U3D rootMotion

Body Transform

The Body Transform is the mass center of the character. It is used in Mecanim’s retargeting engine and provides the most stable displacement model. The Body Orientation is an average of the lower and upper body orientation relative to the Avatar T-Pose.

The Body Transform and Orientation are stored in the Animation Clip (using the Muscle definitions set up in the Avatar). They are the only world-space curves stored in the Animation Clip. Everything else: muscle curves and IK goals (Hands and Feet) are stored relative to the body transform.

Root Transform

The Root Transform is a projection on the Y plane of the Body Transform and is computed at runtime. At every frame, a change in the Root Transform is computed. This change in transform is then applied to the Game Object to make it move.

总结：根动画是不断累加的，动画集内的位移是循环的（每次循环起始都归0）。