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()
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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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