LOD's do not share lightmaps anymore

With 4.15 using only auto generated LOD’s static mesh LOD levels can’t share computed lightmaps anymore. This cause severe memory increase and it’s making lightmass build times way slower. It’s also cause visible LOD’s popping even with production quality lights.
With 4.14 lightmaps could be shared between LOD’s.

For my game it takes more than 5 hours to build lightmass with production quality, where the exact same scene was taken less than 2 hours in 4.14. It’s a real problem for working with static lighting and Epic should seriously investigate this for the next hotfix.

How much bigger your level_builtData is now?

it’s hard to answer because i have many sublevel but they are bigger, some of them are a little bit but some others are more than 2x bigger…

Hi, I saw your comment on the github commit. The commit was supposed to only affect instanced static meshes. We’re looking into it. I’ve entered ticket UE-42196 to track this issue. It should be visible in the public tracker soon.


Separately, I think it would be great if even auto-generated lods shared the light maps! It’s generally a good trade-off; you want the higher-resolution light map/shadowing data, even if the rendered geometry is lower-resolution. Re-computing light maps for the higher resolution is actually wasting CPU and user time to achieve lower-quality outputs!

This issue is indeed about auto-generated lods. Here is a link to the bug tracker:

(altho this issue concerns all static meshes apparently)

In 4.14 static meshes could share lightmaps if uv’s were similar. Now it just broken.

Thanks, we’re working on a fix now. 4.15 fixed LOD lightmap sharing for foliage/instancedstaticmeshes (which was broken in 4.14) and in the process unfortunately broke it for all other static meshes.

No, instanced static meshes can have multiple LODs but they must all share the same lightmap UVs. (This is not a new limitation). Are they not working for you?

Note that this particular commit has some bugs that were fixed for the final 4.15.1, specifically this one: https://github.com/EpicGames/UnrealEngine/commit/4abd6ec573a550700a9dc36456cc051f63573090

Looking at this fix in 4.15.1 ( https://github.com/EpicGames/UnrealEngine/commit/7876e4e585f9532dea9059e605d504525d97f1f8 ) it now seems instancing meshes can only have 1 LOD now? Am I reading that correctly? Thanks!

I was wondering if there are any more steps needed to have this issue fixed ? I’m currently trying to get a stable Unreal 4.15 Version with VXGI integrated I adjusted all the fixes shown in the links above. Everything works fine while in editor mode but as soon as I package the scene the Lightmap popping from LOD’s surface again. Have I missed something extra that had to be adjusted or ?