[FEATURE REQUEST] UE 5.8 Spotlights + Megalights + Skeletal Meshes shadow issue

Development Programming & Scripting
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1

Hello,

I noticed a shadow issue in UE 5.8 involving spotlights, MegaLights, and skeletal meshes when Global Illumination is set to Low or Medium.

I tested it in my custom project, an empty project, and a default UE project.

What happens:

The shadows of any skeletal mesh (UE4, UE5, Mixamo, or custom) are broken and do not render correctly. They look partially translucent.

How to reproduce it in any project:

  1. Enable MegaLights
  2. Add a Spotlight to your scene with Cast Shadows enabled
  3. Add any Skeletal Mesh to your scene with Cast Shadows enabled
  4. Set Global Illumination to Low or Medium
  5. It doesn’t matter whether you use Lumen or not. The shadows will still be broken
  6. The issue is visible in the viewport, in Standalone mode, and in a packaged project

I didn’t find anything online about this issue, and I have only performed these tests on my own computer. So, please let me know if you can reproduce the same issue or if you know of a solution.

If this issue is reproducible by others, I hope this post will help get it fixed.

Thank you very much for your time and understanding.

2

Hello,

I also ran into this problem and was able to reproduce it using the steps you outlined. I found 2 settings that seem to cause this issue.

r.RayTracing.Geometry.SkeletalMeshes - Changes from 1 to 0 when you go from high to medium GI and is the main reason the shadows get messed up. Set it to 1 when set to medium GI and your shadows will be fixed.

r.RayTracing.DynamicGeometry.MaxUpdatePrimitivesPerFrame - If you notice your skeletal mesh shadows updating too slowly change this to -1, which is the setting on high or a number larger than 1000, which is the setting on medium. The description says this is the max number of triangles updated per frame with < 0 being unlimited.

This fixed the issue for me and doesn’t seem to have a huge performance impact, but that probably depends on your project.