SEUS PTGI Development Update: Sunlight and Infinite Bounces!

EDIT: SEUS PTGI E3 is out now! https://www.patreon.com/posts/22415508

Exciting news about SEUS PTGI!

So, first of all, I've gotten sunlight with proper GI contribution working with path traced GI! I also was able to optimize the inner path tracing code, so optimized path tracing + sunlight contribution ended up actually being faster than previously.

Then, I created a system that allows for infinite bounces with path-traced GI! Reducing the main per-pixel number of bounces to 1 (from 2) greatly improves performance, so I figured that would make room for a system where per-block, light rays are randomly traced and accumulated in a feedback loop so that, with each new frame, an additional bounce is calculated. Since 2nd and onward bounces don't need to be super spatially precise, this works really well.

In simple scenes, this new approach actually vastly outperforms the previous brute-force 2 bounces approach. In typical scenes, there's still an improvement, and that performance gain narrows as scenes get more complex. I haven't yet encountered a situation where it performed worse!

One drawback is that, in areas that aren't well-lit (like a large room with only one glowstone block in it), you can see random blocks show a sort of "light breathing", or very low-frequency undulation. This can be pretty bad at its worst, but I think it's overall worth it.

Also, it takes a while for secondary bounces to "catch up" to lighting changes. Again, I feel the benefits outweigh the drawbacks, especially considering that the primary path traced lighting took some time to catch up anyway.

I've also made some pretty substantial improvements to the filtering stage so that details in shadows/lighting aren't blurred out nearly as much as they were before. That's just as exciting to me!

Here's a scene where infinite bounces really makes a difference. Here's with the previous, 2-bounce-only approach:

And here's with infinite bounces (this was before I improved the filter, so things are a bit blurry):

And finally, here's a comparison between SEUS PTGI E2 and my latest progress.

Check out the improved detail in the shadows in this scene!