Matrix multiplications/ to_quat/ to_euler outputs incorrect rotation in some cases #83196

New Issue

lucas veber · 2020-11-29T17:46:59+01:00

lucas veber commented

2020-11-29 17:46:59 +01:00

System Information
Operating system: Windows-10-10.0.19041-SP0 64 Bits
Graphics card: GeForce GTX 1080/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 446.14

Blender Version
Broken: version: 2.91.0, branch: master, commit date: 2020-11-25 08:34, hash: 0f45cab862
Worked: /

Short description of error
The matrix multiplication function is buggy, or the matrix > to_quat/to_euler conversion is buggy. This issue propagate in python addons that uses such functions, including the Fbx export where bones rotation are calculated in bone parent space:
https://developer.blender.org/T77811
It happens when a child bone has a nearly 180° angle or 0° with its parent bone, and possibly related to scale value being non equal to 1.

Exact steps for others to reproduce the error

Open this blend file:
matrix_mul_error.blend
It contains two bones on the right: the longest one, named "2" is the child of "1". "2" is animated, making a simple rotation.
The bone on the left named "3" is used to testify the issue, as well as the mesh object on the left "Cube" to testify it doesn't happen with bones only
Click "Run Script". The script does the following > get the matrix in local space (parent space) of bone "2" > apply this matrix either by extracting the quaternion rotation from the matrix and set this rotation to bone "3", or by setting directly the matrix_local of "Cube"
Notice that rotations are incorrect, they jitter, while the rotation of bone "2" is pretty linear.
Now select bone "1" in Edit Mode, scale it bigger and rotate it upside down > No more jitters

**System Information** Operating system: Windows-10-10.0.19041-SP0 64 Bits Graphics card: GeForce GTX 1080/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 446.14 **Blender Version** Broken: version: 2.91.0, branch: master, commit date: 2020-11-25 08:34, hash: `0f45cab862` Worked: / **Short description of error** The matrix multiplication function is buggy, or the matrix > to_quat/to_euler conversion is buggy. This issue propagate in python addons that uses such functions, including the Fbx export where bones rotation are calculated in bone parent space: https://developer.blender.org/T77811 It happens when a child bone has a nearly 180° angle or 0° with its parent bone, and possibly related to scale value being non equal to 1. **Exact steps for others to reproduce the error** - Open this blend file: [matrix_mul_error.blend](https://archive.blender.org/developer/F9414027/matrix_mul_error.blend) - It contains two bones on the right: the longest one, named "2" is the child of "1". "2" is animated, making a simple rotation. - The bone on the left named "3" is used to testify the issue, as well as the mesh object on the left "Cube" to testify it doesn't happen with bones only - Click "Run Script". The script does the following > get the matrix in local space (parent space) of bone "2" > apply this matrix either by extracting the quaternion rotation from the matrix and set this rotation to bone "3", or by setting directly the matrix_local of "Cube" - Notice that rotations are incorrect, they jitter, while the rotation of bone "2" is pretty linear. - Now select bone "1" in Edit Mode, scale it bigger and rotate it upside down > No more jitters

lucas veber commented

2020-11-29 17:46:59 +01:00

Added subscriber: @LucasVeber

champions commented

2020-11-30 00:14:07 +01:00

Added subscriber: @schampions

champions commented

2020-11-30 00:14:07 +01:00

Perhaps there is a change that is not expected in Blenderbold text

Perhaps there is a change that is not expected in Blender**bold text**

lucas veber changed title from ~~Matrix > to_quaternion outputs incorrect rotation in some cases~~ to Matrix multiplications outputs incorrect rotation in some cases

2020-11-30 13:29:36 +01:00

lucas veber changed title from ~~Matrix multiplications outputs incorrect rotation in some cases~~ to Matrix multiplications/ to_quat/ to_euler outputs incorrect rotation in some cases

2020-11-30 14:29:36 +01:00

Alexander Gavrilov commented

2020-11-30 15:44:16 +01:00

Added subscriber: @angavrilov

Alexander Gavrilov commented

2020-11-30 15:44:16 +01:00

This looks like a numerical precision bug in matrix to quaternion conversion - if you convert matrix to euler directly, the problem seems to disappear.

lucas veber commented

2020-11-30 16:00:36 +01:00

Thanks for looking into this @angavrilov ! Well if this can be fixed as simply as that this is reassuring. Will test it thoroughly.

blender-admin commented

2020-11-30 17:31:21 +01:00

This issue was referenced by 814b2787ca

This issue was referenced by 814b2787caddf5bd81477bd7b5dea8c45c402a72

Alexander Gavrilov commented

2020-11-30 19:47:48 +01:00

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

Alexander Gavrilov closed this issue

2020-11-30 19:47:48 +01:00

Alexander Gavrilov self-assigned this 2020-11-30 19:47:48 +01:00

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Matrix multiplications/ to_quat/ to_euler outputs incorrect rotation in some cases #83196