Vulkan: SDFGI incorrectly reads certain high-contrast textures for cascade generation

[fLindahl]

Godot version

v4.1.3

System information

Godot v4.1.3.stable.mono - Windows 10.0.19045 - Vulkan (Forward+) - dedicated AMD Radeon RX 6900 XT (Advanced Micro Devices, Inc.; 31.0.22023.1014) - AMD Ryzen 9 5900X 12-Core Processor (24 Threads)

Issue description

Trying to use SDFGI, but I'm getting strange artefacts and incorrect bounce colors. Checked the cascades and the pictures show (I think) the problem.

Any ideas on why this happens?

I've tried loading different scenes with different textures, and it seems to work fine with most assets, but with these specific textures (no matter if they're jpg, bmp or png), it just doesn't work as expected. The textures are quite basic and without a lot of color, and I'm thinking that it might be a compression issue specifically for SDFGI. I've attached the GLB as well, so that others can test.

Steps to reproduce

1. Setup SDFGI in scene with directional light.
2. Add entrance.glb into scene
3. Enable visualization of SDFGI cascades

Minimal reproduction project

entrance.zip

[Calinou]

SDFGI doesn't use VRAM compression (it's generated in real-time), so this looks like a more generic type of corruption.

[fLindahl]

I did some further testing and took some more screens:

Those are the same view, same material, in sdfgi cascade view and normal view.
I set the SDFGI cascades to be a single cascade and changed the cellsize to be 0.02 (very small voxels). You can make out that the "general shape" of the colors are there, but the actual colors are crunched into oblivion. Is there some bias towards more vibrant colors that goes bonkers with such low fidelity textures? I know I've seen biasing towards vibrant colors in other GI implementations to get more pronounced color bleeding effect.

[fLindahl]

SDFGCornell.zip

Minimal repro

[Calinou]

I don't see anything out of the ordinary in #85058 (comment) (4.2.beta da0b1eb, Linux, GeForce RTX 4090 with NVIDIA 535.129.03):

SDFGI disabled	SDFGI enabled

Remember to disable VRAM compression on the textures in the Import dock by using Lossless compression instead. The textures used are low-resolution, so they don't use much VRAM. That said, this doesn't affect SDFGI appearance in any noticeable manner either way. I've done this on the above screenshots, which fixes the grid pattern appearing on the gray checkerboard texture on the floor.

The SDFGI debug view does have this "crunchy" appearance that you mention, but in this particular example, it doesn't really affect how visuals will look in practice. Also, remember that the normal view uses specular lighting, while the SDFGI debug view doesn't. If I set the specular mode to Disabled on the materials used by the brick textures, it looks closer to the SDFGI debug view as the bricks' mortar can actually become black in the normal view:

Normal view	SDFGI Cascades view

Either way, SDFGI is planned to get a rework in a future 4.x version, so this may be incindentally resolved.

---

With entrance.glb, I can reproduce the issue mentioned in OP:

Disabling VRAM compression on textures doesn't resolve the issue. I've also tried increasing texture resolution by 4× on each axis using parallel mogrify -resize 200% ::: *.png to no avail.

Reducing texture contrast using parallel magick {} +sigmoidal-contrast 10,50% {} ::: *.png largely alleviates the situation:

That said, even with this reduced contrast (and increased brightness), lighting from SDFGI has a lot of trouble bouncing (it's barely visible in most cases).

Testing project: SDFGCornell_2.zip