[Sidefx-houdini-list] Curves normals
craigleehoffman at aol.com
Thu Aug 26 15:34:13 EDT 2010
I think this is exactly what OpenGL instancing would be good with- creating tons of geometry on the fly on the GPU without the hit of being created on the CPU and pushed over the bus. Basically you create an object like a tree or a feather and a parent surface like a ground or bird with points scattered on it (like you would for the Fur Procedural) then the GPU copies the one tree or feather to each point you have scattered on the surface and point attributes on the scattered points are used to drive variety in the hardware render using OpenGL shaders.
We should be able to see and interact with large systems of fur/forest/feathers/grass/city buildings/etc. (albeit simpler lower resolution versions of them perhaps) with modern hardware than we currently can. Houdini has the instancing and geometry shader paradigm setup already and that just needs to be supported in OpenGL also- I hope Houdini can be a leader in this arena as it would open up a lot of capabilities for a lot of things. (But the geometry shader thing would only work on the latest DX11/OGL4.0 graphics cards, although the instancing and hardware rendering stuff will work with the older cards).
From: Alex Czetwertynski <alex at franktheplumber.com>
To: <sidefx-houdini-list at sidefx.com> <sidefx-houdini-list at sidefx.com>
Sent: Thu, Aug 26, 2010 11:21 am
Subject: Re: [Sidefx-houdini-list] Curves normals
Ah that makes sense. Haven't played with hair in Houdini yet.
With particles though I find it difficult to visualize the scale of the width
attribute, even though I do see the points. I'm sure this will come in handy at
On Aug 26, 2010, at 11:18 AM, Pablo Giménez wrote:
> 2010/8/26 Alex Czetwertynski <alex at franktheplumber.com>:
>> How about creating so low res geo to preview what you are doing? Or do you
>> just get to used to knowing what you are doing you don't even need that
>> anymore :)
> You have particles points and heirs guide lines as a preview.
> In this case my filaments are created from poly lines that exists in
> you scene and you visualize in the viewport. So you are not absolutely
>> On 8/26/10 11:13 AM, "Pablo Giménez" <pablogipi at gmail.com> wrote:
>>> 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
>>>> do this blindfolded somehow to not create too much geometry in the
>>>> 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
>>>> On Aug 26, 2010, at 8:05 AM, Pablo Giménez wrote:
>>>>> 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
>>>>> 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.
>>>>> Un saludo
>>>>> Best Regards
>>>>> Pablo Giménez
>>>>> Sidefx-houdini-list mailing list
>>>>> Sidefx-houdini-list at sidefx.com
>>>> Sidefx-houdini-list mailing list
>>>> Sidefx-houdini-list at sidefx.com
>> Sidefx-houdini-list mailing list
>> Sidefx-houdini-list at sidefx.com
> Un saludo
> Best Regards
> Pablo Giménez
> Sidefx-houdini-list mailing list
> Sidefx-houdini-list at sidefx.com
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