Force LOD1 foliage to use LOD0 lightmaps?

Just came across this bug Unreal Engine Issues and Bug Tracker (UE-32299) after UE4 told me that lightmaps may look incorrect on LOD1 foliage, after building lighting:

I have foliage in my project that uses the same lightmap UVs for LOD0 and LOD1, and the language in that editor message and in the bug report imply that LOD1 meshes will just use the LOD0 lightmaps, which would be perfect for me, but it seems like no lighting at all has been built for LOD1, and the meshes are black.

Is the wording “may be incorrect” just a formality, and it’s actually impossible to have statically lit LOD1 meshes? Lightmap settings for LOD0 and LOD1 meshes are set up in the exact same way in my project, and the lightmap UVs cover the exact same space.

Yes. It means that it detected a difference between the lightmap UVs on LOD1+ which could be something very minor. It will only use LOD0 to bake lightmaps, and then the other LODs will use the same lightmap. As long as the UVs mostly match it should be fine.

Thanks for the reply, I thought the same thing about the bolded but it turns out this is no longer true in 4.14.

I believe this is the bug report for the new issue.

have you actually viewed the lightmap UV in unreal in the static mesh viewer, while cycling through the UVs? I can’t think of any reason this would happen. Post images of the UV layout for the lightmap UV for each LOD.

Challenge accepted,

LOD0, UV channel 1

LOD1, UV channel 1

Lightmass coordinate settings, showing that channel 1 should be used

The LOD1 is simply the LOD0 with some parts deleted, so the remaining UVs are in the exact same position, if there are errors it should be simple to spot them with such a simple mesh.

This is the result of a lightbuild in a fully statically lit scene:

Ok thanks for the details. Definitely looks like a bug then.

Which programmer should I send flowers to to get the fix expedited :o

Jack Porter, most likely but I am not 100% sure.

Bumping to show my thanks, this issue is fixed in 4.15 as of Jan 30th :o Unreal Engine Issues and Bug Tracker (UE-39884)

Thank you JackP and Unreal Devs