Vue实现移动端圆形旋钮：触摸旋转与吸附逻辑详解

<div class="_touch">
 <div class="round_box" ref="box" @touchstart="touchStart" @touchmove="touchMove">
  <div v-if="able" style="position:absolute;width:100%;height:100%;top:0;left:0;">
   <div class="round_right" ref="right" :style="{ transform: 'rotate(' + angle +'deg)' }">
    <div class="round_info"></div>
   </div>
   <div class="round_num">{{level}}</div>
  </div>
 </div>
</div>

._touch {
 padding-top: 48px;
 .round_box {
  position: relative;
  width: 54%;
  padding-top: 54%;
  margin: 0 auto;
  background-image: url(../../assets/img/round_box.png);
  background-size: auto 100%;
  background-position: center top;
  background-repeat: no-repeat;
  .round_right {
   width: 8%;
   height: 27%;
   position: absolute;
   left: 46%;
   top: 23%;
   transform-origin: 50% 100%;
   -webkit-transform-origin: 50% 100%;
   z-index: 2;
   .round_info {
    background: linear-gradient(#858585, #b3b3b3);
    background: -webkit-gradient(#858585, #b3b3b3);
    background: -moz-linear-gradient(#858585, #b3b3b3);
    width: 100%;
    padding-top: 100%;
    border-radius: 100%;
   }
  }
  .round_num {
   display: inline-block;
   position: absolute;
   z-index: 1;
   text-align: center;
   width: 30%;
   top: 38%;
   left: 35%;
   font-size: 2.4em;
   font-weight: 900;
   background: linear-gradient(#b0b0b0, #c8c8c8);
   background: -webkit-gradient(#b0b0b0, #c8c8c8);
   -webkit-background-clip: text;
   background-clip: text;
   -webkit-text-fill-color: transparent;
   text-fill-color: transparent;
  }
 }
}

methods: {
 ......,
 touchStart(e) {
  e.preventDefault();
  e.stopPropagation();
  let round_box = this.$refs.box;
  var w = round_box.offsetWidth / 2;
  var h = round_box.offsetHeight / 2;
  this.px = round_box.getBoundingClientRect().left + w;
  this.py = round_box.getBoundingClientRect().top + h;
 },
 touchMove(e) {
  e.preventDefault();
  e.stopPropagation();
  this.getAngle(e.changedTouches[0].clientX, e.changedTouches[0].clientY);
 },
 touchEnd(e) {
  e.preventDefault();
  e.stopPropagation();
 },
 resetAngle(angle) {
  let list = [
   { angle: 0, level: 5 },
   { angle: 36, level: 6 },
   { angle: 72, level: 7 },
   { angle: 108, level: 8 },
   { angle: 144, level: 9 },
   { angle: 180, level: 10 },
   { angle: 216, level: 1 },
   { angle: 252, level: 2 },
   { angle: 288, level: 3 },
   { angle: 324, level: 4 },
   { angle: 360, level: 5 }
  ];
  let result = list.filter(function(currentVal, index, arr) {
   return Math.abs(angle - currentVal.angle) <= 18;
  });
  this.angle = result[0].angle;
  this.level = result[0].level;
 },
 getAngle(mx, my) {
  var px = this.px;
  var py = this.py;
  var x = Math.abs(px - mx);
  var y = Math.abs(py - my);
  var z = Math.sqrt(Math.pow(x, 2) + Math.pow(y, 2));
  var cos = y / z;
  var radina = Math.acos(cos); //用反三角函数求弧度
  var angle = Math.floor(180 / (Math.PI / radina)); //将弧度转换成角度
  if (mx > px && my > py) {
   //鼠标在第四象限
   angle = 180 - angle;
  }
  if (mx == px && my > py) {
   //鼠标在y轴负方向上
   angle = 180;
  }
  if (mx > px && my == py) {
   //鼠标在x轴正方向上
   angle = 90;
  }
  if (mx < px && my > py) {
   //鼠标在第三象限
   angle = 180 + angle;
  }
  if (mx < px && my == py) {
   //鼠标在x轴负方向
   angle = 270;
  }
  if (mx < px && my < py) {
   //鼠标在第二象限
   angle = 360 - angle;
  }
  this.angle = angle;
  this.$nextTick(function() {
   this.resetAngle(this.angle);
  });
 },
......