Developer Notes

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Description

Meshes that animate via vertex deformations using worldposition offset display incorrect surface normals while animating. The reflections of the environment smear as the mesh moves making it look translucent or otherwise incorrect. The expected result gif was taken from 4.13 binary. The broken gif was taken in 4.19. 

Original Repro:
Follow this guild and finally I can't get correct surface Normals when the geometry vertexes are animating

https://docs.unrealengine.com/latest/INT/Engine/Animation/Tools/VertexAnimationTool/VAT_TL_Meshes/index.html

For simplified things, you can just go to StaticMesh'/Engine/Functions/Engine_MaterialFunctions02/ExampleContent/TextureBasedWPO/DemoBoxMesh.DemoBoxMesh'

This is a TexturebasedMorph demo we provided, it looks also has incorrect normals

Steps to Reproduce
  1. Open any project in the editor
  2. In the content browser, enable "Show Engine Content" in the view options
  3. Find and open the "DemoBoxMesh" static mesh
    • Located in (Engine/Functions/Engine_MaterialsFunctions02/ExampleContent/TextureBasedWPO)

Result:
Observe that the surface of the mesh displays inaccurate, smearing reflections when animating with world position offset

Have Comments or More Details?

There's no existing public thread on this issue, so head over toAnswerHub just mention UE-53957 in the post.

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Unresolved
ComponentRendering
Affects Versions4.14.34.15.34.16.34.17.24.18.1
Target Fix4.25
CreatedJan 11, 2018
UpdatedOct 28, 2019