On 4 Jan 2001 08:33:56 -0500, Geoff Wedig wrote:
>> However, this doesn't change the fact that changing the way media is 
>> calculated for triangles with different interiors would break existing 
>> functionality.
>
>I don't see that it'd *break* functionality.  If there's a constant ior,
>then everything should be as before.  I do see a number of big problems for
>it, though (which I've posted elsewhere)

You don't need a constant IOR either.  The same example I gave for media,
that of a cube inside another cube, could apply to different IOR as well.
The point is, POV doesn't keep track of what *objects* it is in, it keeps
track of what *interiors* it is in.  Refraction, media, attenuation, and
other interior effects are calculated when the ray hits a given interior
again, without regard for whether it's still in the object.  (This isn't
exactly true, in that if the interiors don't "pair" right it will get
even more hopelessly confused, but it's close enough for our purposes.)
If you change the way POV acts when it encounters a surface with a different
interior from the last one it hit, you invalidate this method of bookkeeping.

If you invalidate this method of bookkeeping, you destroy the existing 
property that allows well-formed unions of polygons, triangles, discs, 
bezier patches, open cylinders and other surfaces of revolution, and other
patch objects to be treated as solid for the purposes of refraction, media,
attenuation, and so on.

-- 
Ron Parker   http://www2.fwi.com/~parkerr/traces.html
My opinions.  Mine.  Not anyone else's.

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