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Normals flip when applying scale after global mirror
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Description

System Information
Operating system: Windows home x64
Graphics card: gefoce gtx 1050

Blender Version
Broken: 2.83.5, 2.92.0

Short description of error
The normals flip when applying the scale after a global mirror operation around the x axis.

Exact steps for others to reproduce the error

  1. Select an object
  2. Use Object > Mirror > X Global
  3. Use Ctrl+A > Scale

Event Timeline

Robert Guetzkow (rjg) renamed this task from bug with mirror to Normals aren't mirrored when applying scale after global mirror.Jan 6 2021, 10:46 AM
Robert Guetzkow (rjg) updated the task description. (Show Details)

The global mirror in object mode inverts the scale of the object along the axis (assuming the object hasn't been rotated). This can be seen in the sidebar N in the Item tab. Applying the -1.0 scale causes the normals to face in the other direction along that axis. While this may not be the intention, this is the expected outcome of applying the negative scale factor to the mesh.

The normals can be quickly corrected by recalculating them outside through +N or Mesh > Normals > Recalculate Outside .

Robert Guetzkow (rjg) renamed this task from Normals aren't mirrored when applying scale after global mirror to Normals flip when applying scale after global mirror.Jan 6 2021, 10:53 AM
Robert Guetzkow (rjg) closed this task as Archived.