There seems to be a problem with release 3.5 candidate #6 and specular
transparent image-maps. The specular highlight is visible where the
image-map is transparent.

Richard

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Richard Borsheim <rbo### [at] shawca> wrote:
> There seems to be a problem with release 3.5 candidate #6 and specular
> transparent image-maps. The specular highlight is visible where the
> image-map is transparent.

  Have you tested that:

  a) it doesn't happen with other pigments but just with image maps?
  b) it happens only in 3.5 and not previous versions?

-- 
#macro M(A,N,D,L)plane{-z,-9pigment{mandel L*9translate N color_map{[0rgb x]
[1rgb 9]}scale<D,D*3D>*1e3}rotate y*A*8}#end M(-3<1.206434.28623>70,7)M(
-1<.7438.1795>1,20)M(1<.77595.13699>30,20)M(3<.75923.07145>80,99)// - Warp -

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>   Have you tested that:
>
>   a) it doesn't happen with other pigments but just with image maps?

I'm not sure how that would be done. You would need to have a pigment with
transparent regions.

>   b) it happens only in 3.5 and not previous versions?

The model uses Mesh2/UV Mapping so it doesn't work in versions prior to 3.5,
and all the earlier betas of 3.5 have expired of course.

Richard

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"Richard Borsheim" <rbo### [at] shawca> wrote...
> There seems to be a problem with release 3.5 candidate #6 and specular
> transparent image-maps. The specular highlight is visible where the
> image-map is transparent.

This is a known feature that has existed for many versions of POV.  Think of
it like glass... you want the highlight to show up even though the glass is
clear.

You'd have to use a material_map or a texture_map with an image_pattern to
really make it work the way you want.

-Nathan

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Richard Borsheim <rbo### [at] shawca> wrote:
>>   a) it doesn't happen with other pigments but just with image maps?

> I'm not sure how that would be done. You would need to have a pigment with
> transparent regions.

  Easily. Specify a color_map with some of the values being rgbf 1

>>   b) it happens only in 3.5 and not previous versions?

> The model uses Mesh2/UV Mapping so it doesn't work in versions prior to 3.5,
> and all the earlier betas of 3.5 have expired of course.

  You should have tried the same thing with other objects. Your conclusion
that it's a problem with image_maps was too premature.
  As Nathan said, it's not a problem with image_maps, nor meshes. It's not a
problem at all. It works as it should.
  (Why? If not, how would you make clear glass with highlights?)


-- 
#macro M(A,N,D,L)plane{-z,-9pigment{mandel L*9translate N color_map{[0rgb x]
[1rgb 9]}scale<D,D*3D>*1e3}rotate y*A*8}#end M(-3<1.206434.28623>70,7)M(
-1<.7438.1795>1,20)M(1<.77595.13699>30,20)M(3<.75923.07145>80,99)// - Warp -

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> >>   a) it doesn't happen with other pigments but just with image maps?
> > I'm not sure how that would be done. You would need to have a pigment
with
> > transparent regions.
>   Easily. Specify a color_map with some of the values being rgbf 1

Fair enough. That doesn't sound too hard, but from my perspective the two
are not the same, though I can see that from POVRay's perspective they
likely are.

> >>   b) it happens only in 3.5 and not previous versions?
> > The model uses Mesh2/UV Mapping so it doesn't work in versions prior to
3.5,
> > and all the earlier betas of 3.5 have expired of course.
>   You should have tried the same thing with other objects. Your conclusion
> that it's a problem with image_maps was too premature.

I don't think I was premature at all. The renders looked wrong and I
isolated it to specularity. I think I put in a reasonable effort to
determine the cause. Since Mesh2 and UV mapped image-maps are new to POVRay
3.5 it is not unreasonable that I would come to the conclusion that it is a
new issue. I posted here in order to be of assistance.

>   As Nathan said, it's not a problem with image_maps, nor meshes. It's not
a
> problem at all. It works as it should.
>   (Why? If not, how would you make clear glass with highlights?)

I wouldn't necessarily say that it works as it should. It all depends on
your perspective. From my perspective it is more important to support
punch-through transparency with image-maps
(http://www.btinternet.com/~mike.pye/transparency4.jpg) but I recognize that
not everyone would agree.

Richard

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> > There seems to be a problem with release 3.5 candidate #6 and specular
> > transparent image-maps. The specular highlight is visible where the
> > image-map is transparent.
> This is a known feature that has existed for many versions of POV.  Think
of
> it like glass... you want the highlight to show up even though the glass
is
> clear.
> You'd have to use a material_map or a texture_map with an image_pattern to
> really make it work the way you want.
>
> -Nathan

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.

Richard

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Richard Borsheim <rbo### [at] shawca> wrote:
> 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.

  Are you sure that if you use phong highlights in a scanline-rendering
engine (eg. OpenGL) it will not do the same thing as POV-Ray?

-- 
#macro M(A,N,D,L)plane{-z,-9pigment{mandel L*9translate N color_map{[0rgb x]
[1rgb 9]}scale<D,D*3D>*1e3}rotate y*A*8}#end M(-3<1.206434.28623>70,7)M(
-1<.7438.1795>1,20)M(1<.77595.13699>30,20)M(3<.75923.07145>80,99)// - Warp -

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"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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> > 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.
>
>   Are you sure that if you use phong highlights in a scanline-rendering
> engine (eg. OpenGL) it will not do the same thing as POV-Ray?

This is standard practice when modelling for games. Certainly Direct3D
supports it and correctly renders it (in my experience). It is an incredibly
effective technique (as long as you don't look too closely :-) ) For example
the holes punched through the side of the wheel supports in this image
(http://www.amabilis.com/gallery/Alex%20Grigny%20de%20Castro%20-%20Sojourner
%20-%20Large.jpg) would not be renderable with POVRay. They would look like
they have a shiny glass surface over them.

Richard

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