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Tk_RestrictEvents(3tk) Tk Library Procedures Tk_RestrictEvents(3tk) 





NAME


Tk_RestrictEvents - filter and selectively delay X events






SYNOPSIS


#include <tk.h>

Tk_RestrictProc *
Tk_RestrictEvents(proc, arg, prevArgPtr)






ARGUMENTS



  
Tk_RestrictProc *proc (in)

  
Predicate procedure to call to filter incoming X events. NULL means do not
      restrict events at all.

  
void *arg (in)

  
Arbitrary argument to pass to proc.

  
void **prevArgPtr (out)

  
Pointer to place to save argument to previous restrict procedure.
    
    

    

  








DESCRIPTION


This procedure is useful in certain situations where applications
    are only prepared to receive certain X events. After
    Tk_RestrictEvents is called, Tcl_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(


        void *arg,


        XEvent *eventPtr);



The arg argument is a copy of the arg 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 Tcl_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
    prevArgPtr 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 Tcl_DoOneEvent to retrieve the desired
    event(s).






KEYWORDS


delay, event, filter, restriction







  

    
    Tk