微信小程序 基于wepy使用canvas简单的画波柱状图

参考了 https://www.cnblogs.com/yxysu...
这里只是给自己简单的记录下代码
发现很多变量不知道咋称呼它 - -
意会意会

<canvas canvas-id="chart" class="mychart" style="width: 600rpx;height: 600rpx"></canvas>

全局定义一个

const cx = wepy.createCanvasContext('chart')

drawChart() {
      // 轴
      let grades = [7,8,6,10,8,5,7,30,1,8,5,7,5,1,8,12,52,12,49,30,12] //数据源
      let max = Math.max.apply(null,grades);
      let min = Math.min.apply(null,grades);
      this.Ydiff = max-min
      let xW = this.Xwidth / grades.length
      this.$apply()
      let kedu = Math.round((max-min) / 10) // 10是y轴的刻度数量
      this.drawLine(0,0,300,0,0.5,'#999999')
      this.drawLine(0,200,0,-80,0.5,'#999999')
      // 刻度线
      for(let i=kedu; i<=max; i=i+kedu){
        cx.fillText(i,this.x(-15),this.y(this.gg(i))+10)
        this.drawLine(0,this.gg(i),250,this.gg(i),0.5,'#eee')
      }
      let color = []
      for (let i in grades ) {
        color[i] = this.getRandomColor()
      }
      for(let i=xW,j=0;j<color.length;j++,i=i+xW){
        this.drawLine(i,1,i,this.gg(grades[j]),8,color[j]);
      }
      cx.draw()
    }

x(x) {
      return x + 20
    }
    y(y) {
      return 300-y
    }
    g(grade) {
      return 15 * grade;
    }
    gg(grade) {
      return 200 / this.Ydiff * grade
    }
    drawLine(b_x, b_y, e_x, e_y, width, color) {
      cx.strokeStyle = color
      cx.lineWidth = width
      cx.beginPath()
      cx.moveTo(this.x(b_x), this.y(b_y))
      cx.lineTo(this.x(e_x), this.y(e_y))
      cx.closePath()
      cx.stroke()
    }
    getRandomColor() {
      let color = '#'
      let alArr = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 'a', 'b', 'c', 'd', 'e', 'f'],
      for (let i = 0; i < 6; i++) {
        color += alArr[Math.floor(Math.random() * (16))]
      }
      return(color)
    }