Why do foliage objects occlude meshes, even when "Use as Occluder" is off?

My project uses a lot of foliage, and my occlusion queries are high because it’s taking all of my foliage into account when running occlusion queries. This is despite the fact that “Use as Occluder” is set to OFF. To repro:

  • Generate some foliage objects.
  • Place some static meshes behind them.
  • Ensure “Use As Occluder” is set to OFF in the foliage mesh’s settings.
  • Move the camera behind the foliage.
  • Enter r.VisualizeOccludedPrimitives 1 at the console
  • Observe that Foliage is still occluding static meshes.

UseAsOccluder is not working unless occlusion test runs before BasePass.
After BassPass, the depth buffer is filled with every objects except transparent objects.
find the source code “bOcclusionBeforeBasePass”.
I’m not sure it is bug or not but Unreal should have to mention this.