Overlapping shadows of MNEE Caustics and filter glossy caustics produce incorrect result #97932

New Issue

Alaska · 2022-05-07T11:16:58+02:00

Alaska commented

2022-05-07 11:16:58 +02:00

System Information:
Operating system: Linux-5.17.0-1-amd64-x86_64-with-glibc2.33 64 Bits
Graphics card: NVIDIA GeForce RTX 3060/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 510.68.02

Blender Version:
Broken: version: 3.3.0 Alpha, branch: master, commit date: 2022-05-06 21:48, hash: 98a04ed452
Worked: NA as this issue is probably in all builds of Blender with MNEE

Short description of error:
When the shadows of an Shadow Caustic light and a normal light overlap and filter glossy is set higher than 0, then the caustics produced in this overlapping area by the normal light will be rendered partially with the set filter glossy setting and partially with a filter glossy of 0.

Here is some images demonstrating the issue (The file I used for testing is attached below):


Expected result	Actual result	Actual result - Label image

Exact steps for others to reproduce the error:

Change the render engine to Cycles.
Setup the scene for MNEE caustics by adding a caustic caster, caustic receiver, shadow caustic light, and configuring them properly.
Add another light to the scene and ensure the Shadow Caustic option is NOT enabled.
Place this new light somewhere in the scene where part of the shadow and caustics caused by the light passing through the caustic caster onto the caustic receiver overlaps with the shadow from the light with the Shadow Caustic option enabled.
Ensure the {nav Render Properties > Light Paths > Caustics > Filter Glossy} is set to a value larger than 0.
Reduce the power of the light with the Shadow Caustic option enabled so it has only a small impact on the final render. (Note: The power of the light must be above 0 for this to work) - This step is not necessary, but it makes it much easier to see what's happening.
Render the scene.
Compare that render to another render with the Shadow Caustic light excluded from the final render. Notice how there was an impact on the shadow and caustics produced by the non-Shadow Caustic light.

Here is a .blend file with steps 1-6 done for you:

#97932 - Overlapping Caustic Shadows issue.blend

The steps for testing with the file is as follows:

Open the attached file.
Render the scene. Notice the weird line in the caustics.
Disable MNEE Light from the final render and render again, comparing the result to the first render you did.

**System Information:** Operating system: Linux-5.17.0-1-amd64-x86_64-with-glibc2.33 64 Bits Graphics card: NVIDIA GeForce RTX 3060/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 510.68.02 **Blender Version:** Broken: version: 3.3.0 Alpha, branch: master, commit date: 2022-05-06 21:48, hash: `98a04ed452` Worked: NA as this issue is probably in all builds of Blender with MNEE **Short description of error:** When the shadows of an `Shadow Caustic` light and a normal light overlap and filter glossy is set higher than 0, then the caustics produced in this overlapping area by the normal light will be rendered partially with the set filter glossy setting and partially with a filter glossy of 0. Here is some images demonstrating the issue (The file I used for testing is attached below): |![Overlapping Shadows - Expected Result.png](https://archive.blender.org/developer/F13056200/Overlapping_Shadows_-_Expected_Result.png)|![Overlapping Shadows - Actual Result.jpg](https://archive.blender.org/developer/F13056202/Overlapping_Shadows_-_Actual_Result.jpg)|![Overlapping Shadows - Labeled Result.jpg](https://archive.blender.org/developer/F13056204/Overlapping_Shadows_-_Labeled_Result.jpg)| | -- | -- | -- | |Expected result|Actual result|Actual result - Label image| **Exact steps for others to reproduce the error:** 1. Change the render engine to Cycles. 2. Setup the scene for MNEE caustics by adding a caustic caster, caustic receiver, shadow caustic light, and configuring them properly. 3. Add another light to the scene and ensure the `Shadow Caustic` option is NOT enabled. 4. Place this new light somewhere in the scene where part of the shadow and caustics caused by the light passing through the caustic caster onto the caustic receiver overlaps with the shadow from the light with the `Shadow Caustic` option enabled. 5. Ensure the {nav Render Properties > Light Paths > Caustics > Filter Glossy} is set to a value larger than 0. 6. Reduce the power of the light with the `Shadow Caustic` option enabled so it has only a small impact on the final render. (Note: The power of the light must be above 0 for this to work) - This step is not necessary, but it makes it much easier to see what's happening. 7. Render the scene. 8. Compare that render to another render with the `Shadow Caustic` light excluded from the final render. Notice how there was an impact on the shadow and caustics produced by the non-`Shadow Caustic` light. Here is a .blend file with steps 1-6 done for you: [#97932 - Overlapping Caustic Shadows issue.blend](https://archive.blender.org/developer/F13056206/T97932_-_Overlapping_Caustic_Shadows_issue.blend) The steps for testing with the file is as follows: 1. Open the attached file. 2. Render the scene. Notice the weird line in the caustics. 3. Disable `MNEE Light` from the final render and render again, comparing the result to the first render you did.

Alaska commented

2022-05-07 11:16:58 +02:00

Added subscriber: @Alaska

Alaska changed title from ~~Overlapping shadows of MNEE Caustics and filter glossy caustics produce errors~~ to Overlapping shadows of MNEE Caustics and filter glossy caustics produce incorrect result

2022-05-08 10:29:38 +02:00

Pratik Borhade commented

2022-05-09 08:02:19 +02:00

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

Pratik Borhade commented

2022-05-09 08:02:19 +02:00

Added subscribers: @PratikPB2123, @olivier.fx

Olivier Maury commented

2022-05-10 05:30:13 +02:00

Added subscribers: @Christophe-Hery, @brecht

Olivier Maury commented

2022-05-10 05:30:13 +02:00

Thanks @Alaska. As I understand it, this is an inherent problem due to the combination of:

the "Filter Glossy" feature being global and not light specific.
the overlap area being in the shadow of a caustic light.
The Filter Glossy feature blurs bsdfs indiscriminately at the cost of bias, which we need to disable for any point in the shadow of a caustic light in order to support true selective caustics. I will think about it more but that seems like challenging limitation to lift unless you disable Filter Glossy. Please let me know what you think.

cc @Christophe-Hery @brecht

Thanks @Alaska. As I understand it, this is an inherent problem due to the combination of: - the "Filter Glossy" feature being global and not light specific. - the overlap area being in the shadow of a caustic light. The Filter Glossy feature blurs bsdfs indiscriminately at the cost of bias, which we need to disable for any point in the shadow of a caustic light in order to support true selective caustics. I will think about it more but that seems like challenging limitation to lift unless you disable Filter Glossy. Please let me know what you think. cc @Christophe-Hery @brecht

Brecht Van Lommel commented

2022-05-17 21:17:20 +02:00

I've been thinking about this for a while but still can't see an obvious solution..