Tk_GetGC — C Library Procedures

NAME

Tk_GetGC, Tk_FreeGC − maintain database of read-only graphics contexts

SYNOPSIS

#include <tk.h>
GC
Tk_GetGC(tkwin, valueMask, valuePtr)
Tk_FreeGC(gc)

ARGUMENTS

Tk_Windowtkwin(in) Token for window in which the graphics context will be used.

unsigned longvalueMask(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.

GCgc(in) X identifier for graphics context that is no longer needed.

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 and Tk_GetGCFromData maintain a database of all the graphics contexts they have created. Whenever possible, a call to Tk_GetGC or Tk_GetGCFromData 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