FBX Exported Animation Has Unstable Rotation #105209

New Issue

Ailuridae · 2024-03-03T14:09:33+01:00

Ailuridae commented

2024-03-03 14:09:33 +01:00

System Information
Operating system: Linux-6.6.16-2-MANJARO-x86_64-with-glibc2.39 64 Bits, X11 UI
Graphics card: NVIDIA GeForce GTX 1660 Ti/PCIe/SSE2 NVIDIA Corporation 4.6.0 NVIDIA 545.29.06

Blender Version
Broken: version: 4.0.2, branch: blender-v4.0-release, commit date: 2023-12-05 07:41, hash: 9be62e85b727

Short description of error
When exporting to FBX, some animated bones will start to shake. I've attached a Blend file as an example.

Steps to Reproduce

Open the attached example Blend file
Export as FBX with options
- Transform:Forward Y
- Transform:Up Z
Import the generated FBX with default options

Debugging
It seems only Bone.001 is affected. The wrong rotation at certain frames is either caused by an incorrectly generated matrix during the baking step, or by incorrectly converting that matrix to Euler rotations. However, I doubt it is the latter. I've printed some values of Bone.001 in the fbx_object_tx function, while it was called by frame_values_gen.

# Frame: 4
matrix = Matrix((( 0.000001980912,  1.000000000000, -0.000000075535,  0.000000986483),
                 (-0.000002013889,  0.000000075554,  1.000000000000,  0.000000149974),
                 ( 1.000000000000, -0.000001921286,  0.000002038500,  0.000000041622),
                 ( 0.000000000000,  0.000000000000,  0.000000000000,  1.000000000000)))

rot = Euler((-43.26432041054461, -89.99983857993809, -46.73573332035233))

# Frame: 5
matrix = Matrix((( 0.000001980919,  1.000000000000, -0.000000075499, -0.000000197244),
                 (-0.000002053577,  0.000000075510,  0.999999940395,  0.000000219111),
                 ( 0.999999940395, -0.000001921337,  0.000002088037,  0.000000060298),
                 ( 0.000000000000,  0.000000000000,  0.000000000000,  1.000000000000)))

rot = Euler((-45.00002515790118, -89.99983857993809, -48.366488796017066))
# This rotation deviates from frame 4 and 6 and is what causes the shaking effect

# Frame: 6
matrix = Matrix((( 0.000001980945,  1.000000000000, -0.000000075506, -0.000001380893),
                 (-0.000002035912,  0.000000075463,  1.000000000000,  0.000000285914),
                 ( 1.000000119209, -0.000001921362,  0.000002016113,  0.000000079287),
                 ( 0.000000000000,  0.000000000000,  0.000000000000,  1.000000000000)))

rot = Euler((-43.26432041054461, -89.99983857993809, -46.73573332035233))

**System Information** Operating system: Linux-6.6.16-2-MANJARO-x86_64-with-glibc2.39 64 Bits, X11 UI Graphics card: NVIDIA GeForce GTX 1660 Ti/PCIe/SSE2 NVIDIA Corporation 4.6.0 NVIDIA 545.29.06 **Blender Version** Broken: version: 4.0.2, branch: blender-v4.0-release, commit date: 2023-12-05 07:41, hash: `9be62e85b727` **Short description of error** When exporting to FBX, some animated bones will start to shake. I've attached a Blend file as an example. ![ExampleBlend.gif](/attachments/256f2ff9-e45a-4d11-9944-95adace4376c) ![ExampleFBX.gif](/attachments/a7c3e4cf-0b8c-43f3-b83d-79ce60a79b50) **Steps to Reproduce** - Open the attached example Blend file - Export as FBX with options - Transform:Forward Y - Transform:Up Z - Import the generated FBX with default options **Debugging** It seems only `Bone.001` is affected. The wrong rotation at certain frames is either caused by an incorrectly generated matrix during the baking step, or by incorrectly converting that matrix to Euler rotations. However, I doubt it is the latter. I've printed some values of `Bone.001` in the `fbx_object_tx` function, while it was called by `frame_values_gen`. ```python # Frame: 4 matrix = Matrix((( 0.000001980912, 1.000000000000, -0.000000075535, 0.000000986483), (-0.000002013889, 0.000000075554, 1.000000000000, 0.000000149974), ( 1.000000000000, -0.000001921286, 0.000002038500, 0.000000041622), ( 0.000000000000, 0.000000000000, 0.000000000000, 1.000000000000))) rot = Euler((-43.26432041054461, -89.99983857993809, -46.73573332035233)) # Frame: 5 matrix = Matrix((( 0.000001980919, 1.000000000000, -0.000000075499, -0.000000197244), (-0.000002053577, 0.000000075510, 0.999999940395, 0.000000219111), ( 0.999999940395, -0.000001921337, 0.000002088037, 0.000000060298), ( 0.000000000000, 0.000000000000, 0.000000000000, 1.000000000000))) rot = Euler((-45.00002515790118, -89.99983857993809, -48.366488796017066)) # This rotation deviates from frame 4 and 6 and is what causes the shaking effect # Frame: 6 matrix = Matrix((( 0.000001980945, 1.000000000000, -0.000000075506, -0.000001380893), (-0.000002035912, 0.000000075463, 1.000000000000, 0.000000285914), ( 1.000000119209, -0.000001921362, 0.000002016113, 0.000000079287), ( 0.000000000000, 0.000000000000, 0.000000000000, 1.000000000000))) rot = Euler((-43.26432041054461, -89.99983857993809, -46.73573332035233)) ```

Example.blend

1.7 MiB

ExampleFBX.gif

170 KiB

Example.fbx

85 KiB

ExampleBlend.gif

297 KiB

Ailuridae added the

labels 2024-03-03 14:09:33 +01:00

Ailuridae commented

2024-03-04 20:24:15 +01:00

Replacing the conversion of quaternion to Euler rotations in fbx_object_tx with the scipy implementation seems to solve the issue for this specific example. This neglects the compatibility check for the Euler rotations. I've not yet checked the underlying implementations of both methods.

    def fbx_object_tx(self, scene_data, rest=False, rot_euler_compat=None):
        """
        Generate object transform data (always in local space when possible).
        """
        matrix = self.fbx_object_matrix(scene_data, rest=rest)
        loc, rot, scale = matrix.decompose()
        matrix_rot = rot.to_matrix()

        # Original
        # quat -> euler, we always use 'XYZ' order, use ref rotation if given.
        # if rot_euler_compat is not None:
        #     rot = rot.to_euler('XYZ', rot_euler_compat)
        # else:
        #     rot = rot.to_euler('XYZ')

        # Workaround
        from scipy.spatial.transform import Rotation as R

        from mathutils import Euler

        rot = R.from_quat((rot.x, rot.y, rot.z, rot.w)).as_euler('xyz')

        rot = Euler((rot[0], rot[1], rot[2]), 'XYZ')

        return loc, rot, scale, matrix, matrix_rot

Replacing the conversion of quaternion to Euler rotations in `fbx_object_tx` with the scipy implementation seems to solve the issue for this specific example. This neglects the compatibility check for the Euler rotations. I've not yet checked the underlying implementations of both methods. ```python def fbx_object_tx(self, scene_data, rest=False, rot_euler_compat=None): """ Generate object transform data (always in local space when possible). """ matrix = self.fbx_object_matrix(scene_data, rest=rest) loc, rot, scale = matrix.decompose() matrix_rot = rot.to_matrix() # Original # quat -> euler, we always use 'XYZ' order, use ref rotation if given. # if rot_euler_compat is not None: # rot = rot.to_euler('XYZ', rot_euler_compat) # else: # rot = rot.to_euler('XYZ') # Workaround from scipy.spatial.transform import Rotation as R from mathutils import Euler rot = R.from_quat((rot.x, rot.y, rot.z, rot.w)).as_euler('xyz') rot = Euler((rot[0], rot[1], rot[2]), 'XYZ') return loc, rot, scale, matrix, matrix_rot ```

Thomas Barlow commented

2024-03-14 12:17:19 +01:00

Thanks for the report. I can reproduce the issue in 3.6 and 4.0, but not in 4.1. It looks like 5b00141144 fixed the underlying issue.

Thanks for the report. I can reproduce the issue in 3.6 and 4.0, but not in 4.1. It looks like https://projects.blender.org/blender/blender/commit/5b00141144d41ae7d3fcf709f4a97e7eb02a9b99 fixed the underlying issue.

Ailuridae commented

2024-03-15 09:19:27 +01:00

Thanks a lot! I'll check out 4.1 next week and close the issue accordingly.