html5 转盘 例子 附完整源码 有截图 亲测通过

【实例简介】html5 转盘实例 可直接拿来做 抽奖程序
【实例截图】

 【核心代码】

<input type="button" value="开始旋转" onclick="spin();" style="float: left;" />
<meta http-equiv="Content-Type" content="text/html;charset=utf-8" />

<canvas id="wheelcanvas" width="500" height="500"></canvas> 
<script type="application/javascript"> 
  var colors = ["#B8D430", "#3AB745", "#029990", "#3501CB",
               "#2E2C75", "#673A7E", "#CC0071", "#F80120",
               "#F35B20", "#FB9A00", "#FFCC00", "#FEF200"];
  var restaraunts = ["北京", "上海", "天津", "南京",
                     "杭州", "深圳", "武汉", "济南",
                     "重庆", "大连", "合肥", "郑洲"];
  
  var startAngle = 0;
  var arc = Math.PI / 6;
  var spinTimeout = null;
  
  var spinArcStart = 10;
  var spinTime = 0;
  var spinTimeTotal = 0;
  
  var ctx;
  
  function draw() {
    drawRouletteWheel();
  }
  
  function drawRouletteWheel() {
    var canvas = document.getElementById("wheelcanvas");
    if (canvas.getContext) {
      var outsideRadius = 200;
      var textRadius = 160;
      var insideRadius = 125;
      
      ctx = canvas.getContext("2d");
      ctx.clearRect(0,0,500,500);
      
      
      ctx.strokeStyle = "black";
      ctx.lineWidth = 2;
      
      ctx.font = 'bold 12px sans-serif';
      
      for(var i = 0; i < 12; i  ) {
        var angle = startAngle   i * arc;
        ctx.fillStyle = colors[i];
        
        ctx.beginPath();
        ctx.arc(250, 250, outsideRadius, angle, angle   arc, false);
        ctx.arc(250, 250, insideRadius, angle   arc, angle, true);
        ctx.stroke();
        ctx.fill();
        
        ctx.save();
        ctx.shadowOffsetX = -1;
        ctx.shadowOffsetY = -1;
        ctx.shadowBlur    = 0;
        ctx.shadowColor   = "rgb(220,220,220)";
        ctx.fillStyle = "black";
        ctx.translate(250   Math.cos(angle   arc / 2) * textRadius, 250   Math.sin(angle   arc / 2) * textRadius);
        ctx.rotate(angle   arc / 2   Math.PI / 2);
        var text = restaraunts[i];
        ctx.fillText(text, -ctx.measureText(text).width / 2, 0);
        ctx.restore();
      } 
      
      //Arrow
      ctx.fillStyle = "black";
      ctx.beginPath();
      ctx.moveTo(250 - 4, 250 - (outsideRadius   5));
      ctx.lineTo(250   4, 250 - (outsideRadius   5));
      ctx.lineTo(250   4, 250 - (outsideRadius - 5));
      ctx.lineTo(250   9, 250 - (outsideRadius - 5));
      ctx.lineTo(250   0, 250 - (outsideRadius - 13));
      ctx.lineTo(250 - 9, 250 - (outsideRadius - 5));
      ctx.lineTo(250 - 4, 250 - (outsideRadius - 5));
      ctx.lineTo(250 - 4, 250 - (outsideRadius   5));
      ctx.fill();
    }
  }
  
  function spin() {
    spinAngleStart = Math.random() * 10   10;
    spinTime = 0;
    spinTimeTotal = Math.random() * 3   4 * 1000;
    rotateWheel();
  }
  
  function rotateWheel() {
    spinTime  = 30;
    if(spinTime >= spinTimeTotal) {
      stopRotateWheel();
      return;
    }
    var spinAngle = spinAngleStart - easeOut(spinTime, 0, spinAngleStart, spinTimeTotal);
    startAngle  = (spinAngle * Math.PI / 180);
    drawRouletteWheel();
    spinTimeout = setTimeout('rotateWheel()', 30);
  }
  
  function stopRotateWheel() {
    clearTimeout(spinTimeout);
    var degrees = startAngle * 180 / Math.PI   90;
    var arcd = arc * 180 / Math.PI;
    var index = Math.floor((360 - degrees % 360) / arcd);
    ctx.save();
    ctx.font = 'bold 30px sans-serif';
    var text = restaraunts[index]
    ctx.fillText(text, 250 - ctx.measureText(text).width / 2, 250   10);
    ctx.restore();
  }
  
  function easeOut(t, b, c, d) {
    var ts = (t/=d)*t;
    var tc = ts*t;
    return b c*(tc   -3*ts   3*t);
  }
  
  draw();
</script>