Mesh normals error in fbx export, Blender to Unreal #117470

New Issue

Nahuel Belich · 2024-01-24T06:02:24+01:00

Nahuel Belich commented

2024-01-24 06:02:24 +01:00

System Information
Operating system: Linux-6.5.0-14-generic-x86_64-with-glibc2.35 64 Bits, X11 UI
Graphics card: NVIDIA GeForce GTX 1070/PCIe/SSE2 NVIDIA Corporation 4.6.0 NVIDIA 525.147.05

Blender Version
Broken: version: 4.1.0 Alpha, branch: main, commit date: 2024-01-23 20:10, hash: 99f9084bee58
Worked: 4.0.2 official

Short description of error
Something change in the fbx exporter in Blender 4.1 alpha, same file same model same settings fail upon importing in unreal 5.3, however the fbx exporter in 4.0 works fine.
4.1 alpha

4.0

Note: if i choose to recalculate normals in the unreal importer it would fix the problem but loose custom normals, also importing in blender 4.1 works fine, the only place i saw the error its unreal because at the moment its the only software where im importing meshes, didn't test other softwares.

Exact steps for others to reproduce the error

FBX EXPORT BUG.blend
Export fbx using this settings

Try importing it in unreal 5.3 in blender from blender to blender works fine.

Here are the fbx exported to sabe time.
FBX EXPORT BUG 4-0.fbx
FBX EXPORT BUG 4-1.fbx

**System Information** Operating system: Linux-6.5.0-14-generic-x86_64-with-glibc2.35 64 Bits, X11 UI Graphics card: NVIDIA GeForce GTX 1070/PCIe/SSE2 NVIDIA Corporation 4.6.0 NVIDIA 525.147.05 **Blender Version** Broken: version: 4.1.0 Alpha, branch: main, commit date: 2024-01-23 20:10, hash: `99f9084bee58` Worked: 4.0.2 official **Short description of error** Something change in the fbx exporter in Blender 4.1 alpha, same file same model same settings fail upon importing in unreal 5.3, however the fbx exporter in 4.0 works fine. 4.1 alpha ![image](/attachments/1a45d74d-f17d-44db-9072-960f9b434d95) 4.0 ![image](/attachments/2e61b012-5102-4058-9290-48fbfa834ae7) Note: if i choose to recalculate normals in the unreal importer it would fix the problem but loose custom normals, also importing in blender 4.1 works fine, the only place i saw the error its unreal because at the moment its the only software where im importing meshes, didn't test other softwares. **Exact steps for others to reproduce the error** [FBX EXPORT BUG.blend](/attachments/a8a1fef6-68a6-4b4d-8376-67efddb5b40d) Export fbx using this settings ![image](/attachments/ccec5357-981d-476f-bad6-019d39cf797f) Try importing it in unreal 5.3 in blender from blender to blender works fine. Here are the fbx exported to sabe time. [FBX EXPORT BUG 4-0.fbx](/attachments/0ab74c27-64b1-4b26-8854-2de046471c4e) [FBX EXPORT BUG 4-1.fbx](/attachments/03d83fc6-0484-4d48-9df5-9ee8cb84ae43)

FBX EXPORT BUG.blend

184 KiB

image.png

607 KiB

image.png

74 KiB

FBX EXPORT BUG 4-0.fbx

124 KiB

FBX EXPORT BUG 4-1.fbx

115 KiB

image.png

674 KiB

Nahuel Belich added the

labels 2024-01-24 06:02:25 +01:00

Nahuel Belich commented

2024-01-24 06:18:44 +01:00

If this is usefull in any way, this is the mesh broken in unreal exported to fbx so you can see what unreal import's, it has a bounding box, probably the collider created in unreal, i didn't remove it so you get the pure fbx model.
Broken mesh.fbx

If this is usefull in any way, this is the mesh broken in unreal exported to fbx so you can see what unreal import's, it has a bounding box, probably the collider created in unreal, i didn't remove it so you get the pure fbx model. [Broken mesh.fbx](/attachments/02db64d6-89cd-45fb-b13d-fe65d2644cfd)

Broken mesh.fbx

125 KiB

Pratik Borhade commented

2024-01-24 08:25:14 +01:00

cc @Mysteryem

Thomas Barlow commented

2024-01-24 11:51:20 +01:00

I did suspect this might happen, which is why I got the normal export changes into 4.1 early (https://developer.blender.org/docs/release_notes/4.1/add_ons/#fbx-io), but I was not expecting this to happen with Unreal because it uses the FBX SDK.

Both Unity and Autodesk's own FBX Review program import the FBX EXPORT BUG 4-1.fbx without issue, as does Microsoft 3D Viewer.

Unreal 5.3 is documented as importing using FBX 2020.2 (https://docs.unrealengine.com/5.3/en-US/fbx-animation-pipeline-in-unreal-engine/), yet Unity 2020.3.41f1 also uses FBX SDK version 2020.2 and imports the file without issue.

The Broken mesh.fbx exported by Unreal has invalid normals, as reported by FBX Review:

I suspect this is an issue with Unreal and that it should be reported to them, though one or both of the normal export changes to FBX in Blender 4.1 may want to be reverted to ensure compatibility across external software.

I'll find out exactly which part of the normal changes it is that Unreal doesn't like and report back when I have more info.

I did suspect this might happen, which is why I got the normal export changes into 4.1 early (https://developer.blender.org/docs/release_notes/4.1/add_ons/#fbx-io), but I was not expecting this to happen with Unreal because it uses the FBX SDK. Both Unity and Autodesk's own FBX Review program import the `FBX EXPORT BUG 4-1.fbx` without issue, as does Microsoft 3D Viewer. Unreal 5.3 is documented as importing using FBX 2020.2 (https://docs.unrealengine.com/5.3/en-US/fbx-animation-pipeline-in-unreal-engine/), yet Unity 2020.3.41f1 also uses FBX SDK version 2020.2 and imports the file without issue. The `Broken mesh.fbx` exported by Unreal has invalid normals, as reported by FBX Review: ![image](/attachments/1aac3b3f-76eb-4d6b-bad7-294136010b06) I suspect this is an issue with Unreal and that it should be reported to them, though one or both of the normal export changes to FBX in Blender 4.1 may want to be reverted to ensure compatibility across external software. I'll find out exactly which part of the normal changes it is that Unreal doesn't like and report back when I have more info.

image.png

17 KiB

Thomas Barlow commented

2024-01-24 12:39:44 +01:00

Ok, so Unreal just doesn't support face normals for whatever reason. It works fine with vertex normals and corner normals, and with either of the Direct (one normal per element) or IndexToDirect (an index into a unique normals array per element) reference modes.

Ok, so Unreal just doesn't support face normals for whatever reason. It works fine with vertex normals and corner normals, and with either of the `Direct` (one normal per element) or `IndexToDirect` (an index into a unique normals array per element) reference modes.

Pratik Borhade commented

2024-01-25 05:25:22 +01:00