David Burnett wrote:
> 
> 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.

> A function (in this case a shader)
> applied to an object, sphere, mesh, plane etc which change its
> geometry.
> 
> As I stated IMHO isosurfaces are not displacement as there is no 
> original object expect the one created by the function. It doesn't 
> matter what you do within that function what you get is still the 
> 'original' object not a displaced one.
> 
> Picky, oh yes.

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.

Christoph

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