HTML5 canvas implements the example code of the winning carousel

The content of this article is about the example code of HTML5 canvas to implement the winning carousel. It has certain reference value. Friends in need can refer to it. I hope it will be helpful to you.

Recently I am learning to do animation with canvas, so I wrote a turntable to practice.
The last simple result picture (the middle one is the rotating pointer, the outer circle is the picture, I am too lazy to write it hahaha)

The code is very simple, it’s all commented, just go to the code, 嘤嘤嘤

html

  <canvas>您的浏览器不支持canvas</canvas>
  <img  alt="HTML5 canvas implements the example code of the winning carousel" >

css

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

js

  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>

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