In article <3d635bd4@news.povray.org>, Warp <war### [at] tagpovrayorg> 
wrote:

>   First it's "the intersection with an invisible object should be ignored"
> and now it should not be ignored, but taken into account.
>   Can you people decide whether to make the intersection calculation or not?

It is ignored as far as texturing and lighting is concerned, only the 
media matters. Or you could extend it to work with non-refracting 
transparency, in which case it simply wouldn't cast extra rays for 
intersection calculations it has already done.


>   And not incrementing the trace level counter does not mean that there
> wouldn't be as many recursion levels as intersections.

Depends on what you mean by "recursion levels". Non-refracting 
transparency would not require any new rays to be traced, so the 
overhead will be much lower.


> > A similar thing would apply to transparent but non-refracting surfaces.
> 
>   You still need the intersection points. In order to get the intersection
> points, you need to trace rays.

Of course. Avoiding the calculation isn't the point, avoiding 
recalculation of the same intersections is.
As I said above, make a list of intersections instead of throwing away 
the farther ones. Do this once instead of recomputing them for every 
transparent non-refracting surface. For scenes with a lot of media 
containers (particle system smoke being a good example) this would be a 
lot faster. All the intersections would be found the first time around, 
and the code would step through the list instead of tracing additional 
rays.

This would be easy without the bounding, but I don't know how well it 
could be integrated with the bounding tree code. One possible problem is 
that it seems to ignore objects whose bounding boxes are further than 
the nearest intersection point, this logic would need to be extended to 
only ignore objects with bounding boxes further than the nearest opaque 
and non-refracting intersection, and it will have to return a list of 
all valid intersections instead of just the nearest one.

-- 
Christopher James Huff <cja### [at] earthlinknet>
http://home.earthlink.net/~cjameshuff/
POV-Ray TAG: chr### [at] tagpovrayorg
http://tag.povray.org/

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