UE4 4.24 SSGI + AO Implementation

[Poet_11 (William K)]

@Rawalanche

Why would you introduce AO to SSGI though? AO is an old trick originally designed to fake indirect light occlusion in areas lit by fake constant ambient light contribution. Later, in some earlier inaccurate offline renderers, it was used to introduce indirect illumination occlusion detail for extremely inaccurate global illumination solutions, such as Final Gathering in Mental Ray (which had especially poor Final Gather implementation) or Irradiance Cache in VRay.

But SSGI is neither of those. It’s not just constant ambient light, or is terribly inaccurate when it comes to spatial detail density. Introducing AO into SSGI would give you worse, less realistic results and additional computational overhead at the same time. Or in other words, your rendering is slower and you get worse quality in return. A loss/loss scenario.

There seems to be indeed occlusion already built into SSGI already, and I believe that any attempts at artistic control of it will just give you more bias and reduce realism. And trust me, despite what you may think, there’s nothing artistic about overkilled amount of AO in scenes, unless your artistic intent was to simulate consistently uniform accumulation of a smoke ash in concave areas if your map

Because SSGI is still a hack and faaaar from anything remotely accurate or even GI, it is a desperate one bounce color bleed on a post process effect and it has tons of its own smears and limitations. AO is what you need to catch those edges, we still use AO heavily in a subtle way on offline raytrace renderers!

Both post process AO and SSGI should be used in a very subtle manner as an addition to whatever base shaders you built any excessive or primary uses of these effects creates horrible visual artifacts during motion and muddy imagery during both motion and stills.