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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  GCFore‐
					     ground  or	 GCStipple) indicating
					     which  fields  of	*valuePtr  are
					     valid.

       XGCValues *valuePtr (in)		     Pointer  to  structure describing
					     the desired values for the graph‐
					     ics context.

       Display *display (in)		     Display  for  which  gc was allo‐
					     cated.

       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 cre‐
       ated.  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 con‐
       text 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

Tk								   Tk_GetGC(3)
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