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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

       Token  for  window in which the graphics context will be used.  Mask of
       bits (such as GCForeground or GCStipple)  indicating  which  fields  of
       *valuePtr  are valid.  Pointer to structure describing the desired val-
       ues for the graphics context.  Display for which gc was  allocated.   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)

GetGC 8.5.4 - Generated Sat Aug 23 16:23:36 CDT 2008
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