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Light Map Overlapping Issue by using multiple materials / uvs

Hello everyone!

It’s been almost a year since I’ve started to develop with UE4 and it’s always been a really fun time

  • thanks to developers for this really cool engine and dev suite and the great comunity for all that tutorials, answers and help!

But since yesterday I face a problem I’ve not yet had:

I have modeled a mesh in blender with 4 objects and asigned to them 4 Materials (respectevely).
I UV-unwrapped them (as I always did, but now 4 times, each for every object / material).
Then I’ve created for every object a second UV as needed.

My problem is (exactly as I was afraid I would have) when I import the FBX file,
all the uv’s of all 4 materials are merged on one channel and of cause overlapping each other…

Does anybody know how to fix it (I suppose my workflow in blender is wrong)?

Screenshot (30).png

Thank you in advance!

When you import to UE4 there’s an option to Combine Meshes, uncheck that if you want the separate meshes to remain separated.

Also you have to take in to consideration that lightmaps are a per-mesh thing, not per-material. So even if you have one mesh with 4 materials each unwrapped properly themselves, Lightmass will still treat the whole mesh as one material for lighting.

If you have UE4 generate the light map, you can overlap all you want, as long as one island isn’t overlapping with itself.

Seems to work!!! Thank you!!!

No, lightmap UV’s can never overlap

What I meant was your UV0 channel can be stacked or overlap, and when UE4 generates the light map UVs, it will unstack the UVs.

Right, any other UV channel outside of the channel that the lightmaps use can be overlapping.