In this article, the author explains the fundamentals of Radiance Cascades (RC), a method for efficiently representing radiance fields for real-time diffuse global illumination in 2D (Flatland). The key observations of RC involve angular and spatial resolutions, which determine probe spacing and interval counts. By exploiting these observations, RC uses cascades, grids of probes with equal properties that cascade outwards, to capture radiance data from the scene. The merging process involves merging intervals and cones from top to bottom cascade, utilizing bilinear interpolation for smooth penumbrae. This method allows for high-quality global illumination without temporal re-use, making it a clever and efficient solution for modern hardware.
https://m4xc.dev/articles/fundamental-rc/