Tk_GetGC (3)

SYNOPSIS

#include <tk.h>
GC
Tk_GetGC(tkwin, valueMask, valuePtr)
Tk_FreeGC(display, gc)

ARGUMENTS

"unsigned long" valueMask Tk_Window tkwin in Token for window in which the graphics context will be used. "unsigned long" valueMask in Mask of bits (such as GCForeground or GCStipple) indicating which fields of *valuePtr are valid. XGCValues *valuePtr in Pointer to structure describing the desired values for the graphics context. Display *display in Display for which gc was allocated. GC gc in X identifier for graphics context that is no longer needed. Must have been allocated by Tk_GetGC.

DESCRIPTION

Tk_GetGC and Tk_FreeGC 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. Tk_GetGC 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 valueMask and valuePtr.

Tk_GetGC maintains a database of all the graphics contexts it has created. Whenever possible, a call to Tk_GetGC will return an existing graphics context rather than creating a new one. This approach can substantially reduce server overhead, so Tk_GetGC should generally be used in preference to the Xlib procedure XCreateGC, which creates a new graphics context on each call.

Since the return values of Tk_GetGC are shared, callers should never modify the graphics contexts returned by Tk_GetGC. If a graphics context must be modified dynamically, then it should be created by calling XCreateGC instead of Tk_GetGC.

When a graphics context is no longer needed, Tk_FreeGC should be called to release it. There should be exactly one call to Tk_FreeGC for each call to Tk_GetGC. When a graphics context is no longer in use anywhere (i.e. it has been freed as many times as it has been gotten) Tk_FreeGC will release it to the X server and delete it from the database.

KEYWORDS

graphics context '\" '\" Copyright (c) 1994 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: GetImage.3,v 1.2 1998/09/14 18:22:49 stanton Exp $ '\" '\" The definitions below are for supplemental macros used in Tcl/Tk '\" manual entries. '\" '\" .AP type name in/out ?indent? '\" Start paragraph describing an argument to a library procedure. '\" type is type of argument (int, etc.), in/out is either "in", "out", '\" or "in/out" to describe whether procedure reads or modifies arg, '\" and indent is equivalent to second arg of .IP (shouldn't ever be '\" needed; use .AS below instead) '\" '\" .AS ?type? ?name? '\" Give maximum sizes of arguments for setting tab stops. Type and '\" name are examples of largest possible arguments that will be passed '\" to .AP later. If args are omitted, default tab stops are used. '\" '\" .BS '\" Start box enclosure. From here until next .BE, everything will be '\" enclosed in one large box. '\" '\" .BE '\" End of box enclosure. '\" '\" .CS '\" Begin code excerpt. '\" '\" .CE '\" End code excerpt. '\" '\" .VS ?version? ?br? '\" Begin vertical sidebar, for use in marking newly-changed parts '\" of man pages. The first argument is ignored and used for recording '\" the version when the .VS was added, so that the sidebars can be '\" found and removed when they reach a certain age. If another argument '\" is present, then a line break is forced before starting the sidebar. '\" '\" .VE '\" End of vertical sidebar. '\" '\" .DS '\" Begin an indented unfilled display. '\" '\" .DE '\" End of indented unfilled display. '\" '\" .SO '\" Start of list of standard options for a Tk widget. The '\" options follow on successive lines, in four columns separated '\" by tabs. '\" '\" .SE '\" End of list of standard options for a Tk widget. '\" '\" .OP cmdName dbName dbClass '\" Start of description of a specific option. cmdName gives the '\" option's name as specified in the class command, dbName gives '\" the option's name in the option database, and dbClass gives '\" the option's class in the option database. '\" '\" .UL arg1 arg2 '\" Print arg1 underlined, then print arg2 normally. '\" '\" RCS: @(#) $Id: man.macros,v 1.2 1998/09/14 18:39:54 stanton Exp $ '\" '\" # Set up traps and other miscellaneous stuff for Tcl/Tk man pages. t .wh -1.3i ^B ^l \n(.l b '\" # Start an argument description AP !"\\$4"" .TP \\$4 \{\ !"\\$2"" .TP \\n()Cu .TP 15