vue 刮刮乐功能实现

<template><!--游玩区域-->
<div class="panel">
    <canvas
     id="canvas" @touchstart.prevent="touchStart($event)" @touchmove.prevent="eventMove($event)"
     :style='{"background-image":"url("+backgroundImage+")"}'
     width="550" height="380"></canvas>
    <div id="canvasMask" v-if="start">
        <div class="start" @touchstart="StartTouch()">
            <div class="startContain">
                <span>刮开试试手气</span>
                <span >开始刮开</span>
            </div>
            <img src="../assets/scratch/u611.png" alt="">
        </div>    </div>
    <div class="reStart" v-if="restart">
        <span @touchstart="ContinueScratch()">继续刮奖</span>
    </div></div></template>
<script>
let canvas;
let ctx;export default {
//   inject:["reload"],
  data(){
      return{
          start:true,
          restart:false,
          clientWidth:null,
          canvasWidth:null,
          canvasHeight:null,
          backgroundImage: require('../assets/scratch/prize2.png'),
          num:2
      }
  },
  mounted(){
      this.initCanvas()
  },
  methods:{
      initCanvas() {
        console.log("初始化canvas")
        canvas = document.getElementById('canvas');
        ctx = canvas.getContext('2d');
        this.clientWidth = document.documentElement.clientWidth,
        this.canvasWidth = Math.floor(this.clientWidth * 550 / 750),//canvas宽 = 屏幕宽 * 设计稿里canvas宽 / 750
        this.canvasHeight = Math.floor(this.clientWidth * 380 / 750),//canvas高 = 屏幕宽 * 设计稿里canvas高 / 750        canvas.style.width=this.canvasWidth+'px';
        canvas.style.height=this.canvasHeight+'px';
        console.log(canvas.style.backgroundImage);
        this.drawPic()
    },
    drawPic() {      ctx.beginPath();
      ctx.fillStyle = '#999';//刮刮乐图层的填充色
      ctx.lineCap = "round";//绘制的线结束时为圆形
      ctx.lineJoin = "round";//当两条线交汇时创建圆形边角
      ctx.lineWidth = 30;//单次刮开面积
      ctx.fillRect(0, 0, this.canvasWidth, this.canvasHeight);
      ctx.save();//保存画布上面的状态
      ctx.closePath();
    //   ctx.clip();      ctx.globalCompositeOperation = 'destination-out';//新图像和原图像重合部分变透明      //下面代码是为了修复部分手机浏览器不支持destination-out
      canvas.style.display="inherit";    },
    touchStart(e){        e = e || window.event;
        if (typeof e.touches !== 'undefined') {
            e = e.touches[0];//获取触点
        }
        var x = e.pageX-e.target.offsetLeft,
            y = e.pageY-e.target.offsetTop;
        ctx.moveTo(x, y);
        //touchmove事件
        this.eventMove(e);
    },
    eventMove(e){
        e = e || window.event;
        if (typeof e.touches !== 'undefined') {
            e = e.touches[0];
        }
        var x = e.pageX-e.target.offsetLeft,
            y = e.pageY-e.target.offsetTop;
        ctx.lineTo(x, y);
        ctx.stroke();
        this.clear();
    },
    clear() {
        let data = ctx.getImageData(0, 0, this.canvasWidth, this.canvasHeight).data,//得到canvas的全部数据
            half = 0;
        //length = canvasWidth * canvasHeight * 4，一个像素块是一个对象rgba四个值，a范围为0~255
        for (var i = 3, length = data.length; i < length; i += 4) {//因为有rgba四个值，下标0开始，所以初始i=3
            data[i] === 0 && half++;//存在imageData对象时half加1  PS:该像素区域透明即为不存在该对象
        }
        //当刮开的区域大于等于30%时，则可以开始处理结果
        if (half >= this.canvasWidth * this.canvasHeight * 0.3) {
            // alert(111)
            ctx.clearRect(0, 0, this.canvasWidth, this.canvasHeight);//清空画布
            this.restart=true;        }
    },
    StartTouch(){
        this.start=false;
    },
    ContinueScratch(){
        this.num--;
        if(this.num<=0){
            this.num=0;
            console.log(this.num)
            alert("没有剩余刮奖次数")
        }else{
            this.start=true;
            this.restart=false;
            ctx.restore();//恢复上面保存的画布内容
            this.initCanvas();
        }
    }
  }
}
</script>
<style scoped>.panel{
}
.panel{
}
.panel #canvas{
    position: absolute;
    top: 5.5rem;
    left: 1rem;
    border-radius: 10%;
    /* background: url('../assets/scratch/prize2.png'); */
    background-size:100% 100%;
}
.panel #canvasMask{
    position: absolute;
    top: 5.3rem;
    left: 1rem;
    width: 6rem;
    height: 4rem;
    overflow: hidden;
}
.panel #canvasMask .start{
    width: 6rem;
    height: 4rem;
    display: flex;
    /* background-color: sandybrown; */
    padding-left: 1.2rem;
    padding-top: 0.6rem;
}
.panel #canvasMask .start img{
    display: inline-block;
    width: 2rem;
    height: 2rem;
}
.panel #canvasMask .start .startContain{
    padding-top: 0.8rem;
}
.panel #canvasMask .start .startContain span{
    display: block;
    font-size: 0.3rem;
    text-align: center;
}
.panel #canvasMask .start .startContain span:last-child{
    margin-top: 0.2rem;
    font-weight: bold;
}
.panel .reStart{
    position: absolute;
    top: 8.4rem;
    left: 2.8rem;
    color: red;
    border: 0.01rem solid;
    border-radius: 0.1rem;
    padding: 0 0.1rem;
}
.panel .reStart span{
    font-size: 0.4rem;
}
</style>