Updating ray tracing acceleration structure in realtime is very difficult and usually quite slow. But given how many miracles Epic has managed to do in a row (Lumen, Nanite (even with foliage), Megalights, etc…) I am pretty sure they will crack this one too eventually.
Right now, ray tracing, even path tracing with realtime rebuilding of geometry works, it’s just not very fast. That’s why r.Nanite.Mode is set to 0 by default.
I am talking about this because when it comes to HW ray tracing, it’s not just about deforming instances. As long as you are using nanite, pretty much all geometry is “deforming” in a sense as long as you are moving the camera because nanite is constantly replacing mesh patches depending on the distance and culling. So entire scene is essentially constantly dynamic and requires updating ray tracing acceleration structure constantly.
But despite that, even quite heavy scenes still run relatively ok with HW ray tracing or path tracing and r.Nanite.Mode set to 1. Relatively ok in a sense that there are FPS drops and stutters, but the editor doesn’t slow down to single digit FPS numbers or crash, which alone is quite an achievement. Especially considering that UE can rebuild acceleration structure of entirely path traced geometrically complex scene at higher framerates than FAB plugin can rasterize a few 2D product thumbnails while scrolling 