I have a lot of re-balancing to do with my ENB (any tone changes there effect the RT/path-traced GI,) but there is no going back. I disabled the HBAO+ from the engine... actually disabled the AO completely, going for nothing but a little ENB SSAO (carefully dialed-in to add just a little dimension, reducing sampling to further cut both effect and performance hit.) FO4's HBAO+ is nice, but with the GI, it becomes too distracting and overrides too much of both the bounce light and shadows drawn. That's aside from the fact that it's fairly heavy when you are running a lot of extremely GPU-intensive stuff. I had to drop the ENB IL considerably for similar reasons - it sets off odd beams of distracting glow around some edges, even though a little bit is still needed to blend the GI in, like with the AO. I needed the performance boost regardless, but I realized I had too much in general and the images look smoother and less crowded with far less. The GI can add its own contrast quite a lot *like* MXAO, but more meticulously congruent with light angles than an AO algorithm would ever manage. ENB has localshadows to add a sense of dimension to ground foliage and other smaller polygonal contours and shapes close-to/on the ground - you don't need AO for that and in fact, strong AO crowds it out with darkness eating grass. Leave room for more dynamic GI.
I had to capitulate on performance with that stuff either way - the RTGI shader needs a decent amount of samples to work to its fullest, which had my 2060 dipping as low as 45fps at times - hence delving into the AO downsize. I did gain ~3-4 frames in the worst cases that way.
When it comes to the RTGI shader, the sample-per-ray count adds to what catches and how much/far. Basically, RTGI throws rays out from the camera towards sources, but on the bounce path, it diffuses out on tangential 'sub-bounces'. I crank it to 14 out of 20. Every ray hits up to 14 sub-bounces, only stopped if it surpasses its 'ray length' (actually more of a time-out,) before hitting a bounce point again. Technically, it goes a step further than RTX in this regard. You crank the ray length to smooth it out a little, so it doesn't poke too starkly through fog or cause 'lighter burn' black marks on smaller surfaces (it can even turn actors into black silhouettes.) If they time-out sooner, the effect gets condensed closer to the bounce-point - the more 'time' you give them, the further that same total amount of light/shadow stretches out.
I was able to pull a lot more bounce lights and shadows out of RTGI by dialing up the path-tracing samples and increasing how long it runs. Keep the ray count at 4-6 and sample at half-res for +35% performance boost without noticeable loss in effect or quality. This got me back to 50-60 fps everywhere.
RadiantGI only ever uses one ray, can run on just 4 samples, and allows for half-res sampling, but the main cost is always the amount of denoise filtering you add, which is absolutely needed to avoid unsightly haloing at higher GI power levels. It forms massive jello globs of light without it. But it's so great with brightly-lit areas when set to catch on the right distance range. It also has that distance ground emittance that sets off levels in the mid-background. But generalized emittance also catches on a lot of what the bloom itself throws out on surfaces, creating this blended effect. All said and done, they add a great amount of depth and dimension to everything - I love what it does, even though it can be very GPU-heavy. It just took some re-configuring to get the power to run them right and still have them both doing what they do best - together.
This has taught me a lot about what it must take to work RTX GI into a game and have it look right. It takes some changes to the imagespace and post-processing, in addition to tuning the many non-intuitive parameters of the GI itself, which I imagine are much more involved with the Nvidia-sauce. Though one of the shaders I'm using is supposedly informed directly by said sauce. Either way, it is the real deal. Color me impressed. It was well worth the learning curve.
In the process of streamlining, I dropped the Kawase blur bloom I was feeding as an override via ENB from 25 stages to just 5... which as I expected, gave me back about 4-5 frames constant. But as I hadn't expected, gave me a noticeably stronger, but softer bloom at lower overall values in the main settings. Still looks pretty high-fidelity. I do recommend that shader for ENB users, it's so nice and 'modern' looking. It plays with this GI stuff to give everything this warmly-saturated, misty look that I think really suits the game and gives it an almost next-gen level fancyness. But even on its own, Kawase really adds a lot of organic general warmth to things - especially in the exponentially less GPU-intensive 5-stage mode.
When you factor in all of the the grading, lighting, tone/contrast-shaping, and massively upgraded bloom dialed in via ENB, I think it finally starts breaking away from the base game on a level that has already been possible in Skyrim. It helps to have upgraded textures, too. Better materials come out smoother and more natural under the GI. More than anything it is about the quality of the normal and specular mapping. And I don't just mean like, the data fidelity of them, but how well-done they really are - UV coherence included. I've spent a lot of time scouting those out for nearly every object and surface in FO4.
I need to get screenshots with characters in them. It has a really dramatic effect on actors, mostly in the shadows drawn onto them by RTGI (though the bounce-light does catch prominently when they're near enough to a strong enough source.) Actors also benefit a lot from the path-trace-assisted subsurface scattering provided by RadiantGI. The latter really has a way of cleaning up their faces and giving them smooth, fleshy substance, while the former puts them much more *where they are* in the scene. RTGI is most consistently dramatic on them.
The only downside to doing path-traced lighting through ReShade is that it draws *over* engine-generated fog. With interiors, shadows on some objects have that same starkness as AO over fog in spots. The shadowed sections just cut sharply through the fog as the object/surface stretches into the distance. I'll need to mod the distance fog inside down a bit to make it less obvious.
Outside, this isn't often an issue, as I have the fog far out enough that GI shadows do nothing by the time fog is a major factor. Stuff that's close enough to catch is better cutting through. It does catch gobs of bounce lighting and sky emittance that wash-out a lot of occlusion not on the backs of trees, which gives it a lot of extra dimension over distance. The shadows mostly hit on things blocking the sun close to you, combining with the aforementioned distant-fog-gathering to give a stronger sense of separation across the whole image. The fog grows brighter between the trees it courses through in the distance, and pockets of shadow cast by those same trees loom darker behind and beneath them.
I need to mess with my gamma and tone shaping in ENB more to maximize the effect. It will actually multiply the strength of the GI. I can give it more headroom in ENB, make room starting with the engine-level output and proceed to make the global illumination stronger in order bring more clean, dimensional contrast than is otherwise possible without cooking the image like a bad photoshop from the 2000's. That's where the magic of this whole path-traced lighting effect is - it essentially creates a new lighting dynamic that is both stronger and more nuanced, both making the images appear more natural and adding a subtle, but crucial form of depth. That is the one engine-level part about this. It uses engine depth information to draw path-traced illumination effects.
It's not that I can't see what they're doing with the effect enabled normally... what they do is just inconsistent... as in how they factor in varies by scene. Both shaders have different ways of being tailored with lots of oddly specific options that you could never guess that you absolutely need. I think this would always have to be configured very closely to the game to really look right at all. It's tricky, but rewarding.
