详解canvas在圆弧周围绘制文本的两种写法

var canvas=document.getElementById("canvas")
    var context=canvas.getContext("2d")

    var TEXT_FILL_STYLE="rgba(100,130,240,0.5)"
    var TEXT_STROKE_STYLE="rgba(200,0,0,0.7)"
    var TEXT_SIZE=64;
    circle={
        x:canvas.width/2,
        y:canvas.height/2,
        radius:200
    }
    function drawCircularText(string,startAngle,endAngle){
      var radius=circle.radius //圆的半径
      var angleDecrement=(startAngle-endAngle)/(string.length-1)//每个字母占的弧度
      var angle=parseFloat(startAngle) //转一下数字
      var index=0;
      var character;

      context.save()
      context.fillStyle=TEXT_FILL_STYLE;
      context.strokeStyle=TEXT_STROKE_STYLE;
      context.font=TEXT_SIZE+"px Lucida Sans"

      while(index<string.length){
        character=string.charAt(index)
        context.save()
        context.beginPath()
        context.translate(circle.x+Math.cos(angle)*radius,circle.y-Math.sin(angle)*radius)
        context.rotate(Math.PI/2-angle)   //Math.PI/2为旋转90度  Math.PI/180*X为旋转多少度
        context.fillText(character,0,0)
        context.strokeText(character,0,0)
        angle-=angleDecrement
        index++
        context.restore()

      }
      context.restore()
    }
    context.textAlign="center"
    context.textBaseLine="middle"
   drawCircularText("clockwise around the circle",Math.PI*2,Math.PI/8)  //第三个参数表示文字首位是否相接 差了多少弧度

var canvas=document.getElementById("canvas")
    var context=canvas.getContext("2d")

    var TEXT_FILL_STYLE="rgba(100,130,240,0.5)"
    var TEXT_STROKE_STYLE="rgba(200,0,0,0.7)"
    var TEXT_SIZE=64;
    circle={
        x:canvas.width/2,
        y:canvas.height/2,
        radius:200
    }
    function drawCircularText(string,startAngle,endAngle){
      var radius=circle.radius //圆的半径
      var angleDecrement=(startAngle-endAngle)/(string.length-1)//每个字母占的弧度
      var angle=startAngle //
      
      var index=0;
      var character;

      context.save()
      context.fillStyle=TEXT_FILL_STYLE;
      context.strokeStyle=TEXT_STROKE_STYLE;
      context.font=TEXT_SIZE+"px Lucida Sans"

      while(index<string.length){
        character=string.charAt(index)
        context.save()
        context.beginPath()
        context.translate(circle.x+Math.cos((Math.PI/180)*angle)*radius,circle.y-Math.sin((Math.PI/180)*angle)*radius)
        context.rotate((Math.PI/2)-(Math.PI/180)*angle)   //Math.PI/2为旋转90度  Math.PI/180*X为旋转多少度
        context.fillText(character,0,0)
        context.strokeText(character,0,0)
        angle-=angleDecrement
        index++
        context.restore()

      }
      context.restore()
    }
    context.textAlign="center"
    context.textBaseLine="middle"
   drawCircularText("clockwise around the circle",360,10)  //第三个参数表示文字首位是否相接 差了多少弧度