AS3:使用actionscript设置DisplayObject的注册点？

var mySprite:Sprite = new Sprite();
mySprite.graphics.beginFill(0xFF0000);
mySprite.graphics.drawCircle(0, 0, 50);
mySprite.graphics.endFill();

mySprite.registrationPoint = new Point(mySprite.width / 2, mySprite.height / 2);

var mySprite:Sprite = new Sprite();
mySprite.graphics.beginFill(0xFF0000);
mySprite.graphics.drawCircle(0, 0, 50);
mySprite.graphics.endFill();

var matrix:Matrix = new Matrix();
matrix.translate(-mySprite.width / 2, -mySprite.height / 2);
mySprite.transform.matrix = matrix;