So I have been playing with my real time Global Illumination renderer some more. I added a particle system to model a rocket engine. The particle system is comprised of 1024 particles. And the kicker is: each and every particle is a light source that casts both direct and indirect light. For each particle, 24 photons are fired in random directions. When a photon hits a surface, a secondary photon is emitted in a diffusely reflected direction. This bounced photon creates the indirect illumination. See for instance the red and green glows that are created if the engine is close to a coloured wall.
In the video, the best demonstration of indirect light happens as very short flashes of green and red on the sides of the center block. If the engine flame is directly above the center block, its light cannot directly reach the sides. So mainly the light bouncing off the coloured walls reaches the sides, causing them to briefly flash in green or red before going bright white as the engine light shines directly upon it.
It currently runs 60fps on a single Haswell core. But I plan on multi threading the code so that I can increase the photon count. This should reduce the light flicker. The code is in AVX2 intrinsics, so it's rather incompatible with most PCs. I may have to port it to AVX or SSE at some point in time.
Next up in my GI research is integration into an actual game, preferably with rockets of course. I feel like making a GI homage to the ZX Spectrum classic JetPac.