Vertex interpolator (semi-randomly) causes visual artifacts on meshes. This did not happen initially when using or creating this material function but started about 24 hours later but now happens steadily.

This was reported and tested in 4.23.1 (CL-9631420). This was reproduced in 4.24.3 (CL-11590370), 4.25 Preview 7 (CL-12759524), and Main 4.26 (CL-12945139)

Steps to Reproduce
  1. Download the attached files and add them to an existing or new project then open it
  2. Find "SM_MF_MatCap_Exmpl" and drag it into the level
  3. Apply the "M_MF_Exmpl_RotoAndTwistMesh" material to it
  4. Notice the visual artifacts
  5. Open the "Luos_RotoAndTwistMesh" Material function and remove VertexInterpolator, drag the end of TransformVector to BaseNormal (V3).

Results: The preview mesh's polygons will start to flicker and in some cases the reflection/fresnel won't update properly when VertexInterpolator is used

Expected: Visually behave (near) identical to not using the vertexInterp, no flickering polygons, no reflection/fresnel errors.

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Won't Fix
ComponentUE - Graphics Features
Affects Versions4.
CreatedApr 23, 2020
ResolvedAug 31, 2021
UpdatedAug 31, 2021
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