text: export default (ctx) => {
    // 加载图片
    var img = new Image()
    img.src = "./images/bg.jpg"
    var data = {
      draw(top) {
        ctx.drawImage(img, 0, -canvas.height + top, canvas.width, canvas.height)
        ctx.drawImage(img, 0, top, canvas.width, canvas.height)
      }
    }
  
    return data
  }