[置顶] 我理解中的cocos2dx之Node

	auto pNode = Node::create();
	this->addChild(pNode);
	pNode->setPosition(Vec2::ZERO);
	pNode->setScale(1.0f);
	pNode->setRotation(0.0f);
	pNode->setColor(Color3B::RED);
	pNode->setName("node");
	pNode->setTag(1);
	pNode->setVisible(true);
	pNode->setUserData((void*)1);

简简单单的一句代码，可以看出，Node是2dx最基本的类,它是Scene,Layer,Sprite,Label等等的父类，它定义了position,scale,color等常用参数及其的setget方法，还有非常重要的visit、draw方法，它提供子类的渲染接口，具体可以看看！

void Node::visit(Renderer* renderer, const Mat4 &parentTransform, uint32_t parentFlags)
{
    // quick return if not visible. children won't be drawn.
    if (!_visible)
    {
        return;
    }

    uint32_t flags = processParentFlags(parentTransform, parentFlags);

    // IMPORTANT:
    // To ease the migration to v3.0, we still support the Mat4 stack,
    // but it is deprecated and your code should not rely on it
    Director* director = Director::getInstance();
    director->pushMatrix(MATRIX_STACK_TYPE::MATRIX_STACK_MODELVIEW);
    director->loadMatrix(MATRIX_STACK_TYPE::MATRIX_STACK_MODELVIEW, _modelViewTransform);
    
    bool visibleByCamera = isVisitableByVisitingCamera();

    int i = 0;

    if(!_children.empty())
    {
        sortAllChildren();
        // draw children zOrder < 0
        for( ; i < _children.size(); i++ )
        {
            auto node = _children.at(i);

            if ( node && node->_localZOrder < 0 )
                node->visit(renderer, _modelViewTransform, flags);
            else
                break;
        }
        // self draw
        if (visibleByCamera)
            this->draw(renderer, _modelViewTransform, flags);

        for(auto it=_children.cbegin()+i; it != _children.cend(); ++it)
            (*it)->visit(renderer, _modelViewTransform, flags);
    }
    else if (visibleByCamera)
    {
        this->draw(renderer, _modelViewTransform, flags);
    }

    director->popMatrix(MATRIX_STACK_TYPE::MATRIX_STACK_MODELVIEW);
    
    // FIX ME: Why need to set _orderOfArrival to 0??
    // Please refer to https://github.com/cocos2d/cocos2d-x/pull/6920
    // reset for next frame
    // _orderOfArrival = 0;
}

其中sortAllChildren();对不同层级的子类进行排序，从而将zorder最高的和相同层级的最后被addChild的显示出来。
this->draw(renderer, _modelViewTransform, flags);这个函数则画出自身，由于c++的多态性，它将调用自己的draw方法，如，Sprite就会调用

void Sprite::draw(Renderer *renderer, const Mat4 &transform, uint32_t flags)
{
    // Don't do calculate the culling if the transform was not updated
    _insideBounds = (flags & FLAGS_TRANSFORM_DIRTY) ? renderer->checkVisibility(transform, _contentSize) : _insideBounds;

    if(_insideBounds)
    {
        _quadCommand.init(_globalZOrder, _texture->getName(), getGLProgramState(), _blendFunc, &_quad, 1, transform);
        renderer->addCommand(&_quadCommand);
#if CC_SPRITE_DEBUG_DRAW
        _debugDrawNode->clear();
        Vec2 vertices[4] = {
            Vec2( _quad.bl.vertices.x, _quad.bl.vertices.y ),
            Vec2( _quad.br.vertices.x, _quad.br.vertices.y ),
            Vec2( _quad.tr.vertices.x, _quad.tr.vertices.y ),
            Vec2( _quad.tl.vertices.x, _quad.tl.vertices.y ),
        };
        _debugDrawNode->drawPoly(vertices, 4, true, Color4F(1.0, 1.0, 1.0, 1.0));
#endif //CC_SPRITE_DEBUG_DRAW
    }
}

        for(auto it=_children.cbegin()+i; it != _children.cend(); ++it)
            (*it)->visit(renderer, _modelViewTransform, flags);
   

这里是一个递归，从而渲染出节点树所有的节点！

2dx中的大循环中就是调用Node的visit方法，我们去看看

main.cpp ->  director->mainLoop() -> drawScene() ->  _runningScene->render(_renderer) -> visit(renderer, Mat4::IDENTITY, 0);

    AppDelegate app;
    return Application::getInstance()->run();

.....

    while(!glview->windowShouldClose())
    {
        QueryPerformanceCounter(&nNow);
        if (nNow.QuadPart - nLast.QuadPart > _animationInterval.QuadPart)
        {
            nLast.QuadPart = nNow.QuadPart;
            
            director->mainLoop();
            glview->pollEvents();
        }
        else
        {
            Sleep(0);
        }
    }

......

    else if (! _invalid)
    {
        drawScene();
     
        // release the objects
        PoolManager::getInstance()->getCurrentPool()->clear();
    }

......

    if (_runningScene)
    {
        //clear draw stats
        _renderer->clearDrawStats();
        
        //render the scene
        _runningScene->render(_renderer);
        
        _eventDispatcher->dispatchEvent(_eventAfterVisit);
    }

......

//visit the scene
        visit(renderer, Mat4::IDENTITY, 0);
        

这个visit就是Node的visit函数。