Nicolas George <nicolas$george@salle-s.org> wrote:
> "Tom York"  wrote in message
> > 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 do not think that can be called "writing" a shader.

Does it matter? As I said, I really doubt POV 4 will include such a visual
editor.

> And what you describe seems to me quite similar to what is possible already
> with the numerous pigments of POV-Ray. Isn't it?

You can look though the archives of this NG to find out. Some of it is not
exactly straightforward. A lot of it is impossible. For an example of the
first, consider a surface whose specularity varies independently of its
roughness. To vary one or the other property requires only a texture_map.
To vary both independently requires two nested levels of texture maps.
That's very clumsy, and hopefully you do not want to vary the diffuse
property as well, or that will be another nesting level working off 8
textures at the lowest level.

For an example of the second, there's plenty of stuff it can't do. Off the
top of my head, apart from launching new rays as Warp suggested (essential
for ambient occlusion), there's ramp/gradient shaders (shaders that can use
the level of illumination to select a colour), using any BDRF apart from
tweaked lambert with tweaked phong specularity, anisotropic highlights. You
can probably find more in the NG archives.


Tom

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