EEVEE: Volumetric shadows disappear when facing sun light #87182

New Issue

RoyTheKoi · 2021-04-03T23:39:58+02:00

RoyTheKoi commented

2021-04-03 23:39:58 +02:00

System Information
Operating system: MacOS Catalina 10.15.7
Graphics card: AMD Radeon Pro 5500M 8 GB, Intel UHD Graphics 630 1536 MB

Blender Version
Broken:

2.93 master 2021-03-31
Worked:
2.92
2.93 master 2021-03-18

Short description of error
Volumetric shadows disappear when looking towards a sun light, within around 45 degrees. Especially apparent when volume density is much greater than 1.
Point and area light shadows seem unaffected.

Comparison:

2.93 video example:
EEVEE Volumetric Shadows Bug 2.9.3.mp4

Exact steps for others to reproduce the error

Create a mesh
Add a principled volume material with density of 10
Add a sun light
Enable volumetric shadows
Enter EEVEE rendered view
Rotate the view to face the sun light, notice the shadows disappear on the volume.

EEVEE Volumetric Shadows Bug.blend

**System Information** Operating system: MacOS Catalina 10.15.7 Graphics card: AMD Radeon Pro 5500M 8 GB, Intel UHD Graphics 630 1536 MB **Blender Version** Broken: - 2.93 master 2021-03-31 Worked: - 2.92 - 2.93 master 2021-03-18 **Short description of error** Volumetric shadows disappear when looking towards a sun light, within around 45 degrees. Especially apparent when volume density is much greater than 1. Point and area light shadows seem unaffected. **Comparison:** ![EEVEE Volumetric Shadow Comparison.jpg](https://archive.blender.org/developer/F9919249/EEVEE_Volumetric_Shadow_Comparison.jpg) **2.93 video example:** [EEVEE Volumetric Shadows Bug 2.9.3.mp4](https://archive.blender.org/developer/F9919231/EEVEE_Volumetric_Shadows_Bug_2.9.3.mp4) **Exact steps for others to reproduce the error** 1. Create a mesh 2. Add a principled volume material with density of 10 3. Add a sun light 4. Enable volumetric shadows 5. Enter EEVEE rendered view 6. Rotate the view to face the sun light, notice the shadows disappear on the volume. [EEVEE Volumetric Shadows Bug.blend](https://archive.blender.org/developer/F9919253/EEVEE_Volumetric_Shadows_Bug.blend)

RoyTheKoi commented

2021-04-03 23:39:58 +02:00

Added subscriber: @RoyTheKoi

Alaska commented

2021-04-04 00:28:09 +02:00

Added subscribers: @fclem, @Alaska

Alaska commented

2021-04-04 00:28:09 +02:00

Changed status from 'Needs Triage' to: 'Confirmed'

Alaska commented

2021-04-04 00:28:10 +02:00

I'm able to confirm this bug in latest master.

I have decided to bisect the issue and found commit 884f934a85 to be the culprit
CC @fclem

System Information:
Operating system: Linux-5.10.0-5-amd64-x86_64-with-glibc2.31 64 Bits
Graphics card: GeForce RTX 3070/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 460.67

Blender Version: 2.93.0 Alpha, branch: master, commit date: 2021-04-03 16:32, hash: 8681504f06

I'm able to confirm this bug in latest master. I have decided to bisect the issue and found commit 884f934a85 to be the culprit CC @fclem **System Information:** Operating system: Linux-5.10.0-5-amd64-x86_64-with-glibc2.31 64 Bits Graphics card: GeForce RTX 3070/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 460.67 **Blender Version:** 2.93.0 Alpha, branch: master, commit date: 2021-04-03 16:32, hash: `8681504f06`

Dean Jones commented

2021-04-17 20:32:57 +02:00

Added subscriber: @DeanKJones

Dean Jones self-assigned this 2021-04-17 20:32:57 +02:00

Dean Jones commented

2021-04-17 20:32:57 +02:00

Hi, I have a working fix [here: D11004 ](https://developer.blender.org/D11004)

Hi, I have a working fix [here: [D11004](https://archive.blender.org/developer/D11004) ](https://developer.blender.org/D11004)

Clément Foucault commented

2021-04-19 16:44:19 +02:00

Well it is complex. I fixed the previous behavior (in 2.92) where only the local volume (1m) was considered for shadowing. Now it goes through the whole camera frustum but when the shadow ray is parallel to the camera ray it needs to cover the whole view range (up to the far clip distance). With the limited number of shader samples steps under-sampling arises (the volume steps are too big).

The problem is that there is no real fix for that. Current implementation is taking samples at the end of volume steps to not miss the light position sample. Using the start position of a step makes the volume object go fully shadowed in your test scene and might miss shadowing if the light is in a volume. I don't know which is better.

Note that using a noise to distribute the error will only make the result blurry and make performance terrible due to texture cache misses.

A workaround is to lower the clip end distance of the camera. But I know it's not possible in every scene.

I have plans for making the volume shadows part of the shadow maps. This would fix the isssue and even improve performance drastically. I think I'll consider this a known issue until then.

Well it is complex. I fixed the previous behavior (in 2.92) where only the local volume (1m) was considered for shadowing. Now it goes through the whole camera frustum but when the shadow ray is parallel to the camera ray it needs to cover the whole view range (up to the far clip distance). With the limited number of shader samples steps under-sampling arises (the volume steps are too big). The problem is that there is no real fix for that. Current implementation is taking samples at the end of volume steps to not miss the light position sample. Using the start position of a step makes the volume object go fully shadowed in your test scene and might miss shadowing if the light is in a volume. I don't know which is better. Note that using a noise to distribute the error will only make the result blurry and make performance terrible due to texture cache misses. A workaround is to lower the clip end distance of the camera. But I know it's not possible in every scene. I have plans for making the volume shadows part of the shadow maps. This would fix the isssue and even improve performance drastically. I think I'll consider this a known issue until then.

Philipp Oeser removed the

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EEVEE: Volumetric shadows disappear when facing sun light #87182