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'\"
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'\" Copyright (c) 1990 The Regents of the University of California.
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'\" Copyright (c) 1994-1996 Sun Microsystems, Inc.
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'\"
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'\" See the file "license.terms" for information on usage and redistribution
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'\" of this file, and for a DISCLAIMER OF ALL WARRANTIES.
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'\"
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'\" RCS: @(#) $Id: GetGC.3,v 1.1.1.1 2002-01-16 10:25:48 markom Exp $
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'\"
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.so man.macros
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.TH Tk_GetGC 3 "" Tk "Tk Library Procedures"
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.BS
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.SH NAME
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Tk_GetGC, Tk_FreeGC \- maintain database of read-only graphics contexts
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.SH SYNOPSIS
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.nf
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\fB#include \fR
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.sp
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GC
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\fBTk_GetGC\fR(\fItkwin, valueMask, valuePtr\fR)
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.sp
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\fBTk_FreeGC(\fIdisplay, gc\fR)
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.SH ARGUMENTS
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.AS "unsigned long" valueMask
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.AP Tk_Window tkwin in
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Token for window in which the graphics context will be used.
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.AP "unsigned long" valueMask in
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Mask of bits (such as \fBGCForeground\fR or \fBGCStipple\fR)
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indicating which fields of \fI*valuePtr\fR are valid.
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.AP XGCValues *valuePtr in
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Pointer to structure describing the desired values for the
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graphics context.
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.AP Display *display in
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Display for which \fIgc\fR was allocated.
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.AP GC gc in
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X identifier for graphics context that is no longer needed.
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Must have been allocated by \fBTk_GetGC\fR.
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.BE
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.SH DESCRIPTION
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.PP
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\fBTk_GetGC\fR and \fBTk_FreeGC\fR manage a collection of graphics contexts
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being used by an application. The procedures allow graphics contexts to be
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shared, thereby avoiding the server overhead that would be incurred
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if a separate GC were created for each use. \fBTk_GetGC\fR takes arguments
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describing the desired graphics context and returns an X identifier
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for a GC that fits the description. The graphics context that is returned
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will have default values in all of the fields not specified explicitly
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by \fIvalueMask\fR and \fIvaluePtr\fR.
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.PP
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\fBTk_GetGC\fR maintains a
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database of all the graphics contexts it has created. Whenever possible,
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a call to \fBTk_GetGC\fR will
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return an existing graphics context rather than creating a new one. This
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approach can substantially reduce server overhead, so \fBTk_GetGC\fR
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should generally be used in preference to the Xlib procedure
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\fBXCreateGC\fR, which creates a new graphics context on each call.
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.PP
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Since the return values of \fBTk_GetGC\fR
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are shared, callers should never modify the graphics contexts
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returned by \fBTk_GetGC\fR.
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If a graphics context must be modified dynamically, then it should be
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created by calling \fBXCreateGC\fR instead of \fBTk_GetGC\fR.
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.PP
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When a graphics context
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is no longer needed, \fBTk_FreeGC\fR should be called to release it.
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There should be exactly one call to \fBTk_FreeGC\fR for
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each call to \fBTk_GetGC\fR.
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When a graphics context is no longer in use anywhere (i.e. it has
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been freed as many times as it has been gotten) \fBTk_FreeGC\fR
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will release it to the X server and delete it from the database.
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.SH KEYWORDS
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graphics context
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