> > I mean displacement in the renderman displacement shader sense which
> > is what Roberto was asking about, hence in this case 'true
> > displacement'.
>
> Renderman (at least the PRMan implementation) is not a raytracer.

There are Renderman compliant renderers with raytracing support that do true
displacement without problems (BMRT being one of them, and Pixie a more
current example). Of course, true displacement is best used with Reyes
renderers, since you have almost infinite precision with that particular
algorythm.

> No, it's simply wrong.  Isosurfaces are just a more general feature than
> a displacement shader.  Displacement there is limited to mesh
> geomentries since - as mentioned above - it has to work for a scanline
> renderer.  You can model a shape as an isosurface function and then
> displace it - just like with a shader.  The only difference is that with
> isosurfaces you can also do much more.

Displacement can be applied to any primitive that takes shaders on a
Renderman compliant renderer. The original object retains the same
geometry - it's only displaced by the shader when rendering. However, with
isosurfaces, you have to modify the original function, thus the original
object is modified before parsing or rendering. As David said, picky, but
true.

Both approaches have their weak and strong points. However, that doesn't
change the fact that I'd like to apply displacement on pure primitives on
POV, or even meshes without any workarounds. And I can't do that.

At least not for now (hint, hint). ;-)

Best regards,

Roberto

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