Copy Rotation Constraint - adding rotations causes unexpected behaviour #74266

New Issue

Mustafa Quraish · 2020-02-27T20:45:19+01:00

Mustafa Quraish commented

2020-02-27 20:45:19 +01:00

System Information
Operating system: Windows
Graphics card: GTX 1650 Max-Q`

Blender Version
Broken: v2.81a, v2.81, v2.82

Short description of error
When adding a Copy Rotation constraint to an object, the Add mode seems to not work correctly
(or at least how I would expect it to work). For example, setting the rotation of the object to (x,x,x) and
the target to (-x, -x, -x) does not consistently result in having no net effect. The value for which this stops
working is x >= 54.

Exact steps for others to reproduce the error
1 - Add an object, give it a rotation of (80, 80, 80), Euler XYZ (default)
2 - Add an empty, give it a rotation of (-80, -80, -80)
3 - Add a Copy rotation constraint on the object, and set the target to empty

The included bug.blend file contains an animation that goes over the values of x as described in the
above example from 0-100. The problem can be seen around halfway through the animation at the
critical value above.

Result
Object seems to have a weird rotation, which is not the expected outcome. The same happens
when only one of the axes is rotated more, and also when they don't necessarily add up to 0.

This has been tested on multiple Windows machines.

bug.blend

**System Information** Operating system: Windows Graphics card: GTX 1650 Max-Q` **Blender Version** Broken: v2.81a, v2.81, v2.82 **Short description of error** When adding a Copy Rotation constraint to an object, the `Add` mode seems to not work correctly (or at least how I would expect it to work). For example, setting the rotation of the object to (x,x,x) and the target to (-x, -x, -x) does not consistently result in having no net effect. The value for which this *stops* working is x >= 54. **Exact steps for others to reproduce the error** 1 - Add an object, give it a rotation of (80, 80, 80), Euler XYZ (default) 2 - Add an empty, give it a rotation of (-80, -80, -80) 3 - Add a Copy rotation constraint on the object, and set the target to empty The included `bug.blend` file contains an animation that goes over the values of x as described in the above example from 0-100. The problem can be seen around halfway through the animation at the critical value above. **Result** Object seems to have a weird rotation, which is not the expected outcome. The same happens when only one of the axes is rotated more, and also when they don't necessarily add up to 0. This has been tested on multiple Windows machines. [bug.blend](https://archive.blender.org/developer/F8376253/bug.blend)

Mustafa Quraish commented

2020-02-27 20:45:19 +01:00

Added subscriber: @mustafaquraish

blender-admin commented

2020-02-27 20:45:19 +01:00

#78119 was marked as duplicate of this issue

blender-admin commented

2020-02-27 20:45:19 +01:00

#74988 was marked as duplicate of this issue

Mustafa Quraish changed title from ~~Copy Rotation Constraint - Adding rotations~~ to Copy Rotation Constraint - adding rotations causes unexpected behaviour

2020-02-27 20:46:33 +01:00

Germano Cavalcante commented

2020-02-28 12:13:17 +01:00

Added subscriber: @mano-wii

Germano Cavalcante commented

2020-02-28 12:13:17 +01:00

Changed status from 'Needs Triage' to: 'Confirmed'

Germano Cavalcante commented

2020-02-28 12:13:17 +01:00

Euler rotation is not very reliable to obtain a final position. Partly because you have to follow an order when applying the values.
And here we need to be concerned with 3 orders. The one for the Cube, the one for the Cylinder and the one indicated in the Constraint.

But it is interesting to see in the file that the constraint seems to work as expected before the angle value reaches 55.3.
I think it deserves an investigation.

Euler rotation is not very reliable to obtain a final position. Partly because you have to follow an order when applying the values. And here we need to be concerned with 3 orders. The one for the Cube, the one for the Cylinder and the one indicated in the Constraint. But it is interesting to see in the file that the constraint seems to work as expected before the angle value reaches 55.3. I think it deserves an investigation.

Germano Cavalcante commented

2020-02-28 13:15:48 +01:00

Observing the code I could see that Constraint does not directly use the Euler values of the object, but generates then from the matrix of each object (because they can be modified by other constraints).
However, for the same final position, two Euler values are possible. One is the same set by the user and the other is different. The constraint chooses Euler values that are less different between themselves.

Given the limitations of Euler, I don't see how to indicate to the constraint which of the values should be used. So I don't think we can solve this problem (unless we remove this constraint).

Observing the code I could see that Constraint does not directly use the Euler values of the object, but generates then from the matrix of each object (because they can be modified by other constraints). However, for the same final position, two Euler values are possible. One is the same set by the user and the other is different. The constraint chooses Euler values that are less different between themselves. Given the limitations of Euler, I don't see how to indicate to the constraint which of the values should be used. So I don't think we can solve this problem (unless we remove this constraint).

Germano Cavalcante commented

2020-04-02 14:08:23 +02:00

Added subscribers: @MatBrady, @ankitm

Mat Brady commented

2020-04-02 22:31:23 +02:00

@mano-wii "Given the limitations of Euler, I don't see how to indicate to the constraint which of the values should be used. So I don't think we can solve this problem (unless we remove this constraint)."

Is there a way for the User to choose manually?

I.e. Could a manual toggle switch be used as a temporary fix until the code can be overhauled? Or in a drop down menu? See pic.

https://i.imgur.com/LdUz2s1.gif

@mano-wii "Given the limitations of Euler, I don't see how to indicate to the constraint which of the values should be used. So I don't think we can solve this problem (unless we remove this constraint)." Is there a way for the User to choose manually? I.e. Could a manual toggle switch be used as a temporary fix until the code can be overhauled? Or in a drop down menu? See pic. https://i.imgur.com/LdUz2s1.gif

Germano Cavalcante commented

2020-06-24 17:04:05 +02:00

Added subscribers: @DimaM, @iss

Philipp Oeser removed the

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Copy Rotation Constraint - adding rotations causes unexpected behaviour #74266