This section describes functions for creating a new window by splitting an existing one. Note that some windows are special in the sense that these functions may fail to split them as described here. Examples of such windows are side windows (see Side Windows) and atomic windows (see Atomic Windows).
This function creates a new live window next to the window
window. If window is omitted or nil, it defaults
to the selected window. That window is split, and reduced in
size. The space is taken up by the new window, which is returned.
The optional second argument size determines the sizes of
window and/or the new window. If it is omitted or nil,
both windows are given equal sizes; if there is an odd line, it is
allocated to the new window. If size is a positive number,
window is given size lines (or columns, depending on the
value of side). If size is a negative number, the new
window is given −size lines (or columns).
If size is nil, this function obeys the variables
window-min-height and window-min-width (see Window Sizes). Thus, it signals an error if splitting would result in making
a window smaller than those variables specify. However, a
non-nil value for size causes those variables to be
ignored; in that case, the smallest allowable window is considered to be
one that has space for a text that is one line tall and/or two columns
wide.
Hence, if size is specified, it’s the caller’s responsibility to
check whether the emanating windows are large enough to encompass all of
their decorations like a mode line or a scroll bar. The function
window-min-size (see Window Sizes) can be used to determine
the minimum requirements of window in this regard. Since the new
window usually inherits areas like the mode line or the scroll bar from
window, that function is also a good guess for the minimum size of
the new window. The caller should specify a smaller size only if it
correspondingly removes an inherited area before the next redisplay.
The optional third argument side determines the position of the
new window relative to window. If it is nil or
below, the new window is placed below window. If it is
above, the new window is placed above window. In both
these cases, size specifies a total window height, in lines.
If side is t or right, the new window is placed on
the right of window. If side is left, the new
window is placed on the left of window. In both these cases,
size specifies a total window width, in columns.
The optional fourth argument pixelwise, if non-nil, means
to interpret size in units of pixels, instead of lines and
columns.
If window is a live window, the new window inherits various properties from it, including margins and scroll bars. If window is an internal window, the new window inherits the properties of the window selected within window’s frame.
The behavior of this function may be altered by the window parameters
of window, so long as the variable
ignore-window-parameters is nil. If the value of
the split-window window parameter is t, this function
ignores all other window parameters. Otherwise, if the value of the
split-window window parameter is a function, that function is
called with the arguments window, size, and side, in
lieu of the usual action of split-window. Otherwise, this
function obeys the window-atom or window-side window
parameter, if any. See Window Parameters.
As an example, here is a sequence of split-window calls that
yields the window configuration discussed in Windows and Frames.
This example demonstrates splitting a live window as well as splitting
an internal window. We begin with a frame containing a single window
(a live root window), which we denote by W4. Calling
(split-window W4) yields this window configuration:
______________________________________
| ____________________________________ |
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||_________________W4_________________||
| ____________________________________ |
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||_________________W5_________________||
|__________________W3__________________|
The split-window call has created a new live window, denoted by
W5. It has also created a new internal window, denoted by
W3, which becomes the root window and the parent of both
W4 and W5.
Next, we call (split-window W3 nil 'left), passing the
internal window W3 as the argument. The result:
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| ______ ____________________________ |
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|| |||____________W4____________|||
|| || __________________________ ||
|| ||| |||
|| ||| |||
|| |||____________W5____________|||
||__W2__||_____________W3_____________ |
|__________________W1__________________|
A new live window W2 is created, to the left of the internal window W3. A new internal window W1 is created, becoming the new root window.
For interactive use, Emacs provides two commands which always split
the selected window. These call split-window internally.
This function splits the window window-to-split into two side-by-side windows, putting window-to-split on the left. window-to-split defaults to the selected window. If size is positive, the left window gets size columns; if size is negative, the right window gets −size columns.
This function splits the window window-to-split into two windows, one above the other, leaving the upper window selected. window-to-split defaults to the selected window. If size is positive, the upper window gets size lines; if size is negative, the lower window gets −size lines.
This function splits the whole frame in two. The current window
configuration is retained on the top, and a new window is created
below, taking up the whole width of the frame. size is treated
as by split-window-below.
This function splits the whole frame in two. The current window
configuration is retained on the left, and a new window is created on
the right, taking up the whole height of the frame. size is treated
as by split-window-right.
If the value of this variable is non-nil (the default),
split-window-below behaves as described above.
If it is nil, split-window-below adjusts point in each
of the two windows to minimize redisplay. (This is useful on slow
terminals.) It selects whichever window contains the screen line that
point was previously on. Note that this only affects
split-window-below, not the lower-level split-window
function.