fix: use shortest-path rotation interpolation in playback

Switch viewer playback from Magnum Math::slerp() to Math::slerpShortestPath() when interpolating adjacent OpenSim frame orientations.

Why:

- Adjacent OpenSim quaternions can cross sign while representing nearly identical orientations.

- Non-shortest-path interpolation can create artificial long-arc spins between valid sampled poses.

- That makes playback exaggerate or invent visible bone flips that are not present in the sampled frame states.

What changed:

- Updated playback interpolation in src/ViewerApp.cpp to use shortest-path quaternion slerp.

- Added docs/motion-troubleshooting.md documenting the distinction between viewer interpolation artifacts and upstream IK discontinuities.

- Added a README pointer to the troubleshooting note.

Investigation log:

- Verified the viewer loads .mot through OpenSim state storage and renders PhysicalFrame transforms directly.

- Reproduced the target Sports2D/Pose2Sim/OpenSim clip and confirmed the .mot already contains large coordinate discontinuities and limit clamping, indicating upstream IK failure.

- Confirmed the viewer also had a separate interpolation issue due to non-shortest-path quaternion slerp.

Validation:

- Rebuilt with: cmake --build build -j

- Relaunched the viewer successfully against the problematic .osim/.mot pair after the fix.

This commit is contained in:

crosstyan

2026-03-11 11:54:41 +08:00

parent 3e7ef53799

commit ab728c7e9a

3 changed files with 53 additions and 1 deletions

									
										README.md
									
		+4
		
												View File
												
				@@ -31,3 +31,7 @@ Sample run:

				  /home/crosstyan/Code/opensim-core/OpenSim/Moco/Test/walk_gait1018_subject01.osim \

				  /home/crosstyan/Code/opensim-core/OpenSim/Moco/Test/walk_gait1018_state_reference.mot

				```

				## Notes

				- Motion troubleshooting notes: [`docs/motion-troubleshooting.md`](docs/motion-troubleshooting.md)