path: root/libX11/man/XIfEvent.man

.\" Copyright \(co 1985, 1986, 1987, 1988, 1989, 1990, 1991, 1994, 1996 X Consortium
.\"
.\" Permission is hereby granted, free of charge, to any person obtaining
.\" a copy of this software and associated documentation files (the
.\" "Software"), to deal in the Software without restriction, including
.\" without limitation the rights to use, copy, modify, merge, publish,
.\" distribute, sublicense, and/or sell copies of the Software, and to
.\" permit persons to whom the Software is furnished to do so, subject to
.\" the following conditions:
.\"
.\" The above copyright notice and this permission notice shall be included
.\" in all copies or substantial portions of the Software.
.\"
.\" THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
.\" OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
.\" MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
.\" IN NO EVENT SHALL THE X CONSORTIUM BE LIABLE FOR ANY CLAIM, DAMAGES OR
.\" OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
.\" ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
.\" OTHER DEALINGS IN THE SOFTWARE.
.\"
.\" Except as contained in this notice, the name of the X Consortium shall
.\" not be used in advertising or otherwise to promote the sale, use or
.\" other dealings in this Software without prior written authorization
.\" from the X Consortium.
.\"
.\" Copyright \(co 1985, 1986, 1987, 1988, 1989, 1990, 1991 by
.\" Digital Equipment Corporation
.\"
.\" Portions Copyright \(co 1990, 1991 by
.\" Tektronix, Inc.
.\"
.\" Permission to use, copy, modify and distribute this documentation for
.\" any purpose and without fee is hereby granted, provided that the above
.\" copyright notice appears in all copies and that both that copyright notice
.\" and this permission notice appear in all copies, and that the names of
.\" Digital and Tektronix not be used in in advertising or publicity pertaining
.\" to this documentation without specific, written prior permission.
.\" Digital and Tektronix makes no representations about the suitability
.\" of this documentation for any purpose.
.\" It is provided ``as is'' without express or implied warranty.
.\" 
.\"
.ds xT X Toolkit Intrinsics \- C Language Interface
.ds xW Athena X Widgets \- C Language X Toolkit Interface
.ds xL Xlib \- C Language X Interface
.ds xC Inter-Client Communication Conventions Manual
.na
.de Ds
.nf
.\\$1D \\$2 \\$1
.ft CW
.\".ps \\n(PS
.\".if \\n(VS>=40 .vs \\n(VSu
.\".if \\n(VS<=39 .vs \\n(VSp
..
.de De
.ce 0
.if \\n(BD .DF
.nr BD 0
.in \\n(OIu
.if \\n(TM .ls 2
.sp \\n(DDu
.fi
..
.de IN		\" send an index entry to the stderr
..
.de Pn
.ie t \\$1\fB\^\\$2\^\fR\\$3
.el \\$1\fI\^\\$2\^\fP\\$3
..
.de ZN
.ie t \fB\^\\$1\^\fR\\$2
.el \fI\^\\$1\^\fP\\$2
..
.de hN
.ie t <\fB\\$1\fR>\\$2
.el <\fI\\$1\fP>\\$2
..
.ny0
.TH XIfEvent __libmansuffix__ __xorgversion__ "XLIB FUNCTIONS"
.SH NAME
XIfEvent, XCheckIfEvent, XPeekIfEvent \- check the event queue with a predicate procedure
.SH SYNTAX
.HP
int XIfEvent\^(\^Display *\fIdisplay\fP\^, XEvent *\fIevent_return\fP\^, Bool
(\^*\fIpredicate\fP\^)\^(\^)\^, XPointer \fIarg\fP\^); 
.HP
Bool XCheckIfEvent\^(\^Display *\fIdisplay\fP\^, XEvent *\fIevent_return\fP\^,
Bool (\^*\fIpredicate\fP\^)\^(\^)\^, XPointer \fIarg\fP\^); 
.HP
int XPeekIfEvent\^(\^Display *\fIdisplay\fP\^, XEvent *\fIevent_return\fP\^,
Bool (\^*\fIpredicate\fP\^)\^(\^)\^, XPointer \fIarg\fP\^); 
.SH ARGUMENTS
.IP \fIarg\fP 1i
Specifies the user-supplied argument that will be passed to the predicate procedure.
.IP \fIdisplay\fP 1i
Specifies the connection to the X server.
.ds Ev \ either a copy of or 
.IP \fIevent_return\fP 1i
Returns\*(Ev the matched event's associated structure.
.IP \fIpredicate\fP 1i
Specifies the procedure that is to be called to determine
if the next event in the queue matches what you want.
.SH DESCRIPTION
The
.ZN XIfEvent
function completes only when the specified predicate
procedure returns 
.ZN True 
for an event, 
which indicates an event in the queue matches.
.ZN XIfEvent
flushes the output buffer if it blocks waiting for additional events.
.ZN XIfEvent
removes the matching event from the queue 
and copies the structure into the client-supplied
.ZN XEvent
structure.
.LP
When the predicate procedure finds a match,
.ZN XCheckIfEvent
copies the matched event into the client-supplied
.ZN XEvent
structure and returns 
.ZN True .
(This event is removed from the queue.)
If the predicate procedure finds no match,
.ZN XCheckIfEvent
returns
.ZN False ,
and the output buffer will have been flushed.
All earlier events stored in the queue are not discarded.
.LP
The
.ZN XPeekIfEvent
function returns only when the specified predicate
procedure returns 
.ZN True
for an event.
After the predicate procedure finds a match,
.ZN XPeekIfEvent
copies the matched event into the client-supplied
.ZN XEvent
structure without removing the event from the queue.
.ZN XPeekIfEvent
flushes the output buffer if it blocks waiting for additional events.
.LP
Each of these functions requires you to pass a predicate procedure that 
determines if an event matches what you want.
Your predicate procedure must decide if the event is useful
without calling any Xlib functions.
If the predicate directly or indirectly causes the state of the event queue
to change, the result is not defined.
If Xlib has been initialized for threads, the predicate is called with
the display locked and the result of a call by the predicate to any
Xlib function that locks the display is not defined unless the caller
has first called
.ZN XLockDisplay .
.LP
The predicate procedure and its associated arguments are:
.HP
Bool (\^*\fIpredicate\fP\^)\^(\^Display *\fIdisplay\fP, XEvent *\fIevent\fP, XPointer \fIarg\fP\^)
.IP \fIdisplay\fP 1i
Specifies the connection to the X server.
.IP \fIevent\fP 1i
Specifies the
.ZN XEvent
structure.
.IP \fIarg\fP 1i
Specifies the argument passed in from the 
.ZN XIfEvent ,
.ZN XCheckIfEvent ,
or
.ZN XPeekIfEvent 
function.
.LP
The predicate procedure is called once for each
event in the queue until it finds a match. 
After finding a match, the predicate procedure must return 
.ZN True .
If it did not find a match, it must return
.ZN False .
.SH "SEE ALSO"
XAnyEvent(__libmansuffix__),
XNextEvent(__libmansuffix__),
XPutBackEvent(__libmansuffix__)
XSendEvent(__libmansuffix__)
.br
\fI\*(xL\fP