UE4 4.24 SSGI + AO Implementation

[Riley1389]

@Goldwaters

This thread is entertaining, but unfortunately as Rawalanche correctly pointed out, AO is being misunderstood on a conceptual level.

GI is a more accurate lighting model that makes AO unnecessary in your lighting stage. GI encompasses far more of light’s actual behavior as rays travel through a scene than AO can ever be made to represent.

The comments about whether studios use AO or not… that’s kind of a moot point. But yes, big studios use AO. They use it for compositing and in shaders and material development yes, like both Rawalanche and K mentioned. (Not contradictory points, by the way)

Big studios who have raytracers would be foolish to use AO in any way in their base light transport and rendering model, and they don’t. But they do use it in grading, comp, shader dev, etc… for dirt and wear masks etc…

The GIF mentioned before does in fact make it clear that GI is a better and more realistic look. The SSAO shows artifacts and unnatural shadowing in comparison. Why would you want it?

i disagree. At least in this stage of real-time lighting solution like dynamic GI. The problem you get when relying on the SSGI, aside from it’s awful performance impact, stems from a lack of two different things. The first being an inherent limitation of screen space algorithms in general. Is that they falloff radically the closer the requested information starts going outside of the current camera POV. So when you combine a bunch of screen space techniques like SSSSS (Screen space subsurface scattering), SSR (Screen Space Reflections), SSAO (Screen space ambient occlusion), and/or SSGI you often get extremely noticeable fading.

However, knowing this, SSAO has an inherent advantage compared to SSGI’s current implementation. Which is the parameterization of how much the area the AO can influence. With a smaller radius, (say between 10-40), the AO is able to flesh out smaller details that bring more life and complexity to a scene than anything SSGI in UE4 could allow for. And the new alternative GTAO (Ground Truth AO) introduced in 4.24 also has a visual bug itself where the AO blur calculation seems to happen at the wrong step in the GTAO pass, leaving an extraordinary washout of detail shaidng. In addition, SSAO with a smaller radius requires just as much less screen info than it’s radius. So, it fades off futher out on screen when compared to the other screen space effects, breaking up the transition into something a bit less noticeable.

To compensate for only having short raidus SSAO, I often supplement it with DFAO for larger scale occlusion. I get great performing and looking results, everytime.