Virtual shadow maps are definitely…interesting. They’re a strange component of the UE rendering stack IMHO because they’re really an enhancement of an existing solution, as opposed to a completely new paradigm change. Nanite altered how we can do geometry, lumen made real-time GI feasible, but VSMs are, to the point, just really high-res shadowmaps with sometimes brutal perf. characteristics. They’re obviously intertwined with lumen and nanite in big ways, but especially for open-world and SWRT-based lumen projects, distance-field shadows mixed with contact shadows seems like a much more performant solution. And since SDFs in UE5 are on average 2x the linear resolution of their UE4 counterparts, your shadow resolve can be very good.
Apologies for the rant, I’ve been looking into and profiling VSMs lately and how they interact with lumen and nanite, and I’ve been frustrated by some pretty massive and inexplicable performance drops. In the western demo scene Epic released for 5.1, disabling VSMs saves a massive amount of performance and the profiling data is pretty inconsistent. It’s weird when they seem to be costing more than RT shadows while simultaneously delivering worse visual quality.