[Sidefx-houdini-list] Curves normals

Louis Dunlevy louisdunlevy at gmail.com
Thu Aug 26 16:50:44 EDT 2010

parametric s should not be zero. If it is, I'm thinking it may be a bug

On 27/08/10 03:02, Pablo Giménez wrote:
> Hi Andrew.
> I have done similar things for other stuff, but my problem is that the
> s coordinate is constant 0 for all the points in the curve geometry.
> The t is fine, going from 0 to 1 along the curve lenght, but s is
> supposed to be along the curve "cross sections" width, and this is not
> happening.
> With a proper s coordinate along the width of the curve would be easy
> to fake a rounded look.
> cheers
> 2010/8/26 Andrew D Lyons<tstexture at gmail.com>:
>> 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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