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Volume scatter shader affects data render passes.
Open, Confirmed, MediumPublic

Description

System Information
Operating system: Win 10
Graphics card: GTX 980ti

Blender Version
Broken: 2.80.74 2019-07-12 17:50 e3c586e262dd
Worked: unknown (2.79 allegedly has the same issue)

Short description of error
Volume scatter shader affects data render pass (AO, Depth, Normal).

Exact steps for others to reproduce the error

Render the scene below. The file has two view layers, one called FOG, and the other NO FOG. The former includes a volumetric object.

Developer Note

I tweaked the file a bit (mainly added a texture to compare the changes in the AO pass and the normal and UV.

And a comparison between the AO and normal pass for each view layer:

Blob from original report

Hello, I'm facing an annoying problem and it's blocking our tries to use Blender as a production tool here at Lightfarm. So, every time we try to use a volume scatter shader to create fog doesn't matter if I use the option inside the world tab or create a cube, invert its normals and apply a volume scatter shader to it. Blender applies noise or color coming from the volume scatter shader in Data render passes, AO, Depth, Mist, Vector, Normal and etc... what gives us a wrong output to be used in Post-Production. I shouldn't be happening. I tried different solutions in a way to get around this problem. Tried different values for alpha threshold, tried to apply a transparent shader in the BOX that has the volume scatter shader applied. Nothing seems to solve the problem. I'd love to hear from you a solution for this.

Also, using mist pass to comp fog in the post isn't an option here because it's not as realistic as we want or separate the fog in a different render layer because it'll increase our render times a lot.

Details

Type
Bug

Event Timeline

Sebastian Parborg (zeddb) lowered the priority of this task from Needs Triage by Developer to Confirmed, Medium.

Talked to @Brecht Van Lommel (brecht) and this is indeed a bug, however volume + render passes has always been weak, thus this is not a high priority:
"It's more of a design issue really, no way to cleanly separate volumes and render passes. So we have to make some choices or add settings to control it."

Talked to @Brecht Van Lommel (brecht) and this is indeed a bug, however volume + render passes has always been weak, thus this is not a high priority:
"It's more of a design issue really, no way to cleanly separate volumes and render passes. So we have to make some choices or add settings to control it."

Thank you, Dalai! The way I found to work around it is to create and isolate the fog volume object in a separated collection and create a new view layer where I disable the collection of the volume object and then render only the data passes I need.