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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  cer-tain certain
       tain  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 con-sideration. consideration.
       sideration.  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 immediately.  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
       window  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)