[Sidefx-houdini-list] H9 : CVEX shader question

Ben Schrijvers ben.schrijvers at guerrilla-games.com
Thu Oct 11 11:56:46 EDT 2007


Uhmmm... CVEX?
Scanning through this email it seems to looks like it might have 
anything to do with GL shading?
Or maybe that gl_cvex_... is a bit misleading?
I'm very interested in that.. strungling a lot with the new GL tab of 
shaders being spare channels.

cheers,
benS


calin casian wrote:
> I use cvex mainly to tweak geometry, fur in our case, on a strand by 
> strand base. For example if you want to apply noise on the whole fur, 
> not just the one you see in the viewport you'll use a cvex shader.
> If you want to change the color of the fur based on a map you can pass 
> the UV attribute to the SHOP shader and apply a normal SHOP shader.
> You can pass attributes to the shader in the 2 corresponding fields from 
> the fur sop. If you don't pass anything all the attributes that goes 
> into the fur sop will be deleted.
> Some common attributes you might want to pass are, "width" for the 
> guides guideUV if your shader changes color from root to tip and UV for 
> the skin.
> You need to pass UV to the skin so that the fur knows it's position 
> relative to the skin and it can pick up color from the texture map.
> If you want to see the color feedback in the viewer you have to 
> implement some of the shader capabilities in the cvex shader and export 
> as a "cd" attribute.
>
> I hope this mekes sense
>
> cheers
> calin
>
>
>
>
> guillaume laforge wrote:
>   
>> Sorry for the noise, I think I understand my mistake now...
>>
>> In example 2, scale is just a parameter used for the result (P). It looks
>> like the standard houdini behaviour to "override" this parameter if an
>> attribute got the same name and type.
>> CVEX is not so easy to understand for me :P.
>>
>> Cheers
>>
>> Guillaume.
>>
>> On 10/11/07, guillaume laforge <guillaume.laforge.3d at gmail.com> wrote:
>>   
>>     
>>> Hi,
>>>
>>> I'm learning the new workflow with the CVEX shaders and fur (sop and
>>> procedural) in Houdini 9.
>>> I don't understand completely how it works. Sometime the CVEX shader can
>>> modify an attribute and sometime it creates this attribute.
>>>
>>> Example 1 : a CVEX applied in the skin shader parameter of a fur sop :
>>>
>>> If I create a Cd attribute on the rest skin geometry and add this cvex
>>> shader on the fur sop it changes the fur color based on a color map file.
>>> If I remove the Cd attribute, it doesn't work anymore.
>>>
>>> Code :
>>>
>>> cvex
>>> gl_cvex_s_colormap(
>>>             vector uv = 0;
>>>             export vector Cd = 1;
>>>             string map = "";)
>>> {
>>>     Cd = colormap(map,uv);
>>> }
>>>
>>>
>>>
>>>
>>> Example 2 : a CVEX applied in the guide shader parameter of a fur sop:
>>>
>>> If I add a scale attribute on the rest skin geometry, this code does
>>> nothing. I must remove the scale attribute to see the effect.
>>>
>>> Code :
>>>
>>> cvex
>>> gl_cvex_g_furrandomscale(
>>>         export vector P=1;
>>>         vector origin = 1;
>>>         int fur_id = 0;
>>>         float scale=0.5;
>>>         )
>>> {
>>>     float r = random(fur_id);
>>>     P += scale * r * (P - origin);
>>> }
>>>
>>>
>>> Why an existing  attribute is needed in example 1 and not example 2 ?
>>> Any explanation on the CVEX shaders is welcome !
>>>
>>> Cheers,
>>>
>>> --
>>> Guillaume Laforge | La Maison
>>>
>>>     
>>>       
>>
>>   
>>     
>
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