There is moving blotchy noise on the head and face from hair when Lumen HZB tracing hits hair.  CL 33258050 fixes the noise in the hair, but tracing still hits hair when it starts from surfaces like the skin under the hair.  For foliage we have


to prevent this issue for grass and I think we need something similar for hair.  In my tests modifying LumenScreenProbeTracing.usf so line 321 includes hair resolves the issue, though it's not a proper solution because it's gated by bSkipFoliageHits.


if (LumenMaterial.bHasBackfaceDiffuse || IsHair(LumenMaterial))
Steps to Reproduce
  1. Download and open the sample project from the Additional Info URL
    1. Note if you don't have CL 33258050 applied you will also see noise in the Hair which was fixed by CL  33258050, (it wasn't merged to the 5.4 branch)
  2. Open the Flicker_on_Hair_n_Shadow map


The shadow/ambient occlusion of the hair on the skin of the head and face is not noisy or moving.


There is moving blotchy noisy shadows on the head and face from the hair

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Fix Commit33855283
CreatedMay 17, 2024
ResolvedMay 27, 2024
UpdatedMay 27, 2024
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