'Copy Rotation' constraint computes the axis rotation value that should not be modified (like the Z axis when you only specify the X and Y) #117579

New Issue

Phil Stopford · 2024-01-27T22:35:15+01:00

Phil Stopford commented

2024-01-27 22:35:15 +01:00

System Information
Operating system: Linux-6.7.1-arch1-1-x86_64-with-glibc2.38 64 Bits, WAYLAND UI
Graphics card: AMD Radeon Graphics (radeonsi, renoir, LLVM 16.0.6, DRM 3.56, 6.7.1-arch1-1) AMD 4.6 (Core Profile) Mesa 23.3.4-arch1.2

Blender Version
Broken: version: 4.0.2, branch: blender-v4.0-release, commit date: 2023-12-05 07:41, hash: 9be62e85b727
Worked: tested down to 2.93 and the bug is still there.

Short description of error
If the 'Copy Rotation' constraint is only set to copy the X and Y axis from the 'Target' object, depending on the original rotation of the original object, sometimes the Euler Z rotation may be -180 degrees instead of the original 0 degrees .

Since 'Copy Rotation' is ignoring Z rotation, if the constraint changes the Z rotation, the other axis are misaligned.

Ideally, this -180 degrees value should not be computed, since 0 degrees is the original Z value and should not be modified.

Exact steps for others to reproduce the error

Load the attached copy_rotation__bug.blend file
scrub the Euler Y value of the 'Transfer' Object in the Transform panel

Note that sometimes the calculated Z value remains 0 degrees and the axes remain aligned, but other times it changes to 180 degrees, misaligning the axes.

Notes:
This bug was originally identified in copy_rotation_oddness.blend
In this .blend file, we have a 'Driver' object that is intended to be rotated in X and Z. The 'Driver' object is an empty with a delta rotation in X of 90 degrees so that the circle lies in the right plane for the user to work with.
The 'Transfer' object has a driver on its Y rotation that comes from the 'Rotation' empty. It has a constraint applied to 'Copy Rotation' from the 'Driver' object. It also has a delta rotation of 90 degrees in the X channel to make the circle appear correctly in the viewport.
If the 'Copy Rotation' is only set to copy the X and Y rotations from the 'Driver' object, quirks appear at certain frames (e.g. 125) compared to other frames. The inconsistencies are not seen if all rotations are copied, or if "Offset (Legacy)" is used.

Removing the delta transform on the driver object removes the issue.

**System Information** Operating system: Linux-6.7.1-arch1-1-x86_64-with-glibc2.38 64 Bits, WAYLAND UI Graphics card: AMD Radeon Graphics (radeonsi, renoir, LLVM 16.0.6, DRM 3.56, 6.7.1-arch1-1) AMD 4.6 (Core Profile) Mesa 23.3.4-arch1.2 **Blender Version** Broken: version: 4.0.2, branch: blender-v4.0-release, commit date: 2023-12-05 07:41, hash: `9be62e85b727` Worked: tested down to 2.93 and the bug is still there. **Short description of error** If the 'Copy Rotation' constraint is only set to copy the X and Y axis from the 'Target' object, depending on the original rotation of the original object, sometimes the Euler Z rotation may be -180 degrees instead of the original 0 degrees . Since 'Copy Rotation' is ignoring Z rotation, if the constraint changes the Z rotation, the other axis are misaligned. Ideally, this -180 degrees value should not be computed, since 0 degrees is the original Z value and should not be modified. **Exact steps for others to reproduce the error** - Load the attached [copy_rotation__bug.blend](attachments/031c0896-5321-4fc7-aed3-b9e3d59adfb8) file - scrub the Euler Y value of the 'Transfer' Object in the Transform panel Note that sometimes the calculated Z value remains 0 degrees and the axes remain aligned, but other times it changes to 180 degrees, misaligning the axes. --- Notes: This bug was originally identified in [copy_rotation_oddness.blend](attachments/204704fa-12f9-45ce-9b6d-58da9fc0e068) In this .blend file, we have a 'Driver' object that is intended to be rotated in X and Z. The 'Driver' object is an empty with a delta rotation in X of 90 degrees so that the circle lies in the right plane for the user to work with. The 'Transfer' object has a driver on its Y rotation that comes from the 'Rotation' empty. It has a constraint applied to 'Copy Rotation' from the 'Driver' object. It also has a delta rotation of 90 degrees in the X channel to make the circle appear correctly in the viewport. If the 'Copy Rotation' is only set to copy the X and Y rotations from the 'Driver' object, quirks appear at certain frames (e.g. 125) compared to other frames. The inconsistencies are not seen if all rotations are copied, or if "Offset (Legacy)" is used. Removing the delta transform on the driver object removes the issue.

copy_rotation__bug.blend

114 KiB

copy_rotation_oddness.blend

106 KiB

Phil Stopford added the

labels 2024-01-27 22:35:16 +01:00

Pratik Borhade commented

2024-01-30 10:58:03 +01:00

Thanks for the report. Can confirm. Seems related to the euler rotation order.

Pratik Borhade added

and removed

labels 2024-01-30 10:58:16 +01:00

Phil Stopford commented

2024-02-17 20:42:38 +01:00

@PratikPB2123 : I'm curious about the modeling module being set here and wanted to check in case this was a mistake.

Iliya Katushenock added

and removed

labels 2024-02-17 20:47:23 +01:00

Pratik Borhade commented

2024-02-19 10:06:34 +01:00

Hi, this is mostly related to transform code As far as I understand.
cc @mano-wii

Hi, this is mostly related to transform code As far as I understand. cc @mano-wii

Germano Cavalcante changed title from ~~'Copy Rotation' modifier acts oddly if the Z rotation is not copied in this test case~~ to 'Copy Rotation' constraint computes the axis rotation value that should not be modified (like the Z axis when you only specify the X and Y)

2024-02-19 15:03:54 +01:00

Germano Cavalcante commented

2024-02-19 15:12:19 +01:00

I simplified the file and could better understand the problem.

The problem happens when you set only 2 axes to copy in the contraint 'Copy Rotation' (in this case: X and Y).

The 'Copy Rotation' contraint first calculates an XYZ Euler rotation that aligns the 3 axes.
Sometimes it calculates a rotation whose Z value is 0 degrees, matching the target object.
Other times it calculates rotation values where the Z axis is -180 degrees.

When the calculated Z axis does not correspond to the original value, the axis will become misaligned as the constraint only applies to the X and Y axes.

I edited the description and added a simplified file to better describe the problem.

As this only involves Contraints, it is something else for the Animation & Rigging team to investigate.

copy_rotation__bug.blend

I simplified the file and could better understand the problem. The problem happens when you set only 2 axes to copy in the contraint 'Copy Rotation' (in this case: X and Y). The 'Copy Rotation' contraint first calculates an XYZ Euler rotation that aligns the 3 axes. Sometimes it calculates a rotation whose Z value is 0 degrees, matching the target object. Other times it calculates rotation values where the Z axis is -180 degrees. When the calculated Z axis does not correspond to the original value, the axis will become misaligned as the constraint only applies to the X and Y axes. I edited the description and added a simplified file to better describe the problem. As this only involves Contraints, it is something else for the `Animation & Rigging` team to investigate. [copy_rotation__bug.blend](attachments/031c0896-5321-4fc7-aed3-b9e3d59adfb8)

Christoph Lendenfeld commented

2024-02-22 11:28:15 +01:00

I built a test file with 2.93 and I can reproduce the bug there as well (file attached).
Important thing to reproduce it was to add a 90 degree rotation to the delta transform of the "Driver".
Removing that also resolves the flipping in the original file.

I built a test file with 2.93 and I can reproduce the bug there as well (file attached). Important thing to reproduce it was to add a 90 degree rotation to the delta transform of the "Driver". Removing that also resolves the flipping in the original file.

copy_rotation_bug.blend

777 KiB

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'Copy Rotation' constraint computes the axis rotation value that should not be modified (like the Z axis when you only specify the X and Y) #117579