The pole vector constraint calculation within the IK system would sometimes compute the incorrect rotations.
This would be visible as an instantaneous snap of the elbow joint as the bicep was curled.
When applying pole vector constraints, there needs to be two methods of determining the current orientation of the elbow joint.
One for when the arm/elbow joint is bent, and one for when the arm/elbow is straight.
Previously, the way we would switch between these two solutions could cause a large rotation delta to accur between very small angles.
Now we use the more accurate method (1) more often, and we smoothly blend between the solutions as the joint gets straighter.
467a7eaf2d