Landscape Opacity Mask ignored in Lumen

Development Rendering
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1

We are observing a problem with the Opacity mask in Lumen - on all materials, but most notably on the Landscape:

The opacity mask is ignored in the Lumen scene. This means that when we paint a hole in the terrain, e.g. for a cave or underground entrance, the gobal illumination acts as if there was an invisible virtual blanket that doesn’t pass any ambient light through.

Observe the attached files for a minimal repro:

The hole painted in the terrain, which is visible in regular Lit scene, is not there in the Lumen scene visualization. As a result. the surfaces inside the hole which are in the shade, but should still be illuminated by the sky and bounced light, are completely black.

Is this a known issue? Any workarounds?

2

Steps to Reproduce

  • Make sure HW Lumen is on in your project
  • Create a map
  • Add Landscape
  • Switch Editor to Landscape mode and using the Sculpt -> Visibiliy tool, paint a hole in the landscape
  • Switch visualization to Lumen -> Lumen scene
  • Observe that the hole you just painted is not reflected in the Lumen proxy mesh
3

Hello,

This sounds similar to a known issue with HWRT Lumen and Landscapes with masked materials that was reported here:

[Content removed]

The issue has not been addressed yet: https://issues.unrealengine.com/issue/UE-347428, but the workaround was to enable r.RayTracing.Geometry.Landscape.VertexMask=1, however that depends on if you are using HWRT or not.

Are you using HWRT (hardware Ray Tracing) Lumen and is the Landscape Nanite or non-Nanite?

4

We are using HWRT and Nanite Terrain.

Enabling the VertexMask cvar does the trick, thanks a lot!