AS3中BitmapData的draw()平移转换

要绘制对象的定位点不在图像的左上角时，draw需要平移转换

var mc:MovieClip;
var rect:Rectangle = mc.getBounds(mc);
var bmd:BitmapData=new BitmapData(int(rect.width.toFixed()) ,int(rect.height.toFixed()),true,0);
bmd.draw(mc, new Matrix(1, 0, 0, 1,- rect.x, - rect.y));
stage.addChild(new Bitmap(bmd));