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

Ben Schrijvers ben.schrijvers at guerrilla-games.com
Thu Oct 11 12:58:33 EDT 2007


Hi hi... that's funny :-)

merci,
benS

guillaume laforge wrote:
>> Scanning through this email it seems to looks like it might have
>> anything to do with GL shading?
>>     
>
> gl_cvex_s_colormap() is not an open GL function !
>
> It just means "Guillaume Laforge cvex skin shader colormap function" :P.
>
> I'm not a programmer so it doesn't disturb me too much :-).
>
> Cheers
>
> Guillaume
>
> On 10/11/07, Ben Schrijvers <ben.schrijvers at guerrilla-games.com> wrote:
>   
>> 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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>>>       
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>
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