Face Normals display as NOT mirrored when Mirror Modifier is used #94826

New Issue

Adam Janz · 2022-01-11T19:51:33+01:00

Adam Janz commented

2022-01-11 19:51:33 +01:00

System Information
Operating system: Windows-8.1-6.3.9600-SP0 64 Bits
Graphics card: GeForce GTX 970/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 460.89

Blender Version
Broken: version: 3.0.0, branch: master, commit date: 2021-12-02 18:35, hash: f1cca30557
Worked: version: 2.79b, hash: f4dc9f9d68b

Short description of error
Activating "Display Face Normals" from the Viewport Overlays menu when a Mirror Modifier is used will incorrectly show the mirrored Face Normals as if NOT mirrored. This is only a display error, applying the Mirror Modifier will result in correctly mirrored normals. Vertex Normals and Edge Normals display correctly from the Viewport Overlays menu, the bug only affects Face Normals, as shown in the attached images. This bug appears to date back to at least 2.92, but perhaps further. The only Blender version I have installed where the bug does not occur is 2.79b.

Exact steps for others to reproduce the error

Open a new file, and delete all but one face of the default cube.
Add a mirror modifier and enable display on Edit and Cage.
Enter Edit Mode and check the Face button beside "Display Normals" in the Viewport Overlays menu.
Observe that the Normal drawn on the mirrored face is facing the same direction as the non-mirrored face.

**System Information** Operating system: Windows-8.1-6.3.9600-SP0 64 Bits Graphics card: GeForce GTX 970/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 460.89 **Blender Version** Broken: version: 3.0.0, branch: master, commit date: 2021-12-02 18:35, hash: `f1cca30557` Worked: version: 2.79b, hash: `f4dc9f9d68b` **Short description of error** Activating "Display Face Normals" from the Viewport Overlays menu when a Mirror Modifier is used will incorrectly show the mirrored Face Normals as if NOT mirrored. This is only a display error, applying the Mirror Modifier will result in correctly mirrored normals. Vertex Normals and Edge Normals display correctly from the Viewport Overlays menu, the bug only affects Face Normals, as shown in the attached images. This bug appears to date back to at least 2.92, but perhaps further. The only Blender version I have installed where the bug does not occur is 2.79b. **Exact steps for others to reproduce the error** 1. Open a new file, and delete all but one face of the default cube. 2. Add a mirror modifier and enable display on Edit and Cage. 3. Enter Edit Mode and check the Face button beside "Display Normals" in the Viewport Overlays menu. 4. Observe that the Normal drawn on the mirrored face is facing the same direction as the non-mirrored face. ![Display Face Normals not mirrored-Blender.png](https://archive.blender.org/developer/F12801438/Display_Face_Normals_not_mirrored-Blender.png) ![Display Vertex and Edge Normals correctly mirrored-Blender.png](https://archive.blender.org/developer/F12801444/Display_Vertex_and_Edge_Normals_correctly_mirrored-Blender.png) ![Display Face Normals correctly mirrored-Blender 2.79b.png](https://archive.blender.org/developer/F12801442/Display_Face_Normals_correctly_mirrored-Blender_2.79b.png)

Adam Janz commented

2022-01-11 19:51:33 +01:00

Added subscriber: @AdamJanz

Philipp Oeser commented

2022-01-12 14:19:33 +01:00

Added subscriber: @lichtwerk

Philipp Oeser commented

2022-01-12 14:19:33 +01:00

Changed status from 'Needs Triage' to: 'Confirmed'

Philipp Oeser commented

2022-01-12 14:19:33 +01:00

Can confirm, will check

Philipp Oeser commented

2022-01-12 15:14:26 +01:00

Just noticed this has been reported before (and unfortunately closed as a design choice), see #77090 (Generative modifiers (solidify, mirror) draw face normals from original face (wrong direction))

I left a comment there that the situation is very unfortunate (this was done for the subd modifier - but others suffer from this), but will still have to merge these reports.
Lets see if there is a reaction [maybe we can still improve upon this].

Just noticed this has been reported before (and unfortunately closed as a design choice), see #77090 (Generative modifiers (solidify, mirror) draw face normals from original face (wrong direction)) I left a comment there that the situation is very unfortunate (this was done for the subd modifier - but others suffer from this), but will still have to merge these reports. Lets see if there is a reaction [maybe we can still improve upon this].

Philipp Oeser commented

2022-01-12 15:14:38 +01:00

Closed as duplicate of #77090

Philipp Oeser closed this issue

2022-01-12 15:14:38 +01:00

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Face Normals display as NOT mirrored when Mirror Modifier is used #94826