[Sidefx-houdini-list] Curves normals

Pablo Giménez pablogipi at gmail.com
Thu Aug 26 12:02:31 EDT 2010


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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-- 
Un saludo
Best Regards
Pablo Giménez



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