TinCanMan wrote:

>> IMO it is a bug in POV-Ray. The ray passes through the box and is
> refracted
>> when it leaves it. That means it is refracted even though the ior before
>> the hit and after the hit both are 1.0.
> 
> This is not a bug, it is the intended operation as AFAIK.  Even though ior
> is specified in 'interior'  it isn't treated as an interior property but
> rather acts only on surfaces.  This is whay you can't have ior mapping or
> variable iors within a single object.  When a ray passes through a surface
> it is refracted according to the iors at that surface.  In your example
> only the surface of the intersection that belonged to the box with an ior
> of 1 has an ior of 1, the other surface has the ior of 1.2 so when the ray
> hits this face, with the 1.2 ior, it gets refracted as if the interior had
> an ior of 1.2 and the exterior had an ior of 1.
> 

I do not think this behavior can be intended.

From the documentation part 6.6.1
"... It is totally illogical to have a ray enter an object with one index 
or refraction and then recalculate with another index. The result is not an 
average of the two ior values. Similarly it makes no sense to have a ray 
enter at one ior and exit at a different ior without transitioning between 
them along the way. ..."

That is the reason why ior was moved from finish to interior. But exactly 
what one wanted to prevent happens with the merges boxes!

Another point to consider is that refraction is directional, so ior A -> 
ior B gives a different result than B -> A. That means it has to be 
distinguished between entering and leaving objects. Now at the back surface 
of the box should the ray be refracted 1.0 -> 1.2 or 1.2 -> 1.0?

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