Le 2021-11-10 à 17:06, Samuel B. a écrit :
> Thomas de Groot <tho### [at] degrootorg> wrote:
>> Op 09/11/2021 om 20:02 schreef Kenneth:
>>>
>>> BTW, I did not realize that an object with ior could have inclusions (other
>>> objects) with *different* ior's-- I thought such constructs would be an example
>>> of 'variable' ior within an object, which cannot be accomplished in POV-ray,
>>> AFAIU. I had a mistaken notion that the camera ray would 'see' the outer object
>>> surface first, (...)
>>>
>> To tell the truth, I really do not know /how/ the different ior's are
>> treated together. Afaik, this is not explained in the wiki pages. To
>> keep on the safe side, I kept the inclusion's ior at 1.0 which is
>> cheating of course, but at least I was not confronted to strange
>> effects.
> 
> If I'm not mistaken, a ray evaluates all objects and their iors along its path
> and changes its trajectory accordingly. So in a union, it is not really
> 'cheating' to have objects with an ior of 1 inside. They are treated as air
> until the ray moves on. It's a reasonable alternative to using a difference
> which - while not requiring objects with different iors - is very slow to trace.
> 
> Oh, and a while back, I found out that if you want to pretend that the camera is
> inside some volume, say water, and you want to see air bubbles in that volume,
> then for the air bubbles you would use the reciprocal of water's ior. So, the
> bubbles would have an ior of 1/1.325, iinm.
> 
> Sam
> 

If you want to use a difference, then, you should use a blob instead of 
100' to 1000's of spheres.
That way, you benefit from the blob's hierarchy and internal bounding 
mechanism.

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