Solari v7

[JMS55]

This is a major rewrite of Solari.

The old version did DI, diffuse GI, and specular GI / mirror DI in 3 separate passes. Only diffuse rays were resampled, and no rays were traced for cross-domain MIS weight, leading to bias.

This new version is one unified algorithm that handles diffuse and specular DI and GI all in one reservoir. Resampling takes the full BRDF into account, as well as cross-domain visibility in MIS weights.

Advantages:

• Much less biased
• Much less prone to GI light-leaks
• Improved specular GI quality
• Improved DI quality for nearby lights thanks to BRDF sampling for DI
• Less memory usage

Disadvantages:

• A bit slower due to the extra rays traced

Showcase

Reference

This PR (with DLSS)

Main (with DLSS)

This PR

Main

[github-actions]

You added a new example but didn't add metadata for it. Please update the root Cargo.toml file.

[stuartparmenter]

The math looks right, but given the complexity and to double check it all I ran a small simulation against using your math to check for bias and it looks good after your fixes. I also wired it in to a number of example scenes (bistro, etc) and it looks better / don't see any visual regressions.

[github-actions]

It looks like your PR has been selected for a highlight in the next release blog post, but you didn't provide a release note.

Please review the instructions for writing release notes, then expand or revise the content in the release notes directory to showcase your changes.

[alice-i-cecile]

This is a good candidate for a dedicated release note. Feel free to just copy-paste the stuff from your PR description as the stub if you'd like :)