this._back1Sprite = new TilingSprite();
  this.origin = new Point();


function Point() {
    this.initialize.apply(this, arguments);
}

Point.prototype = Object.create(PIXI.Point.prototype);
Point.prototype.constructor = Point;

Point.prototype.initialize = function(x, y) {
    PIXI.Point.call(this, x, y);
};

不明觉厉....