[Sidefx-houdini-list] Curves normals

Andrew D Lyons tstexture at gmail.com
Thu Aug 26 11:48:03 EDT 2010

I did this recently to generate fur sprites. If you get the curve
tangent and stack some cross products with another version of the
curve with normals hard coded to point towards the camera (or some
cardinal axis) then you should be able to derive a normal that is
always pointing in a general direction - but which follows the
contours of the curve.

2010/8/26 Pablo Giménez <pablogipi at gmail.com>:
> Hi.
> I am rendering some poly lines as curves, using the 'width' attribute
> to control every filament width.
> That's all right.
> Problem is that this geometry is created at render time and the
> normals and texture coordinates are a little bit odd.
> My main problem is that Mantra creates the needed geometry using the
> width attribute but seems that is only shading the original curve
> attributes.
> I mean the hair geometry is created extendin the shaded point,
> perpendicular to the point of view, and the new geo seems to use the
> same shading as the original point.
> Is similar to what happens with points rendering, where the point is
> shaded once, and then all the geometry created at render time around
> the origian lpoint use the same shading from the original one.
> So you don't have proper normals to make for instance a diffuse
> lighting that gives you some "rounded" look.
> I have tried the hairNormalVOP, creating my own tangents, created
> texture coordinates with s going along the hair line from 0 to 1, but
> the normals I got are just pointin towards camera, they are not doing
> the "Rounding2 effect that is suppose to do this operator.
> So is there any way to go away from the planar look of curves shading,
> any way to have sense whre you shading point is in the new created
> gemetry so you can for instance fake normals o apply any othe rtrick.
> Thanks
> --
> Un saludo
> Best Regards
> Pablo Giménez
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Andrew D Lyons | Digital Artist | http://www.tstex.com

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