These changes would definetly help. But on mobile problem is that when you active planar reflections all materials will use clip plane. This is implemented with discard. On iOS performance will drop to half by just enabling global clip plane. Even if you never use planar reflections.
To actually make planar reflections viable for mobile Materials would need two permutations with and without clip plane. Futher optimization would only use clip plane shader at planar reflection pass when object bounding box is actually clipping with the reflection plane. This would limit use of the really expensive shader to only couple objects instead of all of them.
Nice work - I have a planar reflection in use almost 100% of the time in my game so any optimisations like these are always welcomed if Epic will approve them. Not sure it will help lots in my case (not a lot of occlusion culling happening, and I don’t use prefiltering), but when you’re going for 60FPS, every fraction of a ms is useful!
How big you planar reflection actors are? Biggest improvement is when actor isn’t covering whole screen.
Usually most of the screen for mine yea. Think resident evil style rooms, where most rooms have a planar ref on the floor.