Hard shadow edges appear when using Displacement Fade on a Nanite tessellated landscape

A hard shadow edge occurs when displacement fade is enabled on a Nanite landscape with tessellation. This occurs on the edge between two clipmap levels of the VSM.

The artefact can be somewhat reduced by increasing the shadow resolution (by setting r.Shadow.Virtual.ResolutionBiasDirectional to negative values) which pushes the hard edge further away from the camera.

• Create a level with a landscape (default settings)

• Enable Nanite on the landscape and build it

• Add a material with displacement to the landscape (with a suitable displacement texture assigned to the displacement channel) and enable Nanite tessellation

• Enable the displacement fade (Startfade=14, Endfade=8)

• Run the game in editor and slowly move the camera forwards. A hard shadow edge will occur on the edge between two VSM clipmap levels (this can be in the VSM debug visualization mode)