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To answer: Image based diffuse GI isn’t very good, there’s a lot of errors that creep up because you’re just projecting what amounts to a box of 6 flat planes onto a large area, and there’s a lot of light leak and incorrect lighting going on as a result. I.E. a column or other object “in the middle” of the box isn’t going to contribute to GI in any way because it’s in the middle rather than “along the walls” of the box. In fact anything but a solid wall along the flat planes of the “box” are going to look pretty bad when contributing to GI.
It’s also really expensive and limiting to do any image based GI in realtime, only Assassin’s Creed Unity and whatever that new one is really even try, and they spend a lot of time on it, and it still ends up with a lot of errors. Considering UE4 has both a prebaked lightmap/cubemap solution already in place, and an actually dynamic GI system under development, there doesn’t really seem to be any need for this.
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Not really, did you really see any light leak in that Marmoset Skyshop tech demo? It’s just not a physically correct lighting solution, some corners out of probes bounds would look not so correct, but a good probes placement tactic would somehow fix it, additionaly, combining a good AO solution(UE4’s DFAO is really good at working with IBL). Actually you won’t get any physically correct lighting solution in game devlopment until the day realtime path tracing comes. Even baking lightmap will get light leak when you have to use very low lightmap resolution for large scenes. For most “real” dynamic GI solutions nowadays, you will suffer even much more light leak results, and other problems such as performance hit, view distance issues, over-time artifact… etc. You know, even CryEngine had abandoned their LPV GI solution which they used to be proud of and went for local IBL to simulating GI I mentioned previously (They entirly used it combining SSDO with color bleeding for GI lighting in “RYSE”). They also recommended users for turning off LPV in new projects.
PS: This solution is really cheap comparing to other dynamic GI solutions. I’d tried Marmoset Skyshop in Unity3D, I didn’t see any performance hit at all running on a very old, low-end graphic card such as AMD HD6700. But for VXGI in UE4, just ony a cornell box scene would drop the framerate down to under 20.