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);
- /**
- called after the action has finished. It will set the 'target' to nil.
- IMPORTANT: You should never call "[action stop]" manually. Instead,use: "target->stopAction(action);"
- */
- 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;
- }