28.15 Changing the Size of a Window

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.

Command: enlarge-window size &optional horizontal

This function makes the selected window size lines taller, stealing lines from neighboring windows. It takes the lines from one window at a time until that window is used up, then takes from another. If a window from which lines are stolen shrinks below 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.

Command: enlarge-window-horizontally columns

This function makes the selected window columns wider. It could be defined as follows:

(defun enlarge-window-horizontally (columns) (enlarge-window columns t))

Command: shrink-window size &optional horizontal

This function is like 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.

Command: shrink-window-horizontally columns

This function makes the selected window columns narrower. It could be defined as follows:

(defun shrink-window-horizontally (columns) (shrink-window columns t))

Command: shrink-window-if-larger-than-buffer &optional window

This command shrinks window to be as small as possible while still showing the full contents of its buffer--but not less than 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.

Variable: window-size-fixed

If this variable is non-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.

User Option: window-min-height

The value of this variable determines how short a window may become before it is automatically deleted. Making a window smaller than 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.

User Option: window-min-width

The value of this variable determines how narrow a window may become before it is automatically deleted. Making a window smaller than 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.