[SDL] HW overlays

Birju Shah birju_shah0 at yahoo.com
Thu Jul 11 09:56:01 PDT 2002

There is actually a massive performance difference. 
If you do all writes to video memory it is fine. 
Current generation processors use write combining
buffers to write to AGP memory.  However reads are
still painfully slow.  For most video decoders and
graphics apps you never read from video memory.  For
my non optimized decoder I get a frame rate of 29 FPS
when I do not display (very little time in memcpy from
pixel buffer to video memory).  If I display I get 17
FPS.  When I display almost 40% of the time is spent
in memcpy.  If I could write directly to the frame HW
buffer than none of these memcpys would be required. 
The code I wrote works on windows and linux.  Because
I can write directly to the HW frame buffer in windows
the performance is much better.  That said, do you
know of anyway to access the HW frame buffer directly?
--- "Ryan C. Gordon" <icculus at clutteredmind.org>
> > Hi I am trying to use HW_SURFACE to display some
> > video.  I have a GForce 2 GTS gfx card with the
> latest
> > nvidia drivers on a Red Hat 7.2 system.  This
> should
> > have HW overlay capabilites.  The hw_available
> flag in
> > the SDL_VideoInfo structure returned from
> > SDL_GetVideoInfo() is always set to 0. Do I need
> to
> > install something else to enable this capability?
> > When I call SetVideoMode with with either
> > or SW_SURFACE I see no difference in performance.
> --ryan.
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> SDL at libsdl.org
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