Tk_GetGC(3tk) Tk Library Procedures Tk_GetGC(3tk)
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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.
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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 de-
scribing 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(3tk)
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