Gilles Tran wrote:

> 453e47e2$1@news.povray.org...
>> See what you gain? Your modeler now needs to first generate the 
>> displacement
>> map. The displacement map images have lower precision than the original
>> mesh, and POV-Ray needs an additional processing step to turn the
>> displacement map back into more triangles (or you use geometry caching,
>> which makes rendering somewhat slower but reduces memory need).
> 
> I've been using displacement maps (with subpolygon displacements) in two 
> other renderers and these maps are either painted or generated procedurally 
> (on the fly), not generated by a modeler.

Indeed you can do it procedurally, but that was not the point in that
particular section of my post (I pointed out procedural displacement in the
last paragraph of the post). However, in real-time rendering applications
(in particular video games), displacement mapping is used as a kind of LOD
technique, and closely related to normal mapping (which, as the original
posted implied correctly, is a simplified form to get a kind of displacement
mapping appearance).

This was what the original poster seems to have been hinting at by asking
for both features at once, as they are closely related for exactly this kind
of application. Especially for normal mapping the method I describes is how
it actually came to be - a poor-mans, ahem, scanline renderers way of
simulating rather computational expensive displacement mapping of scanline
hardware renderers at the time.

> The workflow is to create a mesh
> with as few polygons as possible and then create the fine details through
> displacement.

Indeed that is one way to use it, depending on your application and modeler
capabilities (decimating meshes is a complex algorithmic problem and makes
most use if you need to to real-time rendering with the model). However, in
ray-tracing, as you know, there are nicer ways to do things like this, and
especially in POV-Ray directly (rather than using a modeler).

BTW, one very simple way to do in essence what some ray-tracing displacement
mapping algorithms do, you can just use a height field. By clipping, one can
even get them to behave like triangles. Of course, this is not as optimal as
having a mesh directly.

	Thorsten

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