> I was thinking more along the lines of a patch which used isosurfaces to
> implement displacement mapping

I was thinking about it & came up with the attached image
This is explained as follows
1 the ray is traced to the surface normally
2 from the point of intersection take a point d (the displacement value for
that poin in space) units along the normal for that point of intersection
this is the center of a 5*5 rectangle of points used to make a bicubic
surface (or something like that)
3 the other points are found by tracing back to the surface and then going
up the normals
4 the ray is reflected off the bicubic surface

There are a lot of problems with this but it is a start
1 It will be slow (as slow/slower as/than proximity pigment??)
2 at small angles of intersection the ray may go under the surface and miss
it
maybe the points could be got by shooting from a point along the ray instead

3 when he ray doesn't hit the original surface (but it should hit the
displaced surface) this means that edges of an object will be smooth as the
original object - maybe we could use a proximity function added to a
displacement function and convert it to an isosurface... or we could just
tesselate the whole primitive into bicubic patches...

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