Volume render element?

[koncepd]

Hi, been trying all day to get volume to show up alone in a render-pass for GPU/RTX. I'm using a simple cube with some noises on it to test with a grid volume shader. Closest I get is by putting it in it's own object-id group and then changing the render to render mask mode.

Is this the appropriate way? I read in maya forum that to get passes I need to use volume grid with volumetric-geometry mode, this disables volumetric render elements at the bottom of the shader..


I tried alot of combinations, between changing from CPU/GPU/RTX, changing all types of volume attributes (Heat, Temperature, Density, but primarily the later). As well as above mentioned configurations.

I've tried about every setting I can find related to mattes/alphas/transparencies/masks/cryptomattes, modes like bucket/progressive as well as exporting and looking through _all_elements_ export mode for anything close to a volume pass.

Obviously I'm missing something.

Atmosphere (which is only pass mentioned in documentation) only seem to wanna display environment fog. I read in another forum that you have to set transparency related to this pass.., but I dont seem to be able to figure this out...

Any help would be greatly appreciated!


Edit* Atmosphere outputs the volumes in CPU mode...as well as creates the two passes from the volume grid shader...so I guess this is another unsupported feature... : /

[chakarov]

Hello koncepd , you could set VolumeGrid Shader Mode to "Volumetric Geometry", it is in Rendering Tab of the shader. Than the volume object will visible in crytomatte by Node Name. Be sure that sampler is set to Bucket in order to get crytomatte element rendered. Is that work for you?

[Gosho.Genchev]

There's this table in the Phoenix FD documentation. I vaguely remember it was copied over to the V-Ray documentation but apparently that is not the case - I'll add a reminded for myself to take care of this, apologies for the inconvenience.
Supported render elements: https://docs.chaosgroup.com/display/...ements+Support

There is also this page which covers most of your questions: https://docs.chaosgroup.com/display/...ering+In-Depth

Cheers!

[koncepd]

Thank you both for your replies! I am experimenting with the cryptomatte option now but from experience it's not been the best solution. My trick for yesterday ended up being rendering it out as it's own object-id. I also rendered it as a pass on the CPU but things were flickering (probably @rest or volumesample attribute glitching out aka my fault).

Gosho.Genchev the last link you sent doesn't work for me. It sends me to a login page which I don't seem to have access to. I tried logging in with both forum credentials as well as my license-page credentials without luck. Thanks anyways, I think I arrived at the same conclusions through trial and error as this page from phoenix4maya suggest support-wise.

[Gosho.Genchev]

I am experimenting with the cryptomatte option now but from experience it's not been the best solution. My trick for yesterday ended up being rendering it out as it's own object-id.

That is surprising - anything in particular causing issues for you ? Cryptomatte should, in theory, make the multimatte / material IDs workflow obsolete.
I've updated the link - indeed it was the wrong one.

Cheers!

[koncepd]

Edit* removing my question after finding out how to do this**

Question: Multi-channel option was ignored. Answer: Remove $.AOV from filename in export.

[Gosho.Genchev]

edit: just saw your edited message. More info on multi-part: https://www.mail-archive.com/nuke-us.../msg11799.html (hopefully it's correct, my compositing skills extend no further than dropping grade and shuffle nodes in Nuke )

V-Ray will write out a multi-channel EXR automatically if the ${AOV} tag is not present in the file name. Maybe you're confusing this with the Multi-Part toggle in the EXR settings?

[koncepd]

Gosho.Genchev Reason why it wasn't optimal in my situation was because I needed to extract from background. Not just select/color correct etc. Thats why I wanted the pass itself so I could composite it into other render.

And again, thank you so much for putting up with my questions! It's very helpful and appreciated Been a bit frustrated here, but learning a lot. Thank you.

[koncepd]

After a lot of problem-solving yesterday and today I can finally say I have a reliable (minus "internal error" crashes...) way of rendering this out on the GPU. Sharing this with the disclaimer "Clear your frames if you use object-id masks"

https://gfycat.com/flashysatisfiedgoldenretriever

Thanks for the help once again!

[Gosho.Genchev]

Haha, nice!

Although I wonder what the deal with those errors is - can you please give us the build number you're using - it's printed in the console when you start Houdini, along with the date and hash.

Cheers!

[koncepd]

I tried a couple of different ones.. I've used Build number:6211 hash:4392cbb from 21 Jan 2020 for everything related to this thread.