Exciting RTGI news!

One of the recurring topics of christmas Q&A talk has been the usage of MXAO on top of the RTGI shader. I wasn't really aware small scale details are that much of an issue before. So to unwind between christmas and NYE, I spent some time drafting some solutions for this problem and this planning came to fruition:

I came up with two improvements to the ray intersector. With the previous code, one really had to choose between small detail or large range GI, both was hardly possible. As can be seen in the first comparison and especially, the magnified area, small areas such as that step on the pillar hardly bounced any light on the wall before. Some rare rays caught this detail but not enough. The new method will catch this and many other small details effortlessly.  The debug app doesn't really do this feature justice but Witcher 3 decided to give up on me..

Now when toying around with this, I found another problem: light leaking. Some objects should cast directional shadows but for some reason, don't do it. Investigation showed that the calculated intersection and the actual intersection were often quite off. The shader efficiently found intersections (creating accurate ambient occlusion) but wasn't really good at pinpointing them (creating incorrect bounce light). A quick and dirty fix solved that problem for good, but I'm investigating even better methods. Additionally, the new method makes the GI overall darker, so I'm trying to find ways to boost the GI intensity without going haywire with the physical correctness [too much].

Incidentally, one of the new features even improves performance. So after the significant gain of 0.8.2, this new feature might even give some headroom for other shenanigans where one can trade performance for quality, who knows. Filter needs a bit reworking as well, as the newly found details can be so small, the current filter just washes them away.

Promising stuff to kick off 2020!