A real time GI solver ( faked anyway, because you can't do physically accurate GI in realtime.. yet ) is the 'Graal' of any realtime engine these days.
In order to have a realtime GI solver you first have to implement a linear workflow or else you get awefull wrong results.
Then, most realtime GI solvers use local IBL lighting ( a 2d or 3d grid of cubic or spherical or spherical-harmonic light maps ) where the IBL lights are precomputed but updated in realtime according to local changes ( a character passing by, a light change, a shadow crossing, etc.. ). This makes the process fast because usualy little changes occur at a time at one place.
This is why I've mentioned linear workflow and local IBL lighting in another thread. Having local IBL lighting decoupled from an automatic GI illumination solver would be interresting though, so we could decide local lighting manualy if we want to.
I'm not sure what you mean by "a simple GI solver", but there is the SSAO ( Screen Space Ambient Occlusion ) way, with a variant that can fake GI, but it's far from beeing accurate and is very biased.
From my point of view, the most important factor for nice GI like rendering is the ambient occlusion one. With it and any IBL ( even with IBL that has nothing to do with the current lighting set ) you can start to have very nice results.
In fact, you can start to have some decent results already with pre-baked ambient occlusion maps in the 'Blend' channel ( with multiply ). It require some work, but the results worth the effort. I intent to show some exemples of this approach soon. It works for all static geometries ( sets, some props, etc.. ).
I'm working on another idea to simulate multiple local IBL lighting with multi-passes rendering ( you render several times the same take with different light sets and settings, then you composite those passes together ). This way you also get ride of the 4 lights ( spot or omni ) limit. I'll show some results as well soon.
I'm confident it's possible to have some very nice results, granted using some elbow grease, results yet unseen still using the current iClone renderer.
guy rabiller | GOETZIWOOD STUDIOS
"N.O.E." (Nations Of Earth) Sci-Fi TV Show, Showrunner.