Let's begin implementing the createGameScreen method in GameLayer.cpp. Just below the lines that add the bg sprite, we instantiate our batch node:

void GameLayer::createGameScreen() {

  //add bg
  auto bg = Sprite::create("bg.png");
  ...

  SpriteFrameCache::getInstance()->
  addSpriteFramesWithFile("sprite_sheet.plist");
  
  _gameBatchNode = SpriteBatchNode::create("sprite_sheet.png");
  this->addChild(_gameBatchNode);

In order to create the batch node from a sprite sheet, we first load all the frame information described by the sprite_sheet.plist file into SpriteFrameCache. And then we create the batch node with the sprite_sheet.png file, which is the source texture shared by all sprites added to this batch node. (The background image is not part of the sprite sheet, so it's added separately before we add _gameBatchNode to GameLayer.)

Now we can start putting stuff inside _gameBatchNode.