演示地址
完整代码地址

效果如图

image.png

方案背景

需求

1.圆环需要呈现3/4进度条
2.小球跟随数字大小而准确落在正确的位置
3.可以配置舒适范围的颜色
4.当超出舒适范围变为红色，超出剩余部分变为红色

对应方案

1.用canvas实现3/4圆环
2.利用坐标系计算出小球的位置
3.利用容器百分比实现自适应
4.对应颜色范围使用弧长公式计算

代码实现

在canvas上面定义一个父容器，canvas使用百分比inline-block来达到自适应，
父容器可以使用vw，em等自适应单位就可以达到自适应效果，我这里已经做了全局转换为vw

<template>
  <div class="canvas">
    <canvas :id="id"
            style="width:100%;height:100%;display: inline-block;"></canvas>
  </div>
</template>
<style lang="scss" scoped>
  .canvas {
    display: block;
    margin: 0 auto;
    /*margin-top: 10px;*/
    width: 150px;
    height: 75px;
  }
</style>

定义data和props来接受父组件配置的数据和定义弧长半径数值等

  data() {
    return {
      // num: 0,
      canvas: '',
      context: '',
      cirX: '',
      cirY: '',
      rad: '',
      n: 1,
      speed: 150,
      r: 24
    }
  },
  //percents 范围开始值  percente 范围结束值 num数值  WarningColor错误颜色  ballColor小球颜色 ratioColor 外圈范围值颜色  OuterColor
  props: ['percents', 'ratioColor', 'id','percente','num','WarningColor',"ballColor","OuterColor"],
  mounted() {
    this.canvas = document.getElementById(this.id)
    this.context = this.canvas.getContext('2d')
    this.context.scale(2, 2);
    (this.cirX = 30), //this.canvas.width/ 2
      (this.cirY = 30), //this.canvas.height/ 2
      (this.rad = (Math.PI * 2*0.75) / 100)
    this.DreamLoading()
  },

绘制圆弧方法入口
其实这是一个不断重复绘制，requestAnimationFrame用作于动画浏览器会自动作用最佳的动画时间间隔。每次移动0.4来达到小球运动的效果

    DreamLoading() {
      // console.log(this.n)
      //清除所有，重新绘制
      this.context.clearRect(0, 0, this.canvas.width, this.canvas.height)
      this.writeCircle()
      this.writeText(this.n)
      if(this.num < this.percents || this.num > this.percente) {
        this.writeWarningColor()
      }
      if(this.num >= this.percents && this.num <= this.percente)  {
        this.writeBlueS()
      }
      this.writeSmallCircle(this.n)
      //      if(this.n < 100 && this.n <= 60){
      var count = this.num
      if (this.n <= count) {
        this.n = this.n + 0.4
      } else {
        return (this.n = 0)
      }
      requestAnimationFrame(this.DreamLoading)
    }

绘制外围的3/4圈,从1/4Π开始到7/4Π就是一个3/4圆（一个圆是2Π也就是8/4Π）

    writeCircle() {
      this.context.save() //save和restore可以保证样式属性只运用于该段canvas元素
      this.context.beginPath() //开始路径
      this.context.strokeStyle = this.OuterColor //设置边线的颜色
      this.context.lineWidth = 4
      this.context.arc(
        this.cirX,
        this.cirY,
        this.r,
        Math.PI * 0.75,
        Math.PI * 2.25,
        false
      ) //画一个3/4圆的路径
      this.context.stroke() //绘制边线
      //      this.context.restore();
      //         this.context.closePath();
    },

绘制舒适范围值要加上弧长即可

   writeBlueS() {
      this.context.save()
      this.context.strokeStyle = this.ratioColor
      this.context.lineWidth = 4
      this.context.beginPath()
      this.context.arc(
              this.cirX,
              this.cirY,
              this.r,
              Math.PI * 0.75 + this.percents*this.rad,
              Math.PI * 0.75+ this.percente*this.rad,
              false
      ) // 4/3处开始画
      this.context.stroke()
      this.context.restore()
    },

绘制警告范围值也是同样

    writeWarningColor() {
      this.context.save()
      this.context.strokeStyle = this.WarningColor
      this.context.lineWidth = 4
      this.context.beginPath()
      this.context.arc(
        this.cirX,
        this.cirY,
        this.r,
        Math.PI * 0.75 + this.percente*this.rad,
        Math.PI * 2.25,
        false
      ) // 4/3处开始画
      this.context.stroke()
      this.context.restore()
    },

绘制文本,付按揭是计算好圆心的位置

    writeText(n) {
      this.context.save()
      this.context.font = '30px Arial'
      this.context.fillStyle = 'rgba(255,255,255,1)' //字体颜色
      this.context.fillText(n.toFixed(0), this.cirX-18, this.cirY + 10) //绘制实心
      //context.strokeStyle = "#49f";
      // context.strokeText(n.toFixed(0)+"%",cirX - 30 ,cirY +10); //绘制空心
      this.context.stroke()
      this.context.restore()
    },

绘制小球和小球运动轨迹 关键在于这个xpos ypos的坐标公式

    writeSmallCircle(n) {
      this.context.save()
      this.context.fillStyle = this.ballColor;
      // this.context.lineWidth = 12;
      let angle =2.25 * Math.PI  - this.rad * n;
      let xPos =- Math.cos(angle) * (this.r) + 58/2;
      let yPos = Math.sin(angle) * (this.r) + 58/2;
      this.context.beginPath()
      this.context.arc(xPos,yPos, 5, 0,Math.PI * 2, true) // 4/3处开始画
      this.context.fill()
      this.context.restore()
      //画小球的边框
      this.context.save()
      this.context.lineWidth = 1
      this.context.strokeStyle ='rgba(255,255,255,1)';
      this.context.beginPath()
      this.context.arc(xPos,yPos, 5, 0,Math.PI * 2, true) // 4/3处开始画
      this.context.stroke()
      this.context.restore()

    },

组件用法

引入组件

import canvasCircle from "./circle.vue";
  components: {
    canvasCircle,
  },

data里面定义

  cicleList: [
        {
          Number:'26',
          startRadio: "12", //舒适范围值
          endRadio: "46",
          ballColor:"rgba(208, 232, 254, 1)",
          OuterColor:'rgba(208, 232, 254, 1)',
          ratioColor: "rgba(68, 163, 252, 1)" //外圈颜色
        }
      ],

页面使用

              <canvas-circle
                    v-for="(item, index) in cicleList"
                    :key="index"
                    :ballColor="item.ballColor"
                    :num="item.Number"
                    :percents="item.startRadio"
                    :percente="item.endRadio"
                    :OuterColor="item.OuterColor"
                    :ratioColor="item.ratioColor"
                    :id="index + 'circle'"
                  ></canvas-circle>