实现签名的三个关键方法：

1.mousedown：当鼠标按下时开始绘制签名。

2.mousemove：鼠标移动时持续绘制。

3.mouseup：鼠标抬起时结束绘制。

html：

<div class="setSign">
  <canvas
    ref="canvas"
    @mousedown="startDrawing"
    @mousemove="draw"
    @mouseup="stopDrawing"
  ></canvas>
</div>
<div class="btns">
  <el-button @click="handleClose">取 消</el-button>
  <el-button type="danger" @click="clearCanvas">清 空</el-button>
  <el-button type="primary" @click="saveSignature">保 存</el-button>
</div>

js：

import { getSignNew, saveSignNew } from "@/api/common";
export default {
  mixins: [],
  components: {},
  props: {},
data() {
  return {
    isDrawing: false,
    canvas: null,
    context: null,
    savedImage: null,
    queryObj: {},
  };
},
  created() {},
  mounted() {
    this.queryObj = this.$common.convertKeys(this.$route.query);
    getSignNew(this.queryObj)
      .then((data) => {
        // 请求到签名的base64格式，如果是存在后端的图片那么需要自己转为base64
        if (data && data.data.flag && data.data.datas.length > 0) {
          this.savedImage = data.data.datas[0]["BASE64IMG"];
          var bgImg = new Image();
          bgImg.src = this.savedImage;
          bgImg.onload = () => {
            this.$nextTick(() => {
              // 获取容器的宽高
              let box = document.querySelector(".setSign");
              let w = box.clientWidth;
              let h = box.clientHeight;
              // 给容器设置padding
              let padding = 20;
              this.canvas = this.$refs.canvas;
              this.canvas.height = h - padding; //获取画布的高度
              this.canvas.width = w - padding; //获取画布的宽度
              this.context = this.canvas.getContext("2d");
              this.context.drawImage(bgImg, 0, 0);
              this.context.lineWidth = 3; //设置线条宽度
              this.context.strokeStyle = "#000"; //字体颜色
            });
          };
        }
      })
      .catch((err) => {
        this.$message.error("获取签名图片失败");
      });
  },
  methods: {
    startDrawing() {
      this.isDrawing = true;
      const rect = this.canvas.getBoundingClientRect();
      this.context.beginPath();
      this.context.moveTo(event.clientX - rect.left, event.clientY - rect.top);
    },
    draw() {
      if (!this.isDrawing) return;
      const rect = this.canvas.getBoundingClientRect();
      this.context.lineTo(event.clientX - rect.left, event.clientY - rect.top);
      this.context.stroke();
    },
    stopDrawing() {
      this.isDrawing = false;
    },
    // 清空画布
    clearCanvas() {
      this.context.clearRect(0, 0, this.canvas.width, this.canvas.height);
      this.savedImage = null;
    },
    // 保存签名
    saveSignature() {
      // 获取图片的base64
      this.savedImage = this.canvas.toDataURL();
      let submitObj = {
        base64img: this.savedImage,
        ...this.queryObj,
      };
      saveSignNew(submitObj).then((data) => {
        if (data && data.data.flag) {
          this.$message.success("保存成功");
        }
      });
    },
  },
};
</script>

效果图：