bionic (3) Tk_GetGC.3tk.gz

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) 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