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This is more involved than using simple straight bending targets constructed from the neighboring segments, but necessary for restoring groomed rest shapes. The targets are defined by parallel-transporting a coordinate frame along the hair, which smoothly rotates to avoid sudden twisting (Frenet frame problem). The rest positions of hair vertices defines the target vectors relative to the frame. In the deformed motion state the frame is then recalculated and the targets constructed in world/root space.