Face orientation not showing flipped normals #69959

New Issue

Rafał · 2019-09-16T20:07:45+02:00

Rafał commented

2019-09-16 20:07:45 +02:00

System Information
Operating system: Windows 10
Graphics card: gtx 1060 3gb

Blender Version
Broken: example: 2.80, edbf15d3c0, master, 2018-11-28, as found on the splash screen

Short description of error
After mirroring meshes via 'searchbar -> mirror -> Z' the Face orientation in Viewport Overlays showing that all faces are not flipped (blue) but after exporting to .fbx and importing that file to Unreal Engine or Substance Painter the normals are flipped.

Exact steps for others to reproduce the error
Based on the default startup or an attached .blend file (as simple as possible).
Barrel_LP.blend
Barrel_LP2.fbx

**System Information** Operating system: Windows 10 Graphics card: gtx 1060 3gb **Blender Version** Broken: example: 2.80, edbf15d3c044, master, 2018-11-28, as found on the splash screen **Short description of error** After mirroring meshes via 'searchbar -> mirror -> Z' the Face orientation in Viewport Overlays showing that all faces are not flipped (blue) but after exporting to .fbx and importing that file to Unreal Engine or Substance Painter the normals are flipped. **Exact steps for others to reproduce the error** Based on the default startup or an attached .blend file (as simple as possible). [Barrel_LP.blend](https://archive.blender.org/developer/F7751444/Barrel_LP.blend) [Barrel_LP2.fbx](https://archive.blender.org/developer/F7751443/Barrel_LP2.fbx)

Rafał commented

2019-09-16 20:07:45 +02:00

Added subscriber: @TheBaja

tom k commented

2019-09-17 12:54:49 +02:00

Added subscriber: @tomjk

tom k commented

2019-09-17 12:54:49 +02:00

Face Orientation overlay works on the object's mesh. Your mesh's normals are oriented correctly and the overlay reflects this; however, mirroring your object on an axis will multiply its scale by -1 on that axis. When you export to .fbx and import to your other program, this transformation is being collapsed/applied.

You can see this inside Blender:

Turn on Face Orientation overlay. Your object should show blue outside.
Mirror your object on an axis. Its scale on that axis is now negative. Your object still shows blue outside.
Apply scale (Object menu -> Apply -> Scale). The scale is now 1. Your object shows red outside

So the question is, should the Face Orientation overlay reflect the mesh normals or the object (transformed) normals?

Probably a discussion best suited for the devtalk forum, particularly user feedback . However I won't close this because I'm not sure if this*is// intended behaviour or not.

Face Orientation overlay works on the object's mesh. Your mesh's normals are oriented correctly and the overlay reflects this; however, mirroring your object on an axis will multiply its scale by -1 on that axis. When you export to .fbx and import to your other program, this transformation is being collapsed/applied. You can see this inside Blender: * Turn on Face Orientation overlay. Your object should show blue outside. * Mirror your object on an axis. Its scale on that axis is now negative. Your object still shows blue outside. * Apply scale (Object menu -> Apply -> Scale). The scale is now 1. Your object shows red outside So the question is, should the Face Orientation overlay reflect the mesh normals or the object (transformed) normals? Probably a discussion best suited for the devtalk forum, particularly [user feedback ](https:*devtalk.blender.org/c/user-feedback). However I won't close this because I'm not sure if this*is// intended behaviour or not.

Jeroen Bakker commented

2019-09-17 14:37:40 +02:00

Added subscriber: @Jeroen-Bakker

Jeroen Bakker commented

2019-09-17 14:37:40 +02:00

This is intended behavior for the face orientation overlay. The reason for this is that otherwise the shading will be effected in the display. Cycles, EEVEE and workbench renders them correctly.

So question is that it is a limitation of the FBX exporter or that this also happens in other exporters.

This is intended behavior for the face orientation overlay. The reason for this is that otherwise the shading will be effected in the display. Cycles, EEVEE and workbench renders them correctly. So question is that it is a limitation of the FBX exporter or that this also happens in other exporters.

Jacques Lucke commented

2019-09-18 12:47:01 +02:00

Added subscriber: @JacquesLucke

Jacques Lucke commented

2019-09-18 12:47:01 +02:00

@tomjk Can you prepare a file that shows what you describe?

I checked this yesterday, and the mirror modifier not only scales by -1 along one axis, but also inverts the normals.

Here you can see that the vertex order is different from what you would get when just scaling with -1.

I just don't quite understand why the .fbx exporter is exporting something else. When I import your provided .fbx file, the normals seem to be correct.

@tomjk Can you prepare a file that shows what you describe? I checked this yesterday, and the mirror modifier not only scales by -1 along one axis, but also inverts the normals. Here you can see that the vertex order is different from what you would get when just scaling with -1. ![image.png](https://archive.blender.org/developer/F7755261/image.png) I just don't quite understand why the .fbx exporter is exporting something else. When I import your provided .fbx file, the normals seem to be correct.

tom k commented

2019-09-18 13:04:19 +02:00

This is with mirror operation (Search -> "Mirror" -> Transform: Mirror, or Ctrl-M) as in @TheBaja's post, not the mirror modifier.

Rafał commented

2019-09-18 14:04:11 +02:00

Maybe this helps to understand:

BarrelTest.mp4

Maybe this helps to understand: [BarrelTest.mp4](https://archive.blender.org/developer/F7755423/BarrelTest.mp4)

Campbell Barton commented

2019-09-19 11:54:44 +02:00

Added subscriber: @ideasman42

Campbell Barton commented

2019-09-19 11:54:44 +02:00

Changed status from 'Open' to: 'Archived'

Campbell Barton closed this issue

2019-09-19 11:54:44 +02:00

Campbell Barton self-assigned this 2019-09-19 11:54:44 +02:00

Campbell Barton commented

2019-09-19 11:54:44 +02:00

Blender detects negative matrices which cause flipping and compensates for it to make negative scaled objects usable, not all engines do this.

Closing.

Blender detects negative matrices which cause flipping and compensates for it to make negative scaled objects usable, not all engines do this. Closing.

Ludvik Koutny commented

2019-09-19 12:08:41 +02:00

Added subscriber: @Rawalanche

Ludvik Koutny commented

2019-09-19 12:08:41 +02:00

Yes, I agree here. Correcting normals for negative scale is great, because it allows you to make more unique variations of assets with instancing by just mirroring them, and still get usable normals required for example for normals maps or refraction. When you have any asset which you plan to use with substance painter, or anywhere else really, just make sure to apply transforms first before exporting. That's always the best practice.

So when you know your asset has been mirrored, then:

Apply scale
You will see faces flip immediately
In edit mode, flip them all the right way again

Yes, I agree here. Correcting normals for negative scale is great, because it allows you to make more unique variations of assets with instancing by just mirroring them, and still get usable normals required for example for normals maps or refraction. When you have *any* asset which you plan to use with substance painter, or anywhere else really, just make sure to apply transforms first before exporting. That's always the best practice. So when you know your asset has been mirrored, then: 1. Apply scale 2. You will see faces flip immediately 3. In edit mode, flip them all the right way again

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Face orientation not showing flipped normals #69959