Several issues with constraints in a negative scaled armature #47557

New Issue

Karja Krähwald · 2016-02-25T03:41:58+01:00

Karja Krähwald commented

2016-02-25 03:41:58 +01:00

System Information
Windows 7 64, GTX 980

Blender Version
Broken: f337fea + da81227 (2.77)

Short description of error
As title says, there are problems with armature constraints if the armature object is scaled negativ on at least one axis.
Some constraints get wrong rotation or scale the bone negativ.

Not sure if this is a known issue. Aligorith has mentioned something about rotation & scale handling in this blog: http://code.blender.org/2015/03/animation-system-roadmap-2015-edition/

After reading about the New Interpolation Method for Constraints in 2.77, I was curious to see if this fixes some issues.
But unfortunately it introduces more problems, so 2.77 was a step back in this case.

Exact steps for others to reproduce the error
To find out whats going wrong with the constraints, I have prepared a file with a problem showcase:
NegativeArmatureConstraintTest.blend

Please note that the armature object is scaled negativ on X.
All constraint checkboxes are disabled. Keep this in mind when testing copy/limit rotations.

This causes two main issues:

Some Constraints automatically scale the bone negativ, although nothing should happen.
In 2.77, reducing the influence under 100% causes the same effect and in addition heavy rotation errors, for example on "damped track" and "copy rotation" constraints.

Why scaling armatures or its parents negativ?
To have a mirrored setup without taking much changes or breaking links.
For example to use a right hand object as left hand object.

**System Information** Windows 7 64, GTX 980 **Blender Version** Broken: f337fea + da81227 (2.77) **Short description of error** As title says, there are problems with armature constraints if the armature object is scaled negativ on at least one axis. Some constraints get wrong rotation or scale the bone negativ. Not sure if this is a known issue. Aligorith has mentioned something about rotation & scale handling in this blog: http://code.blender.org/2015/03/animation-system-roadmap-2015-edition/ After reading about the New Interpolation Method for Constraints in 2.77, I was curious to see if this fixes some issues. But unfortunately it introduces more problems, so 2.77 was a step back in this case. **Exact steps for others to reproduce the error** To find out whats going wrong with the constraints, I have prepared a file with a problem showcase: [NegativeArmatureConstraintTest.blend](https://archive.blender.org/developer/F285753/NegativeArmatureConstraintTest.blend) Please note that the armature object is scaled negativ on X. All constraint checkboxes are disabled. Keep this in mind when testing copy/limit rotations. This causes two main issues: - Some Constraints automatically scale the bone negativ, although nothing should happen. - In 2.77, reducing the influence under 100% causes the same effect and in addition heavy rotation errors, for example on "damped track" and "copy rotation" constraints. Why scaling armatures or its parents negativ? To have a mirrored setup without taking much changes or breaking links. For example to use a right hand object as left hand object.

Karja Krähwald commented

2016-02-25 03:41:58 +01:00

Changed status to: 'Open'

Karja Krähwald commented

2016-02-25 03:41:58 +01:00

Added subscriber: @karja

Sergey Sharybin commented

2016-02-25 10:33:21 +01:00

Added subscriber: @Sergey

Sergey Sharybin commented

2016-02-25 10:33:21 +01:00

Changed status from 'Open' to: 'Archived'

Sergey Sharybin closed this issue

2016-02-25 10:33:21 +01:00

Sergey Sharybin self-assigned this 2016-02-25 10:33:21 +01:00

Sergey Sharybin commented

2016-02-25 10:33:21 +01:00

This is just a limitation of conatraint stack, which passes transformation as a 4x4 matrix and when individual transform channels are needed constraint will decomposite the matrix. This decomposition is not mathematically defined for the cases when there's negative scale present: basically you can't distinguish negative scale from 180 rotation, roughly speaking.

There's no simple fix for this issue, any solution would mean re-writing constraints stack from scratch. So thanks for the report, but it's a known limitation.

This is just a limitation of conatraint stack, which passes transformation as a 4x4 matrix and when individual transform channels are needed constraint will decomposite the matrix. This decomposition is not mathematically defined for the cases when there's negative scale present: basically you can't distinguish negative scale from 180 rotation, roughly speaking. There's no simple fix for this issue, any solution would mean re-writing constraints stack from scratch. So thanks for the report, but it's a known limitation.

Joshua Leung commented

2016-02-25 12:10:41 +01:00

Added subscriber: @JoshuaLeung

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Several issues with constraints in a negative scaled armature #47557