Repository: godot
Issue: Godot Garden, A Ground Truth Lighting Reference
Labels: discussion,topic:rendering,topic:3d

### Godot version

4.0 Alpha 12

### System information

Windows 10, GTX1080, i7 6700

### Issue description

Upon request from @clayjohn , I've constructed a scene designed to test Godot 4's lighting tech in a ground-truth comparison (in this case, against Blender's Cycles raytracer).
An identical scene has been constructed across both Blender and Godot, with lighting properties and values matching as closely as I could manage. There is a variety of objects, materials and surfaces to test Godot's lighting in different scenarios.

All assets used are CC0, and everything is included in the files. This world is intended for demo/testing purposes but you're permitted to do whatever you want with it. If Blender cannot find the textures, simply select File > External Data > Find Missing Files, and navigate to the extracted folder the Blender file is contained in. If you have any issues with the files, don't hesitate to contact me here or via my Twitter (https://twitter.com/wickedinsignia).

**Download the Blender project [HERE](https://www.dropbox.com/s/lg07od8c79b02eg/BlenderGarden.zip?dl=0).
Download the Godot project [HERE](https://www.dropbox.com/s/cgyj111gi8ewp1s/GodotGarden.zip?dl=0).**

**Asset credits:**
Detailed PBR props are sourced from Polyhaven and all tiling textures are from AmbientCG/Polyhaven.

I made a few quick comparisons to highlight some shortcomings in Godot's realtime GI solutions, so it felt appropriate to post this in Bug Reports. If this resource would be more appropriate elsewhere please let me know!
All screenshots are taken with the settings default to the provided files, which were designed specifically not to stray far from Blender and Godot's default lighting values. All VoxelGI examples have "Two Bounces" active.

### Voxel GI lacks sky contribution:
SDFGI seems to be sufficiently realistic in the way that it treats sky indirect contribution, but VoxelGI is comparatively a lot warmer. Bounced light from objects seems to propagate in the space more severely and overpower the sky's contribution, but this issue seems to be mostly unique to the "Two Bounces" setting.

![GodotGarden_Render01_Cycles](https://user-images.githubusercontent.com/70243134/180632237-272f0b40-8854-4774-8ed1-b070b09386ad.jpg)
![GodotGarden_Render01_SDFGI](https://user-images.githubusercontent.com/70243134/180632239-f89a69e2-0098-4e46-b6f9-d2b78dce8b5f.jpg)
![GodotGarden_Render01_VoxelGI](https://user-images.githubusercontent.com/70243134/180632240-fc547615-a698-40a2-8d2d-3f3dbe2eeb3b.jpg)

### SDFGI exhibits strong light occlusion in inappropriate areas:
SDFGI will sometimes produce very strong blacks or shadowed areas in places that don't warrant them. This seems to be due to probes that are present inside of objects. The square base used here is non-manifold (bottom face is missing), which may be the cause for this particular example but these dark areas occur even in perfectly manifold intersections or even standalone objects. This issue is emphasized with a higher Min Cell Size, and can be mitigated somewhat with Probe Bias.

![GodotGarden_Render02_Cycles](https://user-images.githubusercontent.com/70243134/180632290-bacd09d5-ca3f-429d-9ccb-53eeab1736f8.jpg)
![GodotGarden_Render02_SDFGI](https://user-images.githubusercontent.com/70243134/180632294-4476c11c-9339-41cd-b535-e1b4a42b7121.jpg)
![GodotGarden_Render03_Cycles](https://user-images.githubusercontent.com/70243134/180632307-f114eb78-59e9-495b-a4a7-d5b11aaa54ec.jpg)
![GodotGarden_Render03_SDFGI](https://user-images.githubusercontent.com/70243134/180632309-f63115b9-8c17-4152-951f-3f5d1795f8e2.jpg)
![GodotGarden_Render08_Cycles](https://user-images.githubusercontent.com/70243134/180632563-60970f92-61ef-4736-9455-2fa58cee5f84.jpg)
![GodotGarden_Render08_SDFGI](https://user-images.githubusercontent.com/70243134/180632569-a22af5b4-783a-4c43-b9d0-8135b52cdd6b.jpg)


### Voxel GI produces strange highlights on highly reflective metals:
The "water" object in these scenes is a simple plane with 1 metallic and 0 roughness. Voxel GI creates superbright areas in the sunlit area of this object regardless of viewing angle.

![GodotGarden_Render04_Cycles](https://user-images.githubusercontent.com/70243134/180632385-8d884a93-7012-41cb-a8ff-0de09d5bf17d.jpg)
![GodotGarden_Render04_VoxelGI](https://user-images.githubusercontent.com/70243134/180632391-dda6ef8d-af84-40c3-978f-0009d80b78f4.jpg)

### SDFGI produces noisy results on large featureless surfaces:
GI results from SDFGI produce noticeable spotty variations on large broad simple surfaces, not unlike sampling noise from a raytracer. This is experienced primarily at higher settings, and can be mitigated with a higher Min Cell Size. Very noticeable on non-textural surfaces.

![GodotGarden_Render05_Cycles](https://user-images.githubusercontent.com/70243134/180632472-d6c3131c-a567-4a6c-82ef-9eb9d85f3c3c.jpg)
![GodotGarden_Render05_SDFGI](https://user-images.githubusercontent.com/70243134/180632474-9732c5eb-718b-44dd-ae49-372707d6a96c.jpg)

### SDFGI reflection light leaks:
The Water object receives light reflections near the base of this large structure, even though it is well-extended into the water object, both objects are manifold and both are considerably thick.

![GodotGarden_Render06_SDFGI](https://user-images.githubusercontent.com/70243134/180632507-217034f1-921c-4de0-90b4-d18143fa889b.jpg)

### SDFGI coarse normal maps:
SDFGI sometimes sends very strong direction information to surrounding normal maps, which seem to be the result of occluded probes.

![GodotGarden_Render07_Cycles](https://user-images.githubusercontent.com/70243134/180632549-61b4226e-88fe-4b88-9d20-3bbb56a74c90.jpg)
![GodotGarden_Render07_SDFGI](https://user-images.githubusercontent.com/70243134/180632553-375f7cd4-57d3-4fc6-ae2d-a7ef6144a035.jpg)

### Steps to reproduce

Please feel free to check out both files and mess around!

### Minimal reproduction project

Attached in description.