Difkvol hadani wrote:
> Does PovRay support shader?

If you mean shaders as in RenderMan, then answer is no. But unofficial 
verion (POVMan) does it in limited way. It can be found there:
http://tofbouf.free.fr/clothray/download_en.html


> Why not?
> 
Ask POVTeam. My speculations:
nobody really-really wanted it
nobody has time/knowledge/wish to implement it
legal problems with Pixar
portability considerations
shader paradigm does not fit into POV-Ray paradigm

> Difficult?
Depends. Implementing all the stuff from RenderMan shaders spex means 
implementation of half of ray-tracer...
> or Unnessecary?
Probably. POV-Ray itself it quite powerful and in some cases same 
outcome could be achieved with POV-Ray textures/pigments/functions.

One problem is different conepts: in RenderMan (all) surfaces
are parametric and have uv parameters and surface derivatives could
be calculated, this makes  shaders really powerful. POV-Ray does not 
have support for uv-surfaces
(MegaPOV and 3.5 beta have for some primitives) and using uv and their
derivatives can be done in very limited way. Thats why derivative support
is not yet implemented in POVMan (additionally I'm lazy and don't have 
as much free time as I'd like to have.) For antialiasing in shader code 
ray differentials could be used, but this probably means, that RenderMan 
shaders could not be used without modifications.
Shaders are usually slower than 'native' textures/pigments, this is one 
limiting factor. Additionally handling separate files and performing 
separate compiling of shaders (as it is now in POVMan) seems to be too 
much for some POV-Ray users.

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