MNEE caustics with Multiscatter GGX materials are inconsistent. #96990

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Alaska · 2022-04-03T00:10:10+02:00

Alaska commented

2022-04-03 00:10:10 +02:00

System Information
Operating system: Linux-5.16.0-5-amd64-x86_64-with-glibc2.33 64 Bits
Graphics card: NVIDIA GeForce RTX 3060/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 510.54

Blender Version
Broken: version: 3.2.0 Alpha, branch: master, commit date: 2022-04-02 21:17, hash: 4537eb0c3b
Worked: Never. This feature was introduced very recently.

Short description of error
MNEE caustic behavior with Multiscatter GGX is inconsistent between different materials.

According to D13533: Adding Manifold Next Event Estimation Sampling Technique the MNEE caustics introduced in 1fb0247497 have limited compatibility:

Compatibility: Only the GGX and Beckmann microfacet distribution-based refraction bsdfs are compatible with MNEE currently (e.g. PrincipledBsdf, GlassBsdf).

As such it would be expected that Multiscatter GGX materials would not produce caustics using MNEE. However, they do when the roughness is set to 0, but only on the Principled BSDF. The Glass BSDF does not produce caustics when using Multiscatter GGX, even when set to 0.

This behavior (some materials producing caustics at roughness 0 while others don't) is inconsistent and probably isn't intended. Hence why I am reporting it.


Caustics visible on Multiscatter GGX `Principled BSDF`	Caustics not visible on Multiscatter GGX `Glass BSDF`

Exact steps for others to reproduce the error

Change the render engine to Cycles.
Setup the scene for MNEE caustics. (Set a Caustic caster, caustic receiver, and caustic shadow light)
Give the caustic caster a Principled BSDF, increase the transmission, set the roughness to 0, and change the microfacet distribution to Multiscatter GGX. Notice that the caustic caster is casting caustics.
Change the material of the caustic caster to a Glass BSDF, set the roughness to 0, and change the microfacet distribution to Multiscatter GGX. Notice the lack of caustics/the inconsistent behaviour between the two materials.

Here is a file with steps 1-3 done for you.
#96990 - Multiscatter GGX inconsistency.blend

**System Information** Operating system: Linux-5.16.0-5-amd64-x86_64-with-glibc2.33 64 Bits Graphics card: NVIDIA GeForce RTX 3060/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 510.54 **Blender Version** Broken: version: 3.2.0 Alpha, branch: master, commit date: 2022-04-02 21:17, hash: `4537eb0c3b` Worked: Never. This feature was introduced very recently. **Short description of error** MNEE caustic behavior with Multiscatter GGX is inconsistent between different materials. According to [D13533: Adding Manifold Next Event Estimation Sampling Technique](https://archive.blender.org/developer/D13533) the MNEE caustics introduced in 1fb0247497 have limited compatibility: > Compatibility: Only the GGX and Beckmann microfacet distribution-based refraction bsdfs are compatible with MNEE currently (e.g. PrincipledBsdf, GlassBsdf). As such it would be expected that Multiscatter GGX materials would not produce caustics using MNEE. However, they do when the roughness is set to 0, but only on the `Principled BSDF`. The `Glass BSDF` does not produce caustics when using Multiscatter GGX, even when set to 0. This behavior (some materials producing caustics at roughness 0 while others don't) is inconsistent and probably isn't intended. Hence why I am reporting it. |![Multiscatter GGX Principled.png](https://archive.blender.org/developer/F12965064/Multiscatter_GGX_Principled.png)|![Multiscatter GGX Glass.png](https://archive.blender.org/developer/F12965062/Multiscatter_GGX_Glass.png)| | -- | -- | |Caustics visible on Multiscatter GGX `Principled BSDF`|Caustics not visible on Multiscatter GGX `Glass BSDF`| **Exact steps for others to reproduce the error** 1. Change the render engine to Cycles. 2. Setup the scene for MNEE caustics. (Set a Caustic caster, caustic receiver, and caustic shadow light) 3. Give the caustic caster a `Principled BSDF`, increase the `transmission`, set the roughness to `0`, and change the microfacet distribution to `Multiscatter GGX`. Notice that the caustic caster is casting caustics. 4. Change the material of the caustic caster to a `Glass BSDF`, set the roughness to `0`, and change the microfacet distribution to `Multiscatter GGX`. Notice the lack of caustics/the inconsistent behaviour between the two materials. Here is a file with steps 1-3 done for you. [#96990 - Multiscatter GGX inconsistency.blend](https://archive.blender.org/developer/F12965067/T96990_-_Multiscatter_GGX_inconsistency.blend)

Alaska commented

2022-04-03 00:10:10 +02:00

Added subscriber: @Alaska