CSS3实现转盘抽奖

最近有个转盘抽奖的需求，搜了一下现有的轮子，有的是用jQuery的动画函数实现的，有的是用canvas绘图然后再用高频率的setTimeout调用旋转方法，前者太老了没法简单移植到vue项目，后者感觉性能表现可能不会太好。也有一些用CSS动画的方案，设计了加速-匀速-减速三个动画，再计算偏转角度让三个动画尽可能无缝衔接，但我感觉绕了大远路，应该有更简单轻量的实现方案。个人更倾向于用transition来实现，不过网上的例子感觉还不够好，有的倾斜文字都没有对齐，最后还是自己手写了一个。 无需jQuery，不用js脚本实现动画细节，动画效果完全连续无需衔接，支持动态设置2个以上任意数量的奖项。 核心思路是用transition以及rotate实现旋转动画，使用transition-origin和rotate绘制出定位较为精确的轮盘奖项。

代码及实例展示

<script src="//unpkg.com/vue/dist/vue.js"></script>
<span id="app">
  <span>Prize number: {{ prizeNumber }}</span>
  <button type="button" @click="!rolling && prizeNumber < 8 && (prizeNumber++)" :disabled="rolling || prizeNumber === 8">Add</button>
  <button type="button" @click="!rolling && prizeNumber > 2 && (prizeNumber--)" :disabled="rolling || prizeNumber === 2">Remove</button>
   <div class="wheel-wrapper">
    <div
      class="wheel-pointer"
      @click="onClickRotate"
    >
      Start
    </div>
    <div
      class="wheel-bg"
      :class="{freeze: freeze}"
      :style="`transform: rotate(${wheelDeg}deg)`"
    >
      <div class="prize-list">
        <div
          class="prize-item-wrapper"
          v-for="(item,index) in prizeList"
          :key="index"
        >
          <div
            class="prize-item"
            :style="`transform: rotate(${(360/ prizeList.length) * index}deg)`"
          >
            <div class="prize-name">
              {{ item.name }}
            </div>
            <div class="prize-icon">
              <img :src="item.icon">
            </div>
          </div>
        </div>
      </div>
    </div>
  </div>
</div>

html {
  background: #dd7c7d;
}

.wheel-wrapper {
  width: 300px;
  height: 300px;
  position: absolute;
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%);
}

.wheel-pointer {
  width: 60px;
  height: 60px;
  border-radius: 1000px;
  background: yellow;
  position: absolute;
  left: 50%;
  top: 50%;
  transform: translate(-50%, -50%);
  text-align: center;
  line-height: 60px;
  z-index: 10;
  cursor: pointer;

  &::after {
    content: "";
    position: absolute;
    top: -32px;
    left: 50%;
    border-width: 0 8px 40px;
    border-style: solid;
    border-color: transparent transparent yellow;
    transform: translateX(-50%);
  }
}
.wheel-bg {
  width: 100%;
  height: 100%;
  border-radius: 1000px;
  overflow: hidden;
  transition: transform 4s ease-in-out;
  background: #7eef97;

  &.freeze {
    transition: none;
    background: red;
  }
}

.prize-list {
  width: 100%;
  height: 100%;
  position: relative;
  text-align: center;
}

.prize-item-wrapper {
  position: absolute;
  top: 0;
  left: 50%;
  transform: translateX(-50%);
  width: 150px;
  height: 150px;
}

.prize-item {
  width: 100%;
  height: 100%;
  transform-origin: bottom;

  .prize-name {
    padding: 16px 0;
  }

  .prize-icon {
  }
}

var Main = {
  data() {
    return {
      freeze: false,
      rolling: false,
      wheelDeg: 0,
      prizeNumber: 8,
      prizeListOrigin: [
        {
          icon: "https://picsum.photos/40?random=1",
          name: "$10000"
        },
        {
          icon: "https://picsum.photos/40?random=6",
          name: "Thank you!"
        },
        {
          icon: "https://picsum.photos/40?random=2",
          name: "$500"
        },
        {
          icon: "https://picsum.photos/40?random=3",
          name: "$100"
        },
        {
          icon: "https://picsum.photos/40?random=6",
          name: "Thank you!"
        },
        {
          icon: "https://picsum.photos/40?random=4",
          name: "$50"
        },
        {
          icon: "https://picsum.photos/40?random=5",
          name: "$10"
        },
        {
          icon: "https://picsum.photos/40?random=6",
          name: "Thank you!"
        }
      ]
    };
  },
  computed: {
    prizeList() {
      return this.prizeListOrigin.slice(0, this.prizeNumber);
    }
  },
  methods: {
    onClickRotate() {
      if (this.rolling) {
        return;
      }
      const result = Math.floor(Math.random() * this.prizeList.length);
      this.roll(result);
    },
    roll(result) {
      this.rolling = true;
      const { wheelDeg, prizeList } = this;
      this.wheelDeg =
        wheelDeg -
        wheelDeg % 360 +
        6 * 360 +
        (360 - 360 / prizeList.length * result);
      setTimeout(() => {
        this.rolling = false;
        alert("Result：" + prizeList[result].name);
      }, 4500);
    }
  },
  watch: {
    prizeNumber() {
      this.freeze = true;
      this.wheelDeg = 0;

      setTimeout(() => {
        this.freeze = false;
      }, 0);
    }
  }
};
var App = Vue.extend(Main);
new App().$mount("#app");