<!--
    Name：   手写签名板
    Author： 
    Create time：2020-03-14
    Update time：2020-03-17
-->
<template>
  <div class="canvas">
    <canvas
      ref="canvas"
      style="background: rgba(255,255,155,0)"
      :width="width"
      :height="height"
      @touchstart.stop="touchstart"
      @touchmove.stop="touchmove"
      @touchend.stop="touchend"
      @mousedown.stop="down"
      @mouseup.stop="up"
    >当前浏览器不支持手写签名</canvas>
  </div>
</template>

<script>
export default {
  name: "signCanvas",
  props: {
    width: {
      default: 300
    },
    height: {
      default: 150
    },
    lineWidth: {
      default: 1
    },
    text: {
      default: "签名区"
    },
    fontSize: {
      default: 20
    }
  },
  data() {
    return {
      dom: null,
      cxt: null,
      start: 0,
      end: 0
    };
  },
  mounted() {
    this.init();
  },
  methods: {
    // 初始化
    init() {
      this.dom = this.$refs["canvas"];
      if (!this.dom.getContext) {
        alert("当前浏览器不支持手写签名");
        return;
      }
      this.position();
      this.canvasInit();
      window.addEventListener("touchmove", this.position);
      window.addEventListener("resize", this.position);
      window.addEventListener("wheel", this.position);
      window.addEventListener("scroll", this.position);
    },
    // 位置初始化
    position() {
      let direct = this.dom.getBoundingClientRect();
      this.start = direct.x;
      this.end = direct.y;
    },
    // 画布初始化
    canvasInit() {
      this.cxt = this.dom.getContext("2d");
      // this.cxt.fillStyle = "#ffffff";
      this.cxt.lineCap = "round";
      this.cxt.lineWidth = this.lineWidth;
      this.cxt.clearRect(0, 0, this.width, this.height);
      // this.cxt.font = this.fontSize + "px bold 黑体";
      // this.cxt.fillStyle = "#eee";
      // this.cxt.textAlign = "center";
      // this.cxt.textBaseline = "middle";
      // this.cxt.fillText(this.text, this.width / 2, this.height / 2);
    },
    // pc端鼠标按下开始绘画
    down(e) {
      this.startLine(e.clientX, e.clientY, e);
      e.target.addEventListener("mousemove", this.move);
      document.addEventListener("mouseleave", this.up);
      document.addEventListener("mouseup", this.up);
    },
    // pc端鼠标按下开始绘画后，跟踪移动轨迹
    move(e) {
      this.moveLine(e.clientX, e.clientY, e);
    },
    // pc端鼠标松开结束绘画
    up(e) {
      e.target.removeEventListener("mousemove", this.move);
      this.toSave();
    },
    // 移动端触摸开始绘画
    touchstart(e) {
      this.startLine(
        e.changedTouches[0].clientX,
        e.changedTouches[0].clientY,
        e
      );
    },
    // 移动端触摸开始绘画后，跟踪滑动轨迹
    touchmove(e) {
      this.moveLine(e.touches[0].clientX, e.touches[0].clientY, e);
    },
    touchend() {
      this.toSave();
    },
    // 开始绘画
    startLine(x, y) {
      this.cxt.beginPath();
      x -= this.start;
      y -= this.end;
      this.cxt.moveTo(x, y);
    },
    // 绘制移动轨迹
    moveLine(x, y, event) {
      event && event.preventDefault();
      x -= this.start;
      y -= this.end;
      this.cxt.lineTo(x, y);
      this.cxt.stroke();
    },
    // 清空绘画数据
    toClear() {
      this.init();
    },
    // 保存绘画数据
    toSave() {
      let base64 = this.dom.toDataURL("image/png");
      // base64转为file对象
      let image = dataURLtoFile(base64, Math.ceil(Math.random() * 100));
      function dataURLtoFile(dataurl, filename) {
        var arr = dataurl.split(","),
          mime = arr[0].match(/:(.*?);/)[1],
          bstr = atob(arr[1]),
          n = bstr.length,
          u8arr = new Uint8Array(n);
        while (n--) {
          u8arr[n] = bstr.charCodeAt(n);
        }
        return new File([u8arr], filename, { type: mime });
      }
      this.$emit("input", base64);
      return image;
    }
  },
  beforeDestroy() {
    this.toClear();
  }
};
</script>

<style lang='less' scoped>
.canvas {
  display: flex;
  justify-content: center;
  background: #fff;
}
canvas {
  border: 1px solid #ccc;
}
</style>