这个帖子里关于地图滚动的原理我看懂了，但是下面这个判断和算法我看得不太懂，请大佬们指点一下
http://blog.csdn.net/evankaka/article/details/43972397
//移動并判斷背景
void BackLayerDown::update(float time)
{
Size visibleSize = Director::getInstance()->getVisibleSize();
Point origin = Director::getInstance()->getVisibleOrigin();
Sprite* temMap1 = (Sprite*)this->getChildByTag(MAP_1_Tag);
Sprite* temMap2 = (Sprite*)this->getChildByTag(MAP_2_Tag);
temMap1->setPositionY(temMap1->getPositionY() - 1);
temMap2->setPositionY(temMap2->getPositionY() - 1);
if (temMap1->getPositionY() + temMap1->getContentSize().height / 2 <= origin.y)
{
float offset = temMap1->getPositionY() + temMap1->getContentSize().height / 2 - origin.y;
temMap1->setPosition(Vec2(visibleSize.width / 2 + origin.x, temMap1->getContentSize().height / 2 + origin.y + visibleSize.height + offset));
}
if (temMap2->getPositionY() + temMap2->getContentSize().height / 2 <= origin.x)
{
float offset = temMap2->getPositionY() + temMap2->getContentSize().height / 2 - origin.y;
temMap2->setPosition(Vec2(visibleSize.width / 2 + origin.x, temMap2->getContentSize().height / 2 + origin.y + visibleSize.height + offset));
}
}
请大佬们详细讲一下这个origin.y,getContentSize().height / 2是啥，最好画张图我看下0.0
跪求啊