Why do Virtual Shadow Maps leak through foliage?

VSM resolution insufficient for thin foliage geometry. Lower r.Shadow.Virtual.ResolutionLodBiasLocal (negative values = higher res). Mark foliage Affect Distance Field Lighting.

Pixel-snapped shadows?

r.Shadow.Virtual.SMRT.RayCountLocal default 8; raise to 16 for cleaner contact shadows on foliage edges.

Resolution bias and SMRT ray count both raise GPU cost. Profile with stat GPU; balance per scene.

Fix: VSM Shadows Leak Through Foliage

Quick answer: Lower r.Shadow.Virtual.ResolutionLodBiasLocal to -2 for finer res. Mark foliage Affect DF Lighting.

Sun comes through tree canopy as light spots; shouldn’t. VSM coarse on thin leaves.

The Fix

Console (or DefaultEngine.ini):
r.Shadow.Virtual.ResolutionLodBiasLocal       -2
r.Shadow.Virtual.SMRT.RayCountLocal           16

Foliage Type asset:
  Affect Distance Field Lighting:    true

Negative bias = higher VSM resolution. Combined with SMRT improves shadow accuracy on thin geometry.

Verifying

Tree shadows opaque. Light leak gone. GPU cost up; balance with quality preset.

“Higher res. More rays. Leaks fade.”

Related Issues

For Lumen software, see Lumen software. For Lumen banding, see Lumen banding.

Higher VSM. Less leak.