Karma (XPU/CPU) - Pass tech AOVs through refraction (N, pRef

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Hi all,

Not sure if anyone has tried or successfully achieved this, I’m currently attempting to get tech AOVs (such as N, pRef, or even custom texture-based AOVs) to pass through refractive surfaces (like glass) when rendering with Karma, both XPU and or CPU.

The goal is to hide the glass visually, but still get the underlying deformation from IOR in the resulting AOV, essentially mimicking the look-through-glass warping without rendering the glass itself.

So far, I’ve had some success with LPE-based AOVs, such as diffuse, by tagging the glass and using a pattern like:

C'glassDome'<RD>.*L

That seems to work fine — but it obviously doesn’t help with things not capturable through LPE, like texture-based AOVs or custom maps.

I’ve considered something like trace sets, which I had success within Arnold, but I’m not sure if there’s an equivalent concept or workaround in Karma.

If anyone’s run into this or found a hack or feature that could help, I’d really appreciate a nudge in the right direction.

Thanks in advance!

Kindest regards,
Marco Curado
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Hi there,

Did you have any luck with this? I'm also keen to find ways to refract data AOVs.

Ross.
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H21 Karma has a new feature called UPE's (utility path expressions), which are designed for this.
Edited by brians - Aug. 14, 2025 18:57:33
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