Bake time is very long when baking LODS with PLM

Unity Version: 2018.2.5f1

Issue: Scene has a terrain and some static props. The props have 4 LODs. The bake takes about 30 seconds with only the terrain and props LOD 0 visible / static. The bake time shoots up to 5+ hours with LOD 0 and LOD 1 visible / static. I left a bake overnight with terrain and all LOD levels visible / static that took just over 13 hours. The props with all LODs and no terrain bakes in about 8 minutes. Is this expected behavior?

Lighting Settings and Directional Light Settings attached, but they are scene defaults.

 

Hey @jStinson,
This is currently a known issue that has to do with how we render LODs in a progressive manner (there are a lot of BVH updates that kill the performance).
The currently planned and in progress work:

1. fix LOD viewport calculations, as currently some LOD setups might never finish baking
2. improve the speed of rendering just LOD0s
3. ship a script that allows for setting up LOD projection (where lower LODs just point to the part of the lightmap occupied by LOD0, assuming their UVs match)
4. release LOD projection as a built-in feature

I hope to have 1., 2. and 3. done for 2018.3.
4. needs to tie in with other refactoring on the per renderer lightmapping setup that we're doing, so that will come a bit later (early in the 2019.2 cycle most likely).

 

Hi @Kuba , thanks for the reply. The LOD projection would work well for us since we use custom lightmap UVs. We're able to work around the issue for the moment, but I'm glad to hear it's being worked on.

 

Any news or details or tutorials on this? I have searched and find very little information.

 

Does this bake one lightmap to use on all LOD's, or still bake a separate lightmap for each LOD?

 

If I'm understanding correctly, for Progressive Lightmapper the Lightmap from LOD0 can be projected onto the higher LOD levels? Presumably we cannot use the Lightmap UV generator within Unity to do this as the secondary UVs would be too different between the LOD meshes. Actually, now that I think of it, won't the UVs be different in most cases no matter where they're made, custom or not, since the mesh is different between the various LOD levels? I understand that it's going to depend on the UV islands, but I thought it's always best to separate (lightmap) UV mostly by flat surfaces which usually require very little geometry anyways - anything more than, say 2 degrees, should be separated?