Temporal Antialiasing and Screenspace Ambient Occlusion

[JMS55]

(somewhat outdated screenshot of Sponza SSAO texture - the quality has improved since taking this)

Objective

• Add temporal antialiasing - a method of antialiasing, like MSAA or FXAA.
  • Scales with screen resolution, and not triangle count.
  • Reduces more forms of aliasing than MSAA.
  • Reduces noise in other rendering effects (SSAO, eventually SSR/PCF/RT/etc).
  • Con: chance of "ghosting", often need game-specific tunable heuristics.
  • Closes Temporal Anti-Aliasing #3663.
• Add screen space ambient occlusion.
  • Darkens creases between objects and other occluded areas, creating shadows in areas that should have less indirect light in them due to other geometry occluding light.
  • Closes Screen Space Ambient Occlusion #3632.

These two features are being implemented together as TAA greatly increases the quality of SSAO, and I developed them together in parallel, tweaking one or the other. I would split TAA into it's own PR first, but I don't currently have time to do so, and multiple-dependent PRs (depth prepass -> TAA -> SSAO) is tricky (especially when it comes to rebasing), hence why this is a single PR marked as draft.

Remaining Work

• Double check depth preprocessing for SSAO is correct with bevy's coordinate systems (reverse z)
• More TAA disocclusion heuristics (stencil, velocity, depth?), and make them tunable (maybe future PR)
• Documentation
• Better TAA example
• TAA orthographic projection support (maybe future PR)
• SSAO MSAA support?
• TAA mip bias for sharper textures
• Optimizations (future PR)
  • Faster coordinate space conversions (don't do full matrix multiples, precalculate some converted textures)
  • SSAO spatial denoise 2 pixels per thread, instead of 1 (XeGTAO says this is faster, need to benchmark)
  • F16 math (missing support in wgpu afaik)

Blockers

• Depends on [Merged by Bors] - Add depth and normal prepass  #6284.
• Requires wgpu commit 5a2e60c50e54330607b6886f9107d9ad699274c0 or newer.

Solution

• TODO: Describe general TAA/SSAO overview
• In lieu of a full explanation, here's my main TAA reference: https://www.elopezr.com/temporal-aa-and-the-quest-for-the-holy-trail
• And the GTAO paper: https://www.activision.com/cdn/research/Practical_Real_Time_Strategies_for_Accurate_Indirect_Occlusion_NEW%20VERSION_COLOR.pdf

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Changelog

• TODO

Migration Guide

• TODO

Credits

Huge thanks to robswain, Danciel C, IceSentry, Griffin, cryscan, and others for various help with this PR. Thanks to Intel for XeGTAO, which is a great reference for implementing and optimizing GTAO.

[alice-i-cecile]

For the folks who aren't rendering experts, can you edit your PR description to explain what these are, and why they're being implemented together?

[JMS55]

For the folks who aren't rendering experts, can you edit your PR description to explain what these are, and why they're being implemented together?

I edited my PR to have a brief description. See the linked issues for further explanations. Let me know if it's not detailed enough, still.

[JMS55]

Now that the prepass has been merged, I'm splitting up this PR and opening it as separate PRs.