原理：signature_pad外掛，canvas

<template>
  <div id="app">
    <button @click="handleClick">點選簽名</button>
    <img :src="imgUrl" v-if="showImg" style="border:1px dashed #ccc;"/>
    <div class="sign-box" v-show="showSignature">
      <div class="bgc"></div>
      <div class="main-box">
        <span @click="cancelBgc" class="cancel">取消</span>
        <p class="title">簽名</p>
        <p class="sub-title">請用正楷簽下您的名字</p>
        <div :style="{width:w,height:h}" class="canvass">
          <canvas :id="uid" class="canvas" :data-uid="uid"></canvas>
        </div>
        <div id='reset' @click="clear">
          <span>清除</span>
        </div>
        <div @click="saveSign" class="next">確認</div>
      </div>
    </div>
  </div>
</template>

<script>
  /*
 
 eslint-disable */
  import SignaturePad from 'signature_pad';
  export default {
    data() {
      return {
        showSignature: false,
        showImg:false,
        sig: () => { },
        uid: 'canvas',
        option: {
          backgroundColor: 'rgb(255,255,255)',
          penColor: 'rgb(0, 0, 0)',
          minWidth: 
 
0.8,
          maxWidth: 4
        },
        w: '94.6%',
        h: "240px",
      }
    },
    methods: {
      handleClick() {
        this.showSignature = true;
        this.$nextTick(() => {
          this.draw();
        })
      },
      // 簽名
      draw() {
        var that = this;
        var
 
 canvas = document.getElementById(that.uid);
        that.sig = new SignaturePad(canvas, that.option);
        window.addEventListener('resize', that.resizeCanvas);
        that.resizeCanvas();
      },
      resizeCanvas() {
        var that = this
        var canvas = document.getElementById(that.uid);
        var url;
        var ratio = Math.max(window.devicePixelRatio || 1, 1);
        canvas.width = canvas.offsetWidth * ratio;
        canvas.height = canvas.offsetHeight * ratio;
        canvas.getContext('2d').scale(ratio, ratio);
        that.clear()
        !that.clearOnResize && url !== undefined && that.fromDataURL(url);
      },
      fromDataURL(url) {
        var that = this;
        that.sig.fromDataURL(url);
      },
      // 取消簽名
      cancelBgc() {
        this.showSignature = false;
      },
      // 清除簽名
      clear() {
        var that = this;
        that.sig.clear();
      },
      isEmpty() {
        var that = this;
        return that.sig.isEmpty();
      },
      // 儲存簽名
      saveSign() {
        var that = this;
        if (that.isEmpty()) {
          alert('請用正楷簽下您的名字');
          return
        }
        var sign = {
          signature: that.sig.toDataURL().split(',')[1]
        }
        that.imgUrl = "data:image/png;base64," + sign.signature;
        that.showImg = true;
        that.showSignature = false;
      }
    }
  }
/* eslint-disable */
</script>

<style>
  #app {
    font-family: Avenir, Helvetica, Arial, sans-serif;
    -webkit-font-smoothing: antialiased;
    -moz-osx-font-smoothing: grayscale;
    color: #2c3e50;
    margin-top: 60px;
  }

  .canvass {
    margin: auto;
    background: #fff;
    border: 1px dashed #e5e5e5;
    border-radius: 8px;
    margin-top: 17px;
    position: relative;
  }

  #reset {
    text-align: center;
    font-size: 14px;
    color: #666666;
    margin-top: 26px;
    margin-bottom: 47px;

  }

  #reset img {
    width: 13px;
    height: 13px;
  }

  canvas {
    width: 100%;
    height: 100%;
  }

  .sign-box {
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    min-height: 100vh;

  }

  .bgc {
    opacity: 0.7;
    background: #000000;
    width: 100%;
    height: 100%;
    position: absolute;
    top: 0;
    z-index: 5;
  }

  .main-box {
    height: 500px;
    width: 100%;
    background-color: #fff;
    position: absolute;
    bottom: 0;
    z-index: 10;

  }

  .cancel {
    position: absolute;
    font-size: 18px;
    color: #31A4FF;
    left: 15px;
    top: 16px;
  }

  .title {
    text-align: center;
    font-size: 18px;
    color: #333333;
    padding-top: 16px;
    padding-bottom: 4px;
  }

  .sub-title {
    font-size: 12px;
    color: #999999;
    text-align: center;
  }

  .next {
    border: 1px solid #31A4FF;
    height: 44px;
    text-align: center;
    line-height: 44px;
    font-size: 18px;
    color: #31A4FF;
    background: #fff;
    margin: 0 15px;
  }

  .footer {
    position: fixed;
    left: 0;
    bottom: 0;
    display: flex;
    justify-content: space-between;
    width: 100%;
  }

  .pre {
    width: 28%;
    margin-right: 1px;
    border-top: 1px solid #d6d6d6;
    color: #454545;
    background: #fff;
  }

  .share {
    width: 44%;
    border-top: 1px solid #d6d6d6;
    background: #66b9ff;
    color: #fff;
  }

  .nextOne {
    width: 28%;
    color: #fff;
    background: #31A4FF;
  }

  .commoncss {
    height: calc(110rem / 24);
    line-height: calc(110rem / 24);
    font-size: 1.6rem;
    text-align: center;
    box-sizing: border-box;
    margin-top: 1rem;
  }

  .hasLinkpre {
    margin-top: 1rem;
    background: #fff;
    width: 50%;
    height: calc(110rem / 24);
    line-height: calc(110rem / 24);
    font-size: 1.6rem;
    text-align: center;
    box-sizing: border-box;
    color: #454545;
  }

  .hasLinknextone {
    margin-top: 1rem;
    background: #31A4FF;
    width: 50%;
    height: calc(110rem / 24);
    line-height: calc(110rem / 24);
    font-size: 1.6rem;
    text-align: center;
    box-sizing: border-box;
    color: #fff;
  }
</style>

效果圖：