cocos2dx 锚点

cocos2dx中经常会用到节点的旋转，一旦涉及到物体的旋转则会涉及到旋转所相对的中心点的位置，对于CCNode而言，其提供了设置锚点的接口，用来设置锚点的相对位置。

见CCNode源代码中CCNode.cpp

/// anchorPoint getterconst CCPoint& CCNode::getAnchorPoint(){    return m_obAnchorPoint;}void CCNode::setAnchorPoint(const CCPoint& point){    if( ! point.equals(m_obAnchorPoint))    {        m_obAnchorPoint = point;        m_obAnchorPointInPoints = ccp(m_obContentSize.width * m_obAnchorPoint.x, m_obContentSize.height * m_obAnchorPoint.y );        m_bTransformDirty = m_bInverseDirty = true;    }}

其锚点的坐标值是一个相对值0~1，其中m_obAnchorPoint表示的是相对锚点坐标，m_obAnchorPointInPoints表示的是锚点在屏幕中的像素坐标，所以对于CCNode的坐标系转换会涉及到多种转换方式。

我们也可以通过设置ignoreAnchorPointForPosition来忽略锚点的作用。

对于图层而言其ignoreAnchorPointForPosition的默认值为false，CCSprite默认值为true，但是有时候大家会发现，即便咱们设置了图层的ignoreAnchorPointForPosition为false，但是图层的旋转仍然没有按照预定的结果来进行，原因是因为默认CCLayer的图层的大小为CCSize(0,0)，所以不管你怎么设置图层的大小始终为(0,0)，经过锚点比例进行计算之后其锚点的坐标仍然是(0,0)，如下图所示：

但是设置了CCLayer的大小之后，就会发现，咱们设置的锚点就能起到作用了

void LayerIgnoreAnchorPointPos::onEnter(){    LayerTest::onEnter();bool ignore = this->isIgnoreAnchorPointForPosition();//this->ignoreAnchorPointForPosition(false);//CCSize layerSize = this->getContentSize();setContentSize(CCDirector::sharedDirector()->getWinSize());setAnchorPoint(ccp(0.5, 1));//CCSize layerSize2 = this->getContentSize();//CCPoint pt = this->getPosition();//setPosition(ccp(layerSize2.width/2, layerSize2.height/2));    CCSize s = CCDirector::sharedDirector()->getWinSize();    CCLayerColor *l = CCLayerColor::create(ccc4(255, 0, 0, 255), 150, 150);    l->setAnchorPoint(ccp(0.5f, 0.5f));    l->setPosition(ccp( s.width/2, s.height/2));    CCMoveBy *move = CCMoveBy::create(2, ccp(100,2));    CCMoveBy * back = (CCMoveBy *)move->reverse();    CCSequence *seq = CCSequence::create(move, back, NULL);    l->runAction(CCRepeatForever::create(seq));    this->addChild(l, 0, kLayerIgnoreAnchorPoint);    CCSprite *child = CCSprite::create("Images/grossini.png");    l->addChild(child);    CCSize lsize = l->getContentSize();    child->setPosition(ccp(lsize.width/2, lsize.height/2));    CCMenuItemFont *item = CCMenuItemFont::create("Toggle ignore anchor point", this, menu_selector(LayerIgnoreAnchorPointPos::onToggle));    CCMenu *menu = CCMenu::create(item, NULL);    this->addChild(menu);    menu->setPosition(ccp(s.width/2, s.height/2));//this->setAnchorPoint(ccp(0.5, 0.5));CCDirector::sharedDirector()->getActionManager()->addAction(CCRepeatForever::create(CCSequence::create(CCRotateBy::create(2, 360),CCRotateBy::create(2, -360),0)),this,false);}