绘制海报，绘制完背景图片后怎么绘制二维码图片。还是说只能绘制一张图

  draw(url, qrcode) {
    wx.createSelectorQuery()
      .select('#myCanvas') // 在 WXML 中填入的 id
      .fields({ node: true, size: true })
      .exec((res) => {
        // Canvas 对象
        const canvas = res[0].node
        const ctx = canvas.getContext('2d')
        const width = res[0].width
        const height = res[0].height
        canvas.width = width
        canvas.height = height
        const image = canvas.createImage()
        image.src = url
        image.onload = () => {
          ctx.drawImage(image, 0, 0, 650, 885)
          wx.canvasToTempFilePath({
            canvas,
            success: (res) => {
              const list = [...this.data.imgBuffer, res.tempFilePath]
              // 生成的图片临时文件路径
              this.setData({
                imgBuffer: list,
              })
            },
          })
        }
      })
  },