Ron Parker <ron### [at] povrayorg> wrote:

> 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.

You may be right, though it does bring up an interesting question.  If I do
a CSG intersection between two objects with different interiors.  What does
it do for media and ior and the like?  It would seem that that you could CSG
up any mesh you wanted, though it'd be painful to do that way, with each
surface with the desired interiors, but I'm not certain about the results. 
So what happens?

Geoff

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