Volume Pass Support?

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steveernst117
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Joined: Sat Apr 04, 2020 5:21 pm

Volume Pass Support?

Post by steveernst117 » Sun May 03, 2020 2:46 pm

Hey all, just for fun yesterday, I made a quick scene to test out underwater caustics and volume effects and came up with this result.
underwater_graded_v2.png
I'm wondering if there's a way to render out a pass for the volume, like cycles and most other renderers have. (Side note: It'd be cool if there was also a caustics pass, but I've created a node group that has a workaround for that which is able to isolate caustics for most scenes. In this one though, it also catches the volume lighting effects, which is less than desirable.)
Are there any plans to implement a volume pass, or is there something I'm missing?

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Dade
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Re: Volume Pass Support?

Post by Dade » Mon May 04, 2020 11:27 am

As far as I remember you can use the BY_MATERIAL_ID AOV to extract the volumes (i.e. volumes are just a special type of material).

There is also a trick you can use to have caustic AOV: set the rendering to CPU and set 100% light tracing, it will render only the caustics.
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steveernst117
Posts: 4
Joined: Sat Apr 04, 2020 5:21 pm

Re: Volume Pass Support?

Post by steveernst117 » Fri May 08, 2020 11:03 am

Yeah, I'm aware of the method of setting the cpu to 100% light tracing, but that requires doing a separate render, which isn't so convenient. What my node group does is is takes the combination of rendered passes and subtracts it from the original rendered result, leaving me with everything else (which is typically just the caustics, but in this case, the volume is also included since there's no volume pass I can use either).

I tried setting the volume's material index to a different number, but I couldn't get anything out of the ID mask node in the compositor afterward for whatever reason. Any idea why that would be?

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