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'\" Copyright (c) 1990 The Regents of the University of California.

'\" Copyright (c) 1994-1996 Sun Microsystems, Inc.

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'\" See the file "license.terms" for information on usage and redistribution

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'\" RCS: @(#) $Id: RestrictEv.3,v 1.1.1.1 2002-01-16 10:25:48 markom Exp $

'\"

.so man.macros

.TH Tk_RestrictEvents 3 "" Tk "Tk Library Procedures"

.BS

.SH NAME

Tk_RestrictEvents \- filter and selectively delay X events

.SH SYNOPSIS

.nf

\fB#include \fR

.sp

Tk_RestrictProc *

\fBTk_RestrictEvents\fR(\fIproc, clientData, prevClientDataPtr\fR)

.SH ARGUMENTS

.AS Tk_RestrictProc **prevClientDataPtr

.AP Tk_RestrictProc *proc in

Predicate procedure to call to filter incoming X events.

NULL means do not restrict events at all.

.AP ClientData clientData in

Arbitrary argument to pass to \fIproc\fR.

.AP ClientData *prevClientDataPtr out

Pointer to place to save argument to previous restrict procedure.

.BE

.SH DESCRIPTION

.PP

This procedure is useful in certain situations where applications

are only prepared to receive certain X events.  After

\fBTk_RestrictEvents\fR is called, \fBTk_DoOneEvent\fR (and

hence \fBTk_MainLoop\fR) will filter X input events through

\fIproc\fR.  \fIProc\fR 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.

\fIProc\fR

is a procedure with arguments and result that match

the type \fBTk_RestrictProc\fR:

.CS

typedef Tk_RestrictAction Tk_RestrictProc(

        ClientData \fIclientData\fR,

        XEvent *\fIeventPtr\fR);

.CE

The \fIclientData\fR argument is a copy of the \fIclientData\fR passed

to \fBTk_RestrictEvents\fR; it may be used to provide \fIproc\fR with

information it needs to filter events.  The \fIeventPtr\fR points to

an event under consideration.  \fIProc\fR returns a restrict action

(enumerated type \fBTk_RestrictAction\fR) that indicates what

\fBTk_DoOneEvent\fR should do with the event.  If the return value is

\fBTK_PROCESS_EVENT\fR, then the event will be handled immediately.

If the return value is \fBTK_DEFER_EVENT\fR, then the event will be

left on the event queue for later processing.  If the return value is

\fBTK_DISCARD_EVENT\fR, then the event will be removed from the event

queue and discarded without being processed.

.PP

\fBTk_RestrictEvents\fR uses its return value and \fIprevClientDataPtr\fR

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.

.PP

There are very few places where \fBTk_RestrictEvents\fR is needed.

In most cases, the best way to restrict events is by changing the

bindings with the \fBbind\fR Tcl command or by calling

\fBTk_CreateEventHandler\fR and \fBTk_DeleteEventHandler\fR from C.

The main place where \fBTk_RestrictEvents\fR 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 don't

want to invoke any handlers for any other events).  The ``obvious''

solution in these situations is to call \fBXNextEvent\fR or

\fBXWindowEvent\fR, but these procedures cannot be used because

Tk keeps its own event queue that is separate from the X event

queue.  Instead, call \fBTk_RestrictEvents\fR to set up a filter,

then call \fBTk_DoOneEvent\fR to retrieve the desired event(s).

.SH KEYWORDS

delay, event, filter, restriction