节点渲染顺序

节点渲染顺序

void Engine::stepFrame()中处理update与render,先看render。
render要做的就是从scene的rootNode开始渲染。
我们约定parentNode zorder为0，childeNode 越小越先渲染。childeNode zorder为负时，比parentNode还要先渲染。
对于每个childeNode，也是这样的顺序，这里是一个递归调用。
render()
{
NegativeChildRender();
renderNow();
positiveChildRender();
}

具体代码：

void Engine::stepFrame()
	{
		if (_updateDesignSize)
		{			
			Renderer::getInstance()->resetProjection();
			_updateDesignSize = false;
		}
		//update
		drawScene();
		Renderer::getInstance()->renderQuad();
	}

	void Engine::drawScene()
	{
		glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
		if(_SceneManager.size() > 0)
		{
			Scene * scene =  _SceneManager.back();
			scene->visit();
		}
		Renderer::getInstance()->visit();
	}

void Scene::visit()
	{
		_root.visit();		
	}

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

				if ( node && node->getZOrder() < 0 )
					node->visit();
				else
					break;
			}
			// self draw
			this->render();

			for(auto it=_children.cbegin()+i; it != _children.cend(); ++it)
				(*it)->visit();
		}
		else
		{
			this->render();
		}
	}
	
	void Node::render()
	{

	}

	void Node::sortAllChildren()
	{
		if( _reorderChildDirty ) {
			std::sort( std::begin(_children), std::end(_children), nodeComparisonLess );
			_reorderChildDirty = false;
		}
	}

void Sprite::initQuad() 
	{
		_blendFunc = BlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
		memset(&_quad, 0, sizeof(_quad));
		int x1 = -_textureSize.width * 0.5f ;
		int x2 = _textureSize.width * 0.5f;

		int y1 = -_textureSize.height* 0.5f ;		
		int y2 = _textureSize.height* 0.5f;

		_quad.tl._position = Vec3(x1, y2, 0);
		_quad.bl._position = Vec3(x1, y1, 0);
		_quad.tr._position = Vec3(x2, y2, 0);	
		_quad.br._position = Vec3(x2, y1, 0);

				
		_quad.tl._color = Color::WHITE;
		_quad.bl._color = Color::WHITE;
		_quad.tr._color = Color::WHITE;
		_quad.br._color = Color::WHITE;
					
		_quad.tl._texCoord = Vec2(0,1);
		_quad.bl._texCoord = Vec2(0,0);
		_quad.tr._texCoord = Vec2(1,1);
		_quad.br._texCoord = Vec2(1,0);		

	}

	void Sprite::render()
	{
		Size winSize = Engine::getInstance()->getDesignSize();
		_quadCommand.init(&_quad,_textureID,1,_blendFunc,_model);
		Renderer::getInstance()->addQuadCommand(&_quadCommand);
	}