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'\"
'\" Copyright (c) 1990 The Regents of the University of California.
'\" Copyright (c) 1994-1996 Sun Microsystems, Inc.
'\"
'\" See the file "license.terms" for information on usage and redistribution
'\" of this file, and for a DISCLAIMER OF ALL WARRANTIES.
'\"
'\" RCS: @(#) $Id$
'\"
.so man.macros
.TH Tk_GetGC 3 "" Tk "Tk Library Procedures"
.BS
.SH NAME
Tk_GetGC, Tk_FreeGC \- maintain database of read-only graphics contexts
.SH SYNOPSIS
.nf
\fB#include <tk.h>\fR
.sp
GC
\fBTk_GetGC\fR(\fItkwin, valueMask, valuePtr\fR)
.sp
\fBTk_FreeGC(\fIdisplay, gc\fR)
.SH ARGUMENTS
.AS "unsigned long" valueMask
.AP Tk_Window tkwin in
Token for window in which the graphics context will be used.
.AP "unsigned long" valueMask in
Mask of bits (such as \fBGCForeground\fR or \fBGCStipple\fR)
indicating which fields of \fI*valuePtr\fR are valid.
.AP XGCValues *valuePtr in
Pointer to structure describing the desired values for the
graphics context.
.AP Display *display in
Display for which \fIgc\fR was allocated.
.AP GC gc in
X identifier for graphics context that is no longer needed.
Must have been allocated by \fBTk_GetGC\fR.
.BE
.SH DESCRIPTION
.PP
\fBTk_GetGC\fR and \fBTk_FreeGC\fR manage a collection of graphics contexts
being used by an application. The procedures allow graphics contexts to be
shared, thereby avoiding the server overhead that would be incurred
if a separate GC were created for each use. \fBTk_GetGC\fR takes arguments
describing the desired graphics context and returns an X identifier
for a GC that fits the description. The graphics context that is returned
will have default values in all of the fields not specified explicitly
by \fIvalueMask\fR and \fIvaluePtr\fR.
.PP
\fBTk_GetGC\fR maintains a
database of all the graphics contexts it has created. Whenever possible,
a call to \fBTk_GetGC\fR will
return an existing graphics context rather than creating a new one. This
approach can substantially reduce server overhead, so \fBTk_GetGC\fR
should generally be used in preference to the Xlib procedure
\fBXCreateGC\fR, which creates a new graphics context on each call.
.PP
Since the return values of \fBTk_GetGC\fR
are shared, callers should never modify the graphics contexts
returned by \fBTk_GetGC\fR.
If a graphics context must be modified dynamically, then it should be
created by calling \fBXCreateGC\fR instead of \fBTk_GetGC\fR.
.PP
When a graphics context
is no longer needed, \fBTk_FreeGC\fR should be called to release it.
There should be exactly one call to \fBTk_FreeGC\fR for
each call to \fBTk_GetGC\fR.
When a graphics context is no longer in use anywhere (i.e. it has
been freed as many times as it has been gotten) \fBTk_FreeGC\fR
will release it to the X server and delete it from the database.
.SH KEYWORDS
graphics context
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