重要代码如下：

图片地址 https://oss.qipaistyle.com/3DImage/syst-em718H73870-72K18T71530-09-favorite.png

const query = wx.createSelectorQuery()
  query.select('#canvas')
    .fields({ node: true, size: true })
    .exec((res) => {
      const canvas = res[0].node
      const ctx = canvas.getContext('2d')
      ctx.drawImage(this.img, x, y, manWidth, manHeight)
      ctx.restore()
      var imageData = ctx.getImageData(0, 0, this.img.width, this.img.height);
      ctx.clearRect(0, 0, canvas.width, canvas.height);
      ctx.putImageData(imageData, 0, 0);
}