Unreal Engine 4 can either take in normals only from an FBX file, normals and tangents from an FBX file, or it can simply re-calculate them on its own. The image above shows the difference in computed normals on the left, and imported normals and tangents on the right.
When importing an FBX file, you will find this feature near the top of the import dialog under Mesh. The pull down will have these 3 options:
| Option | Description |
|---|---|
| Compute Normals | The engine computes normals and tangents. Smoothing group and normal info is discarded from the FBX info. |
| Import Normals | The normals are imported from the FBX file, tangents are computed by the engine. |
| Import Normals and Tangents | The normals and tangents are imported from the FBX file and nothing is computed by the engine. |