This command implements simple pointer grabbing for Tk.
When a grab is set for a particular window, Tk restricts all pointer
events to the grab window and its descendants in Tk's window hierarchy.
Whenever the pointer is within the grab window's subtree, the pointer
will behave exactly the same as if there had been no grab at all
and all events will be reported in the normal fashion.
When the pointer is outside window's tree, button presses and
releases and
mouse motion events are reported to window, and window entry
and window exit events are ignored.
The grab subtree ``owns'' the pointer:
windows outside the grab subtree will be visible on the screen
but they will be insensitive until the grab is released.
The tree of windows underneath the grab window can include top-level
windows, in which case all of those top-level windows
and their descendants will continue to receive mouse events
during the grab.
A grab locks out all applications on the screen,
so that only the given subtree of the grabbing application will be
sensitive to pointer events (mouse button presses, mouse button releases,
pointer motions, window entries, and window exits).
During grabs the window manager will not receive pointer
events either (which means that if the grab is not released
the whole GUI will freeze, so be careful!).
The grab command can take any of the following forms:
- grab release window
- Releases the grab on window if there is one, otherwise does
nothing. Returns an empty string.
- grab set window
- If a grab was already in effect for this application on
window's display then it is automatically released.
If there is already a grab on window then the command
does nothing. Returns an empty string.
- grab ifunset window
- Same as
grab set
except that window is only grabbed if there is no
other grab currently in effect.
- grab status window
- Returns none if no grab is currently set on window,
or
window if it has the grab.