根据触摸点将精灵旋转一定角度

void StartLayer::ccTouchEnded(cocos2d::CCTouch* pTouch, cocos2d::CCEvent* pEvent)
{
//得到触摸位置,将弹弓旋转指定的角度
CCPoint glPoint = pTouch->getLocation();
CCPoint layerPoint = convertToNodeSpace(glPoint);    //注意这个转换函数用convertToGL结果是不对的！！！
float degree = atan2(layerPoint.x-barrel->getPositionX(), layerPoint. y - barrel->getPositionY()) *180 / 3.1415926;
barrel->setRotation(degree);  //弧度制转化为角度
crosschairs->setPosition(layerPoint);
crosschairs->setRotation(degree);
}