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@**rosegoldslugs **thank you very much for the link. Everything makes sense for me now. As you said the visual difference between forced surface and volumetric still exists but I hope Epic will improve things even further. But even this was a dream in previous versions so looking forward for the improvement.
By the way. Found this today. This is how the developers improved Call Of Duty infinite warfare lighting. They used both lightmap and probe lighting too. I do not know how technically all that works but I can see they solved the lack of AO and self shadowing problem in prob lighting method and even light leaking from outside to inside through the wall during prob lighting. From my limited understanding those 2 features are really necessary. And on top of that blendable lightmaps would be some serious stuff in UE4.