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This chapter describes most of the functions and variables related to Emacs windows. See 38. Emacs Display, for information on how text is displayed in windows.
28.1 Basic Concepts of Emacs Windows Basic information on using windows. 28.2 Splitting Windows Splitting one window into two windows. 28.3 Deleting Windows Deleting a window gives its space to other windows. 28.4 Selecting Windows The selected window is the one that you edit in. 28.5 Cyclic Ordering of Windows Moving around the existing windows. 28.6 Buffers and Windows Each window displays the contents of a buffer. 28.7 Displaying Buffers in Windows Higher-lever functions for displaying a buffer and choosing a window for it. 28.8 Choosing a Window for Display How to choose a window for displaying a buffer. 28.9 Windows and Point Each window has its own location of point. 28.10 The Window Start Position The display-start position controls which text is on-screen in the window. 28.11 Textual Scrolling Moving text up and down through the window. 28.12 Vertical Fractional Scrolling Moving the contents up and down on the window. 28.13 Horizontal Scrolling Moving the contents sideways on the window. 28.14 The Size of a Window Accessing the size of a window. 28.15 Changing the Size of a Window Changing the size of a window. 28.16 Coordinates and Windows Converting coordinates to windows. 28.17 Window Configurations Saving and restoring the state of the screen. 28.18 Hooks for Window Scrolling and Changes Hooks for scrolling, window size changes, redisplay going past a certain point, or window configuration changes.
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A window in Emacs is the physical area of the screen in which a buffer is displayed. The term is also used to refer to a Lisp object that represents that screen area in Emacs Lisp. It should be clear from the context which is meant.
Emacs groups windows into frames. A frame represents an area of screen available for Emacs to use. Each frame always contains at least one window, but you can subdivide it vertically or horizontally into multiple nonoverlapping Emacs windows.
In each frame, at any time, one and only one window is designated as
selected within the frame. The frame's cursor appears in that
window. At any time, one frame is the selected frame; and the window
selected within that frame is the selected window. The selected
window's buffer is usually the current buffer (except when
set-buffer has been used). See section 27.2 The Current Buffer.
For practical purposes, a window exists only while it is displayed in a frame. Once removed from the frame, the window is effectively deleted and should not be used, even though there may still be references to it from other Lisp objects. Restoring a saved window configuration is the only way for a window no longer on the screen to come back to life. (See section 28.3 Deleting Windows.)
Each window has the following attributes:
Users create multiple windows so they can look at several buffers at once. Lisp libraries use multiple windows for a variety of reasons, but most often to display related information. In Rmail, for example, you can move through a summary buffer in one window while the other window shows messages one at a time as they are reached.
The meaning of "window" in Emacs is similar to what it means in the context of general-purpose window systems such as X, but not identical. The X Window System places X windows on the screen; Emacs uses one or more X windows as frames, and subdivides them into Emacs windows. When you use Emacs on a character-only terminal, Emacs treats the whole terminal screen as one frame.
Most window systems support arbitrarily located overlapping windows. In contrast, Emacs windows are tiled; they never overlap, and together they fill the whole screen or frame. Because of the way in which Emacs creates new windows and resizes them, not all conceivable tilings of windows on an Emacs frame are actually possible. See section 28.2 Splitting Windows, and 28.14 The Size of a Window.
See section 38. Emacs Display, for information on how the contents of the window's buffer are displayed in the window.
t if object is a window.
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The functions described here are the primitives used to split a window
into two windows. Two higher level functions sometimes split a window,
but not always: pop-to-buffer and display-buffer
(see section 28.7 Displaying Buffers in Windows).
The functions described here do not accept a buffer as an argument. The two "halves" of the split window initially display the same buffer previously visible in the window that was split.
If horizontal is non-nil, then window splits into
two side by side windows. The original window window keeps the
leftmost size columns, and gives the rest of the columns to the
new window. Otherwise, it splits into windows one above the other, and
window keeps the upper size lines and gives the rest of the
lines to the new window. The original window is therefore the
left-hand or upper of the two, and the new window is the right-hand or
lower.
If window is omitted or nil, then the selected window is
split. If size is omitted or nil, then window is
divided evenly into two parts. (If there is an odd line, it is
allocated to the new window.) When split-window is called
interactively, all its arguments are nil.
The following example starts with one window on a screen that is 50 lines high by 80 columns wide; then the window is split.
(setq w (selected-window))
=> #<window 8 on windows.texi>
(window-edges) ; Edges in order:
=> (0 0 80 50) ; left--top--right--bottom
;; Returns window created
(setq w2 (split-window w 15))
=> #<window 28 on windows.texi>
(window-edges w2)
=> (0 15 80 50) ; Bottom window;
; top is line 15
(window-edges w)
=> (0 0 80 15) ; Top window
|
The screen looks like this:
__________
| | line 0
| w |
|__________|
| | line 15
| w2 |
|__________|
line 50
column 0 column 80
|
Next, the top window is split horizontally:
(setq w3 (split-window w 35 t))
=> #<window 32 on windows.texi>
(window-edges w3)
=> (35 0 80 15) ; Left edge at column 35
(window-edges w)
=> (0 0 35 15) ; Right edge at column 35
(window-edges w2)
=> (0 15 80 50) ; Bottom window unchanged
|
Now, the screen looks like this:
column 35
__________
| | | line 0
| w | w3 |
|___|______|
| | line 15
| w2 |
|__________|
line 50
column 0 column 80
|
Normally, Emacs indicates the border between two side-by-side windows with a scroll bar (see section Scroll Bars) or `|' characters. The display table can specify alternative border characters; see 38.17 Display Tables.
This function is basically an interface to split-window.
You could define a simplified version of the function like this:
(defun split-window-horizontally (&optional arg)
"Split selected window into two windows, side by side..."
(interactive "P")
(let ((size (and arg (prefix-numeric-value arg))))
(and size (< size 0)
(setq size (+ (window-width) size)))
(split-window nil size t)))
|
nil if there is only one window. The
argument no-mini, if non-nil, means don't count the
minibuffer even if it is active; otherwise, the minibuffer window is
included, if active, in the total number of windows, which is compared
against one.
The argument all-frames specifies which frames to consider. Here are the possible values and their meanings:
nil
t
visible
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A window remains visible on its frame unless you delete it by calling certain functions that delete windows. A deleted window cannot appear on the screen, but continues to exist as a Lisp object until there are no references to it. There is no way to cancel the deletion of a window aside from restoring a saved window configuration (see section 28.17 Window Configurations). Restoring a window configuration also deletes any windows that aren't part of that configuration.
When you delete a window, the space it took up is given to one adjacent sibling.
nil if window is deleted, and
t otherwise.
Warning: Erroneous information or fatal errors may result from using a deleted window as if it were live.
nil.
If window is omitted, then the selected window is deleted. An
error is signaled if there is only one window when delete-window
is called.
nil, then the selected window is used by default.
The return value is nil.
delete-windows-on operates frame by frame. If a frame has
several windows showing different buffers, then those showing
buffer are removed, and the others expand to fill the space. If
all windows in some frame are showing buffer (including the case
where there is only one window), then the frame reverts to having a
single window showing another buffer chosen with other-buffer.
See section 27.8 The Buffer List.
The argument frame controls which frames to operate on. This
function does not use it in quite the same way as the other functions
which scan all windows; specifically, the values t and nil
have the opposite of their meanings in other functions. Here are the
full details:
nil, operate on all frames.
t, operate on the selected frame.
visible, operate on all visible frames.
This function always returns nil.
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When a window is selected, the buffer in the window becomes the current buffer, and the cursor will appear in it.
The return value is window.
(setq w (next-window))
(select-window w)
=> #<window 65 on windows.texi>
|
This macro does not save or restore anything about the sizes, arrangement or contents of windows; therefore, if the forms change them, the change persists.
Each frame, at any time, has a window selected within the frame. This macro saves only the selected window; it does not save anything about other frames. If the forms select some other frame and alter the window selected within it, the change persists.
The following functions choose one of the windows on the screen, offering various criteria for the choice.
The selected window can be the least recently used window if it is the only window. A newly created window becomes the least recently used window until it is selected. A minibuffer window is never a candidate.
The argument frame controls which windows are considered.
nil, consider windows on the selected frame.
t, consider windows on all frames.
visible, consider windows on all visible frames.
If there are two windows of the same size, then the function returns the window that is first in the cyclic ordering of windows (see following section), starting from the selected window.
The argument frame controls which set of windows to
consider. See get-lru-window, above.
walk-windows (see section 28.5 Cyclic Ordering of Windows), calling predicate on each one one of them
with that window as its argument. The function returns the first
window for which predicate returns a non-nil value; if
that never happens, it returns default.
The optional arguments minibuf and all-frames specify the
set of windows to include in the scan. See the description of
next-window in 28.5 Cyclic Ordering of Windows, for details.
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When you use the command C-x o (other-window) to select
the next window, it moves through all the windows on the screen in a
specific cyclic order. For any given configuration of windows, this
order never varies. It is called the cyclic ordering of windows.
This ordering generally goes from top to bottom, and from left to right. But it may go down first or go right first, depending on the order in which the windows were split.
If the first split was vertical (into windows one above each other), and then the subwindows were split horizontally, then the ordering is left to right in the top of the frame, and then left to right in the next lower part of the frame, and so on. If the first split was horizontal, the ordering is top to bottom in the left part, and so on. In general, within each set of siblings at any level in the window tree, the order is left to right, or top to bottom.
The value of the argument minibuf determines whether the
minibuffer is included in the window order. Normally, when
minibuf is nil, the minibuffer is included if it is
currently active; this is the behavior of C-x o. (The minibuffer
window is active while the minibuffer is in use. See section 20. Minibuffers.)
If minibuf is t, then the cyclic ordering includes the
minibuffer window even if it is not active.
If minibuf is neither t nor nil, then the minibuffer
window is not included even if it is active.
The argument all-frames specifies which frames to consider. Here are the possible values and their meanings:
nil
t
visible
This example assumes there are two windows, both displaying the buffer `windows.texi':
(selected-window)
=> #<window 56 on windows.texi>
(next-window (selected-window))
=> #<window 52 on windows.texi>
(next-window (next-window (selected-window)))
=> #<window 56 on windows.texi>
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next-window.
nil.
The argument all-frames has the same meaning as in
next-window, but the minibuf argument of next-window
is always effectively nil.
In an interactive call, count is the numeric prefix argument.
proc
once for each window with the window as its sole argument.
The optional arguments minibuf and all-frames specify the
set of windows to include in the scan. See next-window, above,
for details.
nil or omitted, the
selected frame is used instead; if window is nil or
omitted, the selected window is used instead.
The value of minibuf determines if the minibuffer window will be
included in the result list. If minibuf is t, the
minibuffer window will be included, even if it isn't active. If
minibuf is nil or omitted, the minibuffer window will
only be included in the list if it is active. If minibuf is
neither nil nor t, the minibuffer window is not
included, whether or not it is active.
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This section describes low-level functions to examine windows or to display buffers in windows in a precisely controlled fashion. See section 28.7 Displaying Buffers in Windows, for related functions that find a window to use and specify a buffer for it. The functions described there are easier to use than these, but they employ heuristics in choosing or creating a window; use these functions when you need complete control.
nil. This is the fundamental primitive
for changing which buffer is displayed in a window, and all ways
of doing that call this function.
(set-window-buffer (selected-window) "foo")
=> nil
|
(window-buffer)
=> #<buffer windows.texi>
|
nil if there is none. If there are
several such windows, then the function returns the first one in the
cyclic ordering of windows, starting from the selected window.
See section 28.5 Cyclic Ordering of Windows.
The argument all-frames controls which windows to consider.
nil, consider windows on the selected frame.
t, consider windows on all frames.
visible, consider windows on all visible frames.
The two optional arguments work like the optional arguments of
next-window (see section 28.5 Cyclic Ordering of Windows); they are not
like the single optional argument of get-buffer-window. Perhaps
we should change get-buffer-window in the future to make it
compatible with the other functions.
The argument all-frames controls which windows to consider.
nil, consider windows on the selected frame.
t, consider windows on all frames.
visible, consider windows on all visible frames.
set-window-buffer is called, it sets this variable to
(current-time) in the specified buffer (see section 40.5 Time of Day).
When a buffer is first created, buffer-display-time starts out
with the value nil.
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In this section we describe convenient functions that choose a window
automatically and use it to display a specified buffer. These functions
can also split an existing window in certain circumstances. We also
describe variables that parameterize the heuristics used for choosing a
window.
See section 28.6 Buffers and Windows, for
low-level functions that give you more precise control. All of these
functions work by calling set-window-buffer.
Do not use the functions in this section in order to make a buffer
current so that a Lisp program can access or modify it; they are too
drastic for that purpose, since they change the display of buffers in
windows, which would be gratuitous and surprise the user. Instead, use
set-buffer and save-current-buffer (see section 27.2 The Current Buffer), which designate buffers as current for programmed access
without affecting the display of buffers in windows.
set-buffer, which makes buffer-or-name
the current buffer but does not display it in the selected window.
See section 27.2 The Current Buffer.
If buffer-or-name does not identify an existing buffer, then a new
buffer by that name is created. The major mode for the new buffer is
set according to the variable default-major-mode. See section 23.1.3 How Emacs Chooses a Major Mode.
Normally the specified buffer is put at the front of the buffer list
(both the selected frame's buffer list and the frame-independent buffer
list). This affects the operation of other-buffer. However, if
norecord is non-nil, this is not done. See section 27.8 The Buffer List.
The switch-to-buffer function is often used interactively, as
the binding of C-x b. It is also used frequently in programs. It
always returns nil.
switch-to-buffer.
The currently selected window is absolutely never used to do the job. If it is the only window, then it is split to make a distinct window for this purpose. If the selected window is already displaying the buffer, then it continues to do so, but another window is nonetheless found to display it in as well.
This function updates the buffer list just like switch-to-buffer
unless norecord is non-nil.
If the variable pop-up-frames is non-nil,
pop-to-buffer looks for a window in any visible frame already
displaying the buffer; if there is one, it returns that window and makes
it be selected within its frame. If there is none, it creates a new
frame and displays the buffer in it.
If pop-up-frames is nil, then pop-to-buffer
operates entirely within the selected frame. (If the selected frame has
just a minibuffer, pop-to-buffer operates within the most
recently selected frame that was not just a minibuffer.)
If the variable pop-up-windows is non-nil, windows may
be split to create a new window that is different from the original
window. For details, see 28.8 Choosing a Window for Display.
If other-window is non-nil, pop-to-buffer finds or
creates another window even if buffer-or-name is already visible
in the selected window. Thus buffer-or-name could end up
displayed in two windows. On the other hand, if buffer-or-name is
already displayed in the selected window and other-window is
nil, then the selected window is considered sufficient display
for buffer-or-name, so that nothing needs to be done.
All the variables that affect display-buffer affect
pop-to-buffer as well. See section 28.8 Choosing a Window for Display.
If buffer-or-name is a string that does not name an existing
buffer, a buffer by that name is created. The major mode for the new
buffer is set according to the variable default-major-mode.
See section 23.1.3 How Emacs Chooses a Major Mode.
This function updates the buffer list just like switch-to-buffer
unless norecord is non-nil.
other-buffer. In the usual applications of this function, you
don't care which other buffer is used; you just want to make sure that
buffer is no longer displayed.
This function returns nil.
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This section describes the basic facility that chooses a window to
display a buffer in---display-buffer. All the higher-level
functions and commands use this subroutine. Here we describe how to use
display-buffer and how to customize it.
pop-to-buffer, but it does not select that window and does not
make the buffer current. The identity of the selected window is
unaltered by this function.
If not-this-window is non-nil, it means to display the
specified buffer in a window other than the selected one, even if it is
already on display in the selected window. This can cause the buffer to
appear in two windows at once. Otherwise, if buffer-or-name is
already being displayed in any window, that is good enough, so this
function does nothing.
display-buffer returns the window chosen to display
buffer-or-name.
If the argument frame is non-nil, it specifies which frames
to check when deciding whether the buffer is already displayed. If the
buffer is already displayed in some window on one of these frames,
display-buffer simply returns that window. Here are the possible
values of frame:
nil, consider windows on the selected frame.
t, consider windows on all frames.
visible, consider windows on all visible frames.
Precisely how display-buffer finds or creates a window depends on
the variables described below.
nil, display-buffer searches
existing frames for a window displaying the buffer. If the buffer is
already displayed in a window in some frame, display-buffer makes
the frame visible and raises it, to use that window. If the buffer is
not already displayed, or if display-buffer-reuse-frames is
nil, display-buffer's behavior is determined by other
variables, described below.
display-buffer makes new windows.
If it is non-nil and there is only one window, then that window
is split. If it is nil, then display-buffer does not
split the single window, but uses it whole.
display-buffer may split a window,
if there are multiple windows. display-buffer always splits the
largest window if it has at least this many lines. If the largest
window is not this tall, it is split only if it is the sole window and
pop-up-windows is non-nil.
display-buffer should even out window
heights if the buffer gets displayed in an existing window, above or
beneath another existing window. If even-window-heights is
t, the default, window heights will be evened out. If
even-window-heights is nil, the orginal window heights
will be left alone.
display-buffer makes new frames.
If it is non-nil, display-buffer looks for an existing
window already displaying the desired buffer, on any visible frame. If
it finds one, it returns that window. Otherwise it makes a new frame.
The variables pop-up-windows and split-height-threshold do
not matter if pop-up-frames is non-nil.
If pop-up-frames is nil, then display-buffer either
splits a window or reuses one.
See section 29. Frames, for more information.
pop-up-frames
is non-nil.
Its value should be a function of no arguments. When
display-buffer makes a new frame, it does so by calling that
function, which should return a frame. The default value of the
variable is a function that creates a frame using parameters from
pop-up-frame-alist.
display-buffer makes a new frame. See section 29.3 Frame Parameters, for
more information about frame parameters.
display-buffer handles the
buffer specially.
By default, special display means to give the buffer a dedicated frame.
If an element is a list, instead of a string, then the CAR of the list is the buffer name, and the rest of the list says how to create the frame. There are two possibilities for the rest of the list. It can be an alist, specifying frame parameters, or it can contain a function and arguments to give to it. (The function's first argument is always the buffer to be displayed; the arguments from the list come after that.)
display-buffer handles the buffer
specially.
By default, special display means to give the buffer a dedicated frame.
If an element is a list, instead of a string, then the CAR of the
list is the regular expression, and the rest of the list says how to
create the frame. See above, under special-display-buffer-names.
The default value of this variable is
special-display-popup-frame.
If args is an alist, it specifies frame parameters for the new frame.
If args is a list whose CAR is a symbol, then (car
args) is called as a function to actually create and set up the
frame; it is called with buffer as first argument, and (cdr
args) as additional arguments.
This function always uses an existing window displaying buffer, whether or not it is in a frame of its own; but if you set up the above variables in your init file, before buffer was created, then presumably the window was previously made by this function.
special-display-popup-frame to use when it creates a frame.
display-buffer handles the buffer by switching to it in the
selected window.
display-buffer handles the
buffer by switching to it in the selected window.
display-buffer. If it is non-nil, it should be a function
that display-buffer calls to do the work. The function should
accept two arguments, the same two arguments that display-buffer
received. It should choose or create a window, display the specified
buffer, and then return the window.
This hook takes precedence over all the other options and hooks described above.
A window can be marked as "dedicated" to its buffer. Then
display-buffer will not try to use that window to display any
other buffer.
t if window is marked as dedicated;
otherwise nil.
nil, and nondedicated otherwise.
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Each window has its own value of point, independent of the value of point in other windows displaying the same buffer. This makes it useful to have multiple windows showing one buffer.
As far as the user is concerned, point is where the cursor is, and when the user switches to another buffer, the cursor jumps to the position of point in that buffer.
nil, the selected window is used.
When window is the selected window and its buffer is also the current buffer, the value returned is the same as point in that buffer.
Strictly speaking, it would be more correct to return the
"top-level" value of point, outside of any save-excursion
forms. But that value is hard to find.
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Each window contains a marker used to keep track of a buffer position that specifies where in the buffer display should start. This position is called the display-start position of the window (or just the start). The character after this position is the one that appears at the upper left corner of the window. It is usually, but not inevitably, at the beginning of a text line.
nil, the selected window is
used. For example,
(window-start)
=> 7058
|
When you create a window, or display a different buffer in it, the display-start position is set to a display-start position recently used for the same buffer, or 1 if the buffer doesn't have any.
Redisplay updates the window-start position (if you have not specified it explicitly since the previous redisplay)---for example, to make sure point appears on the screen. Nothing except redisplay automatically changes the window-start position; if you move point, do not expect the window-start position to change in response until after the next redisplay.
For a realistic example of using window-start, see the
description of count-lines in 30.2.4 Motion by Text Lines.
nil, the selected window is
used.
Simply changing the buffer text or moving point does not update the
value that window-end returns. The value is updated only when
Emacs redisplays and redisplay completes without being preempted.
If the last redisplay of window was preempted, and did not finish,
Emacs does not know the position of the end of display in that window.
In that case, this function returns nil.
If update is non-nil, window-end always returns an
up-to-date value for where the window ends, based on the current
window-start value. If the saved value is valid,
window-end returns that; otherwise it computes the correct
value by scanning the buffer text.
Even if update is non-nil, window-end does not
attempt to scroll the display if point has moved off the screen, the
way real redisplay would do. It does not alter the
window-start value. In effect, it reports where the displayed
text will end if scrolling is not required.
The display routines insist that the position of point be visible when a
buffer is displayed. Normally, they change the display-start position
(that is, scroll the window) whenever necessary to make point visible.
However, if you specify the start position with this function using
nil for noforce, it means you want display to start at
position even if that would put the location of point off the
screen. If this does place point off screen, the display routines move
point to the left margin on the middle line in the window.
For example, if point is 1 and you set the start of the window to 2, then point would be "above" the top of the window. The display routines will automatically move point if it is still 1 when redisplay occurs. Here is an example:
;; Here is what `foo' looks like before executing ;; the |
If noforce is non-nil, and position would place point
off screen at the next redisplay, then redisplay computes a new window-start
position that works well with point, and thus position is not used.
t if position is within the range of
text currently visible on the screen in window. It returns
nil if position is scrolled vertically or horizontally out
of view. Locations that are partially obscured are not considered
visible unless partially is non-nil. The argument
position defaults to the current position of point in
window; window, to the selected window.
Here is an example:
(or (pos-visible-in-window-p
(point) (selected-window))
(recenter 0))
|
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Textual scrolling means moving the text up or down though a
window. It works by changing the value of the window's display-start
location. It may also change the value of window-point to keep
point on the screen.
Textual scrolling was formerly called "vertical scrolling," but we changed its name to distinguish it from the new vertical fractional scrolling feature (see section 28.12 Vertical Fractional Scrolling).
In the commands scroll-up and scroll-down, the directions
"up" and "down" refer to the motion of the text in the buffer at which
you are looking through the window. Imagine that the text is
written on a long roll of paper and that the scrolling commands move the
paper up and down. Thus, if you are looking at text in the middle of a
buffer and repeatedly call scroll-down, you will eventually see
the beginning of the buffer.
Some people have urged that the opposite convention be used: they imagine that the window moves over text that remains in place. Then "down" commands would take you to the end of the buffer. This view is more consistent with the actual relationship between windows and the text in the buffer, but it is less like what the user sees. The position of a window on the terminal does not move, and short scrolling commands clearly move the text up or down on the screen. We have chosen names that fit the user's point of view.
The textual scrolling functions (aside from
scroll-other-window) have unpredictable results if the current
buffer is different from the buffer that is displayed in the selected
window. See section 27.2 The Current Buffer.
If count is nil (or omitted), then the length of scroll
is next-screen-context-lines lines less than the usable height of
the window (not counting its mode line).
scroll-up returns nil.
If count is omitted or nil, then the length of the scroll
is next-screen-context-lines lines less than the usable height of
the window (not counting its mode line).
scroll-down returns nil.
nil, are handled
as in scroll-up.
You can specify which buffer to scroll by setting the variable
other-window-scroll-buffer to a buffer. If that buffer isn't
already displayed, scroll-other-window displays it in some
window.
When the selected window is the minibuffer, the next window is normally
the one at the top left corner. You can specify a different window to
scroll, when the minibuffer is selected, by setting the variable
minibuffer-scroll-window. This variable has no effect when any
other window is selected. See section 20.9 Minibuffer Miscellany.
When the minibuffer is active, it is the next window if the selected
window is the one at the bottom right corner. In this case,
scroll-other-window attempts to scroll the minibuffer. If the
minibuffer contains just one line, it has nowhere to scroll to, so the
line reappears after the echo area momentarily displays the message
"Beginning of buffer".
nil, it tells scroll-other-window
which buffer to scroll.
nil or a fraction
f between 0 and 1. If it is a fraction, that specifies where on
the screen to put point when scrolling down. More precisely, when a
window scrolls down because point is above the window start, the new
start position is chosen to put point f part of the window
height from the top. The larger f, the more aggressive the
scrolling.
A value of nil is equivalent to .5, since its effect is to center
point. This variable automatically becomes buffer-local when set in any
fashion.
scroll-up-aggressively, a larger value scrolls more aggressively.
scroll-conservatively. The
difference is that it if its value is n, that permits scrolling
only by precisely n lines, not a smaller number. This feature
does not work with scroll-margin. The default value is zero.
nil, the scroll functions move point so
that the vertical position of the cursor is unchanged, when that is
possible.
scroll-up
with an argument of nil scrolls so that this many lines at the
bottom of the window appear instead at the top. The default value is
2.
If count is a nonnegative number, it puts the line containing
point count lines down from the top of the window. If count
is a negative number, then it counts upward from the bottom of the
window, so that -1 stands for the last usable line in the window.
If count is a non-nil list, then it stands for the line in
the middle of the window.
If count is nil, recenter puts the line containing
point in the middle of the window, then clears and redisplays the entire
selected frame.
When recenter is called interactively, count is the raw
prefix argument. Thus, typing C-u as the prefix sets the
count to a non-nil list, while typing C-u 4 sets
count to 4, which positions the current line four lines from the
top.
With an argument of zero, recenter positions the current line at
the top of the window. This action is so handy that some people make a
separate key binding to do this. For example,
(defun line-to-top-of-window () "Scroll current line to top of window. Replaces three keystroke sequence C-u 0 C-l." (interactive) (recenter 0)) (global-set-key [kp-multiply] 'line-to-top-of-window) |
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Vertical fractional scrolling means shifting the image in the window up or down by a specified multiple or fraction of a line. Starting in Emacs 21, each window has a vertical scroll position, which is a number, never less than zero. It specifies how far to raise the contents of the window. Raising the window contents generally makes all or part of some lines disappear off the top, and all or part of some other lines appear at the bottom. The usual value is zero.
The vertical scroll position is measured in units of the normal line height, which is the height of the default font. Thus, if the value is .5, that means the window contents are scrolled up half the normal line height. If it is 3.3, that means the window contents are scrolled up somewhat over three times the normal line height.
What fraction of a line the vertical scrolling covers, or how many lines, depends on what the lines contain. A value of .5 could scroll a line whose height is very short off the screen, while a value of 3.3 could scroll just part of the way through a tall line or an image.
nil, the selected window is
used.
(window-vscroll)
=> 0
|
The actual vertical scroll position must always correspond to an integral number of pixels, so the value you specify is rounded accordingly.
The return value is the result of this rounding.
(set-window-vscroll (selected-window) 1.2)
=> 1.13
|
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Horizontal scrolling means shifting the image in the window left or right by a specified multiple of the normal character width. Each window has a vertical scroll position, which is a number, never less than zero. It specifies how far to shift the contents left. Shifting the window contents left generally makes all or part of some characters disappear off the left, and all or part of some other characters appear at the right. The usual value is zero.
The horizontal scroll position is measured in units of the normal character width, which is the width of space in the default font. Thus, if the value is 5, that means the window contents are scrolled left by 5 times the normal character width. How many characters actually disappear off to the left depends on their width, and could vary from line to line.
Because we read from side to side in the "inner loop", and from top to bottom in the "outer loop", the effect of horizontal scrolling is not like that of textual or vertical scrolling. Textual scrolling involves selection of a portion of text to display, and vertical scrolling moves the window contents contiguously; but horizontal scrolling causes part of each line to go off screen.
Usually, no horizontal scrolling is in effect; then the leftmost column is at the left edge of the window. In this state, scrolling to the right is meaningless, since there is no data to the left of the edge to be revealed by it; so this is not allowed. Scrolling to the left is allowed; it scrolls the first columns of text off the edge of the window and can reveal additional columns on the right that were truncated before. Once a window has a nonzero amount of leftward horizontal scrolling, you can scroll it back to the right, but only so far as to reduce the net horizontal scroll to zero. There is no limit to how far left you can scroll, but eventually all the text will disappear off the left edge.
In Emacs 21, redisplay automatically alters the horizontal scrolling
of a window as necessary to ensure that point is always visible, if
automatic-hscrolling is set. However, you can still set the
horizontal scrolling value explicitly. The value you specify serves as
a lower bound for automatic scrolling, i.e. automatic scrolling
will not scroll a window to a column less than the specified one.
The return value is the total amount of leftward horizontal scrolling in
effect after the change--just like the value returned by
window-hscroll (below).
The return value is the total amount of leftward horizontal scrolling in
effect after the change--just like the value returned by
window-hscroll (below).
Once you scroll a window as far right as it can go, back to its normal position where the total leftward scrolling is zero, attempts to scroll any farther right have no effect.
The value is never negative. It is zero when no horizontal scrolling has been done in window (which is usually the case).
If window is nil, the selected window is used.
(window-hscroll)
=> 0
(scroll-left 5)
=> 5
(window-hscroll)
=> 5
|
The value returned is columns.
(set-window-hscroll (selected-window) 10)
=> 10
|
Here is how you can determine whether a given position position is off the screen due to horizontal scrolling:
(defun hscroll-on-screen (window position)
(save-excursion
(goto-char position)
(and
(>= (- (current-column) (window-hscroll window)) 0)
(< (- (current-column) (window-hscroll window))
(window-width window)))))
|
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An Emacs window is rectangular, and its size information consists of the height (the number of lines) and the width (the number of character positions in each line). The mode line is included in the height. But the width does not count the scroll bar or the column of `|' characters that separates side-by-side windows.
The following three functions return size information about a window:
frame-height on that frame (since the
last line is always reserved for the minibuffer).
If window is nil, the function uses the selected window.
(window-height)
=> 23
(split-window-vertically)
=> #<window 4 on windows.texi>
(window-height)
=> 11
|
frame-width on that frame. The width does not include the
window's scroll bar or the column of `|' characters that separates
side-by-side windows.
If window is nil, the function uses the selected window.
(window-width)
=> 80
|
nil, the selected window is used.
The order of the list is (left top right
bottom), all elements relative to 0, 0 at the top left corner of
the frame. The element right of the value is one more than the
rightmost column used by window, and bottom is one more than
the bottommost row used by window and its mode-line.
If a window has a scroll bar, the right edge value includes the width of the scroll bar. Otherwise, if the window has a neighbor on the right, its right edge value includes the width of the separator line between the window and that neighbor. Since the width of the window does not include this separator, the width does not usually equal the difference between the right and left edges.
Here is the result obtained on a typical 24-line terminal with just one window:
(window-edges (selected-window))
=> (0 0 80 23)
|
The bottom edge is at line 23 because the last line is the echo area.
If window is at the upper left corner of its frame, then
bottom is the same as the value of (window-height),
right is almost the same as the value of (window-width),
and top and left are zero. For example, the edges of the
following window are `0 0 8 5'. Assuming that the frame has
more than 8 columns, the last column of the window (column 7) holds a
border rather than text. The last row (row 4) holds the mode line,
shown here with `xxxxxxxxx'.
0
_______
0 | |
| |
| |
| |
xxxxxxxxx 4
7
|
In the following example, let's suppose that the frame is 7 columns wide. Then the edges of the left window are `0 0 4 3' and the edges of the right window are `4 0 8 3'.
___ ___
| | |
| | |
xxxxxxxxx
0 34 7
|
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The window size functions fall into two classes: high-level commands that change the size of windows and low-level functions that access window size. Emacs does not permit overlapping windows or gaps between windows, so resizing one window affects other windows.
window-min-height lines, that window disappears.
If horizontal is non-nil, this function makes
window wider by size columns, stealing columns instead of
lines. If a window from which columns are stolen shrinks below
window-min-width columns, that window disappears.
If the requested size would exceed that of the window's frame, then the function makes the window occupy the entire height (or width) of the frame.
If there are various other windows from which lines or columns can be
stolen, and some of them specify fixed size (using
window-size-fixed, see below), they are left untouched while
other windows are "robbed." If it would be necessary to alter the
size of a fixed-size window, enlarge-window gets an error
instead.
If size is negative, this function shrinks the window by
-size lines or columns. If that makes the window smaller
than the minimum size (window-min-height and
window-min-width), enlarge-window deletes the window.
enlarge-window returns nil.
(defun enlarge-window-horizontally (columns) (enlarge-window columns t)) |
enlarge-window but negates the argument
size, making the selected window smaller by giving lines (or
columns) to the other windows. If the window shrinks below
window-min-height or window-min-width, then it disappears.
If size is negative, the window is enlarged by -size lines or columns.
(defun shrink-window-horizontally (columns) (shrink-window columns t)) |
window-min-height lines. If window is not given,
it defaults to the selected window.
However, the command does nothing if the window is already too small to display the whole text of the buffer, or if part of the contents are currently scrolled off screen, or if the window is not the full width of its frame, or if the window is the only window in its frame.
nil, in any given buffer,
then the size of any window displaying the buffer remains fixed
unless you explicitly change it or Emacs has no other choice.
(This feature is new in Emacs 21.)
If the value is height, then only the window's height is fixed;
if the value is width, then only the window's width is fixed.
Any other non-nil value fixes both the width and the height.
The usual way to use this variable is to give it a buffer-local value in a particular buffer. That way, the windows (but usually there is only one) displaying that buffer have fixed size.
Explicit size-change functions such as enlarge-window
get an error if they would have to change a window size which is fixed.
Therefore, when you want to change the size of such a window,
you should bind window-size-fixed to nil, like this:
(let ((window-size-fixed nil)) (enlarge-window 10)) |
Note that changing the frame size will change the size of a fixed-size window, if there is no other alternative.
The following two variables constrain the window-size-changing functions to a minimum height and width.
window-min-height automatically deletes it, and no window may be
created shorter than this. The absolute minimum height is two (allowing
one line for the mode line, and one line for the buffer display).
Actions that change window sizes reset this variable to two if it is
less than two. The default value is 4.
window-min-width automatically deletes it, and no window may be
created narrower than this. The absolute minimum width is one; any
value below that is ignored. The default value is 10.
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This section describes how to relate screen coordinates to windows.
window-at returns nil.
If you omit frame, the selected frame is used.
The argument coordinates is a cons cell of the form (x
. y). The coordinates x and y are measured in
characters, and count from the top left corner of the screen or frame.
The value returned by coordinates-in-window-p is non-nil
if the coordinates are inside window. The value also indicates
what part of the window the position is in, as follows:
(relx . rely)
mode-line
header-line
vertical-line
nil
The function coordinates-in-window-p does not require a frame as
argument because it always uses the frame that window is on.
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A window configuration records the entire layout of one frame--all windows, their sizes, which buffers they contain, what part of each buffer is displayed, and the values of point and the mark. You can bring back an entire previous layout by restoring a window configuration previously saved.
If you want to record all frames instead of just one, use a frame configuration instead of a window configuration. See section 29.12 Frame Configurations.
window-min-height, window-min-width and
minibuffer-scroll-window. An exception is made for point in the
current buffer, whose value is not saved.
If frame is omitted, the selected frame is used.
The argument configuration must be a value that was previously
returned by current-window-configuration. This configuration is
restored in the frame from which configuration was made, whether
that frame is selected or not. This always counts as a window size
change and triggers execution of the window-size-change-functions
(see section 28.18 Hooks for Window Scrolling and Changes), because set-window-configuration doesn't
know how to tell whether the new configuration actually differs from the
old one.
If the frame which configuration was saved from is dead, all this
function does is restore the three variables window-min-height,
window-min-width and minibuffer-scroll-window.
Here is a way of using this function to get the same effect
as save-window-excursion:
(let ((config (current-window-configuration)))
(unwind-protect
(progn (split-window-vertically nil)
...)
(set-window-configuration config)))
|
save-excursion also, if you wish to preserve that.
Don't use this construct when save-selected-window is all you need.
Exit from save-window-excursion always triggers execution of the
window-size-change-functions. (It doesn't know how to tell
whether the restored configuration actually differs from the one in
effect at the end of the forms.)
The return value is the value of the final form in forms. For example:
(split-window)
=> #<window 25 on control.texi>
(setq w (selected-window))
=> #<window 19 on control.texi>
(save-window-excursion
(delete-other-windows w)
(switch-to-buffer "foo")
'do-something)
=> do-something
;; The screen is now split again.
|
t if object is a window configuration.
t even if those
aspects differ.
The function equal can also compare two window configurations; it
regards configurations as unequal if they differ in any respect, even a
saved point or mark.
Primitives to look inside of window configurations would make sense, but none are implemented. It is not clear they are useful enough to be worth implementing.
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This section describes how a Lisp program can take action whenever a
window displays a different part of its buffer or a different buffer.
There are three actions that can change this: scrolling the window,
switching buffers in the window, and changing the size of the window.
The first two actions run window-scroll-functions; the last runs
window-size-change-functions. The paradigmatic use of these
hooks is in the implementation of Lazy Lock mode; see section `Font Lock Support Modes' in The GNU Emacs Manual.
Displaying a different buffer in the window also runs these functions.
These functions must be careful in using window-end
(see section 28.10 The Window Start Position); if you need an up-to-date value, you must use
the update argument to ensure you get it.
Each function receives the frame as its sole argument. There is no direct way to find out which windows on that frame have changed size, or precisely how. However, if a size-change function records, at each call, the existing windows and their sizes, it can also compare the present sizes and the previous sizes.
Creating or deleting windows counts as a size change, and therefore causes these functions to be called. Changing the frame size also counts, because it changes the sizes of the existing windows.
It is not a good idea to use save-window-excursion (see section 28.17 Window Configurations) in these functions, because that always counts as a
size change, and it would cause these functions to be called over and
over. In most cases, save-selected-window (see section 28.4 Selecting Windows) is what you need here.
set-window-redisplay-end-trigger. The
functions are called with two arguments: the window, and the end trigger
position. Storing nil for the end trigger position turns off the
feature, and the trigger value is automatically reset to nil just
after the hook is run.
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