I actually had a hard time figuring out how to read surface colors, which is something I need to color indirect lights and obtain color bleeding in the end. In the end I came up with some very hackish code that for sure wouldn’t be accepted in trunk. On the other hand I can’t see a cleaner way to do that without some changes in the existing Blender codebase. I have to talk to some other developer and see what’s the best thing to do.

Anyway, right now I have the ability to generate 1st and 2nd bounce indirect lighting from area lights, taking colours into account. I was able to obtain a rendering like this one:

"Unfinished Match" with indirect lighting - Tree creation time: 00:04.64 - Lights: 19968 (0l + 0s + 19968o) (10000d + 9968i) - Error rate: 0.020 Max cut: 1000 - Average cut size: 362.88 - Shadow rays: 345.63 (1.73%)

The interesting thing is that this model was previously lit by a very complex lighting setup in order to fake indirect lighting. This rendering was obtained by placing a single area light behind the window.

Here are some more tests:

Here there's an area light near the wall, turned upwards at 45°.

Hangar test - Here I exaggerated indirect lighting through post-process.