Can I isolate geometry using LPE's in Arnold?

[abaker976]

I've seen in the renderman doc's that you can add object group names to geometry and then use these in LPE's to render only specific pieces of geo. I can't find any documentation on how to do this in arnold. Is it possible?

Thanks,
Aaron.

[Stephen.Blair · Accepted solution]

No, not yet.

[abaker976]

Thanks for the quick answer!

[arenascdaniel]

there is a workaround.
If you write a shader and tag it's closures, you can isolate the tagged closures with the LPEs.

In OSL it would be like this:
closure color diffuse = diffuse(N, "label","MyTag")

then the LPE:
C<RD'MyTag'>.*

writing a good shader it's hard but if you are into it it should work.

You can find some docs here:
https://support.solidangle.com/display/A5ARP/Light+Path+Expression+AOVs
and here:
https://github.com/imageworks/OpenShadingLanguage/wiki/OSL-Light-Path-Expressions

[theoSPVCF]

Hello,

I'm digging this thread up because I'm trying to reproduce  these workflow: A Custom OSl shader to get per object aov with tag, but without success.

Here my osl code

shader diffuse(
    color DiffuseColor = color(0.8, 0.8, 0.8),
    output closure color CL = diffuse(N,"label","MyTag"))
{
    CL = diffuse(DiffuseColor);
}

and my custom AOV with LPE:

C<RD'MyTag'>.*

C<RD['MyTag']>.*

 (i tried both).

The end goal is to isolate emission contribution from differente emissive object. So i tried also without succes:

shader emit(
    color EmitColor = color(1, 1, 1),
    float Intensity = 1,
    output closure color CL=emission("label","MyTag")
)
{
    CL = emission() * EmitColor * Intensity;
}

C<O.'MyTag'>

[theoSPVCF]

Ok I make it work eventually.

OSL shader

shader emit(
    color EmitColor = color(1, 1, 1),
    float Intensity = 1,
    output closure color CL=emission("label","mytag")
)
{
    CL = emission("label","mytag") * EmitColor * Intensity;
}

LPE

C<R><O.'mytag'>

Which give me only the emission for the object with the osl shader.
To be honest i tried random combination for the regex LPE until it work, so it's may not be the correct way to do that.