2 @c This is part of the GNU Emacs Lisp Reference Manual.
3 @c Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995, 1998 Free Software Foundation, Inc.
4 @c See the file elisp.texi for copying conditions.
5 @setfilename ../info/windows
6 @node Windows, Frames, Buffers, Top
9 This chapter describes most of the functions and variables related to
10 Emacs windows. See @ref{Display}, for information on how text is
14 * Basic Windows:: Basic information on using windows.
15 * Splitting Windows:: Splitting one window into two windows.
16 * Deleting Windows:: Deleting a window gives its space to other windows.
17 * Selecting Windows:: The selected window is the one that you edit in.
18 * Cyclic Window Ordering:: Moving around the existing windows.
19 * Buffers and Windows:: Each window displays the contents of a buffer.
20 * Displaying Buffers:: Higher-lever functions for displaying a buffer
21 and choosing a window for it.
22 * Choosing Window:: How to choose a window for displaying a buffer.
23 * Window Point:: Each window has its own location of point.
24 * Window Start:: The display-start position controls which text
25 is on-screen in the window.
26 * Vertical Scrolling:: Moving text up and down in the window.
27 * Horizontal Scrolling:: Moving text sideways on the window.
28 * Size of Window:: Accessing the size of a window.
29 * Resizing Windows:: Changing the size of a window.
30 * Coordinates and Windows:: Converting coordinates to windows.
31 * Window Configurations:: Saving and restoring the state of the screen.
32 * Window Hooks:: Hooks for scrolling, window size changes,
33 redisplay going past a certain point,
34 or window configuration changes.
38 @section Basic Concepts of Emacs Windows
40 @cindex selected window
42 A @dfn{window} in Emacs is the physical area of the screen in which a
43 buffer is displayed. The term is also used to refer to a Lisp object that
44 represents that screen area in Emacs Lisp. It should be
45 clear from the context which is meant.
47 Emacs groups windows into frames. A frame represents an area of
48 screen available for Emacs to use. Each frame always contains at least
49 one window, but you can subdivide it vertically or horizontally into
50 multiple nonoverlapping Emacs windows.
52 In each frame, at any time, one and only one window is designated as
53 @dfn{selected within the frame}. The frame's cursor appears in that
54 window. At any time, one frame is the selected frame; and the window
55 selected within that frame is @dfn{the selected window}. The selected
56 window's buffer is usually the current buffer (except when
57 @code{set-buffer} has been used). @xref{Current Buffer}.
59 For practical purposes, a window exists only while it is displayed in
60 a frame. Once removed from the frame, the window is effectively deleted
61 and should not be used, @emph{even though there may still be references
62 to it} from other Lisp objects. Restoring a saved window configuration
63 is the only way for a window no longer on the screen to come back to
64 life. (@xref{Deleting Windows}.)
66 Each window has the following attributes:
79 window edges with respect to the screen or frame
82 the buffer it displays
85 position within the buffer at the upper left of the window
88 amount of horizontal scrolling, in columns
97 how recently the window was selected
100 @cindex multiple windows
101 Users create multiple windows so they can look at several buffers at
102 once. Lisp libraries use multiple windows for a variety of reasons, but
103 most often to display related information. In Rmail, for example, you
104 can move through a summary buffer in one window while the other window
105 shows messages one at a time as they are reached.
107 The meaning of ``window'' in Emacs is similar to what it means in the
108 context of general-purpose window systems such as X, but not identical.
109 The X Window System places X windows on the screen; Emacs uses one or
110 more X windows as frames, and subdivides them into
111 Emacs windows. When you use Emacs on a character-only terminal, Emacs
112 treats the whole terminal screen as one frame.
114 @cindex terminal screen
115 @cindex screen of terminal
116 @cindex tiled windows
117 Most window systems support arbitrarily located overlapping windows.
118 In contrast, Emacs windows are @dfn{tiled}; they never overlap, and
119 together they fill the whole screen or frame. Because of the way in
120 which Emacs creates new windows and resizes them, not all conceivable
121 tilings of windows on an Emacs frame are actually possible.
122 @xref{Splitting Windows}, and @ref{Size of Window}.
124 @xref{Display}, for information on how the contents of the
125 window's buffer are displayed in the window.
127 @defun windowp object
128 This function returns @code{t} if @var{object} is a window.
131 @node Splitting Windows
132 @section Splitting Windows
133 @cindex splitting windows
134 @cindex window splitting
136 The functions described here are the primitives used to split a window
137 into two windows. Two higher level functions sometimes split a window,
138 but not always: @code{pop-to-buffer} and @code{display-buffer}
139 (@pxref{Displaying Buffers}).
141 The functions described here do not accept a buffer as an argument.
142 The two ``halves'' of the split window initially display the same buffer
143 previously visible in the window that was split.
145 @deffn Command split-window &optional window size horizontal
146 This function splits @var{window} into two windows. The original
147 window @var{window} remains the selected window, but occupies only
148 part of its former screen area. The rest is occupied by a newly created
149 window which is returned as the value of this function.
151 If @var{horizontal} is non-@code{nil}, then @var{window} splits into
152 two side by side windows. The original window @var{window} keeps the
153 leftmost @var{size} columns, and gives the rest of the columns to the
154 new window. Otherwise, it splits into windows one above the other, and
155 @var{window} keeps the upper @var{size} lines and gives the rest of the
156 lines to the new window. The original window is therefore the
157 left-hand or upper of the two, and the new window is the right-hand or
160 If @var{window} is omitted or @code{nil}, then the selected window is
161 split. If @var{size} is omitted or @code{nil}, then @var{window} is
162 divided evenly into two parts. (If there is an odd line, it is
163 allocated to the new window.) When @code{split-window} is called
164 interactively, all its arguments are @code{nil}.
166 The following example starts with one window on a screen that is 50
167 lines high by 80 columns wide; then the window is split.
171 (setq w (selected-window))
172 @result{} #<window 8 on windows.texi>
173 (window-edges) ; @r{Edges in order:}
174 @result{} (0 0 80 50) ; @r{left--top--right--bottom}
178 ;; @r{Returns window created}
179 (setq w2 (split-window w 15))
180 @result{} #<window 28 on windows.texi>
184 @result{} (0 15 80 50) ; @r{Bottom window;}
189 @result{} (0 0 80 15) ; @r{Top window}
193 The screen looks like this:
209 Next, the top window is split horizontally:
213 (setq w3 (split-window w 35 t))
214 @result{} #<window 32 on windows.texi>
218 @result{} (35 0 80 15) ; @r{Left edge at column 35}
222 @result{} (0 0 35 15) ; @r{Right edge at column 35}
226 @result{} (0 15 80 50) ; @r{Bottom window unchanged}
231 Now, the screen looks like this:
248 Normally, Emacs indicates the border between two side-by-side windows
249 with a scroll bar (@pxref{Window Frame Parameters,Scroll Bars}) or @samp{|}
250 characters. The display table can specify alternative border
251 characters; see @ref{Display Tables}.
254 @deffn Command split-window-vertically size
255 This function splits the selected window into two windows, one above
256 the other, leaving the selected window with @var{size} lines.
258 This function is simply an interface to @code{split-windows}.
259 Here is the complete function definition for it:
263 (defun split-window-vertically (&optional arg)
264 "Split current window into two windows, @dots{}"
266 (split-window nil (and arg (prefix-numeric-value arg))))
271 @deffn Command split-window-horizontally size
272 This function splits the selected window into two windows
273 side-by-side, leaving the selected window with @var{size} columns.
275 This function is simply an interface to @code{split-windows}. Here is
276 the complete definition for @code{split-window-horizontally} (except for
277 part of the documentation string):
281 (defun split-window-horizontally (&optional arg)
282 "Split selected window into two windows, side by side..."
284 (split-window nil (and arg (prefix-numeric-value arg)) t))
289 @defun one-window-p &optional no-mini all-frames
290 This function returns non-@code{nil} if there is only one window. The
291 argument @var{no-mini}, if non-@code{nil}, means don't count the
292 minibuffer even if it is active; otherwise, the minibuffer window is
293 included, if active, in the total number of windows, which is compared
296 The argument @var{all-frames} specifies which frames to consider. Here
297 are the possible values and their meanings:
301 Count the windows in the selected frame, plus the minibuffer used
302 by that frame even if it lies in some other frame.
305 Count all windows in all existing frames.
308 Count all windows in all visible frames.
311 Count all windows in all visible or iconified frames.
314 Count precisely the windows in the selected frame, and no others.
318 @node Deleting Windows
319 @section Deleting Windows
320 @cindex deleting windows
322 A window remains visible on its frame unless you @dfn{delete} it by
323 calling certain functions that delete windows. A deleted window cannot
324 appear on the screen, but continues to exist as a Lisp object until
325 there are no references to it. There is no way to cancel the deletion
326 of a window aside from restoring a saved window configuration
327 (@pxref{Window Configurations}). Restoring a window configuration also
328 deletes any windows that aren't part of that configuration.
330 When you delete a window, the space it took up is given to one
334 @defun window-live-p window
335 This function returns @code{nil} if @var{window} is deleted, and
338 @strong{Warning:} Erroneous information or fatal errors may result from
339 using a deleted window as if it were live.
342 @deffn Command delete-window &optional window
343 This function removes @var{window} from display, and returns @code{nil}.
344 If @var{window} is omitted, then the selected window is deleted. An
345 error is signaled if there is only one window when @code{delete-window}
349 @deffn Command delete-other-windows &optional window
350 This function makes @var{window} the only window on its frame, by
351 deleting the other windows in that frame. If @var{window} is omitted or
352 @code{nil}, then the selected window is used by default.
354 The return value is @code{nil}.
357 @deffn Command delete-windows-on buffer &optional frame
358 This function deletes all windows showing @var{buffer}. If there are
359 no windows showing @var{buffer}, it does nothing.
361 @code{delete-windows-on} operates frame by frame. If a frame has
362 several windows showing different buffers, then those showing
363 @var{buffer} are removed, and the others expand to fill the space. If
364 all windows in some frame are showing @var{buffer} (including the case
365 where there is only one window), then the frame reverts to having a
366 single window showing another buffer chosen with @code{other-buffer}.
367 @xref{The Buffer List}.
369 The argument @var{frame} controls which frames to operate on:
373 If it is @code{nil}, operate on the selected frame.
375 If it is @code{t}, operate on all frames.
377 If it is @code{visible}, operate on all visible frames.
379 If it is 0, operate on all visible or iconified frames.
381 If it is a frame, operate on that frame.
384 This function always returns @code{nil}.
387 @node Selecting Windows
388 @section Selecting Windows
389 @cindex selecting windows
391 When a window is selected, the buffer in the window becomes the current
392 buffer, and the cursor will appear in it.
394 @defun selected-window
395 This function returns the selected window. This is the window in
396 which the cursor appears and to which many commands apply.
399 @defun select-window window
400 This function makes @var{window} the selected window. The cursor then
401 appears in @var{window} (on redisplay). The buffer being displayed in
402 @var{window} is immediately designated the current buffer.
404 The return value is @var{window}.
408 (setq w (next-window))
410 @result{} #<window 65 on windows.texi>
415 @defmac save-selected-window forms@dots{}
416 This macro records the selected window, executes @var{forms}
417 in sequence, then restores the earlier selected window.
419 This macro does not save or restore anything about the sizes, arrangement
420 or contents of windows; therefore, if the @var{forms} change them,
423 Each frame, at any time, has a window selected within the frame. This
424 macro saves only @emph{the} selected window; it does not save anything
425 about other frames. If the @var{forms} select some other frame and
426 alter the window selected within it, the change persists.
429 @cindex finding windows
430 The following functions choose one of the windows on the screen,
431 offering various criteria for the choice.
433 @defun get-lru-window &optional frame
434 This function returns the window least recently ``used'' (that is,
435 selected). The selected window is always the most recently used window.
437 The selected window can be the least recently used window if it is the
438 only window. A newly created window becomes the least recently used
439 window until it is selected. A minibuffer window is never a candidate.
441 The argument @var{frame} controls which windows are considered.
445 If it is @code{nil}, consider windows on the selected frame.
447 If it is @code{t}, consider windows on all frames.
449 If it is @code{visible}, consider windows on all visible frames.
451 If it is 0, consider windows on all visible or iconified frames.
453 If it is a frame, consider windows on that frame.
457 @defun get-largest-window &optional frame
458 This function returns the window with the largest area (height times
459 width). If there are no side-by-side windows, then this is the window
460 with the most lines. A minibuffer window is never a candidate.
462 If there are two windows of the same size, then the function returns
463 the window that is first in the cyclic ordering of windows (see
464 following section), starting from the selected window.
466 The argument @var{frame} controls which set of windows are
467 considered. See @code{get-lru-window}, above.
470 @node Cyclic Window Ordering
471 @comment node-name, next, previous, up
472 @section Cyclic Ordering of Windows
473 @cindex cyclic ordering of windows
474 @cindex ordering of windows, cyclic
475 @cindex window ordering, cyclic
477 When you use the command @kbd{C-x o} (@code{other-window}) to select
478 the next window, it moves through all the windows on the screen in a
479 specific cyclic order. For any given configuration of windows, this
480 order never varies. It is called the @dfn{cyclic ordering of windows}.
482 This ordering generally goes from top to bottom, and from left to
483 right. But it may go down first or go right first, depending on the
484 order in which the windows were split.
486 If the first split was vertical (into windows one above each other),
487 and then the subwindows were split horizontally, then the ordering is
488 left to right in the top of the frame, and then left to right in the
489 next lower part of the frame, and so on. If the first split was
490 horizontal, the ordering is top to bottom in the left part, and so on.
491 In general, within each set of siblings at any level in the window tree,
492 the order is left to right, or top to bottom.
494 @defun next-window &optional window minibuf all-frames
495 @cindex minibuffer window
496 This function returns the window following @var{window} in the cyclic
497 ordering of windows. This is the window that @kbd{C-x o} would select
498 if typed when @var{window} is selected. If @var{window} is the only
499 window visible, then this function returns @var{window}. If omitted,
500 @var{window} defaults to the selected window.
502 The value of the argument @var{minibuf} determines whether the
503 minibuffer is included in the window order. Normally, when
504 @var{minibuf} is @code{nil}, the minibuffer is included if it is
505 currently active; this is the behavior of @kbd{C-x o}. (The minibuffer
506 window is active while the minibuffer is in use. @xref{Minibuffers}.)
508 If @var{minibuf} is @code{t}, then the cyclic ordering includes the
509 minibuffer window even if it is not active.
511 If @var{minibuf} is neither @code{t} nor @code{nil}, then the minibuffer
512 window is not included even if it is active.
514 The argument @var{all-frames} specifies which frames to consider. Here
515 are the possible values and their meanings:
519 Consider all the windows in @var{window}'s frame, plus the minibuffer
520 used by that frame even if it lies in some other frame.
523 Consider all windows in all existing frames.
526 Consider all windows in all visible frames. (To get useful results, you
527 must ensure @var{window} is in a visible frame.)
530 Consider all windows in all visible or iconified frames.
533 Consider precisely the windows in @var{window}'s frame, and no others.
536 This example assumes there are two windows, both displaying the
537 buffer @samp{windows.texi}:
542 @result{} #<window 56 on windows.texi>
545 (next-window (selected-window))
546 @result{} #<window 52 on windows.texi>
549 (next-window (next-window (selected-window)))
550 @result{} #<window 56 on windows.texi>
555 @defun previous-window &optional window minibuf all-frames
556 This function returns the window preceding @var{window} in the cyclic
557 ordering of windows. The other arguments specify which windows to
558 include in the cycle, as in @code{next-window}.
561 @deffn Command other-window count
562 This function selects the @var{count}th following window in the cyclic
563 order. If count is negative, then it moves back @minus{}@var{count}
564 windows in the cycle, rather than forward. It returns @code{nil}.
566 In an interactive call, @var{count} is the numeric prefix argument.
570 @defun walk-windows proc &optional minibuf all-frames
571 This function cycles through all windows, calling @code{proc}
572 once for each window with the window as its sole argument.
574 The optional arguments @var{minibuf} and @var{all-frames} specify the
575 set of windows to include in the scan. See @code{next-window}, above,
579 @node Buffers and Windows
580 @section Buffers and Windows
581 @cindex examining windows
582 @cindex windows, controlling precisely
583 @cindex buffers, controlled in windows
585 This section describes low-level functions to examine windows or to
586 display buffers in windows in a precisely controlled fashion.
588 See the following section for
591 @xref{Displaying Buffers}, for
593 related functions that find a window to use and specify a buffer for it.
594 The functions described there are easier to use than these, but they
595 employ heuristics in choosing or creating a window; use these functions
596 when you need complete control.
598 @defun set-window-buffer window buffer-or-name
599 This function makes @var{window} display @var{buffer-or-name} as its
600 contents. It returns @code{nil}.
604 (set-window-buffer (selected-window) "foo")
610 @defun window-buffer &optional window
611 This function returns the buffer that @var{window} is displaying. If
612 @var{window} is omitted, this function returns the buffer for the
618 @result{} #<buffer windows.texi>
623 @defun get-buffer-window buffer-or-name &optional all-frames
624 This function returns a window currently displaying
625 @var{buffer-or-name}, or @code{nil} if there is none. If there are
626 several such windows, then the function returns the first one in the
627 cyclic ordering of windows, starting from the selected window.
628 @xref{Cyclic Window Ordering}.
630 The argument @var{all-frames} controls which windows to consider.
634 If it is @code{nil}, consider windows on the selected frame.
636 If it is @code{t}, consider windows on all frames.
638 If it is @code{visible}, consider windows on all visible frames.
640 If it is 0, consider windows on all visible or iconified frames.
642 If it is a frame, consider windows on that frame.
646 @defun get-buffer-window-list buffer-or-name &optional minibuf all-frames
647 This function returns a list of all the windows currently displaying
648 @var{buffer-or-name}.
650 The two optional arguments work like the optional arguments of
651 @code{next-window} (@pxref{Cyclic Window Ordering}); they are @emph{not}
652 like the single optional argument of @code{get-buffer-window}. Perhaps
653 we should change @code{get-buffer-window} in the future to make it
654 compatible with the other functions.
656 The argument @var{all-frames} controls which windows to consider.
660 If it is @code{nil}, consider windows on the selected frame.
662 If it is @code{t}, consider windows on all frames.
664 If it is @code{visible}, consider windows on all visible frames.
666 If it is 0, consider windows on all visible or iconified frames.
668 If it is a frame, consider windows on that frame.
672 @node Displaying Buffers
673 @section Displaying Buffers in Windows
674 @cindex switching to a buffer
675 @cindex displaying a buffer
677 In this section we describe convenient functions that choose a window
678 automatically and use it to display a specified buffer. These functions
679 can also split an existing window in certain circumstances. We also
680 describe variables that parameterize the heuristics used for choosing a
683 See the preceding section for
686 @xref{Buffers and Windows}, for
688 low-level functions that give you more precise control.
690 Do not use the functions in this section in order to make a buffer
691 current so that a Lisp program can access or modify it; they are too
692 drastic for that purpose, since they change the display of buffers in
693 windows, which would be gratuitous and surprise the user. Instead, use
694 @code{set-buffer} (@pxref{Current Buffer}) and @code{save-excursion}
695 (@pxref{Excursions}), which designate buffers as current for programmed
696 access without affecting the display of buffers in windows.
698 @deffn Command switch-to-buffer buffer-or-name &optional norecord
699 This function makes @var{buffer-or-name} the current buffer, and also
700 displays the buffer in the selected window. This means that a human can
701 see the buffer and subsequent keyboard commands will apply to it.
702 Contrast this with @code{set-buffer}, which makes @var{buffer-or-name}
703 the current buffer but does not display it in the selected window.
704 @xref{Current Buffer}.
706 If @var{buffer-or-name} does not identify an existing buffer, then a new
707 buffer by that name is created. The major mode for the new buffer is
708 set according to the variable @code{default-major-mode}. @xref{Auto
711 Normally the specified buffer is put at the front of the buffer list
712 (both the selected frame's buffer list and the frame-independent buffer
713 list). This affects the operation of @code{other-buffer}. However, if
714 @var{norecord} is non-@code{nil}, this is not done. @xref{The Buffer
717 The @code{switch-to-buffer} function is often used interactively, as
718 the binding of @kbd{C-x b}. It is also used frequently in programs. It
719 always returns @code{nil}.
722 @deffn Command switch-to-buffer-other-window buffer-or-name &optional norecord
723 This function makes @var{buffer-or-name} the current buffer and
724 displays it in a window not currently selected. It then selects that
725 window. The handling of the buffer is the same as in
726 @code{switch-to-buffer}.
728 The currently selected window is absolutely never used to do the job.
729 If it is the only window, then it is split to make a distinct window for
730 this purpose. If the selected window is already displaying the buffer,
731 then it continues to do so, but another window is nonetheless found to
732 display it in as well.
734 This function updates the buffer list just like @code{switch-to-buffer}
735 unless @var{norecord} is non-@code{nil}.
738 @defun pop-to-buffer buffer-or-name &optional other-window norecord
739 This function makes @var{buffer-or-name} the current buffer and
740 switches to it in some window, preferably not the window previously
741 selected. The ``popped-to'' window becomes the selected window within
744 If the variable @code{pop-up-frames} is non-@code{nil},
745 @code{pop-to-buffer} looks for a window in any visible frame already
746 displaying the buffer; if there is one, it returns that window and makes
747 it be selected within its frame. If there is none, it creates a new
748 frame and displays the buffer in it.
750 If @code{pop-up-frames} is @code{nil}, then @code{pop-to-buffer}
751 operates entirely within the selected frame. (If the selected frame has
752 just a minibuffer, @code{pop-to-buffer} operates within the most
753 recently selected frame that was not just a minibuffer.)
755 If the variable @code{pop-up-windows} is non-@code{nil}, windows may
756 be split to create a new window that is different from the original
757 window. For details, see @ref{Choosing Window}.
759 If @var{other-window} is non-@code{nil}, @code{pop-to-buffer} finds or
760 creates another window even if @var{buffer-or-name} is already visible
761 in the selected window. Thus @var{buffer-or-name} could end up
762 displayed in two windows. On the other hand, if @var{buffer-or-name} is
763 already displayed in the selected window and @var{other-window} is
764 @code{nil}, then the selected window is considered sufficient display
765 for @var{buffer-or-name}, so that nothing needs to be done.
767 All the variables that affect @code{display-buffer} affect
768 @code{pop-to-buffer} as well. @xref{Choosing Window}.
770 If @var{buffer-or-name} is a string that does not name an existing
771 buffer, a buffer by that name is created. The major mode for the new
772 buffer is set according to the variable @code{default-major-mode}.
773 @xref{Auto Major Mode}.
775 This function updates the buffer list just like @code{switch-to-buffer}
776 unless @var{norecord} is non-@code{nil}.
779 @deffn Command replace-buffer-in-windows buffer
780 This function replaces @var{buffer} with some other buffer in all
781 windows displaying it. The other buffer used is chosen with
782 @code{other-buffer}. In the usual applications of this function, you
783 don't care which other buffer is used; you just want to make sure that
784 @var{buffer} is no longer displayed.
786 This function returns @code{nil}.
789 @tindex buffer-display-count
790 @defvar buffer-display-count
791 This variable is always buffer-local in each buffer. When the buffer is
792 created, @code{buffer-display-count} has value 0. Each time the buffer
793 is displayed in a window, that increments the value of
794 @code{buffer-display-count}.
797 @node Choosing Window
798 @section Choosing a Window for Display
800 This section describes the basic facility that chooses a window to
801 display a buffer in---@code{display-buffer}. All the higher-level
802 functions and commands use this subroutine. Here we describe how to use
803 @code{display-buffer} and how to customize it.
805 @deffn Command display-buffer buffer-or-name &optional not-this-window frame
806 This command makes @var{buffer-or-name} appear in some window, like
807 @code{pop-to-buffer}, but it does not select that window and does not
808 make the buffer current. The identity of the selected window is
809 unaltered by this function.
811 If @var{not-this-window} is non-@code{nil}, it means to display the
812 specified buffer in a window other than the selected one, even if it is
813 already on display in the selected window. This can cause the buffer to
814 appear in two windows at once. Otherwise, if @var{buffer-or-name} is
815 already being displayed in any window, that is good enough, so this
816 function does nothing.
818 @code{display-buffer} returns the window chosen to display
819 @var{buffer-or-name}.
821 If the argument @var{frame} is non-@code{nil}, it specifies which frames
822 to check when deciding whether the buffer is already displayed. Its
823 value means the same thing as in functions @code{get-buffer-window}
824 (@pxref{Buffers and Windows}). If the buffer is already displayed
825 in some window on one of these frames, @code{display-buffer} simply
828 Precisely how @code{display-buffer} finds or creates a window depends on
829 the variables described below.
832 @defopt pop-up-windows
833 This variable controls whether @code{display-buffer} makes new windows.
834 If it is non-@code{nil} and there is only one window, then that window
835 is split. If it is @code{nil}, then @code{display-buffer} does not
836 split the single window, but uses it whole.
839 @defopt split-height-threshold
840 This variable determines when @code{display-buffer} may split a window,
841 if there are multiple windows. @code{display-buffer} always splits the
842 largest window if it has at least this many lines. If the largest
843 window is not this tall, it is split only if it is the sole window and
844 @code{pop-up-windows} is non-@code{nil}.
848 @defopt pop-up-frames
849 This variable controls whether @code{display-buffer} makes new frames.
850 If it is non-@code{nil}, @code{display-buffer} looks for an existing
851 window already displaying the desired buffer, on any visible frame. If
852 it finds one, it returns that window. Otherwise it makes a new frame.
853 The variables @code{pop-up-windows} and @code{split-height-threshold} do
854 not matter if @code{pop-up-frames} is non-@code{nil}.
856 If @code{pop-up-frames} is @code{nil}, then @code{display-buffer} either
857 splits a window or reuses one.
859 @xref{Frames}, for more information.
863 @defvar pop-up-frame-function
864 This variable specifies how to make a new frame if @code{pop-up-frames}
867 Its value should be a function of no arguments. When
868 @code{display-buffer} makes a new frame, it does so by calling that
869 function, which should return a frame. The default value of the
870 variable is a function that creates a frame using parameters from
871 @code{pop-up-frame-alist}.
874 @defvar pop-up-frame-alist
875 This variable holds an alist specifying frame parameters used when
876 @code{display-buffer} makes a new frame. @xref{Frame Parameters}, for
877 more information about frame parameters.
880 @defvar special-display-buffer-names
881 A list of buffer names for buffers that should be displayed specially.
882 If the buffer's name is in this list, @code{display-buffer} handles the
885 By default, special display means to give the buffer a dedicated frame.
887 If an element is a list, instead of a string, then the @sc{car} of the
888 list is the buffer name, and the rest of the list says how to create the
889 frame. There are two possibilities for the rest of the list. It can be
890 an alist, specifying frame parameters, or it can contain a function and
891 arguments to give to it. (The function's first argument is always the
892 buffer to be displayed; the arguments from the list come after that.)
895 @defvar special-display-regexps
896 A list of regular expressions that specify buffers that should be
897 displayed specially. If the buffer's name matches any of the regular
898 expressions in this list, @code{display-buffer} handles the buffer
901 By default, special display means to give the buffer a dedicated frame.
903 If an element is a list, instead of a string, then the @sc{car} of the
904 list is the regular expression, and the rest of the list says how to
905 create the frame. See above, under @code{special-display-buffer-names}.
908 @defvar special-display-function
909 This variable holds the function to call to display a buffer specially.
910 It receives the buffer as an argument, and should return the window in
911 which it is displayed.
913 The default value of this variable is
914 @code{special-display-popup-frame}.
917 @defun special-display-popup-frame buffer
918 This function makes @var{buffer} visible in a frame of its own. If
919 @var{buffer} is already displayed in a window in some frame, it makes
920 the frame visible and raises it, to use that window. Otherwise, it
921 creates a frame that will be dedicated to @var{buffer}.
923 This function uses an existing window displaying @var{buffer} whether or
924 not it is in a frame of its own; but if you set up the above variables
925 in your init file, before @var{buffer} was created, then presumably the
926 window was previously made by this function.
929 @defopt special-display-frame-alist
930 This variable holds frame parameters for
931 @code{special-display-popup-frame} to use when it creates a frame.
934 @defopt same-window-buffer-names
935 A list of buffer names for buffers that should be displayed in the
936 selected window. If the buffer's name is in this list,
937 @code{display-buffer} handles the buffer by switching to it in the
941 @defopt same-window-regexps
942 A list of regular expressions that specify buffers that should be
943 displayed in the selected window. If the buffer's name matches any of
944 the regular expressions in this list, @code{display-buffer} handles the
945 buffer by switching to it in the selected window.
949 @defvar display-buffer-function
950 This variable is the most flexible way to customize the behavior of
951 @code{display-buffer}. If it is non-@code{nil}, it should be a function
952 that @code{display-buffer} calls to do the work. The function should
953 accept two arguments, the same two arguments that @code{display-buffer}
954 received. It should choose or create a window, display the specified
955 buffer, and then return the window.
957 This hook takes precedence over all the other options and hooks
962 @cindex dedicated window
963 A window can be marked as ``dedicated'' to its buffer. Then
964 @code{display-buffer} will not try to use that window to display any
967 @defun window-dedicated-p window
968 This function returns @code{t} if @var{window} is marked as dedicated;
969 otherwise @code{nil}.
972 @defun set-window-dedicated-p window flag
973 This function marks @var{window} as dedicated if @var{flag} is
974 non-@code{nil}, and nondedicated otherwise.
978 @section Windows and Point
979 @cindex window position
981 @cindex position in window
982 @cindex point in window
984 Each window has its own value of point, independent of the value of
985 point in other windows displaying the same buffer. This makes it useful
986 to have multiple windows showing one buffer.
990 The window point is established when a window is first created; it is
991 initialized from the buffer's point, or from the window point of another
992 window opened on the buffer if such a window exists.
995 Selecting a window sets the value of point in its buffer from the
996 window's value of point. Conversely, deselecting a window sets the
997 window's value of point from that of the buffer. Thus, when you switch
998 between windows that display a given buffer, the point value for the
999 selected window is in effect in the buffer, while the point values for
1000 the other windows are stored in those windows.
1003 As long as the selected window displays the current buffer, the window's
1004 point and the buffer's point always move together; they remain equal.
1007 @xref{Positions}, for more details on buffer positions.
1010 As far as the user is concerned, point is where the cursor is, and
1011 when the user switches to another buffer, the cursor jumps to the
1012 position of point in that buffer.
1014 @defun window-point window
1015 This function returns the current position of point in @var{window}.
1016 For a nonselected window, this is the value point would have (in that
1017 window's buffer) if that window were selected.
1019 When @var{window} is the selected window and its buffer is also the
1020 current buffer, the value returned is the same as point in that buffer.
1022 Strictly speaking, it would be more correct to return the
1023 ``top-level'' value of point, outside of any @code{save-excursion}
1024 forms. But that value is hard to find.
1027 @defun set-window-point window position
1028 This function positions point in @var{window} at position
1029 @var{position} in @var{window}'s buffer.
1033 @section The Window Start Position
1035 Each window contains a marker used to keep track of a buffer position
1036 that specifies where in the buffer display should start. This position
1037 is called the @dfn{display-start} position of the window (or just the
1038 @dfn{start}). The character after this position is the one that appears
1039 at the upper left corner of the window. It is usually, but not
1040 inevitably, at the beginning of a text line.
1042 @defun window-start &optional window
1043 @cindex window top line
1044 This function returns the display-start position of window
1045 @var{window}. If @var{window} is @code{nil}, the selected window is
1055 When you create a window, or display a different buffer in it, the
1056 display-start position is set to a display-start position recently used
1057 for the same buffer, or 1 if the buffer doesn't have any.
1059 Redisplay updates the window-start position (if you have not specified
1060 it explicitly since the previous redisplay) so that point appears on the
1061 screen. Nothing except redisplay automatically changes the window-start
1062 position; if you move point, do not expect the window-start position to
1063 change in response until after the next redisplay.
1065 For a realistic example of using @code{window-start}, see the
1066 description of @code{count-lines} in @ref{Text Lines}.
1069 @defun window-end &optional window update
1070 This function returns the position of the end of the display in window
1071 @var{window}. If @var{window} is @code{nil}, the selected window is
1074 Simply changing the buffer text or moving point does not update the
1075 value that @code{window-end} returns. The value is updated only when
1076 Emacs redisplays and redisplay completes without being preempted.
1078 If the last redisplay of @var{window} was preempted, and did not finish,
1079 Emacs does not know the position of the end of display in that window.
1080 In that case, this function returns @code{nil}.
1082 If you @var{update} is non-@code{nil}, @code{window-end} always returns
1083 an up-to-date value for where the window ends. If the saved value is
1084 valid, @code{window-end} returns that; otherwise it computes the correct
1085 value by scanning the buffer text.
1088 @defun set-window-start window position &optional noforce
1089 This function sets the display-start position of @var{window} to
1090 @var{position} in @var{window}'s buffer. It returns @var{position}.
1092 The display routines insist that the position of point be visible when a
1093 buffer is displayed. Normally, they change the display-start position
1094 (that is, scroll the window) whenever necessary to make point visible.
1095 However, if you specify the start position with this function using
1096 @code{nil} for @var{noforce}, it means you want display to start at
1097 @var{position} even if that would put the location of point off the
1098 screen. If this does place point off screen, the display routines move
1099 point to the left margin on the middle line in the window.
1101 For example, if point @w{is 1} and you set the start of the window @w{to
1102 2}, then point would be ``above'' the top of the window. The display
1103 routines will automatically move point if it is still 1 when redisplay
1104 occurs. Here is an example:
1108 ;; @r{Here is what @samp{foo} looks like before executing}
1109 ;; @r{the @code{set-window-start} expression.}
1113 ---------- Buffer: foo ----------
1114 @point{}This is the contents of buffer foo.
1120 ---------- Buffer: foo ----------
1126 (1+ (window-start)))
1131 ;; @r{Here is what @samp{foo} looks like after executing}
1132 ;; @r{the @code{set-window-start} expression.}
1133 ---------- Buffer: foo ----------
1134 his is the contents of buffer foo.
1140 ---------- Buffer: foo ----------
1144 If @var{noforce} is non-@code{nil}, and @var{position} would place point
1145 off screen at the next redisplay, then redisplay computes a new window-start
1146 position that works well with point, and thus @var{position} is not used.
1149 @defun pos-visible-in-window-p &optional position window
1150 This function returns @code{t} if @var{position} is within the range
1151 of text currently visible on the screen in @var{window}. It returns
1152 @code{nil} if @var{position} is scrolled vertically out of view. The
1153 argument @var{position} defaults to the current position of point;
1154 @var{window}, to the selected window. Here is an example:
1158 (or (pos-visible-in-window-p
1159 (point) (selected-window))
1164 The @code{pos-visible-in-window-p} function considers only vertical
1165 scrolling. If @var{position} is out of view only because @var{window}
1166 has been scrolled horizontally, @code{pos-visible-in-window-p} returns
1167 @code{t}. @xref{Horizontal Scrolling}.
1170 @node Vertical Scrolling
1171 @section Vertical Scrolling
1172 @cindex vertical scrolling
1173 @cindex scrolling vertically
1175 Vertical scrolling means moving the text up or down in a window. It
1176 works by changing the value of the window's display-start location. It
1177 may also change the value of @code{window-point} to keep it on the
1180 In the commands @code{scroll-up} and @code{scroll-down}, the directions
1181 ``up'' and ``down'' refer to the motion of the text in the buffer at which
1182 you are looking through the window. Imagine that the text is
1183 written on a long roll of paper and that the scrolling commands move the
1184 paper up and down. Thus, if you are looking at text in the middle of a
1185 buffer and repeatedly call @code{scroll-down}, you will eventually see
1186 the beginning of the buffer.
1188 Some people have urged that the opposite convention be used: they
1189 imagine that the window moves over text that remains in place. Then
1190 ``down'' commands would take you to the end of the buffer. This view is
1191 more consistent with the actual relationship between windows and the
1192 text in the buffer, but it is less like what the user sees. The
1193 position of a window on the terminal does not move, and short scrolling
1194 commands clearly move the text up or down on the screen. We have chosen
1195 names that fit the user's point of view.
1197 The scrolling functions (aside from @code{scroll-other-window}) have
1198 unpredictable results if the current buffer is different from the buffer
1199 that is displayed in the selected window. @xref{Current Buffer}.
1201 @deffn Command scroll-up &optional count
1202 This function scrolls the text in the selected window upward
1203 @var{count} lines. If @var{count} is negative, scrolling is actually
1206 If @var{count} is @code{nil} (or omitted), then the length of scroll
1207 is @code{next-screen-context-lines} lines less than the usable height of
1208 the window (not counting its mode line).
1210 @code{scroll-up} returns @code{nil}.
1213 @deffn Command scroll-down &optional count
1214 This function scrolls the text in the selected window downward
1215 @var{count} lines. If @var{count} is negative, scrolling is actually
1218 If @var{count} is omitted or @code{nil}, then the length of the scroll
1219 is @code{next-screen-context-lines} lines less than the usable height of
1220 the window (not counting its mode line).
1222 @code{scroll-down} returns @code{nil}.
1225 @deffn Command scroll-other-window &optional count
1226 This function scrolls the text in another window upward @var{count}
1227 lines. Negative values of @var{count}, or @code{nil}, are handled
1228 as in @code{scroll-up}.
1230 You can specify a buffer to scroll with the variable
1231 @code{other-window-scroll-buffer}. When the selected window is the
1232 minibuffer, the next window is normally the one at the top left corner.
1233 You can specify a different window to scroll with the variable
1234 @code{minibuffer-scroll-window}. This variable has no effect when any
1235 other window is selected. @xref{Minibuffer Misc}.
1237 When the minibuffer is active, it is the next window if the selected
1238 window is the one at the bottom right corner. In this case,
1239 @code{scroll-other-window} attempts to scroll the minibuffer. If the
1240 minibuffer contains just one line, it has nowhere to scroll to, so the
1241 line reappears after the echo area momentarily displays the message
1242 ``Beginning of buffer''.
1246 @defvar other-window-scroll-buffer
1247 If this variable is non-@code{nil}, it tells @code{scroll-other-window}
1248 which buffer to scroll.
1252 This variable controls how scrolling is done automatically when point
1253 moves off the screen. If the value is zero, then redisplay scrolls the
1254 text to center point vertically in the window. If the value is a
1255 positive integer @var{n}, then redisplay brings point back on screen by
1256 scrolling @var{n} lines in either direction, if possible; otherwise, it
1257 centers point. The default value is zero.
1260 @defopt next-screen-context-lines
1261 The value of this variable is the number of lines of continuity to
1262 retain when scrolling by full screens. For example, @code{scroll-up}
1263 with an argument of @code{nil} scrolls so that this many lines at the
1264 bottom of the window appear instead at the top. The default value is
1268 @deffn Command recenter &optional count
1269 @cindex centering point
1270 This function scrolls the selected window to put the text where point
1271 is located at a specified vertical position within the window.
1273 If @var{count} is a nonnegative number, it puts the line containing
1274 point @var{count} lines down from the top of the window. If @var{count}
1275 is a negative number, then it counts upward from the bottom of the
1276 window, so that @minus{}1 stands for the last usable line in the window.
1277 If @var{count} is a non-@code{nil} list, then it stands for the line in
1278 the middle of the window.
1280 If @var{count} is @code{nil}, @code{recenter} puts the line containing
1281 point in the middle of the window, then clears and redisplays the entire
1284 When @code{recenter} is called interactively, @var{count} is the raw
1285 prefix argument. Thus, typing @kbd{C-u} as the prefix sets the
1286 @var{count} to a non-@code{nil} list, while typing @kbd{C-u 4} sets
1287 @var{count} to 4, which positions the current line four lines from the
1290 With an argument of zero, @code{recenter} positions the current line at
1291 the top of the window. This action is so handy that some people make a
1292 separate key binding to do this. For example,
1296 (defun line-to-top-of-window ()
1297 "Scroll current line to top of window.
1298 Replaces three keystroke sequence C-u 0 C-l."
1302 (global-set-key [kp-multiply] 'line-to-top-of-window)
1307 @node Horizontal Scrolling
1308 @section Horizontal Scrolling
1309 @cindex horizontal scrolling
1311 Because we read English first from top to bottom and second from left
1312 to right, horizontal scrolling is not like vertical scrolling. Vertical
1313 scrolling involves selection of a contiguous portion of text to display.
1314 Horizontal scrolling causes part of each line to go off screen. The
1315 amount of horizontal scrolling is therefore specified as a number of
1316 columns rather than as a position in the buffer. It has nothing to do
1317 with the display-start position returned by @code{window-start}.
1319 Usually, no horizontal scrolling is in effect; then the leftmost
1320 column is at the left edge of the window. In this state, scrolling to
1321 the right is meaningless, since there is no data to the left of the
1322 screen to be revealed by it; so this is not allowed. Scrolling to the
1323 left is allowed; it scrolls the first columns of text off the edge of
1324 the window and can reveal additional columns on the right that were
1325 truncated before. Once a window has a nonzero amount of leftward
1326 horizontal scrolling, you can scroll it back to the right, but only so
1327 far as to reduce the net horizontal scroll to zero. There is no limit
1328 to how far left you can scroll, but eventually all the text will
1329 disappear off the left edge.
1331 @deffn Command scroll-left count
1332 This function scrolls the selected window @var{count} columns to the
1333 left (or to the right if @var{count} is negative). The return value is
1334 the total amount of leftward horizontal scrolling in effect after the
1335 change---just like the value returned by @code{window-hscroll} (below).
1338 @deffn Command scroll-right count
1339 This function scrolls the selected window @var{count} columns to the
1340 right (or to the left if @var{count} is negative). The return value is
1341 the total amount of leftward horizontal scrolling in effect after the
1342 change---just like the value returned by @code{window-hscroll} (below).
1344 Once you scroll a window as far right as it can go, back to its normal
1345 position where the total leftward scrolling is zero, attempts to scroll
1346 any farther right have no effect.
1349 @defun window-hscroll &optional window
1350 This function returns the total leftward horizontal scrolling of
1351 @var{window}---the number of columns by which the text in @var{window}
1352 is scrolled left past the left margin.
1354 The value is never negative. It is zero when no horizontal scrolling
1355 has been done in @var{window} (which is usually the case).
1357 If @var{window} is @code{nil}, the selected window is used.
1375 @defun set-window-hscroll window columns
1376 This function sets the number of columns from the left margin that
1377 @var{window} is scrolled from the value of @var{columns}. The argument
1378 @var{columns} should be zero or positive; if not, it is taken as zero.
1380 The value returned is @var{columns}.
1384 (set-window-hscroll (selected-window) 10)
1390 Here is how you can determine whether a given position @var{position}
1391 is off the screen due to horizontal scrolling:
1395 (defun hscroll-on-screen (window position)
1397 (goto-char position)
1399 (>= (- (current-column) (window-hscroll window)) 0)
1400 (< (- (current-column) (window-hscroll window))
1401 (window-width window)))))
1405 @node Size of Window
1406 @section The Size of a Window
1408 @cindex size of window
1410 An Emacs window is rectangular, and its size information consists of
1411 the height (the number of lines) and the width (the number of character
1412 positions in each line). The mode line is included in the height. But
1413 the width does not count the scroll bar or the column of @samp{|}
1414 characters that separates side-by-side windows.
1416 The following three functions return size information about a window:
1418 @defun window-height &optional window
1419 This function returns the number of lines in @var{window}, including its
1420 mode line. If @var{window} fills its entire frame, this is typically
1421 one less than the value of @code{frame-height} on that frame (since the
1422 last line is always reserved for the minibuffer).
1424 If @var{window} is @code{nil}, the function uses the selected window.
1432 (split-window-vertically)
1433 @result{} #<window 4 on windows.texi>
1442 @defun window-width &optional window
1443 This function returns the number of columns in @var{window}. If
1444 @var{window} fills its entire frame, this is the same as the value of
1445 @code{frame-width} on that frame. The width does not include the
1446 window's scroll bar or the column of @samp{|} characters that separates
1447 side-by-side windows.
1449 If @var{window} is @code{nil}, the function uses the selected window.
1459 @defun window-edges &optional window
1460 This function returns a list of the edge coordinates of @var{window}.
1461 If @var{window} is @code{nil}, the selected window is used.
1463 The order of the list is @code{(@var{left} @var{top} @var{right}
1464 @var{bottom})}, all elements relative to 0, 0 at the top left corner of
1465 the frame. The element @var{right} of the value is one more than the
1466 rightmost column used by @var{window}, and @var{bottom} is one more than
1467 the bottommost row used by @var{window} and its mode-line.
1469 When you have side-by-side windows, the right edge value for a window
1470 with a neighbor on the right includes the width of the separator between
1471 the window and that neighbor. This separator may be a column of
1472 @samp{|} characters or it may be a scroll bar. Since the width of the
1473 window does not include this separator, the width does not equal the
1474 difference between the right and left edges in this case.
1476 Here is the result obtained on a typical 24-line terminal with just one
1481 (window-edges (selected-window))
1482 @result{} (0 0 80 23)
1487 The bottom edge is at line 23 because the last line is the echo area.
1489 If @var{window} is at the upper left corner of its frame, then
1490 @var{bottom} is the same as the value of @code{(window-height)},
1491 @var{right} is almost the same as the value of
1492 @code{(window-width)}@footnote{They are not exactly equal because
1493 @var{right} includes the vertical separator line or scroll bar, while
1494 @code{(window-width)} does not.}, and @var{top} and @var{left} are zero.
1495 For example, the edges of the following window are @w{@samp{0 0 5 8}}.
1496 Assuming that the frame has more than 8 columns, the last column of the
1497 window (column 7) holds a border rather than text. The last row (row 4)
1498 holds the mode line, shown here with @samp{xxxxxxxxx}.
1514 When there are side-by-side windows, any window not at the right edge of
1515 its frame has a separator in its last column or columns. The separator
1516 counts as one or two columns in the width of the window. A window never
1517 includes a separator on its left, since that belongs to the window to
1520 In the following example, let's suppose that the frame is 7
1521 columns wide. Then the edges of the left window are @w{@samp{0 0 4 3}}
1522 and the edges of the right window are @w{@samp{4 0 7 3}}.
1536 @node Resizing Windows
1537 @section Changing the Size of a Window
1538 @cindex window resizing
1539 @cindex changing window size
1540 @cindex window size, changing
1542 The window size functions fall into two classes: high-level commands
1543 that change the size of windows and low-level functions that access
1544 window size. Emacs does not permit overlapping windows or gaps between
1545 windows, so resizing one window affects other windows.
1547 @deffn Command enlarge-window size &optional horizontal
1548 This function makes the selected window @var{size} lines taller,
1549 stealing lines from neighboring windows. It takes the lines from one
1550 window at a time until that window is used up, then takes from another.
1551 If a window from which lines are stolen shrinks below
1552 @code{window-min-height} lines, that window disappears.
1554 If @var{horizontal} is non-@code{nil}, this function makes
1555 @var{window} wider by @var{size} columns, stealing columns instead of
1556 lines. If a window from which columns are stolen shrinks below
1557 @code{window-min-width} columns, that window disappears.
1559 If the requested size would exceed that of the window's frame, then the
1560 function makes the window occupy the entire height (or width) of the
1563 If @var{size} is negative, this function shrinks the window by
1564 @minus{}@var{size} lines or columns. If that makes the window smaller
1565 than the minimum size (@code{window-min-height} and
1566 @code{window-min-width}), @code{enlarge-window} deletes the window.
1568 @code{enlarge-window} returns @code{nil}.
1571 @deffn Command enlarge-window-horizontally columns
1572 This function makes the selected window @var{columns} wider.
1573 It could be defined as follows:
1577 (defun enlarge-window-horizontally (columns)
1578 (enlarge-window columns t))
1583 @deffn Command shrink-window size &optional horizontal
1584 This function is like @code{enlarge-window} but negates the argument
1585 @var{size}, making the selected window smaller by giving lines (or
1586 columns) to the other windows. If the window shrinks below
1587 @code{window-min-height} or @code{window-min-width}, then it disappears.
1589 If @var{size} is negative, the window is enlarged by @minus{}@var{size}
1593 @deffn Command shrink-window-horizontally columns
1594 This function makes the selected window @var{columns} narrower.
1595 It could be defined as follows:
1599 (defun shrink-window-horizontally (columns)
1600 (shrink-window columns t))
1605 @cindex minimum window size
1606 The following two variables constrain the window-size-changing
1607 functions to a minimum height and width.
1609 @defopt window-min-height
1610 The value of this variable determines how short a window may become
1611 before it is automatically deleted. Making a window smaller than
1612 @code{window-min-height} automatically deletes it, and no window may be
1613 created shorter than this. The absolute minimum height is two (allowing
1614 one line for the mode line, and one line for the buffer display).
1615 Actions that change window sizes reset this variable to two if it is
1616 less than two. The default value is 4.
1619 @defopt window-min-width
1620 The value of this variable determines how narrow a window may become
1621 before it automatically deleted. Making a window smaller than
1622 @code{window-min-width} automatically deletes it, and no window may be
1623 created narrower than this. The absolute minimum width is one; any
1624 value below that is ignored. The default value is 10.
1627 @node Coordinates and Windows
1628 @section Coordinates and Windows
1630 This section describes how to relate screen coordinates to windows.
1632 @defun window-at x y &optional frame
1633 This function returns the window containing the specified cursor
1634 position in the frame @var{frame}. The coordinates @var{x} and @var{y}
1635 are measured in characters and count from the top left corner of the
1636 frame. If they are out of range, @code{window-at} returns @code{nil}.
1638 If you omit @var{frame}, the selected frame is used.
1641 @defun coordinates-in-window-p coordinates window
1642 This function checks whether a particular frame position falls within
1643 the window @var{window}.
1645 The argument @var{coordinates} is a cons cell of the form @code{(@var{x}
1646 . @var{y})}. The coordinates @var{x} and @var{y} are measured in
1647 characters, and count from the top left corner of the screen or frame.
1649 The value returned by @code{coordinates-in-window-p} is non-@code{nil}
1650 if the coordinates are inside @var{window}. The value also indicates
1651 what part of the window the position is in, as follows:
1654 @item (@var{relx} . @var{rely})
1655 The coordinates are inside @var{window}. The numbers @var{relx} and
1656 @var{rely} are the equivalent window-relative coordinates for the
1657 specified position, counting from 0 at the top left corner of the
1661 The coordinates are in the mode line of @var{window}.
1663 @item vertical-split
1664 The coordinates are in the vertical line between @var{window} and its
1665 neighbor to the right. This value occurs only if the window doesn't
1666 have a scroll bar; positions in a scroll bar are considered outside the
1670 The coordinates are not in any part of @var{window}.
1673 The function @code{coordinates-in-window-p} does not require a frame as
1674 argument because it always uses the frame that @var{window} is on.
1677 @node Window Configurations
1678 @section Window Configurations
1679 @cindex window configurations
1680 @cindex saving window information
1682 A @dfn{window configuration} records the entire layout of one
1683 frame---all windows, their sizes, which buffers they contain, what part
1684 of each buffer is displayed, and the values of point and the mark. You
1685 can bring back an entire previous layout by restoring a window
1686 configuration previously saved.
1688 If you want to record all frames instead of just one, use a frame
1689 configuration instead of a window configuration. @xref{Frame
1692 @defun current-window-configuration
1693 This function returns a new object representing the selected frame's
1694 current window configuration, including the number of windows, their
1695 sizes and current buffers, which window is the selected window, and for
1696 each window the displayed buffer, the display-start position, and the
1697 positions of point and the mark. It also includes the values of
1698 @code{window-min-height}, @code{window-min-width} and
1699 @code{minibuffer-scroll-window}. An exception is made for point in the
1700 current buffer, whose value is not saved.
1703 @defun set-window-configuration configuration
1704 This function restores the configuration of windows and buffers as
1705 specified by @var{configuration}. The argument @var{configuration} must
1706 be a value that was previously returned by
1707 @code{current-window-configuration}. This configuration is restored in
1708 the frame from which @var{configuration} was made, whether that frame is
1709 selected or not. This always counts as a window size change and
1710 triggers execution of the @code{window-size-change-functions}
1711 (@pxref{Window Hooks}), because @code{set-window-configuration} doesn't
1712 know how to tell whether the new configuration actually differs from the
1715 If the frame which @var{configuration} was saved from is dead, all this
1716 function does is restore the three variables @code{window-min-height},
1717 @code{window-min-width} and @code{minibuffer-scroll-window}.
1719 Here is a way of using this function to get the same effect
1720 as @code{save-window-excursion}:
1724 (let ((config (current-window-configuration)))
1726 (progn (split-window-vertically nil)
1728 (set-window-configuration config)))
1733 @defspec save-window-excursion forms@dots{}
1734 This special form records the window configuration, executes @var{forms}
1735 in sequence, then restores the earlier window configuration. The window
1736 configuration includes the value of point and the portion of the buffer
1737 that is visible. It also includes the choice of selected window.
1738 However, it does not include the value of point in the current buffer;
1739 use @code{save-excursion} also, if you wish to preserve that.
1741 Don't use this construct when @code{save-selected-window} is all you need.
1743 Exit from @code{save-window-excursion} always triggers execution of the
1744 @code{window-size-change-functions}. (It doesn't know how to tell
1745 whether the restored configuration actually differs from the one in
1746 effect at the end of the @var{forms}.)
1748 The return value is the value of the final form in @var{forms}.
1754 @result{} #<window 25 on control.texi>
1757 (setq w (selected-window))
1758 @result{} #<window 19 on control.texi>
1761 (save-window-excursion
1762 (delete-other-windows w)
1763 (switch-to-buffer "foo")
1765 @result{} do-something
1766 ;; @r{The screen is now split again.}
1771 @defun window-configuration-p object
1772 This function returns @code{t} if @var{object} is a window configuration.
1775 @defun compare-window-configurations config1 config2
1776 This function compares two window configurations as regards the
1777 structure of windows, but ignores the values of point and mark and the
1778 saved scrolling positions---it can return @code{t} even if those
1781 The function @code{equal} can also compare two window configurations; it
1782 regards configurations as unequal if they differ in any respect, even a
1783 saved point or mark.
1786 Primitives to look inside of window configurations would make sense,
1787 but none are implemented. It is not clear they are useful enough to be
1791 @section Hooks for Window Scrolling and Changes
1793 This section describes how a Lisp program can take action whenever a
1794 window displays a different part of its buffer or a different buffer.
1795 There are three actions that can change this: scrolling the window,
1796 switching buffers in the window, and changing the size of the window.
1797 The first two actions run @code{window-scroll-functions}; the last runs
1798 @code{window-size-change-functions}. The paradigmatic use of these
1799 hooks is in the implementation of Lazy Lock mode; see @ref{Support
1800 Modes, Lazy Lock, Font Lock Support Modes, emacs, The GNU Emacs Manual}.
1802 @defvar window-scroll-functions
1803 This variable holds a list of functions that Emacs should call before
1804 redisplaying a window with scrolling. It is not a normal hook, because
1805 each function is called with two arguments: the window, and its new
1806 display-start position.
1808 Displaying a different buffer in the window also runs these functions.
1810 These functions cannot expect @code{window-end} (@pxref{Window Start})
1811 to return a meaningful value, because that value is updated only by
1812 redisplaying the buffer. So if one of these functions needs to know the
1813 last character that will fit in the window with its current
1814 display-start position, it has to find that character using
1815 @code{vertical-motion} (@pxref{Screen Lines}).
1818 @defvar window-size-change-functions
1819 This variable holds a list of functions to be called if the size of any
1820 window changes for any reason. The functions are called just once per
1821 redisplay, and just once for each frame on which size changes have
1824 Each function receives the frame as its sole argument. There is no
1825 direct way to find out which windows on that frame have changed size, or
1826 precisely how. However, if a size-change function records, at each
1827 call, the existing windows and their sizes, it can also compare the
1828 present sizes and the previous sizes.
1830 Creating or deleting windows counts as a size change, and therefore
1831 causes these functions to be called. Changing the frame size also
1832 counts, because it changes the sizes of the existing windows.
1834 It is not a good idea to use @code{save-window-excursion} (@pxref{Window
1835 Configurations}) in these functions, because that always counts as a
1836 size change, and it would cause these functions to be called over and
1837 over. In most cases, @code{save-selected-window} (@pxref{Selecting
1838 Windows}) is what you need here.
1841 @tindex redisplay-end-trigger-functions
1842 @defvar redisplay-end-trigger-functions
1843 This abnormal hook is run whenever redisplay in window uses text that
1844 extends past a specified end trigger position. You set the end trigger
1845 position with the function @code{set-window-redisplay-end-trigger}. The
1846 functions are called with two arguments: the window, and the end trigger
1847 position. Storing @code{nil} for the end trigger position turns off the
1848 feature, and the trigger value is automatically reset to @code{nil} just
1849 after the hook is run.
1852 @tindex set-window-redisplay-end-trigger
1853 @defun set-window-redisplay-end-trigger window position
1854 This function sets @var{window}'s end trigger position at
1858 @tindex window-redisplay-end-trigger
1859 @defun window-redisplay-end-trigger window
1860 This function returns @var{window}'s current end trigger position.
1863 @tindex window-configuration-change-hook
1864 @defvar window-configuration-change-hook
1865 A normal hook that is run every time you change the window configuration
1866 of an existing frame. This includes splitting or deleting windows,
1867 changing the sizes of windows, or displaying a different buffer in a
1868 window. The frame whose window configuration has changed is the
1869 selected frame when this hook runs.