"Richard Borsheim" <rbo### [at] shawca> wrote in message
news:3d10062c@news.povray.org...
>
> So, I guess punch-through transparency
> (http://www.btinternet.com/~mike.pye/transparency4.jpg) for image-maps is
> not supported then? It's a pretty common technique in real-time rendering
to
> reduce polygon count, and for simplifying the modelling process.

Not as directly as you'd like. What you found should be the same as with any
pigment, when a finish which has specular highlighting added; the image_map
doesn't control finish attributes. More precisely, finish applies to pigment
as a whole, simply because transparency isn't a separate entity unto itself
I guess. When metallic is used, however, then any color does have affect on
the highlights. But again, that's actually due to finish controlling pigment
and not the other way around.

Maybe you understand all this now, but the problem you were describing
seemed to show that you did not before. For those people more acquainted
with POV-Ray this has become a common knowledge sort of thing. Or to be
fair, you might have been using a texture without any finish, in which case
it would certainly be a real problem since highlighting and diffusion
shouldn't be showing on completely transparent parts of a texture (rgbf 1 or
rgbt 1 only). You didn't say whether or not a finish were being used, so
that would be good to know, however you did say "specular image_maps". That
must mean you do have a finish set up.

Anyway, back to the item in question. Fact is, I think all you can do is
like Nathan suggested already. To map out the image via a texture not
pigment. For POV-Ray that would be the way to go about that punch-through as
you called it. The technique you told of isn't something I know about but I
get the idea.

Hope you don't take all the 'not a bug' stuff the wrong way. For instance,
Warp was pointing out the obvious. Some people expect highlights on clear
objects if specular or phong is specified in a finish, others don't.
Likewise, to see reflections if reflection is set, or not. Reflection
behaves this way too.

There isn't a special discerning of a finish within a singular (and
unmapped) texture with regards to pigment, unless you count varying
diffusion and other color changes due to incident angle of lights etcetera.

Well, have I beat this into the ground enough?  :-)

bob h

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