On Fri, 12 Mar 1999 16:32:56 -0000, Andrew Cocker 
	<and### [at] acockerfreeservecouk> wrote:
>
>Ron Parker wrote in message <36e914ac.0@news.povray.org>...
>>On Fri, 12 Mar 1999 15:47:53 +1000, Lance Birch <lan### [at] usanet> wrote:
>>
>>>So basically, it's not possible by using a texture.  The only real way I
>>>could see is to use the Isosurface patch to recreate the colour pattern as
>>>an object and then difference this from the object which you want to erode.
>>
>>If I remembered to include it, the next superpatch will include an isosurface
>>function called pigment() that allows you to use any pigment as the scalar
>>field.
>>
>
>Forgive my ignorance Ron, but I don't understand what this means. Does it mean that
you
>will be able to implement what I'm asking for?

In a sense, yes.  Actually, it means that _you_ will be able to implement 
what you're asking for.  It will only work for CSG-able objects, though, 
so not on meshes or bicubics.
  
What you would do is make an object that is the isosurface of the pigment 
field at a given threshold.  Parts of the pigment below that threshold
would be solid, and other parts would be hollow (or vice versa).  You could 
then use color maps or CSG (depends on what the patch supports; I've forgotten 
and don't have the code in front of me) to make the required intervals hollow
or solid as needed.  CSG intersect the resulting isosurface(s) with your
object, and the result will be what you're looking for.  You will want to 
let the color_map for the solid parts "bleed" into the hollow parts a little,
to avoid unfortunate results similar to the coincident surfaces problem.

It won't be fast, but it might be faster than media.  It won't be available 
for a while, though; I'm still testing stuff.

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