HTML5 canvas implements the example code of the winning carousel

  <canvas>您的浏览器不支持canvas</canvas>
  <img  src="/static/imghw/default1.png" data-src="./zp.jpg" class="lazy" alt="HTML5 canvas implements the example code of the winning carousel" >

<style>
    #canvas{
      position: absolute;
      left: 230px;
      top: 230px;
    }
    #img{
      width: 600px;
      height: 600px;
    }
  </style>

  var canvas = document.getElementById('canvas');
  var context = canvas.getContext('2d');
  //设定画布和宽
  canvas.width=140;
  canvas.height=140;
  var then = Date.now();
  var now;//利用时间差来控制转盘最小转动时间
  var first_deg=0;//用来记录转动的角度
  var rotate_deg=0;//每次转动的角度，用来实现变速运动
  var end_deg =85;//中奖角度
  var speedUp = true;//判断是否在加速阶段
  var f;

  // 因为canvas的rotate函数是根据左上角坐标（0,0）来旋转的，所以移动画布
  context.translate(70,70);
  function draw(){
    context.clearRect(-70, -70, 70, 70);
    context.beginPath();
    context.arc(0, 0, 50, Math.PI / 180 * 0, Math.PI / 180 * 360, true);
    context.moveTo(-50,0);
    context.lineTo(50,0);
    context.lineTo(0,-70);
    context.rotate(rotate_deg*Math.PI/180);
    context.closePath();
    context.fillStyle='red';
    context.fill();    
  }
// 将运动分为3段，加速，匀速，减速
  function loop(){

    //循环调用，产生动画效果
    f = window.requestAnimationFrame(loop);
    now = Date.now();

    //开始加速转动，转到速度为20就不加速了，至于为什么是20，看起来舒服而已
    if(rotate_deg 2000){

      //如果下面设置的是固定角度，那这里的最小速度建议为1，因为每次转动角度过大，一圈很可能错过中奖的角度，导致转很多圈。
      if(rotate_deg>=2){
        speedUp = false;
        rotate_deg -=1;
      }
      //设置中奖区间为+-5度（设置固定角度会让动画有点难看）
      if(first_deg%360>=end_deg-5&&first_deg%360<p><strong>Finally </strong></p><p>The problem with this relatively large turntable is that if the winning interval is relatively small, it will take a longer time to rotate after deceleration, and it will take a long time to rotate at the lowest speed before stopping. When the interval is large, it stops all of a sudden, the deceleration effect is not obvious, and it looks strange visually. </p><p> Recommended related articles: </p><p><a href="http://www.php.cn/html5-tutorial-407703.html" target="_blank" title="html5 canvas用来绘制弧形的代码实现">html5 canvas is used to draw the arc code implementation</a></p><p class="post-topheader custom- pt0"><a href="http://www.php.cn/html5-tutorial-407589.html" target="_blank" title="HTML5实现魔方游戏的代码">HTML5 code to implement the Rubik's Cube game</a> </p><p class="mb20"><a href="http://www.php.cn/html5-tutorial-407331.html" target="_blank" title="HTML5结合互联网+ 实现的3D隧道（附代码）">HTML5 combined with the Internet to realize 3D tunnel (with code)</a></p>