Developer Notes

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When using Precomputed Visibility in conjunction with HLODs and translucent materials without them culling actors occluded by the translucent material.

The example gif attached shows that the base mesh for the HLODs is culling when it shouldn't be. I suspected this potentially being due to the bounds of the HLOD for these three translucent walls and set another mesh far enough behind that it would be out of the bounds but that still occludes.

The sample project has three setups to rule out anything here.

  • Left: Standard default settings for all three walls and material sphere.
  • Center: Material Sphere has been disabled for HLOD generation
  • Right: No HLOD generation for these.
Steps to Reproduce

1. Set up a scene with a translucent material and another actor behind it that could potentially be occluded.
2. In the World Settings enable Precomputed Visibility and Hierarchical LODs
3. Add a Precomputed Visibility Volume to the level around a large enough space that you can pull back and see the HLODs transition.
4. Open the HLOD Outliner (Window > Hiearachical LOD Outliner) and set up two LODs are different distances (I used 750 and 1250 for the two.
5. Generate the LODs
6. Build the Lighting so that Precomputed Visibility is calculated
7. Enable the Visualization of Precomputed Visibility Cells (Show > Visualize > Precomputed Visibility Cells)
8. Move the camera away and towards the actors to see the transition of the HLOD.

If using the sample project:
1. Open the level
2. Move the camera away and towards the translucent wall to see the transition of HLODs
3. Move towards so that the base non-HLOD meshes appear while within the Visibility Cells.

Regression: No

Results: If HLODs are generated the base mesh treats the occluded actor like it's still occluded even though the material is translucent and it should be visible.

Expected: The material sphere should be visible.

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Won't Fix
Affects Versions4.114.124.13
CreatedJul 6, 2016
ResolvedFeb 7, 2017
UpdatedApr 27, 2018