I’m currently investigating these banding artifacts in UE5.6.1 with a World Composition Nanite Landscape + VSM shadows. No tessellation. They primarily happen when the directional light angle is close to perpendicular to the surface normal. So far i’ve tried disabling the VSM cache, and various settings for Nanite Position Precision (update: this does actually help improve some of the artifacts), but not much improvement.
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Less obvious here but still present:
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r.Shadow.Virtual.ResolutionLodBiasDirectional has a significant effect on this artifact, increasing or decreasing the value changes it, but doesn’t eliminate it.
The artifact is in the VSM Shadow Mask:
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From doing some more reading it sounds like this is projective aliasing. Investigating r.Shadow.Virtual.NormalBias next.
r.Shadow.Virtual.NormalBias allows some mitigation of the artifact shown but introduces others. If anyone is aware of any other settings we can adjust for this please let me know. thanks
Hi Chris,
Our documentation calls out these projective aliasing artifacts as the worst-case scenario for VSMs: https://dev.epicgames.com/documentation/en\-us/unreal\-engine/virtual\-shadow\-maps\-in\-unreal\-engine\#shadow\-resolution. We usually recommend that people adjust their content to avoid this entirely. What are you looking to achieve by having the directional light at such a shallow angle? Is this setup needed for only a brief amount of time? Any further details you can share would help us greatly.
Thanks Tim. These artifacts are most noticeable with shallow sun angles as part of our dynamic time-of-day system. It should be brief at either end of the day. If my findings above are the main controls available to mitigate these then we’ll work within those constraints. Oh I should also mention that adjusting nanite landscape precision from the default of 8cm down to 1cm has also helped fix some cases of this.
Yeah, your approach sounds good to me. Just be aware of the memory overhead you might be introducing by biasing the resolution of the directional light. Other than that, I do not have anything else to add here, unfortunately. However, do run with those settings and let us know in case you run into further issues.