Vahur Krouverk <vah### [at] aetecee> wrote:
: Which functionality should shader patch have? Easiest would be to allow
: only change of color and opacity, i.e. it is like pigment replacement in
: texture.

  What would be the advantage of this?

-- 
main(i,_){for(_?--i,main(i+2,"FhhQHFIJD|FQTITFN]zRFHhhTBFHhhTBFysdB"[i]
):5;i&&_>1;printf("%s",_-70?_&1?"[]":" ":(_=0,"\n")),_/=2);} /*- Warp -*/

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Can someone give me a (good) example of the use of a shader and why it's
so innovative?

-- 
main(i,_){for(_?--i,main(i+2,"FhhQHFIJD|FQTITFN]zRFHhhTBFHhhTBFysdB"[i]
):5;i&&_>1;printf("%s",_-70?_&1?"[]":" ":(_=0,"\n")),_/=2);} /*- Warp -*/

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Warp wrote:
> 
> Vahur Krouverk <vah### [at] aetecee> wrote:
> : Which functionality should shader patch have? Easiest would be to allow
> : only change of color and opacity, i.e. it is like pigment replacement in
> : texture.
> 
>   What would be the advantage of this?
> 
As I wrote, it would be probably simplest way to incorporate VM into
povray.

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Warp wrote:
> 
>   Can someone give me a (good) example of the use of a shader and why it's
> so innovative?
> 

Good thing about shader support in POV-Ray is the fact, that this makes
creation of the custom (texture) patches unneccessary. Someone (!)
wrote, that POV-Ray should not incorporate each possible patch, which
someone has written, for it becomes too bloated and slow. 
Shaders could be used for any possible texture, to start with marble,
wood and finish with anisotropic scattering, non-photorealistic
texturing (Advanced RM book has examples of "cel" texture and examples
of texture, which gives engraving (??) look to objects).

But main reason for writing this patch was the complaint from the
rendering gurus (in c.g.r.r. "render wars"), that POV-Ray could not be
taken seriously, for it is raytracer and it does not support shaders.
Hopefully second one will be groundless in some point of time.

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What could be done with the shader not possible with pigment functions
(which are going to be included in pov3.5 most probably)?

-- 
main(i,_){for(_?--i,main(i+2,"FhhQHFIJD|FQTITFN]zRFHhhTBFHhhTBFysdB"[i]
):5;i&&_>1;printf("%s",_-70?_&1?"[]":" ":(_=0,"\n")),_/=2);} /*- Warp -*/

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Warp wrote:
> 
>   What could be done with the shader not possible with pigment functions
> (which are going to be included in pov3.5 most probably)?
> 
I dunno. When I have to compare pigment function and shader, then
following comes to my mind:
pigment function is like isosurface (or polysurface), shader is like
mesh, (created e.g. with modeller). First is general, but somewhat
limited. Second does not have limits, but is more resource demanding. In
mesh you can tweak each node, if required, in SL you can various
algorithm for each pixel. With pigment function (or isosurface) you
can't do this.

Here is link to shader environment description, if you are not familiar
with shaders:

http://www.pixar.com/products/rendermandocs/toolkit/RISpec/section12.html

General link to RM 3.1 (relevant part is shading language):
http://www.pixar.com/products/rendermandocs/toolkit/RISpec/index.html

RM 3.8 SL extensions:
http://www.pixar.com/products/rendermandocs/toolkit/Toolkit/slextensions.html

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In article <38f1b7da@news.povray.org>, Warp <war### [at] tagpovrayorg> 
wrote:

>   What could be done with the shader not possible with pigment functions
> (which are going to be included in pov3.5 most probably)?

One example of something that might be possible is a good starfield that 
is resistant to anti-aliasing. Or possibly textures that anti-alias 
themselves, or blurred reflection that is only blurred in specific 
directions...
You could also test out new highlight models like blinn with a shorter 
development cycle, and if they are popular enough, they could be 
incorporated into the program later.

Like I said before, shaders are to textures as isofunctions are to 
object primitives(and patterns!). They are much more than a pattern 
function, they can handle specialized reflection/refraction/media etc.
A pattern function is actually kind of like a partial shader, or a 
shader specialized and restricted to patterns. As a matter of fact, one 
possibility for implementing a kind of shader would be to use 3 
functions, one for red, green, and blue, and adding functions like 
trace(), eval_pigment(), etc. This would probably be a bit easier to 
use, and would have a syntax more consistant with the rest of POV-Ray, 
but would not be able to use existing RenderMan shaders and would 
probably be less flexible.
Maybe the two are not mutually exclusive, though...it might be possible 
to make a shader patch with an easier to use POV-like syntax(based on 
isofunctions) as well as support for RenderMan type shaders.

-- 
Christopher James Huff - Personal e-mail: chr### [at] yahoocom
TAG(Technical Assistance Group) e-mail: chr### [at] tagpovrayorg
Web page: http://chrishuff.dhs.org/

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this image might help you see what can be done with RM shaders

http://www.bmrt.org/bmrtimages/merritt-fruit3.jpg

if you know of an image that comes close to that level of photorealism in
pov, tell me

also pov has nothing like displacement shaders, which allow you to physiclly
alter the surface of an object based on whatever you tell it to do, examples
include hair shaders, shaders that can create a 3d weave pattern on an object
(or based upon the shape of the object depending upon the shader), etc etc

also like was previoulsy mentioned having the ability to anti-alias specifc
shaders is extremely useful

Warp wrote:

>   What could be done with the shader not possible with pigment functions
> (which are going to be included in pov3.5 most probably)?
>
> --
> main(i,_){for(_?--i,main(i+2,"FhhQHFIJD|FQTITFN]zRFHhhTBFHhhTBFysdB"[i]
> ):5;i&&_>1;printf("%s",_-70?_&1?"[]":" ":(_=0,"\n")),_/=2);} /*- Warp -*/

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In article <38F1FE1D.C8F08B1E@x-press.net>, daishi <das### [at] x-pressnet> 
wrote:

> also pov has nothing like displacement shaders, which allow you to 
> physiclly alter the surface of an object based on whatever you tell 
> it to do, examples include hair shaders, shaders that can create a 3d 
> weave pattern on an object (or based upon the shape of the object 
> depending upon the shader), etc etc

Displacement shaders would not be possible in the current POV-Ray, 
because most of the shapes are not reduced to triangles but are rendered 
directly. However, you should be able to use a shader in a pigment 
function, and use that function in an isosurface...

-- 
Christopher James Huff - Personal e-mail: chr### [at] yahoocom
TAG(Technical Assistance Group) e-mail: chr### [at] tagpovrayorg
Web page: http://chrishuff.dhs.org/

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Warp wrote:

>  a shader and why it's so innovative?

Simply because it can basically do anything - you could create a new type of
lighting model, combine two textures, make new textures that depend on some
obscure algorithmn

Pabs

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