Tk_RestrictEvents(3)					       Tk Library Procedures					      Tk_RestrictEvents(3)

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NAME

       Tk_RestrictEvents - filter and selectively delay X events

SYNOPSIS

       #include <tk.h>

       Tk_RestrictProc *
       Tk_RestrictEvents(proc, clientData, prevClientDataPtr)

ARGUMENTS

       Tk_RestrictProc *proc (in)			 Predicate  procedure  to  call  to  filter incoming X events.	NULL means do not restrict
							 events at all.

       ClientData clientData (in)			 Arbitrary argument to pass to proc.

       ClientData *prevClientDataPtr (out)		 Pointer to place to save argument to previous restrict procedure.
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DESCRIPTION

       This procedure is useful in certain situations where applications are only prepared to receive certain X events.   After  Tk_RestrictEvents
       is  called,  Tk_DoOneEvent  (and hence Tk_MainLoop) will filter X input events through proc.  Proc indicates whether a given event is to be
       processed immediately, deferred until some later time (e.g. when the event restriction is lifted), or discarded.  Proc is a procedure  with
       arguments and result that match the type Tk_RestrictProc:
	      typedef Tk_RestrictAction Tk_RestrictProc(
		  ClientData clientData,
		  XEvent *eventPtr);
       The  clientData	argument is a copy of the clientData passed to Tk_RestrictEvents; it may be used to provide proc with information it needs
       to filter events.  The eventPtr points to an event under consideration.	Proc returns a restrict action (enumerated type Tk_RestrictAction)
       that  indicates what Tk_DoOneEvent should do with the event.  If the return value is TK_PROCESS_EVENT, then the event will be handled imme-
       diately.  If the return value is TK_DEFER_EVENT, then the event will be left on the event queue for later processing.  If the return  value
       is TK_DISCARD_EVENT, then the event will be removed from the event queue and discarded without being processed.

       Tk_RestrictEvents  uses	its return value and prevClientDataPtr to return information about the current event restriction procedure (a NULL
       return value means there are currently no restrictions).  These values may be used to restore the previous restriction state when there	is
       no longer any need for the current restriction.

       There  are  very  few places where Tk_RestrictEvents is needed.	In most cases, the best way to restrict events is by changing the bindings
       with the bind Tcl command or by calling Tk_CreateEventHandler and Tk_DeleteEventHandler from C.	The  main  place  where  Tk_RestrictEvents
       must  be used is when performing synchronous actions (for example, if you need to wait for a particular event to occur on a particular win-
       dow but you do not want to invoke any handlers for any other events).  The "obvious" solution in these situations is to call XNextEvent	or
       XWindowEvent,  but  these procedures cannot be used because Tk keeps its own event queue that is separate from the X event queue.  Instead,
       call Tk_RestrictEvents to set up a filter, then call Tk_DoOneEvent to retrieve the desired event(s).

KEYWORDS

       delay, event, filter, restriction

Tk															      Tk_RestrictEvents(3)