我们如何旋转ENDLESS运行背景？

Question

下面的代码有能力从上到下无限的背景旋转或其他方式。

我只是希望与此轮换相反。我试过但可以解决这个问题。

有人建议我，怎么做？

private void animateBackground() {
    _oddBackground = CCSprite.sprite("sky.png");
    _evenBackground = CCSprite.sprite("sky.png");

    /*from Upward to Downward direction background rotation */

    _oddBackground.setPosition(winSize.width / 2, winSize.height / 2);
    _evenBackground.setPosition(winSize.width / 2, winSize.height + (winSize.height / 2));
    schedule("scroll");

    addChild(_oddBackground).addChild(_evenBackground);
}

public void scroll(float dt) {
    // move them 100*dt pixels down
    _oddBackground.setPosition(_oddBackground.getPosition().x,   _oddBackground.getPosition().y - 100 * dt);
    _evenBackground.setPosition(_evenBackground.getPosition().x, _evenBackground.getPosition().y - 100 * dt);

    // reset position when they are off from view.
    if (_oddBackground.getPosition().y < - winSize.height / 2) {
        _oddBackground.setPosition(winSize.width / 2, winSize.height / 2);
        _evenBackground.setPosition(winSize.width / 2, winSize.height+ (winSize.height / 2));
    }
}