On 11-11-2014 18:31, MichaelJF wrote:
> "Anthony D. Baye" <Sha### [at] spamnomorehotmailcom> wrote:
>   > Thomas
>>
>> Since Trace only returns the point of intersection and the normal vector, and
>> there's really no way to query object attributes, the best I'd think you could
>> do is pass the intersection Point and the pigment to eval_pigment...
>>
>> Although... You might get more information from a function.   It's worth
>> investigating.
>>
>> Regards,
>> A.D.B.
>
> That would be of help in very simple situations only. First the object must have
> a pigment only and not a more complicated texture or worse an uv-mapping. Second
> you must invert all transformations applied to the object after coloring it.
>
> I can understand the wish by Thomas since one can e.g. plant grass of different
> length at the object depending on the color - just a stupid idea. In fact I used
> color maps, which can be evaluated with eval_pigment, sometimes to determine the
> kind of vegetation in a landscape with a corresponding shape.

Yes, that is what I generally do too and it works fine. My question in 
fact derives from that usage and a solution would be a smart addition 
but I am afraid it is not really possible.

>
> May be it is possible to implement it into the trace()-statement as a third
> return value, but this issue and the effort necessary I cannot judge.

Yes, that would be the logical thing indeed.

Thomas

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