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