Am 16.11.2018 um 20:34 schrieb Alain:

> So, it should look somewhat like :
> 
> #declare Location= trace( Object, Start, Dir, Normal, UV_Location );

Yes, that would be the trivial-to-implement solution.

> or
> 
> #declare Location= trace( Object, Start, Dir, Normal, UV_colour );

In this case, it would be more like:

     #declare Location= trace( Object, Start, Dir, Normal, colour );

While I agree that this would be the most desirable solution, I'm not 
sure whether it would be possible to implement in a fully consistent 
manner. As someone hinted at earlier in this thread, objects don't have 
pigments - they have textures, which may be arbitrarily complex. There 
may be cases (either now or in the future) where there's no single 
unambiguous colour associated with the ray-object intersection.

As an extreme example, take SSLT: In the first incarnation (somewhen 
during the beta phase of POV-Ray v3.7.0) the colour of SSLT textures 
wasn't controlled by a pigment, but was an emergent property of quite 
different physics-based parameters.

While it may turn out to be possible to resolve this issue in a 
well-defined manner, it certainly won't be trivial.

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