Tk Library Procedures
Tk_GetGC, Tk_FreeGC - maintain database of read-only graphics contexts
Tk_GetGC(tkwin, valueMask, valuePtr)
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
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.
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.
[ tcl8.0a1 | tk8.0a1 | X-ref ]
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