标签：des blog http os io ar for art div
首先CCAction是所有动作的基类，如下图继承关系：
那么来看看CCAction的定义：
class CC_DLL CCAction : public CCObject
{
public:
CCAction(void);
virtual ~CCAction(void);
const char* description();
virtual CCObject* copyWithZone(CCZone *pZone);
//! return true if the action has finished
virtual bool isDone(void);
virtual void startWithTarget(CCNode *pTarget);
virtual void stop(void);
//! called every frame with it‘s delta time. DON‘T override unless you know what you are doing.
virtual void step(float dt);
virtual void update(float time);
inline CCNode* getTarget(void) { return m_pTarget; }
inline void setTarget(CCNode *pTarget) { m_pTarget = pTarget; }
inline CCNode* getOriginalTarget(void) { return m_pOriginalTarget; }
inline void setOriginalTarget(CCNode *pOriginalTarget) { m_pOriginalTarget = pOriginalTarget; }
inline int getTag(void) { return m_nTag; }
inline void setTag(int nTag) { m_nTag = nTag; }
public:
static CCAction* create();
protected:
CCNode *m_pOriginalTarget;
CCNode *m_pTarget;
int m_nTag;
};
在类定义最后有三个成员变量，而继承自CCAction的CCFiniteTimeAction主要新增加了一个用于保存该动作总完成时间的成员变量float m_fDuration;
对于其两个子类CCActionInstant和CCActionInterval，前者没有新增任何函数和变量，而后者增加了两个成员变量：float m_elapsed（记录从动作开始起逝去的时间）;和bool m_bFirstTick（一个控制变量）;
那么动作是如何执行的呢？
当一个节点调用runAction方法时，动作管理类CCActionManager（单例类）会将新的动作和节点添加到其管理的动作表中。
CCAction * CCNode::runAction(CCAction* action)
{
CCAssert( action != NULL, "Argument must be non-nil");
m_pActionManager->addAction(action, this, !m_bRunning);
return action;
}
在addAction中，将动作添加到动作队列后，就会对该动作调用其成员函数startWithTarget(CCNode* pTarget)来绑定该动作的执行节点，和初始化动作类的成员变量。
这些工作都完成后，每一帧刷新屏幕时，系统就会在CCActionManager中遍历动作表中的每一个动作，并调用动作的step(float)方法。而step方法主要负责计算m_elapsed的值，并调用update(float)方法。
void CCActionInterval::step(float dt)
{
if (m_bFirstTick)
{
m_bFirstTick = false;
m_elapsed = 0;
}
else
{
m_elapsed += dt;
}
this->update(MAX (0, // needed for rewind. elapsed could be negative
MIN(1, m_elapsed / MAX(m_fDuration, FLT_EPSILON) // division by 0
)
)
);
}
传入update方法的float型参数表示逝去的时间与动作完成需要的时间的比值，介于0-1之间，即动作完成的百分比。然后在update方法中，通过完成比例对节点的属性进行操作来达到动作的效果。
例如：对MoveBy调用update时，通过传入的比例调用setPosition直接修改节点的属性。
最后在每一帧结束后，CCActionManager的update会检查动作队列中每个动作的isDone函数是否返回true，如果返回true，则动作结束，将其从队列中删除。
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从上面知道：动作都是由CCActionManager来管理。那我们再来看看CCActionManager的工作原理。
在CCDirector初始化时，执行了如下代码：
// scheduler
m_pScheduler = new CCScheduler();
// action manager
m_pActionManager = new CCActionManager();
m_pScheduler->scheduleUpdateForTarget(m_pActionManager, kCCPrioritySystem, false);
可见动作管理类在创建时就注册了Update定时器，那么CCScheduler在游戏的每一帧mainLoop更新中都会触发CCActionManager注册的update(float )方法。调度器原理请参照此链接：http://www.cnblogs.com/songcf/p/3162414.html
// main loop
void CCActionManager::update(float dt)
{
//枚举动作表中的每一个节点
for (tHashElement *elt = m_pTargets; elt != NULL; )
{
m_pCurrentTarget = elt;
m_bCurrentTargetSalvaged = false;
if (! m_pCurrentTarget->paused)
{
//枚举节点的每一个动作 actions数组可能会在循环中被修改
for (m_pCurrentTarget->actionIndex = 0; m_pCurrentTarget->actionIndex < m_pCurrentTarget->actions->num;
m_pCurrentTarget->actionIndex++)
{
m_pCurrentTarget->currentAction = (CCAction*)m_pCurrentTarget->actions->arr[m_pCurrentTarget->actionIndex];
if (m_pCurrentTarget->currentAction == NULL)
{
continue;
}
m_pCurrentTarget->currentActionSalvaged = false;
m_pCurrentTarget->currentAction->step(dt);
if (m_pCurrentTarget->currentActionSalvaged)
{
// The currentAction told the node to remove it. To prevent the action from
// accidentally deallocating itself before finishing its step, we retained
// it. Now that step is done, it‘s safe to release it.
m_pCurrentTarget->currentAction->release();
} else
if (m_pCurrentTarget->currentAction->isDone())
{
m_pCurrentTarget->currentAction->stop();
CCAction *pAction = m_pCurrentTarget->currentAction;
// Make currentAction nil to prevent removeAction from salvaging it.
m_pCurrentTarget->currentAction = NULL;
removeAction(pAction);
}
m_pCurrentTarget->currentAction = NULL;
}
}
// elt, at this moment, is still valid
// so it is safe to ask this here (issue #490)
elt = (tHashElement*)(elt->hh.next);
// only delete currentTarget if no actions were scheduled during the cycle (issue #481)
if (m_bCurrentTargetSalvaged && m_pCurrentTarget->actions->num == 0)
{
deleteHashElement(m_pCurrentTarget);
}
}
// issue #635
m_pCurrentTarget = NULL;
}
标签：des blog http os io ar for art div
原文地址：http://www.cnblogs.com/MiniHouse/p/3960066.html
