vue中实现图片上传添加自定义水印并下载

<div class="wrap">
  <div class="optea">
    <div class="file-upload">
      <p>选择图片</p>
      <el-button type="text" style="color: #c00;"
        ><label for="uploads">
          <i class="el-icon-upload2" style="margin-right: 5px;"></i>
          选择需要添加水印的图片</label
        ></el-button
      >
      <input
        type="file"
        id="uploads"
        hidden
        accept="image/png, image/jpeg, image/gif, image/jpg"
        @change="uploadImg($event, 1)"
      />
    </div>
    <p>水印文字</p>
    <el-input v-model="watermarkOptions.text" placeholder="请输入水印内容"></el-input>
    <p>字体颜色</p>
    <el-color-picker v-model="watermarkOptions.color"></el-color-picker>
    <p>旋转角度</p>
    <el-slider v-model="watermarkOptions.rotate" :min="0" :max="360"></el-slider>
    <p>透明度</p>
    <el-slider v-model="watermarkOptions.alpha" :min="0" :max="100"></el-slider>
    <p>文本间距</p>
    <el-slider v-model="watermarkOptions.width" :min="0" :max="100"></el-slider>
    <p>字体大小</p>
    <el-slider v-model="watermarkOptions.fontSize" :min="0" :step="0.5" :max="50"></el-slider>
  </div>
  <div>
    <el-button @click="handleDown" class="download-btn" type="primary" plain icon="el-icon-download"
      >下载水印图片</el-button
    >
    <div class="preview" ref="previewImg">
      <img :src="preImg || defaultimg" alt="" />
      <div class="watermark" :style="{ background: paint }"></div>
    </div>
  </div>
</div>

import defaultimg from "@/assets/img/index/index1.jpg";
import DomToImage from "dom-to-image";
export default {
  data() {
    return {
      defaultimg,
      preImg: '',
      watermarkOptions: {
        text: '仅供 xxx 验证使用',
        fontSize: 10,
        width: 5,
        color: '#000000',
        alpha: 35,
        rotate: 35,
      },
    };
  },
  methods: {
    uploadImg(e, num) {
      //上传图片
      // this.option.img
      var file = e.target.files[0];
      if (!/\.(gif|jpg|jpeg|png|bmp|GIF|JPG|PNG)$/.test(e.target.value)) {
        alert('图片类型必须是.gif,jpeg,jpg,png,bmp中的一种');
        return false;
      }
      var reader = new FileReader();
      reader.onload = e => {
        let data;
        if (typeof e.target.result === 'object') {
          // 把Array Buffer转化为blob 如果是base64不需要
          data = window.URL.createObjectURL(new Blob([e.target.result]));
        } else {
          data = e.target.result;
        }
        if (num === 1) {
          this.preImg = data;
        }
      };
      // 转化为base64
      reader.readAsDataURL(file);
      // 转化为blob
      // reader.readAsArrayBuffer(file)
    },
    handleDown() {
      let node = this.$refs.previewImg;
      let that = this;
      DomToImage.toPng(node)
        .then(function(dataUrl) {
          var oLink = document.createElement('a');
          oLink.download = '水印图片.png';
          oLink.href = dataUrl;
          oLink.click();
          that.$nextTick(() => {
            that.$message.success('水印图片下载成功');
          });
        })
        .catch(function(error) {
          console.error('oops, something went wrong!', error);
          that.$message.error('下载失败');
        });
    },
  },
  computed: {
    paint() {
      // 文字长度
      const wordWidth =
        this.watermarkOptions.fontSize * this.watermarkOptions.text.split('').length;
      const width = wordWidth + this.watermarkOptions.width;

      let svgText = `
    <svg xmlns="http://www.w3.org/2000/svg" width="${width}px" height="${width}px">
    <text x="50%" y="50%"
        alignment-baseline="middle"
        text-anchor="middle"
        stroke="${this.watermarkOptions.color}"
        opacity="${this.watermarkOptions.alpha / 100}"
        transform="translate(${width / 2}, ${width / 2}) rotate(${
        this.watermarkOptions.rotate
      }) translate(-${width / 2}, -${width / 2})"
        font-weight="100"
        font-size="${this.watermarkOptions.fontSize}"
        font-family="microsoft yahe"
        >
        ${this.watermarkOptions.text}
    </text>
   </svg>`;

      return `url(data:image/svg+xml;base64,${btoa(unescape(encodeURIComponent(svgText)))})`;
    },
  },
};