In article <3ede573a@news.povray.org>,
 "Ray Gardener" <ray### [at] daylongraphicscom> wrote:

> > POV textures *are* procedural. Image maps are relatively rarely used.
> 
> Sorry, I meant 'procedural' in the user-definable sense.
> POV-Ray's procedural textures are predefined.

No...they are quite user-defined. The system is a bit more structured 
than a shader programming language, but still extremely flexible, and 
far from anything like predefined textures.


> To be fair, I thought I remembered reading
> somewhere that POV 3.5 let textures use
> user-defined functions, although just going
> through the docs again I can't find
> references to that.

You can use functions as patterns, and pigments as vector functions. By 
combining three functions with the average pattern, you can specify a 
function for each color channel of a pigment, though this isn't as 
flexible or convenient as a full shading language. Adding such a 
language would certainly be possible, though.


> There's definitely
> no displacement shading, at any rate,
> except with isosurfaces (more below).

If "displacement shading" means displacement done at render-time, then 
no, there isn't. It could be added without requiring a scanline renderer 
however, in fact there's probably a few people working on it.


> Well, isosurfaces have a sampling function interface
> analogous to regular shading in Renderman. For some
> shapes, this is preferable -- e.g., a sphere is
> just x^2 + y^2 + z^2. But for other shapes,
> determining from (x,y,z) whether the point is
> inside or outside gets complicated.

For insideness testing, just use the inside() function...coming up with 
a custom function for it is overkill. I don't know what this has to do 
with isosurfaces though. If you're talking about the difficulty of 
making specific shapes with isosurfaces, there are functions and macros 
to make it more convenient.

-- 
Christopher James Huff <cja### [at] earthlinknet>
http://home.earthlink.net/~cjameshuff/
POV-Ray TAG: chr### [at] tagpovrayorg
http://tag.povray.org/

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