Provided by: perl-tk_804.036+dfsg1-3_amd64 
NAME
Tk::grab - Confine pointer and keyboard events to a window sub-tree
SYNOPSIS
$widget->grab
$widget->grabOption
DESCRIPTION
This set of methods implement 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 $widget's
tree, button presses and releases and mouse motion events are reported to $widget, 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 local grab affects only the grabbing application:
events will be reported to other applications as if the grab had never occurred. Grabs are local by
default. A global 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 global grabs the window manager will not
receive pointer events either.
During local grabs, keyboard events (key presses and key releases) are delivered as usual: the window
manager controls which application receives keyboard events, and if they are sent to any window in the
grabbing application then they are redirected to the focus window. During a global grab Tk grabs the
keyboard so that all keyboard events are always sent to the grabbing application. The focus method is
still used to determine which window in the application receives the keyboard events. The keyboard grab
is released when the grab is released.
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 methods take any of the following forms:
$widget->grabCurrent
Returns the current grab window in this application for $widget's display, or an empty string if
there is no such window.
$widget->grabs
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.
Not implemented yet!
$widget->grabRelease
Releases the grab on $widget if there is one, otherwise does nothing. Returns an empty string.
$widget->grab
Sets a local grab on $widget. If a grab was already in effect for this application on $widget's
display then it is automatically released. If there is already a local grab on $widget, then the
command does nothing. Returns an empty string.
$widget->grabGlobal
Sets a global grab on $widget. If a grab was already in effect for this application on $widget's
display then it is automatically released. If there is already a global grab on $widget, then the
command does nothing. Returns an empty string.
$widget->grabStatus
Returns none if no grab is currently set on $widget, local if a local grab is set on $widget, and
global if a global grab is set.
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