Huolong, I disagree. With collision detection, you'd just put the person in the shirt in the default pose, click "Drop object to the floor" and the shirt would hang naturally on the body. You see, the shirt would be trying to fall to the floor, but collision with the shoulders, chest, arms, etc would keep it from jitting the floor, so what you end up with is a gravity effect. Then, as you move the body, the shirt would move with it, but you would lose the gravity effect for a while. After re-posing your model, hit "Drop Object to Floor" and it would simulate gravity again. Does that make sense?