In article <3d62e0ae@news.povray.org>, Warp <war### [at] tagpovrayorg> 
wrote:

>   But how do you get the "ray's next intersection" without shooting a new
> ray in the same direction as the original ray, starting from the first
> intersection point?

You already found it, you just rejected it because the first 
intersection was closer. Generate a sorted list of the intersections 
instead and step along it until you find a refracting or opaque surface.


>   Besides, how does the engine decide that the surface is completely
> invisible?

No ior specified (this is not the same as an ior of 1), a solid pigment 
of rgbf and/or rgbt 1, and no funny finish stuff. Or a simple 
"is_container" flag.


>   And even if we had a "completely invisible" type of object, what would
> be the use for this kind of object? If it's completely ignored in the
> intersection tests, that would be the same thing as not having the object
> in the scene at all. What's the use of this kind of non-existent object?

Media containers. The intersection wouldn't be totally ignored, ray 
entry/exit would still be tracked, but no texture calculations would be 
done and trace level wouldn't be incremented.
A similar thing would apply to transparent but non-refracting surfaces.

-- 
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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