Solidify modifier rotates custom normals incorrectly #104885

New Issue

Zsolt Stefan · 2023-02-17T16:06:35+01:00

Zsolt Stefan commented

2023-02-17 16:06:35 +01:00

System Information
Operating system: Windows-10-10.0.19044-SP0 64 Bits
Graphics card: NVIDIA GeForce RTX 2080 Super/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 516.93

Blender Version
Broken: version: 3.4.1, branch: blender-v3.4-release, commit date: 2022-12-20 08:50, hash: rBef9ca44dee7f
Worked: not as far as I know.

Short description of error
When solidifying an object with custom normals, the newly created geometry rotates (destroys) these normals on the newly created geometry. So a smooth surface gets a non-smooth (faceted-looking) surface on the other side.
However, activating the Normals --> Flip option in the modifier actually produces the correct (smooth) normals on the new geometry, but destroys the custom normals of the original surface. The newly created surface then has flipped normals, but these can be flipped again inside edit mode after applying the modifier. They are then facing the right way and still smooth. So the modifier actually has the code to correctly calculate the new split normals.

Exact steps for others to reproduce the error

Take a mesh surface with custom normals, make two copies.
Object 1: Add a solidify modifier with a relatively small thickness. Look at the newly created surface: it's not smooth but faceted.
Object 1:Apply modifier, turn on display of custom normals, zoom in on new geometry: the normals on the new vertices are divergent.
Object 2: Add a solidify modifier activate with Normals --> Flip. Look at newly created surface: it's smooth as the original one. Great. But the original surface is now broken up and not smooth.
Object 2: Apply modifier, turn on display of custom normals, zoom in on new geometry: the normals on the new vertices are identical, do not diverge, they are simply facing the wrong way. Apply "Normals (ALT-N) --> Flip", now they are correct.

So basically there is a work-intensive workaround (which also means losing the flexibility of having a modifier): make two copies of the object, add modifer with flipped normals, apply, flip normals again in edit mode, manually select and delete original geometry, join with the original object (original geometry). This is what the modifier itself should be doing.

See the attached Blend file. Four objects: original, two solidify copies, and one created with the workaround.

**System Information** Operating system: Windows-10-10.0.19044-SP0 64 Bits Graphics card: NVIDIA GeForce RTX 2080 Super/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 516.93 **Blender Version** Broken: version: 3.4.1, branch: blender-v3.4-release, commit date: 2022-12-20 08:50, hash: `rBef9ca44dee7f` Worked: not as far as I know. **Short description of error** When solidifying an object with custom normals, the newly created geometry rotates (destroys) these normals on the newly created geometry. So a smooth surface gets a non-smooth (faceted-looking) surface on the other side. However, activating the Normals --> Flip option in the modifier actually produces the correct (smooth) normals on the new geometry, but destroys the custom normals of the original surface. The newly created surface then has flipped normals, but these can be flipped again inside edit mode after applying the modifier. They are then facing the right way and still smooth. So the modifier actually has the code to correctly calculate the new split normals. ![image](/attachments/a303da90-0d8f-4939-a50e-e1393692cc20) **Exact steps for others to reproduce the error** - Take a mesh surface with custom normals, make two copies. - Object 1: Add a solidify modifier with a relatively small thickness. Look at the newly created surface: it's not smooth but faceted. - Object 1:Apply modifier, turn on display of custom normals, zoom in on new geometry: the normals on the new vertices are divergent. - Object 2: Add a solidify modifier activate with Normals --> Flip. Look at newly created surface: it's smooth as the original one. Great. But the original surface is now broken up and not smooth. - Object 2: Apply modifier, turn on display of custom normals, zoom in on new geometry: the normals on the new vertices are identical, do not diverge, they are simply facing the wrong way. Apply "Normals (ALT-N) --> Flip", now they are correct. So basically there is a work-intensive workaround (which also means losing the flexibility of having a modifier): make two copies of the object, add modifer with flipped normals, apply, flip normals again in edit mode, manually select and delete original geometry, join with the original object (original geometry). This is what the modifier itself should be doing. - See the attached Blend file. Four objects: original, two solidify copies, and one created with the workaround.

image.png

206 KiB

Solidify_normals_bug_01.blend

1.3 MiB

Zsolt Stefan added the

labels 2023-02-17 16:06:36 +01:00

Germano Cavalcante commented

2023-02-17 19:55:34 +01:00

In fact the custom normals of the new geometry could be treated differently than the other customdata and sort of "auto flip" in the solidify modifier.

So I'm confirming the problem, but it's possible this is still expected behavior.

Tagging @weasel as he has worked on this modifier before and maybe understands more about this issue.

In fact the custom normals of the new geometry could be treated differently than the other customdata and sort of "auto flip" in the solidify modifier. So I'm confirming the problem, but it's possible this is still expected behavior. Tagging @weasel as he has worked on this modifier before and maybe understands more about this issue.

Germano Cavalcante added

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Solidify modifier rotates custom normals incorrectly #104885