Normal Flip Modifier

Question

I have 8 objects sharing the same mesh (linked duplicates) and I want half of them to have their normals flipped, so I am searching for a modifier that flips all the normals on an object before I set out to write my own.

The mesh is asymmetric, so I can't use a negative scale. The two normal directions need to be separate objects so I can export them to different files for render order reasons. I'd prefer not to have two meshes, as then I'd have to keep them in sync if I edit one.

jachym michal · Answer 1 · 2020-11-02T19:21:17.783

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One solution would be a Solidify Modifier.
All credits to @lemon for making it work.

Add Solidify Modifier
Set Normals > Flip, and Mode > Complex
Add Weld Modifier

edited Nov 02 '20 at 19:21

answered Nov 02 '20 at 18:43

jachym michal

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Not so silly (and there is a gif here!)... just set it to "complex" (0 thickness and flip normals) and add a weld modifier. – lemon Nov 02 '20 at 18:48
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Damn it, Lemon! That's the one combination of Solidify and Weld I didn't try before! :) – jachym michal Nov 02 '20 at 19:04
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An advice: for each version of Blender, try every combination of everything... (on my side, still working on 2.59 nowadays...) – lemon Nov 02 '20 at 19:07
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ahah better start working on it quick :D – jachym michal Nov 02 '20 at 19:12
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Though, weld could merge that is not wanted to be... – lemon Nov 02 '20 at 19:12
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But it works perfectly on Suzanne :). Exactly 500 faces before/after. – jachym michal Nov 02 '20 at 19:20
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Suzanne is an easter egg, didn't you know? ; ) – lemon Nov 02 '20 at 19:23
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@lemon That's Evil.

Robin Betts

Nov 02 '20 at 20:11

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Thanks! A little awkward to have to add and configure two modifiers, but it works and is a lot easier than writing my own modifier. It looks like it might destroy custom normals though? – Road-hog123 Nov 02 '20 at 20:22

@Road-hog123 Hi :). Keeps custom normals on my end, but if you've ran into any problems, feel free to post another question. – jachym michal Nov 03 '20 at 06:21

score 1 · Accepted Answer · answered Aug 16 '22 at 21:00

As of Blender 3.0 the Solidify + Weld Modifier combination stopped working - the flipped faces are removed when welding instead of the original ones.

As of Blender 3.1 it is possible to Flip Faces with a Geometry Nodes Modifier and a Mesh > Flip Faces node. This node reverses the order of vertices for each face, which implicitly flips the face normals - it does not flip vertex normals.

While not the Normal Flip Modifier I originally asked for, the Face Flip node is doing what I needed the modifier for.

Normal Flip Modifier

2 Answers2

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