Atomic windows are rectangular compositions of at least two live windows. They have the following distinctive characteristics:
split-window(see Splitting Windows), when applied to a constituent of an atomic window, will try to create the new window outside of the atomic window.
delete-window(see Deleting Windows), when applied to a constituent of an atomic window, will try to delete the entire atomic window instead.
delete-other-windows(see Deleting Windows), when applied to a constituent of an atomic window, will try to make the atomic window fill its frame or main window (see Side Windows).
This means that the basic groups of functions that alter the window structure treat an atomic window like a live one, thus preserving the internal structure of the atomic window.
Atomic windows are useful to construct and preserve window layouts that are meaningful only when all involved buffers are shown simultaneously in a specific manner, such as when showing differences between file revisions, or the same text in different languages or markups. They can also be used to permanently display information pertinent to a specific window in bars on that window’s sides.
Atomic windows are implemented with the help of the reserved
window-atom window parameter (see Window Parameters) and an
internal window (see Basic Concepts of Emacs Windows) called the root window of the
atomic window. All windows that are part of the same atomic window have
this root window as their common ancestor and are assigned a
The following function returns the root of the atomic window a specified window is part of:
This functions returns the root of the atomic window window is a
part of. The specified window must be a valid window and defaults
to the selected one. It returns
nil if window is not part
of an atomic window.
The most simple approach to make a new atomic window is to take an existing internal window and apply the following function:
This function converts window into an atomic window. The
specified window must be an internal window. All this function
does is to set the
window-atom parameter of each descendant of
To create a new atomic window from an existing live window or to add a new window to an existing atomic window, the following buffer display action function (see Action Functions for Buffer Display) can be used:
This function tries to display buffer in a new window that will be combined with an existing window to form an atomic window. If the existing window is already part of an atomic window, it adds the new window to that atomic window.
The specified alist is an association list of symbols and values. The following symbols have a special meaning:
The value of such an element specifies an existing window the new window
shall be combined with. If it specifies an internal window, all
children of that window become part of the atomic window too. If no
window is specified, the new window becomes a sibling of the selected
window-atom parameter of the existing window is set
main provided that window is live and its
parameter was not already set.
The value of such an element denotes the side of the existing window
where the new window shall be located. Valid values are
left. The default is
window-atom parameter of the new window is set
to this value.
The return value is the new window,
nil when creating that window
Note that the value of the
window-atom parameter does not really
matter as long as it is non-
nil. The values assigned by
display-buffer-in-atom-window just allow for easy retrieval of
the original and the new window after that function has been applied.
Note also that the
window-atom parameter is the only window
parameter assigned by
parameters have to be set by the application explicitly via a
window-parameters entry in alist.
Atomic windows automatically cease to exist when one of their
constituents gets deleted. To dissolve an atomic window manually,
window-atom parameter of its constituents—the root
of the atomic window and all its descendants.
The following code snippet, when applied to a single-window frame, first splits the selected window and makes the selected and the new window constituents of an atomic window with their parent as root. It then displays the buffer *Messages* in a new window at the frame’s bottom and makes that new window part of the atomic window just created.
(let ((window (split-window-right))) (window-make-atom (window-parent window)) (display-buffer-in-atom-window (get-buffer-create "*Messages*") `((window . ,(window-parent window)) (window-height . 5))))
At this moment typing C-x 2 in any window of that frame produces a new window at the bottom of the frame. Typing C-x 3 instead will put the new window at the frame’s right. In either case, typing now C-x 1 in any window of the atomic window will remove the new window only. Typing C-x 0 in any window of the atomic window will make that new window fill the frame.