HDRI animation bug in eevee #91312

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opened 2021-09-10 13:24:50 +02:00 by Fischer · 5 comments

Fischer commented

2021-09-10 13:24:50 +02:00

System Information
Operating system: Windows-10-10.0.17763-SP0 64 Bits
Graphics card: NVIDIA GeForce RTX 2080 SUPER/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 471.11

Blender Version
Broken: version: 2.93.1, branch: master, commit date: 2021-06-22 05:57, hash: 1b8d33b18c
Worked: (newest version of Blender that worked as expected)

Short description of error
The HDRI illumination shouldn't change on the cube, because every thing including the HDRI is rotating at the same speed.
However, this went wrong in EEVEE... It seems that in Cycles everything went on so well.

Exact steps for others to reproduce the error
This is a simplified bug presenting file of a complex scene which I found this bug, in which I have to rotate an object, a HDRI and camera together, and I'm struggling to get rid of this bug...

BugReport.blend

**System Information** Operating system: Windows-10-10.0.17763-SP0 64 Bits Graphics card: NVIDIA GeForce RTX 2080 SUPER/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 471.11 **Blender Version** Broken: version: 2.93.1, branch: master, commit date: 2021-06-22 05:57, hash: `1b8d33b18c` Worked: (newest version of Blender that worked as expected) **Short description of error** The HDRI illumination shouldn't change on the cube, because every thing including the HDRI is rotating at the same speed. However, this went wrong in EEVEE... It seems that in Cycles everything went on so well. <video src="https://archive.blender.org/developer/F10394023/0001-0096.mkv" controls></video> **Exact steps for others to reproduce the error** This is a simplified bug presenting file of a complex scene which I found this bug, in which I have to rotate an object, a HDRI and camera together, and I'm struggling to get rid of this bug... [BugReport.blend](https://archive.blender.org/developer/F10394020/BugReport.blend)

Omar Emara commented

2022-04-06 12:15:18 +02:00

Member

Changed status from 'Needs Triage' to: 'Needs Developer To Reproduce'

Changed status from 'Needs Triage' to: 'Needs Developer To Reproduce'

Omar Emara commented

2022-04-06 12:15:18 +02:00

Member

I can confirm. But I am not sure if this is something that can be relied upon, so tagging the module for more information.

I can confirm. But I am not sure if this is something that can be relied upon, so tagging the module for more information.

Philipp Oeser removed the

EEVEE & Viewport

label 2023-02-09 15:13:20 +01:00

Germano Cavalcante referenced this issue

2023-10-18 17:03:51 +02:00

HDRI lighting flickers when rotating environment #113867

Germano Cavalcante added the

label 2023-10-18 17:04:46 +02:00

Clément Foucault commented

2024-04-24 00:25:05 +02:00

Member

This is very interesting. Even with clamping threshold set very low, one can reproduce the issue on both the reflections and diffuse surfaces. Here is a way simpler file and HDRI and it still have the same flickering.

BugReport.blend

This might be very well be a bug in our probe processing pipeline.

Need to dig further.

This is very interesting. Even with clamping threshold set very low, one can reproduce the issue on both the reflections and diffuse surfaces. Here is a way simpler file and HDRI and it still have the same flickering. [BugReport.blend](/attachments/7ed08662-2502-4b4c-8eb5-98fb40c6bbc1) This might be very well be a bug in our probe processing pipeline. Need to dig further.

BugReport.blend

1.1 MiB

Clément Foucault added

and removed

Needs Info from Developers

labels 2024-04-24 00:25:18 +02:00

Clément Foucault commented

2024-04-24 20:21:20 +02:00

Member

Spherical Harmonic weighting error

The flickering is due to the imprecision in the spherical harmonic extraction code. We use a slightly off solid angle weight for each pixels of the octahedron map. And this, in turn, make the very bright pixels vary when it rotates around the sphere as its weighting error varies. Also, I am wondering if that can also be a numerical precision because we sum all pixels. The error might add up.

There is also a discretization step that is happening during the remap stage which can also add some error.

The error can be reduced by clamping the world but it never goes away. So I would suggest to implement a LUT with exact weights for each pixels. Other option is to run the SH extraction on the cubemap for which it is much easier to compute the solid angle. Also this would skip the discretization step of the remapping.

One other insight is that the current weighting scheme is broken. The border pixels appear twice in the octahedral map and the corner ones 4 time. So they should be weighted accordingly. We might be able to fix the current code by carefully using symmetries.

Glossy surface interaction

For some reason the glossy surfaces are also affected by the flicker. This is caused by the normalization factor being incorrect. I fixed that in main just now. So at least, it
shouldn't flicker on glossy surfaces for now.

#### Spherical Harmonic weighting error The flickering is due to the imprecision in the spherical harmonic extraction code. We use a slightly off solid angle weight for each pixels of the octahedron map. And this, in turn, make the very bright pixels vary when it rotates around the sphere as its weighting error varies. Also, I am wondering if that can also be a numerical precision because we sum all pixels. The error might add up. There is also a discretization step that is happening during the remap stage which can also add some error. The error can be reduced by clamping the world but it never goes away. So I would suggest to implement a LUT with exact weights for each pixels. Other option is to run the SH extraction on the cubemap for which it is much easier to compute the solid angle. Also this would skip the discretization step of the remapping. One other insight is that the current weighting scheme is broken. The border pixels appear twice in the octahedral map and the corner ones 4 time. So they should be weighted accordingly. We might be able to fix the current code by carefully using symmetries. #### Glossy surface interaction For some reason the glossy surfaces are also affected by the flicker. This is caused by the normalization factor being incorrect. I fixed that in `main` just now. So at least, it shouldn't flicker on glossy surfaces for now.

Clément Foucault commented

2024-04-25 17:05:44 +02:00

Member

So I fixed the several inconsistencies in EEVEE-Next and the lighting is already much stable.
Commits b49333a7a0 and 5938ab099d

However, this doesn't fix the following 2 last issues:

Very tiny bright spots in HDRI (i.e: Sun) can still make it flicker because of 2 discretization steps that both exhibit aliasing issues.
For speed, we decide to choose the light direction per regions of the octahedral map instead of doing the proper SH sum and choosing the light direction per sample.

The former can be mitigated with clamping, which is exactly what we are planning to do with #68478.

The second needs to be addressed regardless because of poor behavior with lower lightprobe resolutions.

So I fixed the several inconsistencies in EEVEE-Next and the lighting is already much stable. Commits b49333a7a050b4ef51c64db8ad58b025b2b9042a and 5938ab099dc2881882fbff5a4bf0ab8bdb2b7aa9 However, this doesn't fix the following 2 last issues: - Very tiny bright spots in HDRI (i.e: Sun) can still make it flicker because of 2 discretization steps that both exhibit aliasing issues. - For speed, we decide to choose the light direction per regions of the octahedral map instead of doing the proper SH sum and choosing the light direction per sample. The former can be mitigated with clamping, which is exactly what we are planning to do with https://projects.blender.org/blender/blender/issues/68478. The second needs to be addressed regardless because of poor behavior with lower lightprobe resolutions.

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Reference: blender/blender#91312

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