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28.26 Window Configurations

A window configuration records the entire layout of one frame—all windows, their sizes, which buffers they contain, how those buffers are scrolled, and their value of point; also their fringes, margins, and scroll bar settings. It also includes the value of minibuffer-scroll-window. As a special exception, the window configuration does not record the value of point in the selected window for the current buffer.

You can bring back an entire frame layout by restoring a previously saved window configuration. If you want to record the layout of all frames instead of just one, use a frame configuration instead of a window configuration. See Frame Configurations.

— Function: current-window-configuration &optional frame

This function returns a new object representing frame's current window configuration. The default for frame is the selected frame. The variable window-persistent-parameters specifies which window parameters (if any) are saved by this function. See Window Parameters.

— Function: set-window-configuration configuration

This function restores the configuration of windows and buffers as specified by configuration, for the frame that configuration was created for.

The argument configuration must be a value that was previously returned by current-window-configuration. The configuration is restored in the frame from which configuration was made, whether that frame is selected or not. In some rare cases this may trigger execution of the window-size-change-functions (see Window Hooks) even if the size of windows did not change at all. The window-configuration-change-hook functions will be called if and only if at least one window was added to or deleted from the frame.

If the frame from which configuration was saved is dead, all this function does is restore the three variables window-min-height, window-min-width and minibuffer-scroll-window. In this case, the function returns nil. Otherwise, it returns t.

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-below nil)
                       ...)
              (set-window-configuration config)))
— Macro: save-window-excursion forms...

This macro records the window configuration of the selected frame, executes forms in sequence, then restores the earlier window configuration. The return value is the value of the final form in forms.

Most Lisp code should not use this macro; save-selected-window is typically sufficient. In particular, this macro cannot reliably prevent the code in forms from opening new windows, because new windows might be opened in other frames (see Choosing Window), and save-window-excursion only saves and restores the window configuration on the current frame.

Do not use this macro in window-size-change-functions; exiting the macro triggers execution of window-size-change-functions, leading to an endless loop.

— Function: window-configuration-p object

This function returns t if object is a window configuration.

— Function: compare-window-configurations config1 config2

This function compares two window configurations as regards the structure of windows, but ignores the values of point and the saved scrolling positions—it can return 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.

— Function: window-configuration-frame config

This function returns the frame for which the window configuration config was made.

Other primitives to look inside of window configurations would make sense, but are not implemented because we did not need them. See the file winner.el for some more operations on windows configurations.

The objects returned by current-window-configuration die together with the Emacs process. In order to store a window configuration on disk and read it back in another Emacs session, you can use the functions described next. These functions are also useful to clone the state of a frame into an arbitrary live window (set-window-configuration effectively clones the windows of a frame into the root window of that very frame only).

— Function: window-state-get &optional window writable

This function returns the state of window as a Lisp object. The argument window must be a valid window and defaults to the root window of the selected frame.

If the optional argument writable is non-nil, this means to not use markers for sampling positions like window-point or window-start. This argument should be non-nil when the state will be written to disk and read back in another session.

Together, the argument writable and the variable window-persistent-parameters specify which window parameters are saved by this function. See Window Parameters.

The value returned by window-state-get can be used in the same session to make a clone of a window in another window. It can be also written to disk and read back in another session. In either case, use the following function to restore the state of the window.

— Function: window-state-put state &optional window ignore

This function puts the window state state into window. The argument state should be the state of a window returned by an earlier invocation of window-state-get, see above. The optional argument window can be either a live window or an internal window (see Windows and Frames) and defaults to the selected one. If window is not live, it is replaced by a live window before putting state into it.

If the optional argument ignore is non-nil, it means to ignore minimum window sizes and fixed-size restrictions. If ignore is safe, this means windows can get as small as one line and/or two columns.

The functions window-state-get and window-state-put also allow to exchange the contents of two live windows. The following function does precisely that:

— Command: window-swap-states &optional window-1 window-2 size

This command swaps the states of the two live windows window-1 and window-2. window-1 must specify a live window and defaults to the selected one. window-2 must specify a live window and defaults to the window following window-1 in the cyclic ordering of windows, excluding minibuffer windows and including live windows on all visible frames.

Optional argument size non-nil means to try swapping the sizes of window-1 and window-2 as well. A value of height means to swap heights only, a value of width means to swap widths only, while t means to swap both widths and heights, if possible. Frames are not resized by this function.