Illumination Tutorial for Software 3D Rendering (2/2+) [c++20] (https://www.youtube.com/watch?v=eXU-6_jmw7Q) was just released by Bisqwit and it goes over a rather naive implementation of real-time global illumination. The demo uses very basic geometry with a Minecraft look and shows the progress of paths being traced on the CPU. Compared to the Godot demo, the naive implementation is unworkably slow. Nevertheless, Bisqwit's video explains the concepts and basic code implementation admirably.