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NAME
grab - Confine pointer and keyboard events to a window sub-tree
SYNOPSIS
grab ?-global? window
grab option ?arg arg ...?
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DESCRIPTION
This command implements simple pointer and keyboard grabs for Tk. Tk's grabs are different than the grabs described in the Xlib documentation. 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.
Two forms of grabs are possible: local and global. A
Grabs apply to particular displays. If an application has windows on multiple displays then it can establish a separate grab on each display. The grab on a particular display affects only the windows on that display. It is possible for different applications on a single display to have simultaneous local grabs, but only one application can have a global grab on a given display at once.
The grab command can take any of the following forms:
grab ?-global? window
Same as grab set, described below.
grab current
?window?
If window is specified, returns the name of the current grab window in this application for window's display, or an empty string if there is no such window. If window is omitted, the command returns a list whose elements are all of the windows grabbed by this application for all displays, or an empty string if the application has no grabs.
grab release
window
Releases the grab on window if there is one, otherwise does nothing. Returns an empty string.
grab set ?-global?
BUGS
It took an incredibly complex and gross implementation to produce the simple grab effect described above. Given the current implementation, it isn't safe for applications to use the Xlib grab facilities at all except through the Tk grab procedures. If applications try to manipulate X's grab mechanisms directly, things will probably break.
If a single process is managing several different Tk applications, only one of those applications can have a local grab for a given display at any given time. If the applications are in different processes, this restriction doesn't exist.
KEYWORDS
grab, keyboard events, pointer events, window