local screenshot = cc.RenderTexture:create(w, h)
self.backSprite:setPosition(cc.p(w/2, h/2))
screenshot:begin()
self.backSprite:visit() --此处将需要渲染的内容再次 visit 即可
screenshot:endToLua()
screenshot:saveToFile("hlbtest.png", cc.IMAGE_FORMAT_PNG, true)

print("=================sp", screenshot:getSprite())