Hopefully not a stupid question because I immediately had the same though.
But at the very least it sounds like it could be done with a custom shading model if needed.
That makes good sense.
Its kind of hard for me to generalize the cases, but I’d say it’s typically at its worst when the screen tracing causes significant visual discontinuities between the ray trace and the screen trace. This is usually due to a difference in how the surface and/or hit lighting is drawing an object vs it’s lit view (and thus its resulting screen traces).
You can see an example of this with the foliage on my last post, where the hit lighting presumably doesn’t evaluate the light transmission and the raytraced leaves are much darker than the screen-traced leaves.
In that example, the screen trace is more believable to my eye, but the discontinuities as you transition between them are the real issue.
Similar problems happen with other materials, for example when using distance fields in the shader. Some of these I hope and expect will be solved as other parts of Lumen are improved.
Materials whose Lumen reflection view representation are a close match to the lit view look great and the transition to screen traces are near invisible.
And all said and done, these discontinuities are still better than the old way of doing things like with SSR and probes.
I’ll test out the threshold setting and post results later tonight.