简述CCNode和Sprite的渲染过程

Sprite创建时，加载纹理，产生纹理id。Sprite重写(override)Node中的draw

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

    }

}

将对应的顶点信息，纹理id，视图矩阵加入render队列。

draw函数在什么时候被调用？

请看Node中的visit函数

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;

}

visit首先根据zorder排列子节点，先调用zorder小于0的子节点的draw函数，再调用自身的draw，接着再调用zorder大于0的子节点的draw函数，最后渲染时，按照render中队列的先后顺序，渲染所有节点。

void Director::drawScene()

｛

  if (_runningScene)

    {

        //clear draw stats

        _renderer->clearDrawStats();

        //render the scene

        _runningScene->render(_renderer);---------调用所有节点的visit和draw函数，添加节点渲染信息到渲染队列中

        _eventDispatcher->dispatchEvent(_eventAfterVisit);

    }

    // draw the notifications node

    if (_notificationNode)

    {

        _notificationNode->visit(_renderer, Mat4::IDENTITY, 0);

    }

    if (_displayStats)

    {

        showStats();

    }

    _renderer->render();------------------渲染所有节点

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