Add minimum roughness project setting to improve VoxelGI/SDFGI performance

[Calinou]

Related to #56804.

The roughness will be clamped for the purposes of VoxelGI and SDFGI rendering. This avoids rendering sharp reflections, which are very demanding when taking significant portions of the screen.

Other sources of reflection such as ReflectionProbes and environment sky aren't affected.

This closes godotengine/godot-proposals#4811 and partially addresses godotengine/godot-proposals#3012.

Testing project: test_gi_opt.zip

Benchmark (using testing project)

Note that the test scene only uses smooth materials, so the performance gain demonstrated here is greater than it would be in a typical real world scene.

OS: Fedora 36
GPU: GeForce GTX 1080 (NVIDIA 510.68.02)
Resolution: 2560×1440

No GI

For reference purposes.

306 FPS (3.27 mspf)

VoxelGI only

VoxelGI min. roughness	Performance
0.0	170 FPS (5.88 mspf)
0.1	171 FPS (5.84 mspf)
0.2	181 FPS (5.52 mspf)
0.3	186 FPS (5.37 mspf)
0.4	195 FPS (5.12 mspf)
0.5	198 FPS (5.05 mspf)
0.6	200 FPS (5.00 mspf)
0.7	202 FPS (4.95 mspf)
0.8	204 FPS (4.90 mspf)
0.9	206 FPS (4.85 mspf)
1.0	208 FPS (4.81 mspf)

SDFGI only

Note: The sudden increase in performance at 0.2 is due to all sharp reflections being disabled within the SDFGI shader.

SDFGI min. roughness	Performance
0.00	122 FPS (8.20 mspf)
0.02	124 FPS (8.06 mspf)
0.04	125 FPS (8.00 mspf)
0.06	127 FPS (7.87 mspf)
0.08	128 FPS (7.81 mspf)
0.10	130 FPS (7.69 mspf)
0.12	132 FPS (7.58 mspf)
0.14	134 FPS (7.46 mspf)
0.16	135 FPS (7.41 mspf)
0.18	136 FPS (7.35 mspf)
0.20	166 FPS (6.02 mspf)

VoxelGI + SDFGI

Min. roughnesses	Performance
VoxelGI: 0.0, SDFGI: 0.00	96 FPS (10.42 mspf)
VoxelGI: 0.1, SDFGI: 0.02	97 FPS (10.31 mspf)
VoxelGI: 0.2, SDFGI: 0.04	101 FPS (9.90 mspf)
VoxelGI: 0.3, SDFGI: 0.06	105 FPS (9.52 mspf)
VoxelGI: 0.4, SDFGI: 0.08	108 FPS (9.26 mspf)
VoxelGI: 0.5, SDFGI: 0.10	110 FPS (9.09 mspf)
VoxelGI: 0.6, SDFGI: 0.12	111 FPS (9.00 mspf)
VoxelGI: 0.7, SDFGI: 0.14	113 FPS (8.85 mspf)
VoxelGI: 0.8, SDFGI: 0.16	115 FPS (8.70 mspf)
VoxelGI: 0.9, SDFGI: 0.18	117 FPS (8.55 mspf)
VoxelGI: 1.0, SDFGI: 0.20	138 FPS (7.25 mspf)

[clayjohn]

I like the idea! Let's reevaluate performance after reduz updates SDFGI and see if this still has the same benefit.

[jcostello]

I like the idea! Let's reevaluate performance after reduz updates SDFGI and see if this still has the same benefit.

Is this going to happen in the beta phase?

[Calinou]

Is this going to happen in the beta phase?

Yes 🙂

[reduz]

This is very hacky because SDFGI switches from sphere tracing to using the probes at a given angle, so at much that should be disabled directly. If you get the value wrong, it will be random when you fall into the sphere tracing range.

I think this should be done different. In fact, for the rewrite I want to make, I want to use a different way to do roughness when TAA is in use that should be a bit faster.

[jcostello]

@Calinou what is the update here?

[Calinou]

@Calinou what is the update here?

Just a rebase – nothing else is included. Note that this PR won't be merged as-is (see reduz's comment above). I'm only keeping it updated for reference purposes.