I faced an issue with smoothing breaking when exporting an FBX from Blender to Unreal Engine. In general, you need to enable smoothing export in Blender, and disable normal and tangents recompute in Unreal. So far, so good.
However, recently I tried exporting an asset with 3 UV maps (tiled texture, shadows, individual elements with baked normals from high-poly). In this case, smoothing on the individual elements breaks (UVs index is chosen correctly in the material). If I delete the 1st and 2nd UV maps (even already in Unreal), it works fine. If I switch the places of the 1st and 3rd UVs, it works fine, except the 3rd (now the tiled texture UV) has minor smoothing/normal issues. I fixed those issues by checking “tangent space” in Blender during export (which does not help if the UV with baked normals for ind.elements remains the 3rd).
Can someone explain to me what was happening and how to avoid it in the future?
Hello there @Hius-2!
I think your workflow is already quite close to avoiding the issue altogether. What happened here is that, by default, UE calculates on import using the UV channel 0 mainly. If you had any extras baked in channel 3, for example, the engine would still look at channel 0, hence the mismatch. SO, when you moved the baked UVs into the first spot, the engine read the correct layout.
So, to round it up, the workflow would look like this:
- In Blender, make sure your baked normals are in the first UV of the stack, reordering your maps accordingly (for example, BakedNormals, TiledTexture, Lightmap)
- Enable “Tangent Space” in export settings
- Ensure your baked normals’s map is active during export
- In UE, during import, confirm that it’s importing normals and tangents
- Set both “Recompute Normals” and “Recompute Tangets” to OFF