Go to the following link to run the demo live in your browser. The demo requires WebGL2 to run which most browsers should support (Safari on ios is one notable exception).
This is a simulation of global illumination using the technique known as Radiosity. The light in this scene has been calculated in real time almost entirely on the GPU through several shader passes, mostly following the method presented in Chapter 39 of GPU Gems. The demo is written in modern C++ using SDL and OpenGL, cross-compiled to WebASM using emscripten.