auto background = Sprite::create("background.png");
//
background->setPhysicsBody(PhysicsBody::createEdgeBox(background->getContentSize())); 
background->setPosition(0, winSize.height);
background->setAnchorPoint(Point(0.f, 1.f));
this->addChild(background, -1000);
给图片精灵设置 PhysicsBody 后 ， 锚点值就不能改变， 是固定值 默认值Point(0.5f,0.5f) 什么原因？