Quick answer: Unreal VSM (Virtual Shadow Maps) producing flicker over foliage? Wind motion invalidates caches every frame — lower invalidation, increase clipmap shadow distance, or use static shadows for distant trees.
Distant foliage flickers as wind moves the leaves. VSM marks the shadow pages as invalid each frame.
Invalidation Cost
VSM caches shadow tiles across frames. Animating geometry (wind) marks tiles dirty — the cache pays a re-rasterization cost. Many overlapping animated meshes cause flicker artifacts during high-load frames.
Reduce Wind Variance
Tone down WindStrength for distant LODs. The micro-motion isn’t visible at distance but still invalidates pages.
Far Distance Settings
r.Shadow.Virtual.UseFarShadowCulling and clipmap distance limits restrict where VSM operates. Beyond that, fall back to traditional shadows or skip dynamic shadows entirely for distant trees.
Static Shadows for Far LODs
Override the foliage material’s shadow behavior at far LODs — use a static shadow proxy with no wind, then cross-fade to dynamic up close.
Verifying
Distant tree canopies hold stable shadows. Up-close trees still respond to wind. No visible flicker during sustained wind.
“VSM flicker is invalidation pressure. Quiet the far LODs and clamp distance.”
Run r.Shadow.Virtual.ShowStats 1 while testing — you see invalidation count per frame and can tune until it’s sane.