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

guillaume laforge guillaume.laforge.3d at gmail.com
Thu Oct 11 12:07:12 EDT 2007


> 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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-- 
Guillaume Laforge



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