Now that I have the downsampled reflection data working, I can start casting rays. The cone step tracing is not a 100% perfect representation of physical light, but it gives a very favorable balance of quality and performance. Somehow I came up with a few formulas that eliminate light leaks and other artifacts.

Quite honestly I did not think the results would be this good. Indoor / outdoor scenes with thin walls are very difficult to prevent light leaks in, but somehow it's working very nicely, even with a blurry reflection. I am seeing some banding, but I'm sure that can be ironed out.

It's good to test reflections first because global illumination is just a bunch of reflection raycasts.

Adding in the GI component will be the next step.