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