Warp wrote:
> John VanSickle <evi### [at] hotmailcom> wrote:
> 
>>The main problem with using a non-linear transform in POV-Ray is that a 
>>non-linear transform can have more than one inverse, or possibly no 
>>inverse, and POV-Ray requires its transforms to have exactly one 
>>inverse.  (This is also the reason that a scaling value of zero results 
>>in an error; such matrices have no inverse.)
> 
>   All POV-Ray users are used to thinking that when the specify a
> transformation (such as rotate, scale and translate) they are actually
> transforming the object itself. In other words, it's the object itself
> which moves and changes orientation and shape.
> 
>   In fact, that's actually true for a limited number of cases. For example,
> if you translate a sphere, what POV-Ray does is to simply move the center
> of the sphere and that's it. In this case the transformation was really
> a modification of the object. However, this was just a special case done
> for efficiency because it's easy to do.

Actually, I had always thought that the inverse of the transform was 
applied to the ray used for ray-object calculations, which accomplishes 
the same thing.

I can see that sometimes the forward transform is needed for things like 
texturing, etc.

I don't snoop through the POV-Ray sources, so this may all be blarney.

Regards,
John

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