UE5 Runtime Landscape Deformation Cause VSM Artifacts

Development Rendering
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Hello,

I’m getting shadow artifacts with Virtual Shadow Maps on UE 5.8 - 5.xx when using a Nanite-tessellated landscape with runtime deformation (footprints via displacement through Nanite tessellation (ex: Sand of Snow). Shadows around the deformed areas look blocky and low-detail, and importantly this persists even when the cache is updating correctly — with Shadow Cache Invalidation Behavior set to Always the pages clearly refresh, but the shadowing of the footprints still shows a noticeable loss of detail compared to what traditional (non-virtual) shadow maps produce on the same deformed geometry, as if the pages are being rendered at too coarse a resolution/mip for fine surface detail. I’ve tried lowering r.Shadow.Virtual.ResolutionLodBiasDirectional and tweaking SMRT ray/sample settings, but nothing brings VSM up to the quality level of legacy shadow maps — so I’m wondering whether there’s a way to force higher-resolution VSM pages in a region around the player and whether this detail loss on small-scale Nanite displacement is a known VSM limitation.

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Hi.

To rule out caching as the issue start by disabling caching via either r.Shadow.Virtual.Cache or r.Shadow.Virtual.Cache.ForceInvalidateDirectional. Beyond that, I wanted to check r.Shadow.Virtual.Nanite.AllowTessellationDirectional has not been enabled (it is off by default)?

Another way to get poor shadows is to not have the shading normal set up correctly, this can cause shadowing on back faces which breaks biasing / filtering. So make sure those are computed correctly when the dynamic displacement is applied.

Displacement fade distance (material param) might also be worth toggling to see if it affects the result, as well as the pixel programmable distance.

Best,

Ola

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