On Thu, 16 Sep 1999 18:37:29 +0200, Tomas Plachetka wrote:
>however, i'm more interested in what would happen if the
>mosaic preview were not used. would the radiosity code
>still work? would it just run slower? would the quality 
>of the rendering suffer?

I think it would just run more slowly.  As far as I can tell, the
main purpose of the mosaic preview is to seed the cache with some 
good candidates for later lookups.  

However, I'm betting that removing the mosaic preview step would
still not solve the discontinuities you get when you render in
parallel.  I'm not sure I see any way to eliminate those.  You 
could eliminate half of them by making every other band render
from bottom to top, but that would probably make the other half
worse.  

Using a mosaic preview of the entire scene on one machine to build 
a cache which you would then send to all the rendering processes
when they start might help, but it still wouldn't be perfect.

The problem is that each process builds its own cache over time, 
and they tend to diverge over time if the processes are doing work 
that varies too much.  The discontinuities at band edges are thus
due to the fact that the process that rendered the first band had a
much larger cache to work from when it rendered the last row of that
band.  One possible solution is to use much smaller bands, on the 
order of a single row of pixels.  Better would be to do that, plus
make all of the running processes share a single cache somehow.
I suspect you'd still get discontinuities that got worse toward the
right edge of the image, though, particularly if you used vastly
different processors or if one or more tasks had much less work to
do.

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