Importing .fbx from blender into UE4. Lightmap issues


I have had a few issues with lightmaps from Blender to UE4. Things such as UE4 not wanting to auto generate any light maps for assets created and exported from blender into .fbx.

Assets randomly on re-import deciding to not update lightmap changes. The settings being used in UE4 are all correct I have no issues with other 3D modeling software’s to UE4 its just with assets created in blender. Only thing I can think of is that there might be some kind of export option I am missing when exporting to .fbx?

A few additional irritants, if the mesh in blender has been given no UV or material, then the .fbx imported into UE4 will refuse to generate lightmaps for the mesh, even when the mesh has been given a UV, UE4 seems very random on if it wants to generate a UV using the usual

Here is an example of one issue I am having:

Left (inside blender) Right (Inside UE4)

It looks as if UE4 is trying to generate a UV’ but I have never had it do such a bad job. Lightmaps just seem really random/bad when using blender exports as .fbx.

UE4 does not like overlapping islands and the right example seems to have some or at least duplicate verts or normals. Create a second UV map in blender, do a lightmap pack unwrap with some margin, export it UE4 and disable the create lightmap checkbox. If the auto generation within UE4 fails, check your mesh for errors (Duplicated geo, wrong normals, overlapping UV’s).

Thanks, Kind of resolved this by completely importing a new mesh and deleting the old one. No changes to settings.

Was using a second UV in blender, this is the one being used for lightmaps as UE4 uses the second map by defualt, the image on the right is what was showing in UE4, not something I created.

Still getting lots of lighting issues in UE4 from the blender assets though, despite creating light maps for all assets. Same assets are completely fine if imported into another 3D software like 3DS Max and then re-exported to UE4. I know that there are a few threads on the UE4 forums about a Blender plugin because of lightmap issues from blender to UE4 with default settings. Looking into this now.

does that mean that UE rejects mirrored meshes with double-up UV’s? I’ve never used it, but that seems kind of goofy…

No it works fine with islands sharing the same space (e.g. repeating or mirrored detail). The light map UV channel, on the other hand, shouldn’t contain any overlaps or flipped islands if you’re making your own light map UVs. If you let UE4 auto-generate the asset’s light map UVs instead of making them yourself it’s supposed to prevent that so OP is getting some weird result.

It seems it could have been to do with the export options, I did not select to only export the mesh. all other default export options where the default.

Not sure if this is the fix but after doing so UE4 is now creating its own UV’s properly and is allowing me to import the UV’s correctly.

Alright so seems its not actually fixed.
It now appears my first impression of Importing and re-exporting out of 3DS Max was wrong and does not fix this issue

Here are some visual examples of the issue in UE4.

The UV’s seem fine now, but it still is giving above results.