Warp <war### [at] tagpovrayorg> wrote:


>   For example, if you have a red sphere and a green sphere of the same size
> in a union, and they partially overlap, and then you cut this union so that
> the overlapping area becomes visible, what should be color of this area?
> Red or green? Why? Why would one choice be more correct than the other?
> What if the user wanted the other choice?
>

I do see the logical conundrum in this example. Taken on it's face, it would
seem to be an insurmountable one--possibly even getting to the 'core' of
logical computation and thought. What could possibly be a 'solution' (or more
likely, a workaround/kludge) to such a situation? It would seem to me that the
best minds in computer-graphics science *must* have given this a great deal of
thought by now (if not an answer.) Yet, it also seems to me that some kind of
practical solution could be arrived at--in POV-Ray--by taking a 'logical
short-cut.'  For example, similar (but only in general concept) to the way POV
handles interior_texture in a semi-transparent object: If you give the object
interior_texture{pigment{rgbt 1}}, the 'back-face' disappears, IIRC. Yet if you
rotate the object around, that invisible back face 'changes its position', to
always be in line with the camera. This strikes me as an acceptable workaround
to another possible problem with logic, although that's just a guess.

The general idea being that a 'non-logical' workwaround might be found in some
way, perhaps not ideal but acceptable. And yes, following my own reasoning I
can agree that the CURRENT 'solution' to the cutaway_textures problem is a
similarly acceptable one.  For now. ;-)

KW

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