2 @c This is part of the GNU Emacs Lisp Reference Manual.
3 @c Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995, 1998, 1999
4 @c Free Software Foundation, Inc.
5 @c See the file elisp.texi for copying conditions.
6 @setfilename ../info/windows
7 @node Windows, Frames, Buffers, Top
10 This chapter describes most of the functions and variables related to
11 Emacs windows. See @ref{Display}, for information on how text is
15 * Basic Windows:: Basic information on using windows.
16 * Splitting Windows:: Splitting one window into two windows.
17 * Deleting Windows:: Deleting a window gives its space to other windows.
18 * Selecting Windows:: The selected window is the one that you edit in.
19 * Cyclic Window Ordering:: Moving around the existing windows.
20 * Buffers and Windows:: Each window displays the contents of a buffer.
21 * Displaying Buffers:: Higher-lever functions for displaying a buffer
22 and choosing a window for it.
23 * Choosing Window:: How to choose a window for displaying a buffer.
24 * Window Point:: Each window has its own location of point.
25 * Window Start:: The display-start position controls which text
26 is on-screen in the window.
27 * Textual Scrolling:: Moving text up and down through the window.
28 * Vertical Scrolling:: Moving the contents up and down on the window.
29 * Horizontal Scrolling:: Moving the contents sideways on the window.
30 * Size of Window:: Accessing the size of a window.
31 * Resizing Windows:: Changing the size of a window.
32 * Coordinates and Windows:: Converting coordinates to windows.
33 * Window Configurations:: Saving and restoring the state of the screen.
34 * Window Hooks:: Hooks for scrolling, window size changes,
35 redisplay going past a certain point,
36 or window configuration changes.
40 @section Basic Concepts of Emacs Windows
42 @cindex selected window
44 A @dfn{window} in Emacs is the physical area of the screen in which a
45 buffer is displayed. The term is also used to refer to a Lisp object that
46 represents that screen area in Emacs Lisp. It should be
47 clear from the context which is meant.
49 Emacs groups windows into frames. A frame represents an area of
50 screen available for Emacs to use. Each frame always contains at least
51 one window, but you can subdivide it vertically or horizontally into
52 multiple nonoverlapping Emacs windows.
54 In each frame, at any time, one and only one window is designated as
55 @dfn{selected within the frame}. The frame's cursor appears in that
56 window. At any time, one frame is the selected frame; and the window
57 selected within that frame is @dfn{the selected window}. The selected
58 window's buffer is usually the current buffer (except when
59 @code{set-buffer} has been used). @xref{Current Buffer}.
61 For practical purposes, a window exists only while it is displayed in
62 a frame. Once removed from the frame, the window is effectively deleted
63 and should not be used, @emph{even though there may still be references
64 to it} from other Lisp objects. Restoring a saved window configuration
65 is the only way for a window no longer on the screen to come back to
66 life. (@xref{Deleting Windows}.)
68 Each window has the following attributes:
81 window edges with respect to the screen or frame
84 the buffer it displays
87 position within the buffer at the upper left of the window
90 amount of horizontal scrolling, in columns
99 how recently the window was selected
102 @cindex multiple windows
103 Users create multiple windows so they can look at several buffers at
104 once. Lisp libraries use multiple windows for a variety of reasons, but
105 most often to display related information. In Rmail, for example, you
106 can move through a summary buffer in one window while the other window
107 shows messages one at a time as they are reached.
109 The meaning of ``window'' in Emacs is similar to what it means in the
110 context of general-purpose window systems such as X, but not identical.
111 The X Window System places X windows on the screen; Emacs uses one or
112 more X windows as frames, and subdivides them into
113 Emacs windows. When you use Emacs on a character-only terminal, Emacs
114 treats the whole terminal screen as one frame.
116 @cindex terminal screen
117 @cindex screen of terminal
118 @cindex tiled windows
119 Most window systems support arbitrarily located overlapping windows.
120 In contrast, Emacs windows are @dfn{tiled}; they never overlap, and
121 together they fill the whole screen or frame. Because of the way in
122 which Emacs creates new windows and resizes them, not all conceivable
123 tilings of windows on an Emacs frame are actually possible.
124 @xref{Splitting Windows}, and @ref{Size of Window}.
126 @xref{Display}, for information on how the contents of the
127 window's buffer are displayed in the window.
129 @defun windowp object
130 This function returns @code{t} if @var{object} is a window.
133 @node Splitting Windows
134 @section Splitting Windows
135 @cindex splitting windows
136 @cindex window splitting
138 The functions described here are the primitives used to split a window
139 into two windows. Two higher level functions sometimes split a window,
140 but not always: @code{pop-to-buffer} and @code{display-buffer}
141 (@pxref{Displaying Buffers}).
143 The functions described here do not accept a buffer as an argument.
144 The two ``halves'' of the split window initially display the same buffer
145 previously visible in the window that was split.
147 @deffn Command split-window &optional window size horizontal
148 This function splits @var{window} into two windows. The original
149 window @var{window} remains the selected window, but occupies only
150 part of its former screen area. The rest is occupied by a newly created
151 window which is returned as the value of this function.
153 If @var{horizontal} is non-@code{nil}, then @var{window} splits into
154 two side by side windows. The original window @var{window} keeps the
155 leftmost @var{size} columns, and gives the rest of the columns to the
156 new window. Otherwise, it splits into windows one above the other, and
157 @var{window} keeps the upper @var{size} lines and gives the rest of the
158 lines to the new window. The original window is therefore the
159 left-hand or upper of the two, and the new window is the right-hand or
162 If @var{window} is omitted or @code{nil}, then the selected window is
163 split. If @var{size} is omitted or @code{nil}, then @var{window} is
164 divided evenly into two parts. (If there is an odd line, it is
165 allocated to the new window.) When @code{split-window} is called
166 interactively, all its arguments are @code{nil}.
168 The following example starts with one window on a screen that is 50
169 lines high by 80 columns wide; then the window is split.
173 (setq w (selected-window))
174 @result{} #<window 8 on windows.texi>
175 (window-edges) ; @r{Edges in order:}
176 @result{} (0 0 80 50) ; @r{left--top--right--bottom}
180 ;; @r{Returns window created}
181 (setq w2 (split-window w 15))
182 @result{} #<window 28 on windows.texi>
186 @result{} (0 15 80 50) ; @r{Bottom window;}
191 @result{} (0 0 80 15) ; @r{Top window}
195 The screen looks like this:
211 Next, the top window is split horizontally:
215 (setq w3 (split-window w 35 t))
216 @result{} #<window 32 on windows.texi>
220 @result{} (35 0 80 15) ; @r{Left edge at column 35}
224 @result{} (0 0 35 15) ; @r{Right edge at column 35}
228 @result{} (0 15 80 50) ; @r{Bottom window unchanged}
233 Now, the screen looks like this:
250 Normally, Emacs indicates the border between two side-by-side windows
251 with a scroll bar (@pxref{Window Frame Parameters,Scroll Bars}) or @samp{|}
252 characters. The display table can specify alternative border
253 characters; see @ref{Display Tables}.
256 @deffn Command split-window-vertically &optional size
257 This function splits the selected window into two windows, one above the
258 other, leaving the upper of the two windows selected, with @var{size}
259 lines. (If @var{size} is negative, then the lower of the two windows
260 gets @minus{} @var{size} lines and the upper window gets the rest, but
261 the upper window is still the one selected.)
264 @deffn Command split-window-horizontally &optional size
265 This function splits the selected window into two windows
266 side-by-side, leaving the selected window with @var{size} columns.
268 This function is basically an interface to @code{split-window}.
269 You could define a simplified version of the function like this:
273 (defun split-window-horizontally (&optional arg)
274 "Split selected window into two windows, side by side..."
278 (let ((size (and arg (prefix-numeric-value arg))))
280 (setq size (+ (window-width) size)))
281 (split-window nil size t)))
286 @defun one-window-p &optional no-mini all-frames
287 This function returns non-@code{nil} if there is only one window. The
288 argument @var{no-mini}, if non-@code{nil}, means don't count the
289 minibuffer even if it is active; otherwise, the minibuffer window is
290 included, if active, in the total number of windows, which is compared
293 The argument @var{all-frames} specifies which frames to consider. Here
294 are the possible values and their meanings:
298 Count the windows in the selected frame, plus the minibuffer used
299 by that frame even if it lies in some other frame.
302 Count all windows in all existing frames.
305 Count all windows in all visible frames.
308 Count all windows in all visible or iconified frames.
311 Count precisely the windows in the selected frame, and no others.
315 @node Deleting Windows
316 @section Deleting Windows
317 @cindex deleting windows
319 A window remains visible on its frame unless you @dfn{delete} it by
320 calling certain functions that delete windows. A deleted window cannot
321 appear on the screen, but continues to exist as a Lisp object until
322 there are no references to it. There is no way to cancel the deletion
323 of a window aside from restoring a saved window configuration
324 (@pxref{Window Configurations}). Restoring a window configuration also
325 deletes any windows that aren't part of that configuration.
327 When you delete a window, the space it took up is given to one
331 @defun window-live-p window
332 This function returns @code{nil} if @var{window} is deleted, and
335 @strong{Warning:} Erroneous information or fatal errors may result from
336 using a deleted window as if it were live.
339 @deffn Command delete-window &optional window
340 This function removes @var{window} from display, and returns @code{nil}.
341 If @var{window} is omitted, then the selected window is deleted. An
342 error is signaled if there is only one window when @code{delete-window}
346 @deffn Command delete-other-windows &optional window
347 This function makes @var{window} the only window on its frame, by
348 deleting the other windows in that frame. If @var{window} is omitted or
349 @code{nil}, then the selected window is used by default.
351 The return value is @code{nil}.
354 @deffn Command delete-windows-on buffer &optional frame
355 This function deletes all windows showing @var{buffer}. If there are
356 no windows showing @var{buffer}, it does nothing.
358 @code{delete-windows-on} operates frame by frame. If a frame has
359 several windows showing different buffers, then those showing
360 @var{buffer} are removed, and the others expand to fill the space. If
361 all windows in some frame are showing @var{buffer} (including the case
362 where there is only one window), then the frame reverts to having a
363 single window showing another buffer chosen with @code{other-buffer}.
364 @xref{The Buffer List}.
366 The argument @var{frame} controls which frames to operate on. This
367 function does not use it in quite the same way as the other functions
368 which scan all windows; specifically, the values @code{t} and @code{nil}
369 have the opposite of their meanings in other functions. Here are the
374 If it is @code{nil}, operate on all frames.
376 If it is @code{t}, operate on the selected frame.
378 If it is @code{visible}, operate on all visible frames.
380 If it is 0, operate on all visible or iconified frames.
382 If it is a frame, operate on that frame.
385 This function always returns @code{nil}.
388 @node Selecting Windows
389 @section Selecting Windows
390 @cindex selecting windows
392 When a window is selected, the buffer in the window becomes the current
393 buffer, and the cursor will appear in it.
395 @defun selected-window
396 This function returns the selected window. This is the window in
397 which the cursor appears and to which many commands apply.
400 @defun select-window window
401 This function makes @var{window} the selected window. The cursor then
402 appears in @var{window} (on redisplay). The buffer being displayed in
403 @var{window} is immediately designated the current buffer.
405 The return value is @var{window}.
409 (setq w (next-window))
411 @result{} #<window 65 on windows.texi>
416 @defmac save-selected-window forms@dots{}
417 This macro records the selected window, executes @var{forms}
418 in sequence, then restores the earlier selected window.
420 This macro does not save or restore anything about the sizes, arrangement
421 or contents of windows; therefore, if the @var{forms} change them,
424 Each frame, at any time, has a window selected within the frame. This
425 macro saves only @emph{the} selected window; it does not save anything
426 about other frames. If the @var{forms} select some other frame and
427 alter the window selected within it, the change persists.
430 @cindex finding windows
431 The following functions choose one of the windows on the screen,
432 offering various criteria for the choice.
434 @defun get-lru-window &optional frame
435 This function returns the window least recently ``used'' (that is,
436 selected). The selected window is always the most recently used window.
438 The selected window can be the least recently used window if it is the
439 only window. A newly created window becomes the least recently used
440 window until it is selected. A minibuffer window is never a candidate.
442 The argument @var{frame} controls which windows are considered.
446 If it is @code{nil}, consider windows on the selected frame.
448 If it is @code{t}, consider windows on all frames.
450 If it is @code{visible}, consider windows on all visible frames.
452 If it is 0, consider windows on all visible or iconified frames.
454 If it is a frame, consider windows on that frame.
458 @defun get-largest-window &optional frame
459 This function returns the window with the largest area (height times
460 width). If there are no side-by-side windows, then this is the window
461 with the most lines. A minibuffer window is never a candidate.
463 If there are two windows of the same size, then the function returns
464 the window that is first in the cyclic ordering of windows (see
465 following section), starting from the selected window.
467 The argument @var{frame} controls which set of windows to
468 consider. See @code{get-lru-window}, above.
471 @cindex window that satisfies a predicate
472 @cindex conditional selection of windows
473 @defun get-window-with-predicate predicate &optional minibuf all-frames default
474 This function returns a window satisfying @var{predicate}. It cycles
475 through all visible windows using @code{walk-windows} (@pxref{Cyclic
476 Window Ordering}), calling @var{predicate} on each one one of them
477 with that window as its argument. The function returns the first
478 window for which @var{predicate} returns a non-@code{nil} value; if
479 that never happens, it returns @var{default}.
481 The optional arguments @var{minibuf} and @var{all-frames} specify the
482 set of windows to include in the scan. See the description of
483 @code{next-window} in @ref{Cyclic Window Ordering}, for details.
486 @node Cyclic Window Ordering
487 @comment node-name, next, previous, up
488 @section Cyclic Ordering of Windows
489 @cindex cyclic ordering of windows
490 @cindex ordering of windows, cyclic
491 @cindex window ordering, cyclic
493 When you use the command @kbd{C-x o} (@code{other-window}) to select
494 the next window, it moves through all the windows on the screen in a
495 specific cyclic order. For any given configuration of windows, this
496 order never varies. It is called the @dfn{cyclic ordering of windows}.
498 This ordering generally goes from top to bottom, and from left to
499 right. But it may go down first or go right first, depending on the
500 order in which the windows were split.
502 If the first split was vertical (into windows one above each other),
503 and then the subwindows were split horizontally, then the ordering is
504 left to right in the top of the frame, and then left to right in the
505 next lower part of the frame, and so on. If the first split was
506 horizontal, the ordering is top to bottom in the left part, and so on.
507 In general, within each set of siblings at any level in the window tree,
508 the order is left to right, or top to bottom.
510 @defun next-window &optional window minibuf all-frames
511 @cindex minibuffer window
512 This function returns the window following @var{window} in the cyclic
513 ordering of windows. This is the window that @kbd{C-x o} would select
514 if typed when @var{window} is selected. If @var{window} is the only
515 window visible, then this function returns @var{window}. If omitted,
516 @var{window} defaults to the selected window.
518 The value of the argument @var{minibuf} determines whether the
519 minibuffer is included in the window order. Normally, when
520 @var{minibuf} is @code{nil}, the minibuffer is included if it is
521 currently active; this is the behavior of @kbd{C-x o}. (The minibuffer
522 window is active while the minibuffer is in use. @xref{Minibuffers}.)
524 If @var{minibuf} is @code{t}, then the cyclic ordering includes the
525 minibuffer window even if it is not active.
527 If @var{minibuf} is neither @code{t} nor @code{nil}, then the minibuffer
528 window is not included even if it is active.
530 The argument @var{all-frames} specifies which frames to consider. Here
531 are the possible values and their meanings:
535 Consider all the windows in @var{window}'s frame, plus the minibuffer
536 used by that frame even if it lies in some other frame.
539 Consider all windows in all existing frames.
542 Consider all windows in all visible frames. (To get useful results, you
543 must ensure @var{window} is in a visible frame.)
546 Consider all windows in all visible or iconified frames.
549 Consider precisely the windows in @var{window}'s frame, and no others.
552 This example assumes there are two windows, both displaying the
553 buffer @samp{windows.texi}:
558 @result{} #<window 56 on windows.texi>
561 (next-window (selected-window))
562 @result{} #<window 52 on windows.texi>
565 (next-window (next-window (selected-window)))
566 @result{} #<window 56 on windows.texi>
571 @defun previous-window &optional window minibuf all-frames
572 This function returns the window preceding @var{window} in the cyclic
573 ordering of windows. The other arguments specify which windows to
574 include in the cycle, as in @code{next-window}.
577 @deffn Command other-window count &optional all-frames
578 This function selects the @var{count}th following window in the cyclic
579 order. If count is negative, then it moves back @minus{}@var{count}
580 windows in the cycle, rather than forward. It returns @code{nil}.
582 The argument @var{all-frames} has the same meaning as in
583 @code{next-window}, but the @var{minibuf} argument of @code{next-window}
584 is always effectively @code{nil}.
586 In an interactive call, @var{count} is the numeric prefix argument.
590 @defun walk-windows proc &optional minibuf all-frames
591 This function cycles through all windows, calling @code{proc}
592 once for each window with the window as its sole argument.
594 The optional arguments @var{minibuf} and @var{all-frames} specify the
595 set of windows to include in the scan. See @code{next-window}, above,
599 @defun window-list &optional frame minibuf window
600 This function returns a list of the windows on @var{frame}, starting
601 with @var{window}. If @var{frame} is @code{nil} or omitted, the
602 selected frame is used instead; if @var{window} is @code{nil} or
603 omitted, the selected window is used instead.
605 The value of @var{minibuf} determines if the minibuffer window will be
606 included in the result list. If @var{minibuf} is @code{t}, the
607 minibuffer window will be included, even if it isn't active. If
608 @var{minibuf} is @code{nil} or omitted, the minibuffer window will
609 only be included in the list if it is active. If @var{minibuf} is
610 neither @code{nil} nor @code{t}, the minibuffer window is not
611 included, whether or not it is active.
614 @node Buffers and Windows
615 @section Buffers and Windows
616 @cindex examining windows
617 @cindex windows, controlling precisely
618 @cindex buffers, controlled in windows
620 This section describes low-level functions to examine windows or to
621 display buffers in windows in a precisely controlled fashion.
623 See the following section for
626 @xref{Displaying Buffers}, for
628 related functions that find a window to use and specify a buffer for it.
629 The functions described there are easier to use than these, but they
630 employ heuristics in choosing or creating a window; use these functions
631 when you need complete control.
633 @defun set-window-buffer window buffer-or-name
634 This function makes @var{window} display @var{buffer-or-name} as its
635 contents. It returns @code{nil}. This is the fundamental primitive
636 for changing which buffer is displayed in a window, and all ways
637 of doing that call this function.
641 (set-window-buffer (selected-window) "foo")
647 @defun window-buffer &optional window
648 This function returns the buffer that @var{window} is displaying. If
649 @var{window} is omitted, this function returns the buffer for the
655 @result{} #<buffer windows.texi>
660 @defun get-buffer-window buffer-or-name &optional all-frames
661 This function returns a window currently displaying
662 @var{buffer-or-name}, or @code{nil} if there is none. If there are
663 several such windows, then the function returns the first one in the
664 cyclic ordering of windows, starting from the selected window.
665 @xref{Cyclic Window Ordering}.
667 The argument @var{all-frames} controls which windows to consider.
671 If it is @code{nil}, consider windows on the selected frame.
673 If it is @code{t}, consider windows on all frames.
675 If it is @code{visible}, consider windows on all visible frames.
677 If it is 0, consider windows on all visible or iconified frames.
679 If it is a frame, consider windows on that frame.
683 @defun get-buffer-window-list buffer-or-name &optional minibuf all-frames
684 This function returns a list of all the windows currently displaying
685 @var{buffer-or-name}.
687 The two optional arguments work like the optional arguments of
688 @code{next-window} (@pxref{Cyclic Window Ordering}); they are @emph{not}
689 like the single optional argument of @code{get-buffer-window}. Perhaps
690 we should change @code{get-buffer-window} in the future to make it
691 compatible with the other functions.
693 The argument @var{all-frames} controls which windows to consider.
697 If it is @code{nil}, consider windows on the selected frame.
699 If it is @code{t}, consider windows on all frames.
701 If it is @code{visible}, consider windows on all visible frames.
703 If it is 0, consider windows on all visible or iconified frames.
705 If it is a frame, consider windows on that frame.
709 @defvar buffer-display-time
710 This variable records the time at which a buffer was last made visible
711 in a window. It is always local in each buffer; each time
712 @code{set-window-buffer} is called, it sets this variable to
713 @code{(current-time)} in the specified buffer (@pxref{Time of Day}).
714 When a buffer is first created, @code{buffer-display-time} starts out
715 with the value @code{nil}.
718 @node Displaying Buffers
719 @section Displaying Buffers in Windows
720 @cindex switching to a buffer
721 @cindex displaying a buffer
723 In this section we describe convenient functions that choose a window
724 automatically and use it to display a specified buffer. These functions
725 can also split an existing window in certain circumstances. We also
726 describe variables that parameterize the heuristics used for choosing a
729 See the preceding section for
732 @xref{Buffers and Windows}, for
734 low-level functions that give you more precise control. All of these
735 functions work by calling @code{set-window-buffer}.
737 Do not use the functions in this section in order to make a buffer
738 current so that a Lisp program can access or modify it; they are too
739 drastic for that purpose, since they change the display of buffers in
740 windows, which would be gratuitous and surprise the user. Instead, use
741 @code{set-buffer} and @code{save-current-buffer} (@pxref{Current
742 Buffer}), which designate buffers as current for programmed access
743 without affecting the display of buffers in windows.
745 @deffn Command switch-to-buffer buffer-or-name &optional norecord
746 This function makes @var{buffer-or-name} the current buffer, and also
747 displays the buffer in the selected window. This means that a human can
748 see the buffer and subsequent keyboard commands will apply to it.
749 Contrast this with @code{set-buffer}, which makes @var{buffer-or-name}
750 the current buffer but does not display it in the selected window.
751 @xref{Current Buffer}.
753 If @var{buffer-or-name} does not identify an existing buffer, then a new
754 buffer by that name is created. The major mode for the new buffer is
755 set according to the variable @code{default-major-mode}. @xref{Auto
758 Normally the specified buffer is put at the front of the buffer list
759 (both the selected frame's buffer list and the frame-independent buffer
760 list). This affects the operation of @code{other-buffer}. However, if
761 @var{norecord} is non-@code{nil}, this is not done. @xref{The Buffer
764 The @code{switch-to-buffer} function is often used interactively, as
765 the binding of @kbd{C-x b}. It is also used frequently in programs. It
766 always returns @code{nil}.
769 @deffn Command switch-to-buffer-other-window buffer-or-name &optional norecord
770 This function makes @var{buffer-or-name} the current buffer and
771 displays it in a window not currently selected. It then selects that
772 window. The handling of the buffer is the same as in
773 @code{switch-to-buffer}.
775 The currently selected window is absolutely never used to do the job.
776 If it is the only window, then it is split to make a distinct window for
777 this purpose. If the selected window is already displaying the buffer,
778 then it continues to do so, but another window is nonetheless found to
779 display it in as well.
781 This function updates the buffer list just like @code{switch-to-buffer}
782 unless @var{norecord} is non-@code{nil}.
785 @defun pop-to-buffer buffer-or-name &optional other-window norecord
786 This function makes @var{buffer-or-name} the current buffer and
787 switches to it in some window, preferably not the window previously
788 selected. The ``popped-to'' window becomes the selected window within
791 If the variable @code{pop-up-frames} is non-@code{nil},
792 @code{pop-to-buffer} looks for a window in any visible frame already
793 displaying the buffer; if there is one, it returns that window and makes
794 it be selected within its frame. If there is none, it creates a new
795 frame and displays the buffer in it.
797 If @code{pop-up-frames} is @code{nil}, then @code{pop-to-buffer}
798 operates entirely within the selected frame. (If the selected frame has
799 just a minibuffer, @code{pop-to-buffer} operates within the most
800 recently selected frame that was not just a minibuffer.)
802 If the variable @code{pop-up-windows} is non-@code{nil}, windows may
803 be split to create a new window that is different from the original
804 window. For details, see @ref{Choosing Window}.
806 If @var{other-window} is non-@code{nil}, @code{pop-to-buffer} finds or
807 creates another window even if @var{buffer-or-name} is already visible
808 in the selected window. Thus @var{buffer-or-name} could end up
809 displayed in two windows. On the other hand, if @var{buffer-or-name} is
810 already displayed in the selected window and @var{other-window} is
811 @code{nil}, then the selected window is considered sufficient display
812 for @var{buffer-or-name}, so that nothing needs to be done.
814 All the variables that affect @code{display-buffer} affect
815 @code{pop-to-buffer} as well. @xref{Choosing Window}.
817 If @var{buffer-or-name} is a string that does not name an existing
818 buffer, a buffer by that name is created. The major mode for the new
819 buffer is set according to the variable @code{default-major-mode}.
820 @xref{Auto Major Mode}.
822 This function updates the buffer list just like @code{switch-to-buffer}
823 unless @var{norecord} is non-@code{nil}.
826 @deffn Command replace-buffer-in-windows buffer
827 This function replaces @var{buffer} with some other buffer in all
828 windows displaying it. The other buffer used is chosen with
829 @code{other-buffer}. In the usual applications of this function, you
830 don't care which other buffer is used; you just want to make sure that
831 @var{buffer} is no longer displayed.
833 This function returns @code{nil}.
836 @node Choosing Window
837 @section Choosing a Window for Display
839 This section describes the basic facility that chooses a window to
840 display a buffer in---@code{display-buffer}. All the higher-level
841 functions and commands use this subroutine. Here we describe how to use
842 @code{display-buffer} and how to customize it.
844 @deffn Command display-buffer buffer-or-name &optional not-this-window frame
845 This command makes @var{buffer-or-name} appear in some window, like
846 @code{pop-to-buffer}, but it does not select that window and does not
847 make the buffer current. The identity of the selected window is
848 unaltered by this function.
850 If @var{not-this-window} is non-@code{nil}, it means to display the
851 specified buffer in a window other than the selected one, even if it is
852 already on display in the selected window. This can cause the buffer to
853 appear in two windows at once. Otherwise, if @var{buffer-or-name} is
854 already being displayed in any window, that is good enough, so this
855 function does nothing.
857 @code{display-buffer} returns the window chosen to display
858 @var{buffer-or-name}.
860 If the argument @var{frame} is non-@code{nil}, it specifies which frames
861 to check when deciding whether the buffer is already displayed. If the
862 buffer is already displayed in some window on one of these frames,
863 @code{display-buffer} simply returns that window. Here are the possible
864 values of @var{frame}:
868 If it is @code{nil}, consider windows on the selected frame.
870 If it is @code{t}, consider windows on all frames.
872 If it is @code{visible}, consider windows on all visible frames.
874 If it is 0, consider windows on all visible or iconified frames.
876 If it is a frame, consider windows on that frame.
879 Precisely how @code{display-buffer} finds or creates a window depends on
880 the variables described below.
883 @defopt display-buffer-reuse-frames
884 If this variable is non-@code{nil}, @code{display-buffer} searches
885 existing frames for a window displaying the buffer. If the buffer is
886 already displayed in a window in some frame, @code{display-buffer} makes
887 the frame visible and raises it, to use that window. If the buffer is
888 not already displayed, or if @code{display-buffer-reuse-frames} is
889 @code{nil}, @code{display-buffer}'s behavior is determined by other
890 variables, described below.
893 @defopt pop-up-windows
894 This variable controls whether @code{display-buffer} makes new windows.
895 If it is non-@code{nil} and there is only one window, then that window
896 is split. If it is @code{nil}, then @code{display-buffer} does not
897 split the single window, but uses it whole.
900 @defopt split-height-threshold
901 This variable determines when @code{display-buffer} may split a window,
902 if there are multiple windows. @code{display-buffer} always splits the
903 largest window if it has at least this many lines. If the largest
904 window is not this tall, it is split only if it is the sole window and
905 @code{pop-up-windows} is non-@code{nil}.
908 @defopt even-window-heights
909 This variable determines if @code{display-buffer} should even out window
910 heights if the buffer gets displayed in an existing window, above or
911 beneath another existing window. If @code{even-window-heights} is
912 @code{t}, the default, window heights will be evened out. If
913 @code{even-window-heights} is @code{nil}, the orginal window heights
918 @defopt pop-up-frames
919 This variable controls whether @code{display-buffer} makes new frames.
920 If it is non-@code{nil}, @code{display-buffer} looks for an existing
921 window already displaying the desired buffer, on any visible frame. If
922 it finds one, it returns that window. Otherwise it makes a new frame.
923 The variables @code{pop-up-windows} and @code{split-height-threshold} do
924 not matter if @code{pop-up-frames} is non-@code{nil}.
926 If @code{pop-up-frames} is @code{nil}, then @code{display-buffer} either
927 splits a window or reuses one.
929 @xref{Frames}, for more information.
933 @defvar pop-up-frame-function
934 This variable specifies how to make a new frame if @code{pop-up-frames}
937 Its value should be a function of no arguments. When
938 @code{display-buffer} makes a new frame, it does so by calling that
939 function, which should return a frame. The default value of the
940 variable is a function that creates a frame using parameters from
941 @code{pop-up-frame-alist}.
944 @defopt pop-up-frame-alist
945 This variable holds an alist specifying frame parameters used when
946 @code{display-buffer} makes a new frame. @xref{Frame Parameters}, for
947 more information about frame parameters.
950 @defopt special-display-buffer-names
951 A list of buffer names for buffers that should be displayed specially.
952 If the buffer's name is in this list, @code{display-buffer} handles the
955 By default, special display means to give the buffer a dedicated frame.
957 If an element is a list, instead of a string, then the @sc{car} of the
958 list is the buffer name, and the rest of the list says how to create the
959 frame. There are two possibilities for the rest of the list. It can be
960 an alist, specifying frame parameters, or it can contain a function and
961 arguments to give to it. (The function's first argument is always the
962 buffer to be displayed; the arguments from the list come after that.)
965 @defopt special-display-regexps
966 A list of regular expressions that specify buffers that should be
967 displayed specially. If the buffer's name matches any of the regular
968 expressions in this list, @code{display-buffer} handles the buffer
971 By default, special display means to give the buffer a dedicated frame.
973 If an element is a list, instead of a string, then the @sc{car} of the
974 list is the regular expression, and the rest of the list says how to
975 create the frame. See above, under @code{special-display-buffer-names}.
978 @defvar special-display-function
979 This variable holds the function to call to display a buffer specially.
980 It receives the buffer as an argument, and should return the window in
981 which it is displayed.
983 The default value of this variable is
984 @code{special-display-popup-frame}.
987 @defun special-display-popup-frame buffer &rest args
988 This function makes @var{buffer} visible in a frame of its own. If
989 @var{buffer} is already displayed in a window in some frame, it makes
990 the frame visible and raises it, to use that window. Otherwise, it
991 creates a frame that will be dedicated to @var{buffer}.
993 If @var{args} is an alist, it specifies frame parameters for the new
996 If @var{args} is a list whose @sc{car} is a symbol, then @code{(car
997 @var{args})} is called as a function to actually create and set up the
998 frame; it is called with @var{buffer} as first argument, and @code{(cdr
999 @var{args})} as additional arguments.
1001 This function always uses an existing window displaying @var{buffer},
1002 whether or not it is in a frame of its own; but if you set up the above
1003 variables in your init file, before @var{buffer} was created, then
1004 presumably the window was previously made by this function.
1007 @defopt special-display-frame-alist
1008 This variable holds frame parameters for
1009 @code{special-display-popup-frame} to use when it creates a frame.
1012 @defopt same-window-buffer-names
1013 A list of buffer names for buffers that should be displayed in the
1014 selected window. If the buffer's name is in this list,
1015 @code{display-buffer} handles the buffer by switching to it in the
1019 @defopt same-window-regexps
1020 A list of regular expressions that specify buffers that should be
1021 displayed in the selected window. If the buffer's name matches any of
1022 the regular expressions in this list, @code{display-buffer} handles the
1023 buffer by switching to it in the selected window.
1027 @defvar display-buffer-function
1028 This variable is the most flexible way to customize the behavior of
1029 @code{display-buffer}. If it is non-@code{nil}, it should be a function
1030 that @code{display-buffer} calls to do the work. The function should
1031 accept two arguments, the same two arguments that @code{display-buffer}
1032 received. It should choose or create a window, display the specified
1033 buffer, and then return the window.
1035 This hook takes precedence over all the other options and hooks
1040 @cindex dedicated window
1041 A window can be marked as ``dedicated'' to its buffer. Then
1042 @code{display-buffer} will not try to use that window to display any
1045 @defun window-dedicated-p window
1046 This function returns @code{t} if @var{window} is marked as dedicated;
1047 otherwise @code{nil}.
1050 @defun set-window-dedicated-p window flag
1051 This function marks @var{window} as dedicated if @var{flag} is
1052 non-@code{nil}, and nondedicated otherwise.
1056 @section Windows and Point
1057 @cindex window position
1058 @cindex window point
1059 @cindex position in window
1060 @cindex point in window
1062 Each window has its own value of point, independent of the value of
1063 point in other windows displaying the same buffer. This makes it useful
1064 to have multiple windows showing one buffer.
1068 The window point is established when a window is first created; it is
1069 initialized from the buffer's point, or from the window point of another
1070 window opened on the buffer if such a window exists.
1073 Selecting a window sets the value of point in its buffer from the
1074 window's value of point. Conversely, deselecting a window sets the
1075 window's value of point from that of the buffer. Thus, when you switch
1076 between windows that display a given buffer, the point value for the
1077 selected window is in effect in the buffer, while the point values for
1078 the other windows are stored in those windows.
1081 As long as the selected window displays the current buffer, the window's
1082 point and the buffer's point always move together; they remain equal.
1085 @xref{Positions}, for more details on buffer positions.
1088 As far as the user is concerned, point is where the cursor is, and
1089 when the user switches to another buffer, the cursor jumps to the
1090 position of point in that buffer.
1092 @defun window-point &optional window
1093 This function returns the current position of point in @var{window}.
1094 For a nonselected window, this is the value point would have (in that
1095 window's buffer) if that window were selected. If @var{window} is
1096 @code{nil}, the selected window is used.
1098 When @var{window} is the selected window and its buffer is also the
1099 current buffer, the value returned is the same as point in that buffer.
1101 Strictly speaking, it would be more correct to return the
1102 ``top-level'' value of point, outside of any @code{save-excursion}
1103 forms. But that value is hard to find.
1106 @defun set-window-point window position
1107 This function positions point in @var{window} at position
1108 @var{position} in @var{window}'s buffer.
1112 @section The Window Start Position
1114 Each window contains a marker used to keep track of a buffer position
1115 that specifies where in the buffer display should start. This position
1116 is called the @dfn{display-start} position of the window (or just the
1117 @dfn{start}). The character after this position is the one that appears
1118 at the upper left corner of the window. It is usually, but not
1119 inevitably, at the beginning of a text line.
1121 @defun window-start &optional window
1122 @cindex window top line
1123 This function returns the display-start position of window
1124 @var{window}. If @var{window} is @code{nil}, the selected window is
1134 When you create a window, or display a different buffer in it, the
1135 display-start position is set to a display-start position recently used
1136 for the same buffer, or 1 if the buffer doesn't have any.
1138 Redisplay updates the window-start position (if you have not specified
1139 it explicitly since the previous redisplay)---for example, to make sure
1140 point appears on the screen. Nothing except redisplay automatically
1141 changes the window-start position; if you move point, do not expect the
1142 window-start position to change in response until after the next
1145 For a realistic example of using @code{window-start}, see the
1146 description of @code{count-lines} in @ref{Text Lines}.
1149 @defun window-end &optional window update
1150 This function returns the position of the end of the display in window
1151 @var{window}. If @var{window} is @code{nil}, the selected window is
1154 Simply changing the buffer text or moving point does not update the
1155 value that @code{window-end} returns. The value is updated only when
1156 Emacs redisplays and redisplay completes without being preempted.
1158 If the last redisplay of @var{window} was preempted, and did not finish,
1159 Emacs does not know the position of the end of display in that window.
1160 In that case, this function returns @code{nil}.
1162 If @var{update} is non-@code{nil}, @code{window-end} always returns an
1163 up-to-date value for where the window ends, based on the current
1164 @code{window-start} value. If the saved value is valid,
1165 @code{window-end} returns that; otherwise it computes the correct
1166 value by scanning the buffer text.
1168 Even if @var{update} is non-@code{nil}, @code{window-end} does not
1169 attempt to scroll the display if point has moved off the screen, the
1170 way real redisplay would do. It does not alter the
1171 @code{window-start} value. In effect, it reports where the displayed
1172 text will end if scrolling is not required.
1175 @defun set-window-start window position &optional noforce
1176 This function sets the display-start position of @var{window} to
1177 @var{position} in @var{window}'s buffer. It returns @var{position}.
1179 The display routines insist that the position of point be visible when a
1180 buffer is displayed. Normally, they change the display-start position
1181 (that is, scroll the window) whenever necessary to make point visible.
1182 However, if you specify the start position with this function using
1183 @code{nil} for @var{noforce}, it means you want display to start at
1184 @var{position} even if that would put the location of point off the
1185 screen. If this does place point off screen, the display routines move
1186 point to the left margin on the middle line in the window.
1188 For example, if point @w{is 1} and you set the start of the window @w{to
1189 2}, then point would be ``above'' the top of the window. The display
1190 routines will automatically move point if it is still 1 when redisplay
1191 occurs. Here is an example:
1195 ;; @r{Here is what @samp{foo} looks like before executing}
1196 ;; @r{the @code{set-window-start} expression.}
1200 ---------- Buffer: foo ----------
1201 @point{}This is the contents of buffer foo.
1207 ---------- Buffer: foo ----------
1213 (1+ (window-start)))
1218 ;; @r{Here is what @samp{foo} looks like after executing}
1219 ;; @r{the @code{set-window-start} expression.}
1220 ---------- Buffer: foo ----------
1221 his is the contents of buffer foo.
1227 ---------- Buffer: foo ----------
1231 If @var{noforce} is non-@code{nil}, and @var{position} would place point
1232 off screen at the next redisplay, then redisplay computes a new window-start
1233 position that works well with point, and thus @var{position} is not used.
1236 @defun pos-visible-in-window-p &optional position window partially
1237 This function returns @code{t} if @var{position} is within the range of
1238 text currently visible on the screen in @var{window}. It returns
1239 @code{nil} if @var{position} is scrolled vertically or horizontally out
1240 of view. Locations that are partially obscured are not considered
1241 visible unless @var{partially} is non-@code{nil}. The argument
1242 @var{position} defaults to the current position of point in
1243 @var{window}; @var{window}, to the selected window.
1249 (or (pos-visible-in-window-p
1250 (point) (selected-window))
1256 @node Textual Scrolling
1257 @section Textual Scrolling
1258 @cindex textual scrolling
1259 @cindex scrolling textually
1261 @dfn{Textual scrolling} means moving the text up or down though a
1262 window. It works by changing the value of the window's display-start
1263 location. It may also change the value of @code{window-point} to keep
1264 point on the screen.
1266 Textual scrolling was formerly called ``vertical scrolling,'' but we
1267 changed its name to distinguish it from the new vertical fractional
1268 scrolling feature (@pxref{Vertical Scrolling}).
1270 In the commands @code{scroll-up} and @code{scroll-down}, the directions
1271 ``up'' and ``down'' refer to the motion of the text in the buffer at which
1272 you are looking through the window. Imagine that the text is
1273 written on a long roll of paper and that the scrolling commands move the
1274 paper up and down. Thus, if you are looking at text in the middle of a
1275 buffer and repeatedly call @code{scroll-down}, you will eventually see
1276 the beginning of the buffer.
1278 Some people have urged that the opposite convention be used: they
1279 imagine that the window moves over text that remains in place. Then
1280 ``down'' commands would take you to the end of the buffer. This view is
1281 more consistent with the actual relationship between windows and the
1282 text in the buffer, but it is less like what the user sees. The
1283 position of a window on the terminal does not move, and short scrolling
1284 commands clearly move the text up or down on the screen. We have chosen
1285 names that fit the user's point of view.
1287 The textual scrolling functions (aside from
1288 @code{scroll-other-window}) have unpredictable results if the current
1289 buffer is different from the buffer that is displayed in the selected
1290 window. @xref{Current Buffer}.
1292 @deffn Command scroll-up &optional count
1293 This function scrolls the text in the selected window upward
1294 @var{count} lines. If @var{count} is negative, scrolling is actually
1297 If @var{count} is @code{nil} (or omitted), then the length of scroll
1298 is @code{next-screen-context-lines} lines less than the usable height of
1299 the window (not counting its mode line).
1301 @code{scroll-up} returns @code{nil}.
1304 @deffn Command scroll-down &optional count
1305 This function scrolls the text in the selected window downward
1306 @var{count} lines. If @var{count} is negative, scrolling is actually
1309 If @var{count} is omitted or @code{nil}, then the length of the scroll
1310 is @code{next-screen-context-lines} lines less than the usable height of
1311 the window (not counting its mode line).
1313 @code{scroll-down} returns @code{nil}.
1316 @deffn Command scroll-other-window &optional count
1317 This function scrolls the text in another window upward @var{count}
1318 lines. Negative values of @var{count}, or @code{nil}, are handled
1319 as in @code{scroll-up}.
1321 You can specify which buffer to scroll by setting the variable
1322 @code{other-window-scroll-buffer} to a buffer. If that buffer isn't
1323 already displayed, @code{scroll-other-window} displays it in some
1326 When the selected window is the minibuffer, the next window is normally
1327 the one at the top left corner. You can specify a different window to
1328 scroll, when the minibuffer is selected, by setting the variable
1329 @code{minibuffer-scroll-window}. This variable has no effect when any
1330 other window is selected. @xref{Minibuffer Misc}.
1332 When the minibuffer is active, it is the next window if the selected
1333 window is the one at the bottom right corner. In this case,
1334 @code{scroll-other-window} attempts to scroll the minibuffer. If the
1335 minibuffer contains just one line, it has nowhere to scroll to, so the
1336 line reappears after the echo area momentarily displays the message
1337 ``Beginning of buffer''.
1341 @defvar other-window-scroll-buffer
1342 If this variable is non-@code{nil}, it tells @code{scroll-other-window}
1343 which buffer to scroll.
1346 @defopt scroll-margin
1347 This option specifies the size of the scroll margin---a minimum number
1348 of lines between point and the top or bottom of a window. Whenever
1349 point gets within this many lines of the top or bottom of the window,
1350 the window scrolls automatically (if possible) to move point out of the
1351 margin, closer to the center of the window.
1354 @defopt scroll-conservatively
1355 This variable controls how scrolling is done automatically when point
1356 moves off the screen (or into the scroll margin). If the value is zero,
1357 then redisplay scrolls the text to center point vertically in the
1358 window. If the value is a positive integer @var{n}, then redisplay
1359 scrolls the window up to @var{n} lines in either direction, if that will
1360 bring point back into view. Otherwise, it centers point. The default
1363 A value of @code{nil} is equivalent to .5, since it centers point. This
1364 variable automatically becomes buffer-local when set in any fashion.
1367 @defopt scroll-up-aggressively
1368 @tindex scroll-up-aggressively
1369 The value of this variable should be either @code{nil} or a fraction
1370 @var{f} between 0 and 1. If it is a fraction, that specifies where on
1371 the screen to put point when scrolling upward. More precisely, when a
1372 window scrolls up because point is above the window start, the new start
1373 position is chosen to put point @var{f} part of the window height from
1374 the top. The larger @var{f}, the more aggressive the scrolling.
1376 A value of @code{nil} is equivalent to .5, since its effect is to center
1377 point. This variable automatically becomes buffer-local when set in any
1381 @defopt scroll-down-aggressively
1382 @tindex scroll-down-aggressively
1383 Likewise, for scrolling down. The value, @var{f}, specifies how far
1384 point should be placed from the bottom of the window; thus, as with
1385 @code{scroll-up-aggressively}, a larger value scrolls more aggressively.
1389 This variable is an older variant of @code{scroll-conservatively}. The
1390 difference is that it if its value is @var{n}, that permits scrolling
1391 only by precisely @var{n} lines, not a smaller number. This feature
1392 does not work with @code{scroll-margin}. The default value is zero.
1395 @defopt scroll-preserve-screen-position
1396 If this option is non-@code{nil}, the scroll functions move point so
1397 that the vertical position of the cursor is unchanged, when that is
1401 @defopt next-screen-context-lines
1402 The value of this variable is the number of lines of continuity to
1403 retain when scrolling by full screens. For example, @code{scroll-up}
1404 with an argument of @code{nil} scrolls so that this many lines at the
1405 bottom of the window appear instead at the top. The default value is
1409 @deffn Command recenter &optional count
1410 @cindex centering point
1411 This function scrolls the selected window to put the text where point
1412 is located at a specified vertical position within the window.
1414 If @var{count} is a nonnegative number, it puts the line containing
1415 point @var{count} lines down from the top of the window. If @var{count}
1416 is a negative number, then it counts upward from the bottom of the
1417 window, so that @minus{}1 stands for the last usable line in the window.
1418 If @var{count} is a non-@code{nil} list, then it stands for the line in
1419 the middle of the window.
1421 If @var{count} is @code{nil}, @code{recenter} puts the line containing
1422 point in the middle of the window, then clears and redisplays the entire
1425 When @code{recenter} is called interactively, @var{count} is the raw
1426 prefix argument. Thus, typing @kbd{C-u} as the prefix sets the
1427 @var{count} to a non-@code{nil} list, while typing @kbd{C-u 4} sets
1428 @var{count} to 4, which positions the current line four lines from the
1431 With an argument of zero, @code{recenter} positions the current line at
1432 the top of the window. This action is so handy that some people make a
1433 separate key binding to do this. For example,
1437 (defun line-to-top-of-window ()
1438 "Scroll current line to top of window.
1439 Replaces three keystroke sequence C-u 0 C-l."
1443 (global-set-key [kp-multiply] 'line-to-top-of-window)
1448 @node Vertical Scrolling
1449 @section Vertical Fractional Scrolling
1450 @cindex Vertical Fractional Scrolling
1452 @dfn{Vertical fractional scrolling} means shifting the image in the
1453 window up or down by a specified multiple or fraction of a line.
1454 Starting in Emacs 21, each window has a @dfn{vertical scroll position},
1455 which is a number, never less than zero. It specifies how far to raise
1456 the contents of the window. Raising the window contents generally makes
1457 all or part of some lines disappear off the top, and all or part of some
1458 other lines appear at the bottom. The usual value is zero.
1460 The vertical scroll position is measured in units of the normal line
1461 height, which is the height of the default font. Thus, if the value is
1462 .5, that means the window contents are scrolled up half the normal line
1463 height. If it is 3.3, that means the window contents are scrolled up
1464 somewhat over three times the normal line height.
1466 What fraction of a line the vertical scrolling covers, or how many
1467 lines, depends on what the lines contain. A value of .5 could scroll a
1468 line whose height is very short off the screen, while a value of 3.3
1469 could scroll just part of the way through a tall line or an image.
1471 @defun window-vscroll &optional window
1472 This function returns the current vertical scroll position of
1473 @var{window}, If @var{window} is @code{nil}, the selected window is
1484 @defun set-window-vscroll window lines
1485 This function sets @var{window}'s vertical scroll position to
1486 @var{lines}. The argument @var{lines} should be zero or positive; if
1487 not, it is taken as zero.
1489 The actual vertical scroll position must always correspond
1490 to an integral number of pixels, so the value you specify
1491 is rounded accordingly.
1493 The return value is the result of this rounding.
1497 (set-window-vscroll (selected-window) 1.2)
1503 @node Horizontal Scrolling
1504 @section Horizontal Scrolling
1505 @cindex horizontal scrolling
1507 @dfn{Horizontal scrolling} means shifting the image in the window left
1508 or right by a specified multiple of the normal character width. Each
1509 window has a @dfn{vertical scroll position}, which is a number, never
1510 less than zero. It specifies how far to shift the contents left.
1511 Shifting the window contents left generally makes all or part of some
1512 characters disappear off the left, and all or part of some other
1513 characters appear at the right. The usual value is zero.
1515 The horizontal scroll position is measured in units of the normal
1516 character width, which is the width of space in the default font. Thus,
1517 if the value is 5, that means the window contents are scrolled left by 5
1518 times the normal character width. How many characters actually
1519 disappear off to the left depends on their width, and could vary from
1522 Because we read from side to side in the ``inner loop'', and from top
1523 to bottom in the ``outer loop'', the effect of horizontal scrolling is
1524 not like that of textual or vertical scrolling. Textual scrolling
1525 involves selection of a portion of text to display, and vertical
1526 scrolling moves the window contents contiguously; but horizontal
1527 scrolling causes part of @emph{each line} to go off screen.
1529 Usually, no horizontal scrolling is in effect; then the leftmost
1530 column is at the left edge of the window. In this state, scrolling to
1531 the right is meaningless, since there is no data to the left of the edge
1532 to be revealed by it; so this is not allowed. Scrolling to the left is
1533 allowed; it scrolls the first columns of text off the edge of the window
1534 and can reveal additional columns on the right that were truncated
1535 before. Once a window has a nonzero amount of leftward horizontal
1536 scrolling, you can scroll it back to the right, but only so far as to
1537 reduce the net horizontal scroll to zero. There is no limit to how far
1538 left you can scroll, but eventually all the text will disappear off the
1541 In Emacs 21, redisplay automatically alters the horizontal scrolling
1542 of a window as necessary to ensure that point is always visible, if
1543 @code{automatic-hscrolling} is set. However, you can still set the
1544 horizontal scrolling value explicitly. The value you specify serves as
1545 a lower bound for automatic scrolling, i.e. automatic scrolling
1546 will not scroll a window to a column less than the specified one.
1548 @deffn Command scroll-left &optional count
1549 This function scrolls the selected window @var{count} columns to the
1550 left (or to the right if @var{count} is negative). The default
1551 for @var{count} is the window width, minus 2.
1553 The return value is the total amount of leftward horizontal scrolling in
1554 effect after the change---just like the value returned by
1555 @code{window-hscroll} (below).
1558 @deffn Command scroll-right &optional count
1559 This function scrolls the selected window @var{count} columns to the
1560 right (or to the left if @var{count} is negative). The default
1561 for @var{count} is the window width, minus 2.
1563 The return value is the total amount of leftward horizontal scrolling in
1564 effect after the change---just like the value returned by
1565 @code{window-hscroll} (below).
1567 Once you scroll a window as far right as it can go, back to its normal
1568 position where the total leftward scrolling is zero, attempts to scroll
1569 any farther right have no effect.
1572 @defun window-hscroll &optional window
1573 This function returns the total leftward horizontal scrolling of
1574 @var{window}---the number of columns by which the text in @var{window}
1575 is scrolled left past the left margin.
1577 The value is never negative. It is zero when no horizontal scrolling
1578 has been done in @var{window} (which is usually the case).
1580 If @var{window} is @code{nil}, the selected window is used.
1598 @defun set-window-hscroll window columns
1599 This function sets the number of columns from the left margin that
1600 @var{window} is scrolled from the value of @var{columns}. The argument
1601 @var{columns} should be zero or positive; if not, it is taken as zero.
1602 Fractional values of @var{columns} are not supported at present.
1604 The value returned is @var{columns}.
1608 (set-window-hscroll (selected-window) 10)
1614 Here is how you can determine whether a given position @var{position}
1615 is off the screen due to horizontal scrolling:
1619 (defun hscroll-on-screen (window position)
1621 (goto-char position)
1623 (>= (- (current-column) (window-hscroll window)) 0)
1624 (< (- (current-column) (window-hscroll window))
1625 (window-width window)))))
1629 @node Size of Window
1630 @section The Size of a Window
1632 @cindex size of window
1634 An Emacs window is rectangular, and its size information consists of
1635 the height (the number of lines) and the width (the number of character
1636 positions in each line). The mode line is included in the height. But
1637 the width does not count the scroll bar or the column of @samp{|}
1638 characters that separates side-by-side windows.
1640 The following three functions return size information about a window:
1642 @defun window-height &optional window
1643 This function returns the number of lines in @var{window}, including its
1644 mode line. If @var{window} fills its entire frame, this is typically
1645 one less than the value of @code{frame-height} on that frame (since the
1646 last line is always reserved for the minibuffer).
1648 If @var{window} is @code{nil}, the function uses the selected window.
1656 (split-window-vertically)
1657 @result{} #<window 4 on windows.texi>
1666 @defun window-width &optional window
1667 This function returns the number of columns in @var{window}. If
1668 @var{window} fills its entire frame, this is the same as the value of
1669 @code{frame-width} on that frame. The width does not include the
1670 window's scroll bar or the column of @samp{|} characters that separates
1671 side-by-side windows.
1673 If @var{window} is @code{nil}, the function uses the selected window.
1683 @defun window-edges &optional window
1684 This function returns a list of the edge coordinates of @var{window}.
1685 If @var{window} is @code{nil}, the selected window is used.
1687 The order of the list is @code{(@var{left} @var{top} @var{right}
1688 @var{bottom})}, all elements relative to 0, 0 at the top left corner of
1689 the frame. The element @var{right} of the value is one more than the
1690 rightmost column used by @var{window}, and @var{bottom} is one more than
1691 the bottommost row used by @var{window} and its mode-line.
1693 If a window has a scroll bar, the right edge value includes the width of
1694 the scroll bar. Otherwise, if the window has a neighbor on the right,
1695 its right edge value includes the width of the separator line between
1696 the window and that neighbor. Since the width of the window does not
1697 include this separator, the width does not usually equal the difference
1698 between the right and left edges.
1700 Here is the result obtained on a typical 24-line terminal with just one
1705 (window-edges (selected-window))
1706 @result{} (0 0 80 23)
1711 The bottom edge is at line 23 because the last line is the echo area.
1713 If @var{window} is at the upper left corner of its frame, then
1714 @var{bottom} is the same as the value of @code{(window-height)},
1715 @var{right} is almost the same as the value of @code{(window-width)},
1716 and @var{top} and @var{left} are zero. For example, the edges of the
1717 following window are @w{@samp{0 0 8 5}}. Assuming that the frame has
1718 more than 8 columns, the last column of the window (column 7) holds a
1719 border rather than text. The last row (row 4) holds the mode line,
1720 shown here with @samp{xxxxxxxxx}.
1736 In the following example, let's suppose that the frame is 7
1737 columns wide. Then the edges of the left window are @w{@samp{0 0 4 3}}
1738 and the edges of the right window are @w{@samp{4 0 8 3}}.
1752 @node Resizing Windows
1753 @section Changing the Size of a Window
1754 @cindex window resizing
1755 @cindex changing window size
1756 @cindex window size, changing
1758 The window size functions fall into two classes: high-level commands
1759 that change the size of windows and low-level functions that access
1760 window size. Emacs does not permit overlapping windows or gaps between
1761 windows, so resizing one window affects other windows.
1763 @deffn Command enlarge-window size &optional horizontal
1764 This function makes the selected window @var{size} lines taller,
1765 stealing lines from neighboring windows. It takes the lines from one
1766 window at a time until that window is used up, then takes from another.
1767 If a window from which lines are stolen shrinks below
1768 @code{window-min-height} lines, that window disappears.
1770 If @var{horizontal} is non-@code{nil}, this function makes
1771 @var{window} wider by @var{size} columns, stealing columns instead of
1772 lines. If a window from which columns are stolen shrinks below
1773 @code{window-min-width} columns, that window disappears.
1775 If the requested size would exceed that of the window's frame, then the
1776 function makes the window occupy the entire height (or width) of the
1779 If there are various other windows from which lines or columns can be
1780 stolen, and some of them specify fixed size (using
1781 @code{window-size-fixed}, see below), they are left untouched while
1782 other windows are ``robbed.'' If it would be necessary to alter the
1783 size of a fixed-size window, @code{enlarge-window} gets an error
1786 If @var{size} is negative, this function shrinks the window by
1787 @minus{}@var{size} lines or columns. If that makes the window smaller
1788 than the minimum size (@code{window-min-height} and
1789 @code{window-min-width}), @code{enlarge-window} deletes the window.
1791 @code{enlarge-window} returns @code{nil}.
1794 @deffn Command enlarge-window-horizontally columns
1795 This function makes the selected window @var{columns} wider.
1796 It could be defined as follows:
1800 (defun enlarge-window-horizontally (columns)
1801 (enlarge-window columns t))
1806 @deffn Command shrink-window size &optional horizontal
1807 This function is like @code{enlarge-window} but negates the argument
1808 @var{size}, making the selected window smaller by giving lines (or
1809 columns) to the other windows. If the window shrinks below
1810 @code{window-min-height} or @code{window-min-width}, then it disappears.
1812 If @var{size} is negative, the window is enlarged by @minus{}@var{size}
1816 @deffn Command shrink-window-horizontally columns
1817 This function makes the selected window @var{columns} narrower.
1818 It could be defined as follows:
1822 (defun shrink-window-horizontally (columns)
1823 (shrink-window columns t))
1828 @deffn Command shrink-window-if-larger-than-buffer &optional window
1829 This command shrinks @var{window} to be as small as possible while still
1830 showing the full contents of its buffer---but not less than
1831 @code{window-min-height} lines. If @var{window} is not given,
1832 it defaults to the selected window.
1834 However, the command does nothing if the window is already too small to
1835 display the whole text of the buffer, or if part of the contents are
1836 currently scrolled off screen, or if the window is not the full width of
1837 its frame, or if the window is the only window in its frame.
1840 @tindex window-size-fixed
1841 @defvar window-size-fixed
1842 If this variable is non-@code{nil}, in any given buffer,
1843 then the size of any window displaying the buffer remains fixed
1844 unless you explicitly change it or Emacs has no other choice.
1845 (This feature is new in Emacs 21.)
1847 If the value is @code{height}, then only the window's height is fixed;
1848 if the value is @code{width}, then only the window's width is fixed.
1849 Any other non-@code{nil} value fixes both the width and the height.
1851 The usual way to use this variable is to give it a buffer-local value in
1852 a particular buffer. That way, the windows (but usually there is only
1853 one) displaying that buffer have fixed size.
1855 Explicit size-change functions such as @code{enlarge-window}
1856 get an error if they would have to change a window size which is fixed.
1857 Therefore, when you want to change the size of such a window,
1858 you should bind @code{window-size-fixed} to @code{nil}, like this:
1861 (let ((window-size-fixed nil))
1862 (enlarge-window 10))
1865 Note that changing the frame size will change the size of a
1866 fixed-size window, if there is no other alternative.
1869 @cindex minimum window size
1870 The following two variables constrain the window-size-changing
1871 functions to a minimum height and width.
1873 @defopt window-min-height
1874 The value of this variable determines how short a window may become
1875 before it is automatically deleted. Making a window smaller than
1876 @code{window-min-height} automatically deletes it, and no window may be
1877 created shorter than this. The absolute minimum height is two (allowing
1878 one line for the mode line, and one line for the buffer display).
1879 Actions that change window sizes reset this variable to two if it is
1880 less than two. The default value is 4.
1883 @defopt window-min-width
1884 The value of this variable determines how narrow a window may become
1885 before it is automatically deleted. Making a window smaller than
1886 @code{window-min-width} automatically deletes it, and no window may be
1887 created narrower than this. The absolute minimum width is one; any
1888 value below that is ignored. The default value is 10.
1891 @node Coordinates and Windows
1892 @section Coordinates and Windows
1894 This section describes how to relate screen coordinates to windows.
1896 @defun window-at x y &optional frame
1897 This function returns the window containing the specified cursor
1898 position in the frame @var{frame}. The coordinates @var{x} and @var{y}
1899 are measured in characters and count from the top left corner of the
1900 frame. If they are out of range, @code{window-at} returns @code{nil}.
1902 If you omit @var{frame}, the selected frame is used.
1905 @defun coordinates-in-window-p coordinates window
1906 This function checks whether a particular frame position falls within
1907 the window @var{window}.
1909 The argument @var{coordinates} is a cons cell of the form @code{(@var{x}
1910 . @var{y})}. The coordinates @var{x} and @var{y} are measured in
1911 characters, and count from the top left corner of the screen or frame.
1913 The value returned by @code{coordinates-in-window-p} is non-@code{nil}
1914 if the coordinates are inside @var{window}. The value also indicates
1915 what part of the window the position is in, as follows:
1918 @item (@var{relx} . @var{rely})
1919 The coordinates are inside @var{window}. The numbers @var{relx} and
1920 @var{rely} are the equivalent window-relative coordinates for the
1921 specified position, counting from 0 at the top left corner of the
1925 The coordinates are in the mode line of @var{window}.
1928 The coordinates are in the header line of @var{window}.
1931 The coordinates are in the vertical line between @var{window} and its
1932 neighbor to the right. This value occurs only if the window doesn't
1933 have a scroll bar; positions in a scroll bar are considered outside the
1934 window for these purposes.
1937 The coordinates are not in any part of @var{window}.
1940 The function @code{coordinates-in-window-p} does not require a frame as
1941 argument because it always uses the frame that @var{window} is on.
1944 @node Window Configurations
1945 @section Window Configurations
1946 @cindex window configurations
1947 @cindex saving window information
1949 A @dfn{window configuration} records the entire layout of one
1950 frame---all windows, their sizes, which buffers they contain, what part
1951 of each buffer is displayed, and the values of point and the mark. You
1952 can bring back an entire previous layout by restoring a window
1953 configuration previously saved.
1955 If you want to record all frames instead of just one, use a frame
1956 configuration instead of a window configuration. @xref{Frame
1959 @defun current-window-configuration &optional frame
1960 This function returns a new object representing @var{frame}'s
1961 current window configuration, including the number of windows, their
1962 sizes and current buffers, which window is the selected window, and for
1963 each window the displayed buffer, the display-start position, and the
1964 positions of point and the mark. It also includes the values of
1965 @code{window-min-height}, @code{window-min-width} and
1966 @code{minibuffer-scroll-window}. An exception is made for point in the
1967 current buffer, whose value is not saved.
1969 If @var{frame} is omitted, the selected frame is used.
1972 @defun set-window-configuration configuration
1973 This function restores the configuration of windows and buffers as
1974 specified by @var{configuration}, for the frame that @var{configuration}
1977 The argument @var{configuration} must be a value that was previously
1978 returned by @code{current-window-configuration}. This configuration is
1979 restored in the frame from which @var{configuration} was made, whether
1980 that frame is selected or not. This always counts as a window size
1981 change and triggers execution of the @code{window-size-change-functions}
1982 (@pxref{Window Hooks}), because @code{set-window-configuration} doesn't
1983 know how to tell whether the new configuration actually differs from the
1986 If the frame which @var{configuration} was saved from is dead, all this
1987 function does is restore the three variables @code{window-min-height},
1988 @code{window-min-width} and @code{minibuffer-scroll-window}.
1990 Here is a way of using this function to get the same effect
1991 as @code{save-window-excursion}:
1995 (let ((config (current-window-configuration)))
1997 (progn (split-window-vertically nil)
1999 (set-window-configuration config)))
2004 @defspec save-window-excursion forms@dots{}
2005 This special form records the window configuration, executes @var{forms}
2006 in sequence, then restores the earlier window configuration. The window
2007 configuration includes the value of point and the portion of the buffer
2008 that is visible. It also includes the choice of selected window.
2009 However, it does not include the value of point in the current buffer;
2010 use @code{save-excursion} also, if you wish to preserve that.
2012 Don't use this construct when @code{save-selected-window} is all you need.
2014 Exit from @code{save-window-excursion} always triggers execution of the
2015 @code{window-size-change-functions}. (It doesn't know how to tell
2016 whether the restored configuration actually differs from the one in
2017 effect at the end of the @var{forms}.)
2019 The return value is the value of the final form in @var{forms}.
2025 @result{} #<window 25 on control.texi>
2028 (setq w (selected-window))
2029 @result{} #<window 19 on control.texi>
2032 (save-window-excursion
2033 (delete-other-windows w)
2034 (switch-to-buffer "foo")
2036 @result{} do-something
2037 ;; @r{The screen is now split again.}
2042 @defun window-configuration-p object
2043 This function returns @code{t} if @var{object} is a window configuration.
2046 @defun compare-window-configurations config1 config2
2047 This function compares two window configurations as regards the
2048 structure of windows, but ignores the values of point and mark and the
2049 saved scrolling positions---it can return @code{t} even if those
2052 The function @code{equal} can also compare two window configurations; it
2053 regards configurations as unequal if they differ in any respect, even a
2054 saved point or mark.
2057 Primitives to look inside of window configurations would make sense,
2058 but none are implemented. It is not clear they are useful enough to be
2062 @section Hooks for Window Scrolling and Changes
2064 This section describes how a Lisp program can take action whenever a
2065 window displays a different part of its buffer or a different buffer.
2066 There are three actions that can change this: scrolling the window,
2067 switching buffers in the window, and changing the size of the window.
2068 The first two actions run @code{window-scroll-functions}; the last runs
2069 @code{window-size-change-functions}. The paradigmatic use of these
2070 hooks is in the implementation of Lazy Lock mode; see @ref{Support
2071 Modes, Lazy Lock, Font Lock Support Modes, emacs, The GNU Emacs Manual}.
2073 @defvar window-scroll-functions
2074 This variable holds a list of functions that Emacs should call before
2075 redisplaying a window with scrolling. It is not a normal hook, because
2076 each function is called with two arguments: the window, and its new
2077 display-start position.
2079 Displaying a different buffer in the window also runs these functions.
2081 These functions must be careful in using @code{window-end}
2082 (@pxref{Window Start}); if you need an up-to-date value, you must use
2083 the @var{update} argument to ensure you get it.
2086 @defvar window-size-change-functions
2087 This variable holds a list of functions to be called if the size of any
2088 window changes for any reason. The functions are called just once per
2089 redisplay, and just once for each frame on which size changes have
2092 Each function receives the frame as its sole argument. There is no
2093 direct way to find out which windows on that frame have changed size, or
2094 precisely how. However, if a size-change function records, at each
2095 call, the existing windows and their sizes, it can also compare the
2096 present sizes and the previous sizes.
2098 Creating or deleting windows counts as a size change, and therefore
2099 causes these functions to be called. Changing the frame size also
2100 counts, because it changes the sizes of the existing windows.
2102 It is not a good idea to use @code{save-window-excursion} (@pxref{Window
2103 Configurations}) in these functions, because that always counts as a
2104 size change, and it would cause these functions to be called over and
2105 over. In most cases, @code{save-selected-window} (@pxref{Selecting
2106 Windows}) is what you need here.
2109 @defvar redisplay-end-trigger-functions
2110 This abnormal hook is run whenever redisplay in a window uses text that
2111 extends past a specified end trigger position. You set the end trigger
2112 position with the function @code{set-window-redisplay-end-trigger}. The
2113 functions are called with two arguments: the window, and the end trigger
2114 position. Storing @code{nil} for the end trigger position turns off the
2115 feature, and the trigger value is automatically reset to @code{nil} just
2116 after the hook is run.
2119 @defun set-window-redisplay-end-trigger window position
2120 This function sets @var{window}'s end trigger position at
2124 @defun window-redisplay-end-trigger &optional window
2125 This function returns @var{window}'s current end trigger position.
2128 @defvar window-configuration-change-hook
2129 A normal hook that is run every time you change the window configuration
2130 of an existing frame. This includes splitting or deleting windows,
2131 changing the sizes of windows, or displaying a different buffer in a
2132 window. The frame whose window configuration has changed is the
2133 selected frame when this hook runs.