elisp: Recombining Windows
27.8 Recombining Windows
========================
When deleting the last sibling of a window W, its parent window is
deleted too, with W replacing it in the window tree. This means that W
must be recombined with its parent’s siblings to form a new window
combination (
Windows and Frames). In some occasions, deleting a
live window may even entail the deletion of two internal windows.
______________________________________
| ______ ____________________________ |
|| || __________________________ ||
|| ||| ___________ ___________ |||
|| |||| || ||||
|| ||||____W6_____||_____W7____||||
|| |||____________W4____________|||
|| || __________________________ ||
|| ||| |||
|| ||| |||
|| |||____________W5____________|||
||__W2__||_____________W3_____________ |
|__________________W1__________________|
Deleting W5 in this configuration normally causes the deletion of W3 and
W4. The remaining live windows W2, W6 and W7 are recombined to form a
new horizontal combination with parent W1.
Sometimes, however, it makes sense to not delete a parent window like
W4. In particular, a parent window should not be removed when it was
used to preserve a combination embedded in a combination of the same
type. Such embeddings make sense to assure that when you split a window
and subsequently delete the new window, Emacs reestablishes the layout
of the associated frame as it existed before the splitting.
Consider a scenario starting with two live windows W2 and W3 and
their parent W1.
______________________________________
| ____________________________________ |
|| ||
|| ||
|| ||
|| ||
|| ||
|| ||
||_________________W2_________________||
| ____________________________________ |
|| ||
|| ||
||_________________W3_________________||
|__________________W1__________________|
Split W2 to make a new window W4 as follows.
______________________________________
| ____________________________________ |
|| ||
|| ||
||_________________W2_________________||
| ____________________________________ |
|| ||
|| ||
||_________________W4_________________||
| ____________________________________ |
|| ||
|| ||
||_________________W3_________________||
|__________________W1__________________|
Now, when enlarging a window vertically, Emacs tries to obtain the
corresponding space from its lower sibling, provided such a window
exists. In our scenario, enlarging W4 will steal space from W3.
______________________________________
| ____________________________________ |
|| ||
|| ||
||_________________W2_________________||
| ____________________________________ |
|| ||
|| ||
|| ||
|| ||
||_________________W4_________________||
| ____________________________________ |
||_________________W3_________________||
|__________________W1__________________|
Deleting W4 will now give its entire space to W2, including the space
earlier stolen from W3.
______________________________________
| ____________________________________ |
|| ||
|| ||
|| ||
|| ||
|| ||
|| ||
|| ||
|| ||
||_________________W2_________________||
| ____________________________________ |
||_________________W3_________________||
|__________________W1__________________|
This can be counterintuitive, in particular if W4 were used for
displaying a buffer only temporarily (Temporary Displays), and
you want to continue working with the initial layout.
The behavior can be fixed by making a new parent window when
splitting W2. The variable described next allows that to be done.
-- User Option: window-combination-limit
This variable controls whether splitting a window shall make a new
parent window. The following values are recognized:
‘nil’
This means that the new live window is allowed to share the
existing parent window, if one exists, provided the split
occurs in the same direction as the existing window
combination (otherwise, a new internal window is created
anyway).
‘window-size’
In this case ‘display-buffer’ makes a new parent window if it
is passed a ‘window-height’ or ‘window-width’ entry in the
ALIST argument (Display Action Functions).
‘temp-buffer’
This value causes the creation of a new parent window when a
window is split for showing a temporary buffer (
Temporary Displays) only.
‘display-buffer’
This means that when ‘display-buffer’ (Choosing
Window) splits a window it always makes a new parent window.
‘t’
In this case a new parent window is always created when
splitting a window. Thus, if the value of this variable is at
all times ‘t’, then at all times every window tree is a binary
tree (a tree where each window except the root window has
exactly one sibling).
The default is ‘nil’. Other values are reserved for future use.
If, as a consequence of this variable’s setting, ‘split-window’
makes a new parent window, it also calls
‘set-window-combination-limit’ (see below) on the newly-created
internal window. This affects how the window tree is rearranged
when the child windows are deleted (see below).
If ‘window-combination-limit’ is ‘t’, splitting W2 in the initial
configuration of our scenario would have produced this:
______________________________________
| ____________________________________ |
|| __________________________________ ||
||| |||
|||________________W2________________|||
|| __________________________________ ||
||| |||
|||________________W4________________|||
||_________________W5_________________||
| ____________________________________ |
|| ||
|| ||
||_________________W3_________________||
|__________________W1__________________|
A new internal window W5 has been created; its children are W2 and the
new live window W4. Now, W2 is the only sibling of W4, so enlarging W4
will try to shrink W2, leaving W3 unaffected. Observe that W5
represents a vertical combination of two windows embedded in the
vertical combination W1.
-- Function: set-window-combination-limit window limit
This function sets the “combination limit” of the window WINDOW to
LIMIT. This value can be retrieved via the function
‘window-combination-limit’. See below for its effects; note that
it is only meaningful for internal windows. The ‘split-window’
function automatically calls this function, passing it ‘t’ as
LIMIT, provided the value of the variable
‘window-combination-limit’ is ‘t’ when it is called.
-- Function: window-combination-limit window
This function returns the combination limit for WINDOW.
The combination limit is meaningful only for an internal window.
If it is ‘nil’, then Emacs is allowed to automatically delete
WINDOW, in response to a window deletion, in order to group the
child windows of WINDOW with its sibling windows to form a new
window combination. If the combination limit is ‘t’, the child
windows of WINDOW are never automatically recombined with its
siblings.
If, in the configuration shown at the beginning of this section,
the combination limit of W4 (the parent window of W6 and W7) is
‘t’, deleting W5 will not implicitly delete W4 too.
Alternatively, the problems sketched above can be avoided by always
resizing all windows in the same combination whenever one of its windows
is split or deleted. This also permits splitting windows that would be
otherwise too small for such an operation.
-- User Option: window-combination-resize
If this variable is ‘nil’, ‘split-window’ can only split a window
(denoted by WINDOW) if WINDOW’s screen area is large enough to
accommodate both itself and the new window.
If this variable is ‘t’, ‘split-window’ tries to resize all windows
that are part of the same combination as WINDOW, in order to
accommodate the new window. In particular, this may allow
‘split-window’ to succeed even if WINDOW is a fixed-size window or
too small to ordinarily split. Furthermore, subsequently resizing
or deleting WINDOW may resize all other windows in its combination.
The default is ‘nil’. Other values are reserved for future use. A
specific split operation may ignore the value of this variable if
it is affected by a non-‘nil’ value of ‘window-combination-limit’.
To illustrate the effect of ‘window-combination-resize’, consider the
following frame layout.
______________________________________
| ____________________________________ |
|| ||
|| ||
|| ||
|| ||
||_________________W2_________________||
| ____________________________________ |
|| ||
|| ||
|| ||
|| ||
||_________________W3_________________||
|__________________W1__________________|
If ‘window-combination-resize’ is ‘nil’, splitting window W3 leaves the
size of W2 unchanged:
______________________________________
| ____________________________________ |
|| ||
|| ||
|| ||
|| ||
||_________________W2_________________||
| ____________________________________ |
|| ||
||_________________W3_________________||
| ____________________________________ |
|| ||
||_________________W4_________________||
|__________________W1__________________|
If ‘window-combination-resize’ is ‘t’, splitting W3 instead leaves all
three live windows with approximately the same height:
______________________________________
| ____________________________________ |
|| ||
|| ||
||_________________W2_________________||
| ____________________________________ |
|| ||
|| ||
||_________________W3_________________||
| ____________________________________ |
|| ||
|| ||
||_________________W4_________________||
|__________________W1__________________|
Deleting any of the live windows W2, W3 or W4 will distribute its space
proportionally among the two remaining live windows.
Info Catalog
elisp: Deleting Windows
elisp: Windows
elisp: Selecting Windows