<template>
  <view class="page">
    <canvas type="2d" id="myCanvas" />
  </view>
</template>

<script>
export default {
  data() {
    return {
      ctx: null,
    };
  },
  methods: {
    draw() {
      if (!this.ctx) return;
      const ctx = this.ctx;
      const size = (s) => uni.upx2px(s);
      const pai = Math.PI;

      // 绘制基础的圆
      ctx.beginPath();
      ctx.moveTo(size(375), size(375));
      ctx.arc(size(375), size(375), size(183), 0, Math.PI * 2);
      ctx.fillStyle = "#fff";
      ctx.fill();
      // ctx.clip();
      // ctx.save();

      let count = 0;
      setInterval(() => {
        count++;
        count = count > 360 ? 0 : count;
        drawCount(count);
      }, 120);

      // 绘制波浪线的部分
      function drawCount(count) {
        ctx.clearRect(0, 0, size(750), size(750));
        // 获取二次贝塞尔曲线的点
        const points = [];
        for (let i = 0; i <= 2 * pai; i += pai / 2) {
          const y = Math.sin(i - (count * pai) / 12);
          points.push([i, Number(y.toFixed(2))]);
        }
        ctx.beginPath();
        const bili = size(375) / pai;
        ctx.lineTo(points[0][0] * bili, points[0][1] + size(375));
        ctx.bezierCurveTo(
          points[1][0] * bili,
          points[1][1] * size(40) + size(375),
          points[3][0] * bili,
          points[3][1] * size(40) + size(375),
          points[4][0] * bili,
          points[4][1] * size(40) + size(375)
        );
        ctx.lineTo(size(750), size(750));
        ctx.lineTo(size(0), size(750));
        ctx.fillStyle = "#fea448";
        ctx.fill();
        // ctx.restore();
      }
    },
  },
  onReady() {
    const _this = this;
    const query = wx.createSelectorQuery();
    query
      .select("#myCanvas")
      .fields({ node: true, size: true })
      .exec((res) => {
        const canvas = res[0].node;
        const ctx = canvas.getContext("2d");

        const dpr = wx.getSystemInfoSync().pixelRatio;

        canvas.width = res[0].width * dpr;
        canvas.height = res[0].height * dpr;
        ctx.scale(dpr, dpr);

        _this.ctx = ctx;
        _this.draw();
      });
  },
};
</script>

<style>
page {
  background: #f6f5f8;
}
</style>
<style lang='scss' scoped>
#myCanvas {
  width: 750rpx;
  height: 750rpx;
  background-color: #c7edcc;
}
</style>

需要注意的是canvas 在微信小程序里面的层级相当的高,  任何定位元素都无法覆盖到 canvas 组件的上面