RenderMan & RISpec, silly shader question : curvature convex and concave.

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RenderMan & RISpec >> silly shader question : curvature convex and concave.

by Sam Hodge » Tue, 20 Jan 2009 16:19:47 GMT

I was wanting to calculate the convexity and concavity and curvature of
a subdivision surface

I found this handy page here:
http://studentpages.scad.edu/~mparro21/curvature/curvature.htm

but it didnt work out so well for a subdivision surface

I have tried replacing Dv(p) with Deriv(p,u) etc

but this hasnt made much difference to the outcome.

The idea is to drive the roughness of a shader with the inverse of the
convexness.

not a very novel idea, I know, shiny on the outside, catch dust on the
inside.

But it might just work, someone here at work mentioned it was used on
Wall-E.

This plugin shows the idea:
http://www.lightengine3d.com/downloads/plugins/curvature/testImages/statue1.jpg

Sam
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RenderMan & RISpec >> silly shader question : curvature convex and concave.

by Sam Hodge » Wed, 21 Jan 2009 06:08:27 GMT



having thought about it , its pretty plain at u and v loop per subd patch.

Unless I compensate for the clock math, I will have to use another
parameterisation such as stangent[2] or s,t

But I think they will suffer from seams, any ideas would be greatly
appricieated

Sam
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RenderMan & RISpec >> silly shader question : curvature convex and concave.

by Moritz » Wed, 04 Feb 2009 18:28:52 GMT

Hey Sam,


you might want to look at Thomas Burge's curvature shader at
http://www.affine.org/curvature.html
It works with subdivs and what you intend is possible with the code in
there. I've done it myself in the past. :)

Beers (Coopers),

Moritz
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