cocos2d-x中的锚点(AnchorPoint)理解

锚点的定义

锚点是指节点在进行形状变换、位置变动时依据的基准点。可以想象为钉在墙上用于固定纸张的小图钉，或者公告栏上用于固定纸张用的围棋状的小磁粒。当对某个节点调用setPosition时，cocos2d-x即会将其锚点移动到相应位置；当对节点进行rotate操作时，节点也是以锚点所在位置为轴心进行旋转的。具体的定义看CCNode.h中的setAnchorPoint说明：
* anchorPoint is the point around which all transformations and positioning manipulations take place.
* It's like a pin in the node where it is "attached" to its parent.

锚点的特征

在cocos2d-x中，锚点是向量化后的点，比如某个480x320的节点，锚点(0,0)在其左下角，锚点(1,1)在其右上角即(480,320)的位置，锚点(0.5,0.5)位于其中点处。注意，锚点可以大于(1,1)或者小于(0,0)，这在后面将会给出演示。
* The anchorPoint is normalized,like a percentage. (0,0) means the bottom-left corner and (1,1) means the top-right corner.
* But you can use values higher than (1,1) and lower than (0,0) too.

锚点的默认值

CCNode：- anchorPoint: (x=0,y=0) -m_bIgnoreAnchorPointForPosition(false)
CCScene/CCLayer/CCSprite：-setAnchorPoint( ccp(0.5f,0.5f) ) -ignoreAnchorPointForPosition(true) (在相应的构造函数中可以看到)

注意：上面提到，设置节点位置时其实是将其锚点移动到指定位置，这有个前提，就是CCNode的m_bIgnoreAnchorPointForPosition成员必须为false，它是告诉标志节点移动时是否忽略锚点的标志。在cocos2d-x中，CCNode/CCSprite将其默认为false，而CCScene/CCLayer则默认为true，因此，若要使CCScene或者CCLayer根据锚点来移动，则要首先调用CCNode::ignoreAnchorPointForPosition(false)

锚点实例一：精灵的锚点

以下分别演示对精灵进行变换操作(transformation/position)时，锚点起到的作用

设置位置

// on "init" you need to initialize your instance
bool HelloWorld::init()
{
    //////////////////////////////
    // 1. super init first
    if ( !CCLayer::init() )
    {
        return false;
    }
    
    CCSize visibleSize = CCDirector::sharedDirector()->getVisibleSize();
    CCPoint origin = CCDirector::sharedDirector()->getVisibleOrigin();

	CCSprite* sprite1 = CCSprite::create("CloseNormal.png");
	sprite1->setAnchorPoint( ccp(0,0) );
	sprite1->setPosition(ccp(origin.x+visibleSize.width/2,origin.y+visibleSize.height/2));
	this->addChild(sprite1);

	CCSprite* sprite2 = CCSprite::create("CloseNormal.png");
	sprite2->setAnchorPoint( ccp(1,0) );
	sprite2->setPosition(ccp(origin.x+visibleSize.width/2,origin.y+visibleSize.height/2));
	this->addChild(sprite2);

	CCSprite* sprite3 = CCSprite::create("CloseNormal.png");
	sprite3->setAnchorPoint( ccp(1,1) );
	sprite3->setPosition(ccp(origin.x+visibleSize.width/2,origin.y+visibleSize.height/2));
	this->addChild(sprite3);

	CCSprite* sprite4 = CCSprite::create("CloseNormal.png");
	sprite4->setAnchorPoint( ccp(0,1) );
	sprite4->setPosition(ccp(origin.x+visibleSize.width/2,origin.y+visibleSize.height/2));
	this->addChild(sprite4);

	CCSprite* sprite5 = CCSprite::create("CloseNormal.png");
	sprite5->setAnchorPoint( ccp(0.5,0.5) );
	sprite5->setPosition(ccp(origin.x+visibleSize.width/2,origin.y+visibleSize.height/2));
	this->addChild(sprite5);

    return true;
}

运行结果：

设置伸缩

bool HelloWorld::init()
{
    //////////////////////////////
    // 1. super init first
    if ( !CCLayer::init() )
    {
        return false;
    }
    
    CCSize visibleSize = CCDirector::sharedDirector()->getVisibleSize();
    CCPoint origin = CCDirector::sharedDirector()->getVisibleOrigin();

	// 锚点(1,1)
	CCSprite* sprite1 = CCSprite::create("CloseNormal.png");
	sprite1->setAnchorPoint( ccp(1,1) );
	sprite1->setPosition(ccp(origin.x+visibleSize.width/2,origin.y+visibleSize.height/2));
	this->addChild(sprite1);

	// 锚点、位置与sprite1相同，X轴以锚点为基点伸缩5.0倍
	CCSprite* sprite2 = CCSprite::create("CloseNormal.png");
	sprite2->setAnchorPoint( ccp(1,1) );
	sprite2->setPosition(ccp(origin.x+visibleSize.width/2,origin.y+visibleSize.height/2));
	this->addChild(sprite2);
	sprite2->setScaleX(5.0f);

	// 锚点(0,0)
	CCSprite* sprite3 = CCSprite::create("CloseNormal.png");
	sprite3->setAnchorPoint( ccp(0,0) );
	sprite3->setPosition(ccp(origin.x+visibleSize.width/2,origin.y+visibleSize.height/2));
	this->addChild(sprite3);

	// 锚点、位置与sprite3相同，X轴以锚点为基点伸缩5.0倍
	CCSprite* sprite4 = CCSprite::create("CloseNormal.png");
	sprite4->setAnchorPoint( ccp(0,0) );
	sprite4->setPosition(ccp(origin.x+visibleSize.width/2,origin.y+visibleSize.height/2));
	this->addChild(sprite4);
	sprite4->setScaleX(5.0f);

    return true;
}

运行结果

设置旋转

bool HelloWorld::init()
{
    //////////////////////////////
    // 1. super init first
    if ( !CCLayer::init() )
    {
        return false;
    }
    
    CCSize visibleSize = CCDirector::sharedDirector()->getVisibleSize();
    CCPoint origin = CCDirector::sharedDirector()->getVisibleOrigin();

	// 锚点(0,origin.y+visibleSize.height/2));
	this->addChild(sprite3);

	// 锚点、位置与sprite3相同，X轴以锚点为轴顺时针旋转90°
	CCSprite* sprite4 = CCSprite::create("CloseNormal.png");
	sprite4->setAnchorPoint( ccp(0,origin.y+visibleSize.height/2));
	this->addChild(sprite4);
	sprite4->setRotation(90);	// 顺时针旋转90°

    return true;
}

运行结果

设置弯曲

bool HelloWorld::init()
{
    //////////////////////////////
    // 1. super init first
    if ( !CCLayer::init() )
    {
        return false;
    }
    
    CCSize visibleSize = CCDirector::sharedDirector()->getVisibleSize();
    CCPoint origin = CCDirector::sharedDirector()->getVisibleOrigin();

	// 锚点(0,origin.y+visibleSize.height/2));
	this->addChild(sprite3);

	// 锚点、位置与sprite3相同，以锚点为固定点，X轴向右弯曲45°
	CCSprite* sprite4 = CCSprite::create("CloseNormal.png");
	sprite4->setAnchorPoint( ccp(0,origin.y+visibleSize.height/2));
	this->addChild(sprite4);
	sprite4->setSkewX(45);

    return true;
}

运行结果

锚点实例二：层的锚点

cocos2d-x中对CCLayer对象setPosition时，若希望以锚点为基点，则需要开启bIgnoreAnchorPointForPosition标志，否则setPosition时不考虑锚点因素。

设置位置

bool HelloWorld::init()
{
    //////////////////////////////
    // 1. super init first
    if ( !CCLayer::init() )
    {
        return false;
    }
    
    CCSize visibleSize = CCDirector::sharedDirector()->getVisibleSize();
    CCPoint origin = CCDirector::sharedDirector()->getVisibleOrigin();

	// 创建一个绿色层
	CCLayerColor* layer1 = CCLayerColor::create(ccc4(0,255,255),100,50);
	layer1->setAnchorPoint( ccp(0.5,0.5) );	// 设置锚点为中点
	// layer->ignoreAnchorPointForPosition(false);
	layer1->setPosition(origin.x+visibleSize.width/2,origin.y+visibleSize.height/2);	// 移动到窗口中点
	this->addChild(layer1);

	// 创建一个黄色层
	CCLayerColor* layer2 = CCLayerColor::create(ccc4(255,50);
	layer2->setAnchorPoint( ccp(0.5,0.5) );	// 设置锚点为中点
	layer2->ignoreAnchorPointForPosition(false);
	layer2->setPosition(origin.x+visibleSize.width/2,origin.y+visibleSize.height/2);	// 移动到窗口中点
	this->addChild(layer2);
	
    return true;
}

运行结果

参考资料

1. cocos2d-x AnchorPoint锚点

2. CSS3中的transform变形详解