[Sidefx-houdini-list] Curves normals

Pablo Giménez pablogipi at gmail.com
Thu Aug 26 14:13:50 EDT 2010


2010/8/26 Alex Czetwertynski <alex at franktheplumber.com>:
> I have recently been wondering about this a lot as I have the same question related to particles.
> If Houdini is creating this geometry at render time, wouldn't it make sense to give the user some kind of representation of what is going on in OpenGL land?  It feels like some remnant of pre-graphics card days where you need to do this blindfolded somehow to not create too much geometry in the viewport.  What is the rationale for keeping these kinds of workflows?
Because that would create looooots of geometry, which can be created
at render time and then be much more eficcient.
We are talking about order of millions in point rendering and fur/heir
in production.
>
> Sorry if this is an obvious question, I'm migrating to Houdini from apps where you barely ever have to deal with this kind of stuff
>
> Thanks
> Alex
>
> On Aug 26, 2010, at 8:05 AM, Pablo Giménez wrote:
>
>> 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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-- 
Un saludo
Best Regards
Pablo Giménez



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