Re: acbuffer problem

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Ran Yakir (rany++at++bvr.co.il)
Tue, 26 Sep 1995 15:16:40 +0000

On Sep 25, 3:11pm, Glenn Waldron wrote:
> Subject: acbuffer problem
>
> I use the accumulation buffer to do motion blurring. I set it up,
> in the open-pipeline callback:
>
> drawmode(NORMALDRAW);
> acsize(12);
> gconfig();
> ...
>
> and I use it in the post-draw callback:
>
> acbuf(AC_MULT, blur);
> acbuf(AC_ACCUMULATE, 1.0);
> acbuf(AC_RETURN, blur);
> ...
>
>
> This always worked fine. In a 800x600 window, I got a consistent
> 30 hertz frame rate on a 1-RM 2-CPU Onyx (with limiting turned on).
> Today, SGI came and installed a second RM4 board. Now I get a
> consistant 8.6 hertz running the same program. Taking out the three
> calls to acbuf() in the post-draw callback alleviates the problem.
> What's happening?
>
> Thanks, Glenn.
>
>
>-- End of excerpt from Glenn Waldron

It seems that acbuf performance is very poor when in multisample mode. Maybe
someone from SGI could answer why. It would be logical to sample the final
frame buffer into the accumulation buffer. However, it seems that the acbuf()
command does something with the sub-samples.
Anyway, Glenn's problem is that, while he had ony 1 RM, he ran with no
multisampling (default Performer behaviour for 1 RM, 1280x1024 vof). When an
additional RM was added, there was suddenly enough room for 8 samples, and
Performer goes into multisample mode.
If you turn off multisampling by pfAntialias(PFAA_OFF), you'll get back to your
fine performance.

Ran

-- 
 __                                  | Ran Yakir
 /_)  _  __   \  / _   / o __        | Graphics App. Chief Engineer
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