Re: Scanline Smear...

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Angus Dorbie (dorbie++at++sgi.com)
Thu, 19 Mar 1998 11:41:37 -0800

Dan Brockway wrote:
>
> We at Paradigm use a similar technique in domes with our Non-Linear
> Distortion Correction module. 60Hz can be maintained. But beware, more
> than half of the 16.6ms frame will be spent copying the frame buffer to
> texture memory.

I just wanted to chip in here since times provided without context can
mislead. The image readback time is entirely dependent on the
resolution and number of readbacks to texture memory.

Please tell it like it is, without simplification. At 1024x768++at++60Hz the
readback time is around 50% but change frame rate or resolution and the
ratio will change dramatically. I got the impression that the resolution
of the slewed scanline problem was low and so readback overhead could be
fairly small.

Given the number of copypixels requests in my earlier advice I'd like to
encourage you to explore readback to texture memory and drawing on quads
or parallelograms. For high slew rates the overhead of the slew may
cause
excessive overdraw requirements so I suspect you still want to split the
channel up into multiple sub channels and go for a hybrid approach.

Cheers,Angus.

-- 
"Only the mediocre are always at their best." -- Jean Giraudoux 


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