02-14-2014
Quote:
Originally Posted by
coolatt
but my question is at a much lower level how the code accesses the bare graphics card?
Nobody except graphics card manufacturers has programmed graphics cards at the bare metal for over 20 years. If you want the best performance, you use the drivers they make. For UNIX, that mostly means using the drivers they make for X11.
Memory-mapped I/O is often involved, yes.
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LEARN ABOUT CENTOS
tk_getgc
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
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 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)