win-start-end)
(dolist (w windows)
- (select-window w)
+ (select-window w 'norecord)
(push (cons w (cons (window-start) (follow-calc-win-end)))
win-start-end))
- (select-window orig-win)
+ (select-window orig-win 'norecord)
(setq follow-windows-start-end-cache (nreverse win-start-end)))))
(defsubst follow-pos-visible (pos win win-start-end)
;; is nil. Start every window directly after the end of the previous
;; window, to make sure long lines are displayed correctly.
+(defvar follow-start-end-invalid t
+ "When non-nil, indicates `follow-windows-start-end-cache' is invalid.")
+(make-variable-buffer-local 'follow-start-end-invalid)
+
(defun follow-redisplay (&optional windows win preserve-win)
"Reposition the WINDOWS around WIN.
Should point be too close to the roof we redisplay everything
(dolist (w windows)
(unless (and preserve-win (eq w win))
(set-window-start w start))
- (setq start (car (follow-calc-win-end w))))))
+ (setq start (car (follow-calc-win-end w))))
+ (setq follow-start-end-invalid nil)))
(defun follow-estimate-first-window-start (windows win start)
"Estimate the position of the first window.
(goto-char start)
(vertical-motion 0 win)
(dolist (w windows-before)
- (vertical-motion (- 1 (window-text-height w)) w))
+ (vertical-motion (- (window-text-height w)) w))
(point))))
(cl-assert (eq (window-buffer win) (current-buffer)))
(when (and follow-mode
(not (window-minibuffer-p win)))
- (let* ((dest (point))
- (windows (follow-all-followers win))
- (win-start-end (progn
- (follow-update-window-start (car windows))
- (follow-windows-start-end windows)))
- (aligned (follow-windows-aligned-p win-start-end))
- (visible (follow-pos-visible dest win win-start-end))
- selected-window-up-to-date)
- (unless (and aligned visible)
- (setq follow-windows-start-end-cache nil))
-
- ;; Select a window to display point.
- (unless follow-internal-force-redisplay
- (if (eq dest (point-max))
- ;; Be careful at point-max: the display can be aligned
- ;; while DEST can be visible in several windows.
- (cond
- ;; Select the current window, but only when the display
- ;; is correct. (When inserting characters in a tail
- ;; window, the display is not correct, as they are
- ;; shown twice.)
- ;;
- ;; Never stick to the current window after a deletion.
- ;; Otherwise, when typing `DEL' in a window showing
- ;; only the end of the file, a character would be
- ;; removed from the window above, which is very
- ;; unintuitive.
- ((and visible
- aligned
- (not (memq this-command
- '(backward-delete-char
- delete-backward-char
- backward-delete-char-untabify
- kill-region))))
- (follow-debug-message "Max: same"))
- ;; If the end is visible, and the window doesn't
- ;; seems like it just has been moved, select it.
- ((follow-select-if-end-visible win-start-end)
- (follow-debug-message "Max: end visible")
- (setq visible t aligned nil)
- (goto-char dest))
- ;; Just show the end...
- (t
- (follow-debug-message "Max: default")
- (select-window (car (last windows)))
- (goto-char dest)
- (setq visible nil aligned nil)))
-
- ;; We're not at the end, here life is much simpler.
- (cond
- ;; This is the normal case!
- ;; It should be optimized for speed.
- ((and visible aligned)
- (follow-debug-message "same"))
- ;; Pick a position in any window. If the display is ok,
- ;; this picks the `correct' window.
- ((follow-select-if-visible dest win-start-end)
- (follow-debug-message "visible")
- (goto-char dest)
- ;; Perform redisplay, in case line is partially visible.
- (setq visible nil))
- ;; Not visible anywhere else, lets pick this one.
- (visible
- (follow-debug-message "visible in selected."))
- ;; If DEST is before the first window start, select the
- ;; first window.
- ((< dest (nth 1 (car win-start-end)))
- (follow-debug-message "before first")
- (select-window (car windows))
- (goto-char dest)
- (setq visible nil aligned nil))
- ;; If we can position the cursor without moving the first
- ;; window, do it. This is the case that catches `RET' at
- ;; the bottom of a window.
- ((follow-select-if-visible-from-first dest windows)
- (follow-debug-message "Below first")
- (setq visible t aligned t))
- ;; None of the above. Stick to the selected window.
- (t
- (follow-debug-message "None")
- (setq visible nil aligned nil))))
-
- ;; If a new window was selected, make sure that the old is
- ;; not scrolled when point is outside the window.
- (unless (eq win (selected-window))
- (let ((p (window-point win)))
- (set-window-start win (window-start win) nil)
- (set-window-point win p))))
-
- (unless visible
- ;; If point may not be visible in the selected window,
- ;; perform a redisplay; this ensures scrolling.
- (let ((opoint (point)))
- (redisplay)
- ;; If this `redisplay' moved point, we got clobbered by a
- ;; previous call to `set-window-start'. Try again.
- (when (/= (point) opoint)
- (goto-char opoint)
- (redisplay)))
-
- (setq selected-window-up-to-date t)
- (follow-avoid-tail-recenter)
- (setq win-start-end (follow-windows-start-end windows)
- follow-windows-start-end-cache nil
- aligned nil))
-
- ;; Now redraw the windows around the selected window.
- (unless (and (not follow-internal-force-redisplay)
- (or aligned
- (follow-windows-aligned-p win-start-end))
- (follow-point-visible-all-windows-p win-start-end))
- (setq follow-internal-force-redisplay nil)
- (follow-redisplay windows (selected-window)
- selected-window-up-to-date)
- (setq win-start-end (follow-windows-start-end windows)
- follow-windows-start-end-cache nil)
- ;; Point can end up in another window when DEST is at
- ;; the beginning of the buffer and the selected window is
- ;; not the first. It can also happen when long lines are
- ;; used and there is a big difference between the width of
- ;; the windows. (When scrolling one line in a wide window
- ;; which will cause a move larger that an entire small
- ;; window.)
- (unless (follow-pos-visible dest win win-start-end)
- (follow-select-if-visible dest win-start-end)
- (goto-char dest)))
-
- ;; If the region is visible, make it look good when spanning
- ;; multiple windows.
- (when (region-active-p)
- (follow-maximize-region
- (selected-window) windows win-start-end)))
+ (let ((windows (follow-all-followers win)))
+ ;; If we've explicitly scrolled, align the windows first.
+ (when follow-fixed-window
+ (follow-debug-message "fixed")
+ (follow-redisplay windows win)
+ (goto-char (follow-get-scrolled-point (point) windows))
+ (setq follow-fixed-window nil))
+ (let* ((dest (point))
+ (win-start-end (progn
+ (follow-update-window-start (car windows))
+ (follow-windows-start-end windows)))
+ (aligned (follow-windows-aligned-p win-start-end))
+ (visible (follow-pos-visible dest win win-start-end))
+ selected-window-up-to-date)
+ (unless (and aligned visible)
+ (setq follow-windows-start-end-cache nil))
+
+ ;; Select a window to display point.
+ (unless follow-internal-force-redisplay
+ (if (eq dest (point-max))
+ ;; Be careful at point-max: the display can be aligned
+ ;; while DEST can be visible in several windows.
+ (cond
+ ;; Select the current window, but only when the display
+ ;; is correct. (When inserting characters in a tail
+ ;; window, the display is not correct, as they are
+ ;; shown twice.)
+ ;;
+ ;; Never stick to the current window after a deletion.
+ ;; Otherwise, when typing `DEL' in a window showing
+ ;; only the end of the file, a character would be
+ ;; removed from the window above, which is very
+ ;; unintuitive.
+ ((and visible
+ aligned
+ (not (memq this-command
+ '(backward-delete-char
+ delete-backward-char
+ backward-delete-char-untabify
+ kill-region))))
+ (follow-debug-message "Max: same"))
+ ;; If the end is visible, and the window doesn't
+ ;; seems like it just has been moved, select it.
+ ((follow-select-if-end-visible win-start-end)
+ (follow-debug-message "Max: end visible")
+ (setq visible t aligned nil)
+ (goto-char dest))
+ ;; Just show the end...
+ (t
+ (follow-debug-message "Max: default")
+ (select-window (car (last windows)))
+ (goto-char dest)
+ (setq visible nil aligned nil)))
+
+ ;; We're not at the end, here life is much simpler.
+ (cond
+ ;; This is the normal case!
+ ;; It should be optimized for speed.
+ ((and visible aligned)
+ (follow-debug-message "same"))
+ ;; Pick a position in any window. If the display is ok,
+ ;; this picks the `correct' window.
+ ((follow-select-if-visible dest win-start-end)
+ (follow-debug-message "visible")
+ (goto-char dest)
+ ;; Perform redisplay, in case line is partially visible.
+ (setq visible nil))
+ ;; Not visible anywhere else, lets pick this one.
+ (visible
+ (follow-debug-message "visible in selected."))
+ ;; If DEST is before the first window start, select the
+ ;; first window.
+ ((< dest (nth 1 (car win-start-end)))
+ (follow-debug-message "before first")
+ (select-window (car windows))
+ (goto-char dest)
+ (setq visible nil aligned nil))
+ ;; If we can position the cursor without moving the first
+ ;; window, do it. This is the case that catches `RET' at
+ ;; the bottom of a window.
+ ((follow-select-if-visible-from-first dest windows)
+ (follow-debug-message "Below first")
+ (setq visible t aligned t))
+ ;; None of the above. Stick to the selected window.
+ (t
+ (follow-debug-message "None")
+ (setq visible nil aligned nil))))
+
+ ;; If a new window was selected, make sure that the old is
+ ;; not scrolled when point is outside the window.
+ (unless (eq win (selected-window))
+ (let ((p (window-point win)))
+ (set-window-start win (window-start win) nil)
+ (set-window-point win p))))
+
+ (unless visible
+ ;; If point may not be visible in the selected window,
+ ;; perform a redisplay; this ensures scrolling.
+ (let ((opoint (point)))
+ (redisplay)
+ ;; If this `redisplay' moved point, we got clobbered by a
+ ;; previous call to `set-window-start'. Try again.
+ (when (/= (point) opoint)
+ (goto-char opoint)
+ (redisplay)))
+
+ (setq selected-window-up-to-date t)
+ (follow-avoid-tail-recenter)
+ (setq win-start-end (follow-windows-start-end windows)
+ follow-windows-start-end-cache nil
+ aligned nil))
+
+ ;; Now redraw the windows around the selected window.
+ (unless (and (not follow-internal-force-redisplay)
+ (or aligned
+ (follow-windows-aligned-p win-start-end))
+ (follow-point-visible-all-windows-p win-start-end))
+ (setq follow-internal-force-redisplay nil)
+ (follow-redisplay windows (selected-window)
+ selected-window-up-to-date)
+ (setq win-start-end (follow-windows-start-end windows)
+ follow-windows-start-end-cache nil)
+ ;; Point can end up in another window when DEST is at
+ ;; the beginning of the buffer and the selected window is
+ ;; not the first. It can also happen when long lines are
+ ;; used and there is a big difference between the width of
+ ;; the windows. (When scrolling one line in a wide window
+ ;; which will cause a move larger that an entire small
+ ;; window.)
+ (unless (follow-pos-visible dest win win-start-end)
+ (follow-select-if-visible dest win-start-end)
+ (goto-char dest)))
+
+ ;; If the region is visible, make it look good when spanning
+ ;; multiple windows.
+ (when (region-active-p)
+ (follow-maximize-region
+ (selected-window) windows win-start-end))))
;; Whether or not the buffer was in follow mode, update windows
;; displaying the tail so that Emacs won't recenter them.
"Redraw all windows in FRAME, when in Follow mode."
;; Below, we call `post-command-hook'. Avoid an infloop.
(unless follow-inside-post-command-hook
- (let ((buffers '())
- (orig-window (selected-window))
- (orig-buffer (current-buffer))
- (orig-frame (selected-frame))
- windows
- buf)
- (select-frame frame)
- (unwind-protect
- (walk-windows
- (lambda (win)
- (setq buf (window-buffer win))
- (unless (memq buf buffers)
- (set-buffer buf)
- (when follow-mode
- (setq windows (follow-all-followers win))
- (if (not (memq orig-window windows))
- (follow-redisplay windows win)
- ;; Make sure we're redrawing around the selected
- ;; window.
- (select-window orig-window)
- (follow-post-command-hook)
- (setq orig-window (selected-window)))
- (setq buffers (cons buf buffers)))))
- 'no-minibuf)
- (select-frame orig-frame)
- (set-buffer orig-buffer)
- (select-window orig-window)))))
+ (save-current-buffer
+ (let ((orig-frame (selected-frame)))
+ (select-frame frame)
+ (let ((picked-window (selected-window)) ; Note: May change below.
+ (seen-buffers '()))
+ (unwind-protect
+ (walk-windows
+ (lambda (win)
+ (let ((buf (window-buffer win)))
+ (unless (memq buf seen-buffers)
+ (set-buffer buf)
+ (when follow-mode
+ (let ((windows (follow-all-followers win)))
+ (if (not (memq picked-window windows))
+ (follow-redisplay windows win)
+ ;; Make sure we're redrawing around the selected
+ ;; window.
+ (select-window picked-window 'norecord)
+ (follow-post-command-hook)
+ (setq picked-window (selected-window))))
+ (push buf seen-buffers)))))
+ 'no-minibuf)
+ (select-window picked-window 'norecord)))
+ (select-frame orig-frame)))))
(add-hook 'window-scroll-functions 'follow-avoid-tail-recenter t)
+;;; Low level window start and end.
+
+;; These routines are the Follow Mode versions of the low level
+;; functions described on page "Window Start and End" of the elisp
+;; manual, e.g. `window-group-start'. The aim is to be able to handle
+;; Follow Mode windows by replacing `window-start' by
+;; `window-group-start', etc.
+
+(defun follow-after-change (_beg _end _old-len)
+ "After change function: set `follow-start-end-invalid'."
+ (setq follow-start-end-invalid t))
+
+(defun follow-window-start (&optional window)
+ "Return position at which display currently starts in the
+Follow Mode group of windows which includes WINDOW.
+
+WINDOW must be a live window and defaults to the selected one.
+This is updated by redisplay or by calling
+`follow-set-window-start'."
+ (let ((windows (follow-all-followers window)))
+ (window-start (car windows))))
+
+(defun follow-window-end (&optional window update)
+ "Return position at which display currently ends in the Follow
+ Mode group of windows which includes WINDOW.
+
+ WINDOW must be a live window and defaults to the selected one.
+ This is updated by redisplay, when it runs to completion.
+ Simply changing the buffer text or setting `window-start' does
+ not update this value.
+
+ Return nil if there is no recorded value. (This can happen if
+ the last redisplay of WINDOW was preempted, and did not
+ finish.) If UPDATE is non-nil, compute the up-to-date position
+ if it isn't already recorded."
+ (let* ((windows (follow-all-followers window))
+ (last (car (last windows))))
+ (when (and update follow-start-end-invalid)
+ (follow-redisplay windows (car windows)))
+ (window-end last update)))
+
+(defun follow-set-window-start (window pos &optional noforce)
+ "Make display in the Follow Mode group of windows which includes
+WINDOW start at position POS in WINDOW's buffer.
+
+WINDOW must be a live window and defaults to the selected one. Return
+POS. Optional third arg NOFORCE non-nil inhibits next redisplay from
+overriding motion of point in order to display at this exact start."
+ (let ((windows (follow-all-followers window)))
+ (setq follow-start-end-invalid t)
+ (set-window-start (car windows) pos noforce)))
+
+(defun follow-pos-visible-in-window-p (&optional pos window partially)
+ "Return non-nil if position POS is currently on the frame in one of
+ the windows in the Follow Mode group which includes WINDOW.
+
+WINDOW must be a live window and defaults to the selected one.
+
+Return nil if that position is scrolled vertically out of view. If a
+character is only partially visible, nil is returned, unless the
+optional argument PARTIALLY is non-nil. If POS is only out of view
+because of horizontal scrolling, return non-nil. If POS is t, it
+specifies the position of the last visible glyph in WINDOW. POS
+defaults to point in WINDOW; WINDOW defaults to the selected window.
+
+If POS is visible, return t if PARTIALLY is nil; if PARTIALLY is non-nil,
+the return value is a list of 2 or 6 elements (X Y [RTOP RBOT ROWH VPOS]),
+where X and Y are the pixel coordinates relative to the top left corner
+of the actual window containing it. The remaining elements are
+omitted if the character after POS is fully visible; otherwise, RTOP
+and RBOT are the number of pixels off-window at the top and bottom of
+the screen line (\"row\") containing POS, ROWH is the visible height
+of that row, and VPOS is the row number \(zero-based)."
+ (let* ((windows (follow-all-followers window))
+ (last (car (last windows))))
+ (when follow-start-end-invalid
+ (follow-redisplay windows (car windows)))
+ (let* ((cache (follow-windows-start-end windows))
+ (last-elt (car (last cache)))
+ our-pos pertinent-elt)
+ (setq pertinent-elt
+ (if (eq pos t)
+ last-elt
+ (setq our-pos (or pos (point)))
+ (catch 'element
+ (while cache
+ (when (< our-pos (nth 2 (car cache)))
+ (throw 'element (car cache)))
+ (setq cache (cdr cache)))
+ last-elt)))
+ (pos-visible-in-window-p our-pos (car pertinent-elt) partially))))
+
+(defun follow-move-to-window-line (arg)
+ "Position point relative to the Follow mode group containing the selected window.
+ARG nil means position point at center of the window group.
+Else, ARG specifies vertical position within the window group;
+zero means top of the first window in the group, negative means
+ relative to bottom of the last window in the group."
+ (let* ((windows (follow-all-followers))
+ (start-end (follow-windows-start-end windows))
+ (rev-start-end (reverse start-end))
+ (lines 0)
+ middle-window elt count)
+ (select-window
+ (cond
+ ((null arg)
+ (setq rev-start-end (nthcdr (/ (length windows) 2) rev-start-end))
+ (prog1 (car (car rev-start-end))
+ (while (setq rev-start-end (cdr rev-start-end))
+ (setq elt (car rev-start-end)
+ count (count-screen-lines (cadr elt) (nth 2 elt)
+ nil (car elt))
+ lines (+ lines count)))))
+ ((>= arg 0)
+ (while (and (cdr start-end)
+ (progn
+ (setq elt (car start-end)
+ count (count-screen-lines (cadr elt) (nth 2 elt)
+ nil (car elt)))
+ (>= arg count)))
+ (setq arg (- arg count)
+ lines (+ lines count)
+ start-end (cdr start-end)))
+ (car (car start-end)))
+ (t ; (< arg 0)
+ (while (and (cadr rev-start-end)
+ (progn
+ (setq elt (car rev-start-end)
+ count (count-lines (cadr elt) (nth 2 elt)))
+ (<= arg (- count))))
+ (setq arg (+ arg count)
+ rev-start-end (cdr rev-start-end)))
+ (prog1 (car (car rev-start-end))
+ (while (setq rev-start-end (cdr rev-start-end))
+ (setq elt (car rev-start-end)
+ count (count-screen-lines (cadr elt) (nth 2 elt)
+ nil (car elt))
+ lines (+ lines count)))))))
+ (+ lines (move-to-window-line arg))))
+
;;; Profile support
;; The following (non-evaluated) section can be used to