简述CCNode和Sprite的渲染过程-创新互联

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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