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Volumetric object not taking into account by cycles depth/mist pass
Open, Confirmed, LowPublic


System Information
Operating system: Linux-4.15.0-52-generic-x86_64-with-debian-buster-sid 64 Bits
Graphics card: GeForce GTX 1080 Ti/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 410.104

Blender Version
Broken: version: 2.80 (sub 75), branch: master, commit date: 2019-07-29 14:47, hash: rBf6cb5f54494e

Short description of error
No matter what "Alpha Threshold" is set to, cycles depth pass does not include volumes.

Expected behavior
In the same way that Alpha Threshold is compared with the alpha transparency of each object, it (or another parameter like Density Threshold) should be compared with the density of each volume in the scene (for the purposes of inclusion in depth passes)

Exact steps for others to reproduce the error

Rendering this file yields a (normalized) depth pass that is missing the cube with the volume shader (but it does include the cube with the 0 alpha principled BSDF)



Event Timeline

Finn Bear (finnb) updated the task description. (Show Details)

For others with this issue, a workaround is applying a zero-alpha principled BSDF to the surface input of the shader output. Then set Alpha Threshold to zero.

Seeing that 2.79b actually did that [render volume objects surface depth into the z (not the mist?)], will check when that was changed (and if that was on purpose) -- 2.79 branch already excludes the surfaces...

Philipp Oeser (lichtwerk) lowered the priority of this task from Needs Triage by Developer to Waiting for Developer to Reproduce.

To me it is a bit unclear what the real usecase of having this would be @Finn Bear (finnb)?

Anyways, before bisecting hundreds of commits, I'll ask straight away: @Brecht Van Lommel (brecht): is this change by design?

Finn Bear (finnb) added a comment.EditedAug 8 2019, 2:11 AM

To me it is a bit unclear what the real usecase of having this would be @Finn Bear (finnb)?

My use case is a cloud scene in which all objects are volumetric clouds. I need the depth pass to work so I can apply compositing effects based on depth in the scene (fading between different view layers as depth increases).

Edit: I should add that high density volumes are not too unlike solid meshes, and should not be considered differently for the purpose of depth passes.

Brecht Van Lommel (brecht) lowered the priority of this task from Waiting for Developer to Reproduce to Confirmed, Low.Wed, Sep 25, 4:56 PM

Volume interaction with render passes is quite weak still, this is something to revise.