grab(3pm)						User Contributed Perl Documentation						 grab(3pm)

NAME

       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

perl v5.14.2							    2010-05-29								 grab(3pm)