Lukas Winter schrieb:
> 
> The existing cache explicitely excludes shadow rays. It also does a poor 
> job when there are several isosurfaces in the scene. The reason is that 
> most of the time subsequent tests come in the same order, i.e. several 
> _different_ kinds of tests repeat in a certain order but the cache only 
> speeds up _similiar_ rays. So one cache entry overrides another and there 
> are a lot of cache misses that could have been avoided if the cache kept 
> older entries. On the other hand the cache should not be too big to avoid 
> expensive tests against very old entries. I usually use 2 or 3 cache 
> entries per isosurface.

is this cache per thread or global?  The former would make more sense 
since the rays are only correlated in a thread and not between several 
ones.  Also it would make sense to exclude radiosity rays.

> The code tries to move the point where it splits the current interval in 
> two intervals to a better place under some circumstances. But a speed-up 
> thanks to this is very rare.

Sounds much like the sphere tracing technique to me - i once tried this 
and it did not seem to be have a significant advantage to me.  Some more 
on this can be found in stuff on:

http://graphics.cs.uiuc.edu/~jch/papers/?cat=implicit

If more information is known about the isosurface function things can be 
different of course.

-- Christoph

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