[Sidefx-houdini-list] dPds, dPdt troubleshooting...

b.fx at free.fr b.fx at free.fr
Thu Aug 31 11:12:25 EDT 2006


Hi

Is that not what you are able to do with Shading Derivative ?

francois

Quoting Ben Schrijvers <Ben.Schrijvers at framestore-cfc.com>:

> It's a real pitty you can't query P in (textured) uv space to calculate
> you own derivatives. Or can you?
> What about the good old baking P in texture space and then query that as
> texture map during the "beauty pass".. ?
>
> hmmm...
> benS
>
>
>
> Dan Seddon wrote:
> > hoknamahn at cgtalk.ru wrote:
> >> > In the case of mantra s and t is the primitive  parameterization -
> >> so this can be discontinuous from one face to another in the case of
> >> poly/subd's.
> >>
> >> I'm trying to figure out when the polygonal geometry behaves as
> >> parametric surface and when as polygonal (with discontinuity).
> >> In some cases the whole piece of polygonal geometry looks like
> >> parametric surface (i.e. with nice anisotropy) in other case the
> >> whole geometry or the part of geometry looks weird.
> > The polygonal geometry doesn't have to behave as a parametric surface
> > to have continuity ( though it may join large numbers of quad faces
> > together in to a grid internally if they can be represented that way)
> > - to appear continuous the derivatives just need to match on
> > neighbouring faces - you're more than likely seeing this when you have
> > quads arranged in a grid like fashion. Try rendering s and t out
> > rather than dPds and dPdt on different surfaces and you'll get an idea
> > of what the problem involves.
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