A frame on a graphical display may be visible, invisible, or iconified. If it is visible, its contents are displayed in the usual manner. If it is iconified, its contents are not displayed, but there is a little icon somewhere to bring the frame back into view (some window managers refer to this state as minimized rather than iconified, but from Emacs’ point of view they are the same thing). If a frame is invisible, it is not displayed at all.
The concept of visibility is strongly related to that of (un-)mapped frames. A frame (or, more precisely, its window-system window) is and becomes mapped when it is displayed for the first time and whenever it changes its state of visibility from iconified or invisible to visible. Conversely, a frame is and becomes unmapped whenever it changes its status from visible to iconified or invisible.
Visibility is meaningless on text terminals, since only the selected frame is actually displayed in any case.
This function returns the visibility status of frame frame. The value is t if frame is visible, nil if it is invisible, and icon if it is iconified.
On a text terminal, all frames are considered visible for the purposes of this function, even though only one frame is displayed. See Raising and Lowering.
This function iconifies frame frame. If you omit frame, it iconifies the selected frame. This usually makes all child frames of frame (and their descendants) invisible (see Child Frames).
This function makes frame frame visible. If you omit frame, it makes the selected frame visible. This does not raise the frame, but you can do that with raise-frame if you wish (see Raising and Lowering).
Making a frame visible usually makes all its child frames (and their descendants) visible as well (see Child Frames).
This function makes frame frame invisible. If you omit frame, it makes the selected frame invisible. Usually, this makes all child frames of frame (and their descendants) invisible too (see Child Frames).
Unless force is non-nil, this function refuses to make frame invisible if all other frames are invisible.
The visibility status of a frame is also available as a frame parameter. You can read or change it as such. See Management Parameters. The user can also iconify and deiconify frames with the window manager. This happens below the level at which Emacs can exert any control, but Emacs does provide events that you can use to keep track of such changes. See Misc Events.
This function returns non-nil if frame is currently being rendered with double buffering. frame defaults to the selected frame.
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Licensed under the GNU GPL license.
https://www.gnu.org/software/emacs/manual/html_node/elisp/Visibility-of-Frames.html