Export bitmap from MovieClip (DisplayObject)

public function createPreview(obj:*):BitmapData
        {
            var resultShirt:BitmapData = new BitmapData(obj.width, obj.height, false, 0xffffff);
           
            var m:Matrix = new Matrix();
            var s:Number = resultShirt.height / obj.width;
           
            obj.mask = null;
            m.translate(-obj.width / 2, -obj.height / 2);

            m.translate(resultShirt.width / 2 , resultShirt.height / 2 );
           
            resultShirt.draw(obj, m, null, null, null, false);

           
            return resultShirt;
        }