Unity Box Projection
Is there a way to replicate this in UE5? I’m lighting a test room, single BoxReflectionCapture in the center on the room. Can confirm that the capture is correct.
Not using Lumen or any SSR methods, it’s for mobile VR so I need to keep it old school.
This warps the reflection lookup vectors? Interesting.
The sphere versus box difference in Unreal has to do with how the texture is stored (spherical versus cube map projection,) but not how the reflection texture lookup is done as far as I know.
If you want reflections that work “right” along a wall, you can use a planar reflection capture (need to turn on clipping plane support) but that’s not a low-cost solution if you need six of them. Of course, if you don’t have that much geometry, it might be perfectly fine – you could try!
The other solution is ray tracing. Mobile VR will do that next generation, so depending on how long your projected project development time is, maybe that’s an option 
Box reflection capture should work. Last time I used the forward renderer you needed to enable “High Quality Reflections” in the material properties in order to get parallax corrected reflections.
Sadly I don’t know if this can be done on mobile. For whatever it’s worth, if you’re fairly adept with materials, it’s pretty easy to implement this yourself (though I have absolutely no idea if this will compile for gles or whatever mobile VR is using…)
It’s not very easy to work with if you need a lot of reflections, but for a few rooms it will work.
Yes! It can be done in UE for mobile VR. This is what you are looking for:
https://developer.arm.com/documentation/100959/0100/optimizations-and-optimization-techniques/cubemaps