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Maniphest T43534

Face "Rotation" Not Preserved by Mirror Modifier
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Description

System Information
64bit Manjaro Linux, kernel 3.14.29
CPU: AMD Phenom II 970 Deneb quad-core
GPU: nVidia GTX 650 Ti, driver 343.36

Blender Version
Broken: 2.73 devel, hash 03cb146

Short description of error
When using the mirror modifier on an object the "rotation" of the faces is not preserved. I say "rotation" because I am unsure of what is actually going on internally, so I am reporting what I see visually.

The issue is normally invisible and causes no trouble, but I am finding it to be a problem because I am using duplifaces, and I find that any duplicated objects are rotated 90 degrees on the mirrored faces, while retaining the correct orientation on the original faces. Since the thing I am doing (wing feathers) depends on correct orientation, I cannot use the mirror modifier for it and must do the mirroring manually.

Exact steps for others to reproduce the error
Simply open this file, it demonstrates the issue:

FaceRotationsNotPreserved.blend95 KBDownload

Related Objects

Event Timeline

Zauber Paracelsus (zauberexonar) created this task.Feb 2 2015, 8:17 PM
Zauber Paracelsus (zauberexonar) raised the priority of this task from to 90.
Zauber Paracelsus (zauberexonar) updated the task description. (Show Details)
Zauber Paracelsus (zauberexonar) added a project: BF Blender.
Zauber Paracelsus (zauberexonar) edited a custom field.
Zauber Paracelsus (zauberexonar) added a subscriber: Zauber Paracelsus (zauberexonar).
Campbell Barton (campbellbarton) changed the task status from Unknown Status to Archived.Feb 2 2015, 10:48 PM
Campbell Barton (campbellbarton) claimed this task.

This isn't a bug, modifiers don't guarantee to preserve rotation.

The current behavior is intentional and a fix for T31190

Zauber Paracelsus (zauberexonar) added a comment.Feb 2 2015, 11:55 PM

Since the behavior is intentional, could the unintended side-effect of it be fixed instead? IE: could duplifaces be fixed/adjusted to account for the mirror modifier?

Campbell Barton (campbellbarton) added a comment.Feb 3 2015, 7:52 AM

@Zauber Paracelsus (zauberexonar) - while possible - it would have to be quite a specific check in the code.

The way Blender works, face order is assumed to be undefined. (no tools exist to adjust it for example).

When using dupli-faces you just dont have good control over orientation. only direction.