vue3利用qrcode.vue并通过canvas合并图片

<template>
  <canvas id="canvas" width="300" height="400"></canvas>
  <el-button
      style="margin-top: 20px"
      type="danger"
      plain
      @click="downloadCode"
  >下载二维码</el-button>
  <div id="qrCode" style="display: none">
    <el-row>
      <qrcode-vue style="margin-left: 15%" :value="qrCodeUrl" :size="200"></qrcode-vue>
    </el-row>
    <el-row>
      <el-button
          style="margin-left: 50px; margin-top: 20px"
          type="danger"
          plain
          @click="downloadCode"
      >下载二维码</el-button>
    </el-row>
  </div>
</template>
<script name="qrcodeInfo" setup>
  const props = defineProps({
    // 二维码地址
    qrCodeUrl: {
      type: String,
      default: "",
    },
    gunCode: {
      type: String,
      default: "",
    }
  })
  import QrcodeVue from 'qrcode.vue'
  import {getCurrentInstance, ref} from "vue";
  import posterImg from '@/assets/images/qrCodeBack.png'
  const { proxy } = getCurrentInstance();
  // const qrCodeUrl = ref("");

  defineExpose({
    generateQRCode
  })

  async function generateQRCode() {

    const canvas = document.getElementById('canvas');
    const context = canvas.getContext('2d')
    //清空画布
    context.clearRect(0, 0, canvas.width, canvas.height);

    const image = new Image();
    image.src = posterImg;
    image.crossOrigin = 'Anonymous';

    // 等待图片加载完成
    await new Promise((resolve) => {
      image.onload = resolve;
    });

    // 绘制图片
    context.drawImage(image, 0, 0, canvas.width, canvas.height);
    // 生成二维码
    //获取canvas标签
    let qrCode = document.getElementById('qrCode').getElementsByTagName('canvas')
    //创建a标签
    let a = document.createElement('a')
    const qrCodeDataUrl = await qrCode[0].toDataURL('img/png');

    // 加载二维码图片
    const qrCodeImage = new Image();
    qrCodeImage.src = qrCodeDataUrl;

    // 等待二维码图片加载完成
    await new Promise((resolve) => {
      qrCodeImage.onload = resolve;
    });

    // 绘制二维码图片 x,y,宽,高
    context.drawImage(qrCodeImage, 55, 120, 190, 190);

    //绘制文字
    context.fillStyle = '#fff';
    context.font = '30px Arial';

    //传入显示的文本 x,y
    context.fillText('NO:' + props.gunCode, 20, 380);

  }

  function downloadCode() {
    const canvas = document.getElementById('canvas');
    const downloadLink = document.createElement('a');
    downloadLink.href = canvas.toDataURL('image/png');
    downloadLink.download = props.gunCode + '.png';
    downloadLink.click();
  }
</script>