Scaling object by -1 (to mirror) leads to odd sculpting brush behavior #118726

New Issue

J.Z · 2024-02-25T18:49:03+01:00

J.Z commented

2024-02-25 18:49:03 +01:00

** System Information **
Operating system: Win11
Graphics card: RTX3080

** Blender Version **
tested in 3.6 and 4.0, same behavior

** Short description of error and 2 workarounds **
Context is sculpting using additive/subtractive brushes, suppose we create an arm for a character (or just add an UV Sphere and make some visible changes to it to see the mirroring applied later), and then go into Object mode, shift-d to duplicate, then mirror it using scale: s > x > "-1" (to scale in X axis), then go back into sculpt mode for this mirror object and when using draw or any other additive/subtractive brushes, the brush is actually subtracting instead of adding in the mirrored axis, but keeps adding/subtracting in the other axes like it is supposed to.

Remeshing, cleaning up or anything else I tried didn't help, first fix involved exporting as obj and reimporting it back, that fixed the problem.

Other workaround I found that fixes the issue:
Object mode: reset scale using ctrl+a (apply) > "Scale", then back to sculpt mode, remesh, and now the brush is adding/subtracting in all axes on that mirrored object like it is supposed to. Just resetting the scale doesn't help, remeshing has to be performed.

Other brushes, like grab, work just fine just after mirroring the scale, the problem is only with the additive/subtractive brushes and that particular mirrored axis, that led me to think that this is an actual bug rather than just an undocumented feature.

** System Information ** Operating system: Win11 Graphics card: RTX3080 ** Blender Version ** tested in 3.6 and 4.0, same behavior ** Short description of error and 2 workarounds ** Context is sculpting using additive/subtractive brushes, suppose we create an arm for a character (or just add an UV Sphere and make some visible changes to it to see the mirroring applied later), and then go into Object mode, shift-d to duplicate, then mirror it using scale: s > x > "-1" (to scale in X axis), then go back into sculpt mode for this mirror object and when using draw or any other additive/subtractive brushes, the brush is actually subtracting instead of adding in the mirrored axis, but keeps adding/subtracting in the other axes like it is supposed to. Remeshing, cleaning up or anything else I tried didn't help, first fix involved exporting as obj and reimporting it back, that fixed the problem. Other workaround I found that fixes the issue: Object mode: reset scale using ctrl+a (apply) > "Scale", then back to sculpt mode, remesh, and now the brush is adding/subtracting in all axes on that mirrored object like it is supposed to. Just resetting the scale doesn't help, remeshing has to be performed. Other brushes, like grab, work just fine just after mirroring the scale, the problem is only with the additive/subtractive brushes and that particular mirrored axis, that led me to think that this is an actual bug rather than just an undocumented feature.

J.Z added the

labels 2024-02-25 18:49:04 +01:00

Nika Kutsniashvili commented

2024-02-26 09:59:44 +01:00

When scaling -1 your normals get inverted. Brushes are subtracting because youre sculpting on back faces.

In overlays enable "Face Orientation" and youll see red faces. Select them and press Shift N (or Ctrl Shift N)

When scaling -1 your normals get inverted. Brushes are subtracting because youre sculpting on back faces. In overlays enable "Face Orientation" and youll see red faces. Select them and press Shift N (or Ctrl Shift N)

J.Z commented

2024-02-26 11:10:47 +01:00

if I create new project, place an uv sphere in it, enable face orientation overlay, all surfaces on the sphere show blue, perform the S > X > -1, all faces remain blue, yet when switching to sculpt mode and using add brush in X direction, it performs as subtractive brush

Nika Kutsniashvili commented

2024-02-26 11:49:05 +01:00

Hm it seems normals are indeed not shown as red, but anyway. That is the problem and its expected as far as I know. You can simply apply scale so that scale becomes 1;1;1 again and brushes will work correctly.

Iliya Katushenock added the

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Scaling object by -1 (to mirror) leads to odd sculpting brush behavior #118726