Finally, finally, finally, finally, for the first time since I started working on this feature several years ago, finally we have real-time global illumination with a second light bounce: Below you can see the direct light hitting the floor, bounding up to the ceiling, and then being reflected back down on the floor again.
Performance is still good and I have not started fine-tuning optimization yet. I was just trying to get the effect working at all, which was quite difficult to do, but now it works great.
In the shot above, ambient light is set to black. Although the GI does light up a lot of the room, there is probably still a place for a small amount of flat ambient light, which can then be darkened by the ambient occlusion effect.
Light leakage is really not an issue. The algorithm does a good job keeping dark indoor areas dark, and only lets light in where it should be.
While areas with more sunlight exposure are quite a lot more bright:
Everything else about Ultra Engine is great, but I think this is going to be the thing that really attracts a lot of people. I am very glad I get to include a feature so groundbreaking and amazing as this.