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Tk_GetGC(3)	      Tk Library Procedures	      Tk_GetGC(3)

_________________________________________________________________

NAME
       Tk_GetGC,  Tk_FreeGC  -	maintain  database  of	read-only
       graphics contexts

SYNOPSIS
       #include <tk.h>

       GC
       Tk_GetGC(tkwin, valueMask, valuePtr)

       Tk_FreeGC(display, gc)

ARGUMENTS
       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)	 indicat-
					     ing which fields  of
					     *valuePtr are valid.

       XGCValues       *valuePtr   (in)	     Pointer to structure
					     describing	      the
					     desired  values  for
					     the   graphics  con-
					     text.

       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 graph-
       ics  context  that is returned will have default values in
       all of the fields not specified	explicitly  by	valueMask

Tk								1

Tk_GetGC(3)	      Tk Library Procedures	      Tk_GetGC(3)

       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 cre-
       ating 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 dynami-
       cally, 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

Tk								2

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