Nicolas George <nicolas$george@salle-s.org> wrote:
> Warp  wrote in message <47076431@news.povray.org>:
> >   Btw, how do you envision the basic user being able to write shaders in
> > this system?
>
> Actually, I do not know exactly what a shader is.

A user-definable function that accepts some information about a scene,
object, surface or ray and returns information that the renderer then uses
to modify the shading, illumination, any other aspect of the rendered
image.

I suspect though  that the shading language under consideration is solely to
replace only what other packages would call surface shaders: these shaders
accept information about a ray and the object it intersects, and return a
final surface colour using some internal process. POV's support for this is
quite focussed on colour, rather than surface properties; almost that you
can have any BDRF so long as it's Lambert.

> Would a basic user be able to write one, in any system?

Yes. Although the actual shader language is usually quite low-level (often
C-like), and therefore not particularly artist-friendly, most applications
provide a specialised visual editor. These days they are usually based on
nodes (plug a texture node into a diffuse shading node to get a texture
mapped diffuse surface, for example). Some systems opt to use layers, but
it ends up being the same. The systems are very powerful indeed, much more
powerful than my textured diffuse example.

I guess the plan in POV is not to ship any such visual support by default,
and make the underlying shader language artist-friendly enough to use. As
far as I know this will be a unique achievement, both in terms of
originality and, as always, difficulty.

Some further reading:

http://www.janwalter.com/
(the shader writing bits show how a few other packages handle this in their
C-like shading language)

http://www.xsi-blog.com/archives/118
(clever use of the visual shading language to speed up ambient occlusion in
XSI/mental ray)


Tom

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