Quite a while ago a dev created a branch that exposed standard reflection probes to the material editor, which allowed it to be sampled for fake refraction. I imagine it’s possible to do the same thing with lumen’s probes. They might be too blurry to do much with, but it would be fine for some cases.
Pretty sure Half Life Alyx also used parallax corrected cubemaps in particular. Seemed like it was using some kind of primitive representation of the rooms. Not a simple, single box intersection test like most implementations.
It should be easy to parallax correct cubemaps in UE5 since you can just trace the existing distance fields to find the intersection point.
I started messing around with that for an alternative reflection system in the past, but never finished it. The idea was to either dynamically re-light the scene with texture-space GI and DF shadows, or make an array of precomputed cubemaps for various times of day if that was too expensive.
It was based on the Mafia reflection system, except the idea was to avoid having to constantly refresh the cubes in real time by re-lighting static cubes dynamically. They used a round-robin update cycle, so each cubemaps only updated once every 8 frames or so.
Not sure if it would’ve been better than lumen in performance or quality but it’s interesting enough I might revisit it eventually.