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Warp wrote:
>
> Vahur Krouverk <vah### [at] aetec ee> 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] tag povray org>
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] yahoo com
TAG(Technical Assistance Group) e-mail: chr### [at] tag povray org
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-press net>
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] yahoo com
TAG(Technical Assistance Group) e-mail: chr### [at] tag povray org
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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daishi <das### [at] x-press net> wrote:
: if you know of an image that comes close to that level of photorealism in
: pov, tell me
http://www.irtc.org/ftp/pub/stills/1998-08-31/afterain.jpg
http://www.irtc.org/ftp/pub/stills/1999-08-31/canyon.jpg
http://www.ctav.es/jaime/images/stillife.jpg
: also pov has nothing like displacement shaders
You are very welcome to give an algorithm on how to calculate displacement
mapping on raytraced mathematical objects. It would be very nice.
--
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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any word on this project :) (wishful thinking)
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