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