In article <pan### [at] gtenet>,
 Mark Wagner <mar### [at] gtenet> wrote:

> If you could create the glass without an inner surface (perhaps by using
> clipped_by), you would get the most realistic performance, since the ray
> would go directly from glass to water, without passing through a layer of
> air.

If you cut away the water surface, the ray never "enters" the water 
object. If you cut away the glass surface, it won't leave the glass 
object until it reaches the other side of the cup, if it exits through 
the top of the cup it will never become "outside" the cup.

As Ron Parker explained though, when there is an overlap the glass/water 
transition is handled as it should be and the ior of the redundant 
surface is ignored, so you don't need any special CSG. Still, there are 
two extra surfaces in the body of the glass...that just bugs me, having 
6 surfaces where 4 should be sufficient.

Maybe it would be possible to specify interior transitions on a 
per-surface basis...instead of a "water object" and a "glass object", 
the glass of water situation would be 3 separate surfaces: glass-air, 
glass-water, and water-air. The modelling would be more difficult...it'd 
probably only be worth it for a scene with a lot of glasses and bottles 
of liquids (a lab or bar?) or if it was somehow automatically generated 
(back to the immerse CSG?). Maybe a good trick for a real-time raytracer 
though.

-- 
Christopher James Huff <chr### [at] maccom>
POV-Ray TAG e-mail: chr### [at] tagpovrayorg
TAG web site: http://tag.povray.org/

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