mainLoop: function () {
    if (this._purgeDirectorInNextLoop) {
        this._purgeDirectorInNextLoop = false;
        this.purgeDirector();
    }
    else if (!this.invalid) {
        this.drawScene();
    }
},

 *  Draw the scene. This method is called every frame. Don‘t call it manually.
 */
drawScene: function () {
    var renderer = cc.renderer;

    // calculate "global" dt
    this.calculateDeltaTime();

    大专栏  Cocos2dx-JS学习01n class="comment">//tick before glClear: issue #533
    if (!this._paused) {
        this._scheduler.update(this._deltaTime);
        cc.eventManager.dispatchEvent(this._eventAfterUpdate);
    }

    
    //首先执行调度器中的任务，然后触发cc.director.EVENT_AFTER_UPDATE事件，检查交互事件,有的话就分发处理
    
    
    
   
    /* to avoid flickr, nextScene MUST be here: after tick and before draw.
     XXX: Which bug is this one. It seems that it can‘t be reproduced with v0.9 */
    if (this._nextScene) {
        this.setNextScene();
    }
    //如果有场景切换，便切换
    
    //渲染当前scene
    // draw the scene
    if (this._runningScene) {
        if (renderer.childrenOrderDirty) {
            cc.renderer.clearRenderCommands();
            cc.renderer.assignedZ = 0;
            this._runningScene._renderCmd._curLevel = 0;                          //level start from 0;
            this._runningScene.visit();
            renderer.resetFlag();
        } 
        else if (renderer.transformDirty()) {
            renderer.transform();
        }
    }

    renderer.clear();

    // draw the notifications node
    if (this._notificationNode)
        this._notificationNode.visit();
    //遍历节点，更新节点的空间转换矩阵，发送命令给渲染器
    cc.eventManager.dispatchEvent(this._eventAfterVisit);
    cc.g_NumberOfDraws = 0;

    renderer.rendering(cc._renderContext);
    this._totalFrames++;
	//排序，绘制
    cc.eventManager.dispatchEvent(this._eventAfterDraw);
    cc.eventManager.frameUpdateListeners();
    //更新帧率
    this._calculateMPF();
},

node.scheduleUpdate()
node.update = function (dt) {
    
}

node.schedule(callback,inteval,repeate,delay,key)