clayjohn
commented
2 years ago For reference, this proposal would require replacing: https://github.com/godotengine/godot/blob/563690347a6b9da4882bca15ebd9f3d79f30d3e6/servers/rendering/renderer_rd/shaders/scene_forward_clustered.glsl#L1326-L1338
with a more accurate DFG LUT.
Describe the project you are working on
The Godot editor :slightly_smiling_face:
Describe the problem or limitation you are having in your project
Godot's current PBR model only simulates a single bounce within material microfacets. Since light in real life can bounce several times, this will darken rough materials, especially those with higher metallic values.
This is especially noticeable if most of your lighting comes from environment reflections. That said, even if you have other direct and indirect light sources, the brightness reduction in metallic rough materials is noticeable:
This also occurs with alternative diffuse modes (all screenshots have a light):
If a good multiscattering approximation is implemented, the spheres would become almost invisible as their reflection would match the background sky (even when there is no DirectionalLight3D).
Testing project (
master): test_multiscatter.zipDescribe the feature / enhancement and how it helps to overcome the problem or limitation
Implement multiscattering in the GGX formula used by Godot materials.
Describe how your proposal will work, with code, pseudo-code, mock-ups, and/or diagrams
Filament uses a fast approximation of multi-scatter GGX. See 4.7.2 Energy loss in specular reflectance in the Filament PBR documentation.
The long-term goal is to make Godot's PBR model as close as possible to Filament, as it provides a good balance between performance and physical accuracy.
Since this will change the visual appearance of some scenes, it's best to implement this feature before Godot 4.0 is released.
If this enhancement will not be used often, can it be worked around with a few lines of script?
No.
Is there a reason why this should be core and not an add-on in the asset library?
PBR appearance is core rendering functionality. Other rendering engines such as Blender's Eevee now feature multi-scatter GGX, so it's important for Godot to stay on the same wavelength to ensure more consistent visuals across rendering engines.
Keywords for easier searching: multiscatter, multiscattering, multi-scattering