vue如何利用canvas做一个电子签名功能？

vue如何利用canvas做一个电子签名功能？下面web建站小编给大家简单介绍一下现实方法！

pc端我们需要用到：mousedown、mousemove、mouseup，手机端我们需要用到：touchstart、touchmove、touchend。

先定义一个canvas

<canvas
  @touchstart="touchStart"
  @touchmove="touchMove"
  @touchend="touchEnd"
  ref="canvasA"
  @mousedown="mouseDown"
  @mousemove="mouseMove"
  @mouseup="mouseUp"
></canvas>

data参数

data() {
  return {
    points: [],
    canvasTxt: null,
    startX: 0,
    startY: 0,
    moveY: 0,
    moveX: 0,
    endY: 0,
    endX: 0,
    w: null,
    h: null,
    isDown: false,
    color: "#000",
    linewidth: 3,
    isDraw: false //签名标记
  };
},

在mounted中获取画布

mounted() {
  let canvas = this.$refs.canvasA;
  canvas.height = this.$refs.canvasHW.offsetHeight - 100;
  canvas.width = this.$refs.canvasHW.offsetWidth - 10;
  this.canvasTxt = canvas.getContext("2d");
  this.canvasTxt.strokeStyle = this.color;
  this.canvasTxt.lineWidth = this.linewidth;
  }

pc端事件

mouseDown

mouseDown(ev) {
  ev = ev || event;
  ev.preventDefault();

  let obj = {
  x: ev.offsetX,
  y: ev.offsetY
  };
  this.startX = obj.x;
  this.startY = obj.y;
  this.canvasTxt.beginPath();//开始作画
  this.points.push(obj);//记录点
  this.isDown = true;
},

mouseMove

mouseMove(ev) {
  ev = ev || event;
  ev.preventDefault();
  if (this.isDown) {
    let obj = {
	x: ev.offsetX,
	y: ev.offsetY
    };
    this.moveY = obj.y;
    this.moveX = obj.x;
    this.canvasTxt.moveTo(this.startX, this.startY); //移动画笔
    this.canvasTxt.lineTo(obj.x, obj.y); //创建线条
    this.canvasTxt.stroke(); //画线
    this.startY = obj.y;
    this.startX = obj.x;
    this.points.push(obj); //记录点
  }
},

mouseUp

mouseUp(ev) {
  ev = ev || event;
  ev.preventDefault();
  if (1) {
  let obj = {
    x: ev.offsetX,
    y: ev.offsetY
  };
  this.canvasTxt.closePath(); //收笔
  this.points.push(obj); //记录点
  this.points.push({
    x: -1,
    y: -1
  });
  this.isDown = false;
  }
},

手机端事件

touchStart

touchStart(ev) {
ev = ev || event;
ev.preventDefault();
  if (ev.touches.length == 1) {
  this.isDraw = true; //签名标记
  let obj = {
    x: ev.targetTouches[0].clientX,
    y: ev.targetTouches[0].clientY - (document.body.offsetHeight * 0.5 + this.$refs.canvasHW.offsetHeight * 0.1)
  }; 
  //y的计算值中：document.body.offsetHeight*0.5代表的是除了整个画板signatureBox剩余的高，
  //this.$refs.canvasHW.offsetHeight*0.1是画板中标题的高
  this.startX = obj.x;
  this.startY = obj.y;
  this.canvasTxt.beginPath();//开始作画
  this.points.push(obj);//记录点
  }
},

touchMove

touchMove(ev) {
  ev = ev || event;
  ev.preventDefault();
  if (ev.touches.length == 1) {
  let obj = {
    x: ev.targetTouches[0].clientX,
    y:
    ev.targetTouches[0].clientY -
    (document.body.offsetHeight * 0.5 +
  this.$refs.canvasHW.offsetHeight * 0.1)
  };
  this.moveY = obj.y;
  this.moveX = obj.x;
  this.canvasTxt.moveTo(this.startX, this.startY);//移动画笔
  this.canvasTxt.lineTo(obj.x, obj.y);//创建线条
  this.canvasTxt.stroke();//画线
  this.startY = obj.y;
  this.startX = obj.x;
  this.points.push(obj);//记录点
  }
},

touchEnd

touchEnd(ev) {
  ev = ev || event;
  ev.preventDefault();
  if (ev.touches.length == 1) {
  let obj = {
    x: ev.targetTouches[0].clientX,
    y:
    ev.targetTouches[0].clientY -
    (document.body.offsetHeight * 0.5 +
  this.$refs.canvasHW.offsetHeight * 0.1)
  };
  this.canvasTxt.closePath();//收笔
  this.points.push(obj);//记录点
  this.points.push({ x: -1, y: -1 });//记录点
  }
},

重写事件

overwrite() {
  this.canvasTxt.clearRect(
  0,
  0,
  this.$refs.canvasF.width,
  this.$refs.canvasF.height
  );
  this.points = [];
  this.isDraw = false; //签名标记
},

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