Maniphest T76084

Faces culled with "backface culling" still receive shadows in the viewport
Confirmed, NormalKNOWN ISSUE
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Assigned To
None
Authored By
Alaska (Alaska)
Apr 25 2020, 5:22 AM
Tags
  • BF Blender
  • EEVEE & Viewport
Subscribers
Alaska (Alaska)
Clément Foucault (fclem)
ogierm
Richard Antalik (ISS)

Description

Sorry if this is a repeat report. I was unable to find another report for this.

System Information
Operating system: NA
Graphics card: NA

Blender Version
Broken: All versions of Blender 2.8X and 2.90 that I am able to test.
Worked: Never

Short description of error:
While the "Backface culling" option is enabled in the viewport, the culled backface will still receive a shadow when the "shadow" option is also enabled.

For example, here's a box with all it's normals facing inwards. With backface culling, we are able to see inside the box. But with shadows also enabled (as seen in the picture), shadows are cast onto the "culled" faces.

Exact steps for others to reproduce the error:

  1. Create scene with an object that has it's normal facing away from the camera (you're seeing the backface).
  2. Enable "Backface culling" in the viewport shading options.
  3. Enabled "Shadows" and adjust the position of the "light" such that the "back face is in shadow.
  4. The backface should now have a shadow placed on it.
  5. If you reproduce the steps above for the workbench render engine, the same issue applies.

Backface Shadowing.blend648 KBDownload

Related Objects

Event Timeline

Alaska (Alaska) created this task.Apr 25 2020, 5:22 AM
Alaska (Alaska) added a project: EEVEE & Viewport.Apr 25 2020, 5:49 AM
ogierm added a subscriber: ogierm.Apr 25 2020, 8:53 PM
Richard Antalik (ISS) changed the task status from Needs Triage to Needs Information from User.Apr 27 2020, 8:03 PM
Richard Antalik (ISS) added a subscriber: Richard Antalik (ISS).

Can not reproduce this.

Please upload example .blend file.

Also make sure you are testing with loaded factory default settings (File > Defaults > Load Factory Settings) and that your GPU drivers are up to date.

Alaska (Alaska) added a comment.EditedApr 28 2020, 12:10 AM

@Richard Antalik (ISS)

Loaded factory default settings and recreated the cube with all face normals pointing towards it's interior. Still had the same issue.
I have also experienced this issue on all drivers I've used on Windows and Linux with Nvidia and AMD GPUs since the later part of development of 2.80. I am currently running Linux with a GTX 1050ti with drivers 440.64.

Also just to expand on my original post because reading over it seems a bit unclear to me now. The shadows I'm talking about are the self shadows. Shadows from another object will not be cast onto the back of a culled backface, but the shadow that the face casts on itself by being in the path to "sun light" is still cast onto backfaces when they're culled.

Here's a blend file:

Backface Shadowing.blend648 KBDownload

I made this bug report now because I experienced this issue is a different scene during the development of Blender 2.80 but was unable to figure out what caused it until recently when I decided to take another look at the project.

Actually, looking at that screenshot now, there's other issues with this scene. For example the hole for the Window is casting a shadow when it should be the other way around. I have split this off into it's own report (T76168).

Alaska (Alaska) mentioned this in T76168: Workbench shadows behind a culled backface are inverted..Apr 28 2020, 12:44 AM
Richard Antalik (ISS) changed the task status from Needs Information from User to Confirmed.Apr 28 2020, 4:32 PM
Richard Antalik (ISS) updated the task description.
Clément Foucault (fclem) moved this task from Backlog to Known Issues on the EEVEE & Viewport board.Jun 30 2020, 1:08 AM
Clément Foucault (fclem) changed the subtype of this task from "Report" to "Known Issue".
Clément Foucault (fclem) added a subscriber: Clément Foucault (fclem).

This is a limitation of workbench shadows.