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原生JS实现的雪花飘落动画效果

网络编程 2021-07-04 16:45www.168986.cn编程入门
这篇文章主要介绍了原生JS实现的雪花飘落动画效果,涉及javascript数值运算及页面元素属性动态操作相关实现技巧,需要的朋友可以参考下

本文实例讲述了原生JS实现的雪花飘落动画效果。分享给大家供大家参考，具体如下

<!DOCTYPE html>
<html>
<head>
  <meta charset="utf-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <title>.jb51. JS下雪动画</title>
  <meta name="description" content="">
  <meta name="viewport" content="width=device-width, initial-scale=1">
</head>
<style>
  .masthead {
    background-color:#333;
    display:block;
    width:100%;
    height:400px;
  }
</style>
<body>
<div class="masthead"></div>
<script>
  (function () {
    var COUNT = 300;
    var masthead = document.querySelector('.masthead');
    var canvas = document.createElement('canvas');
    var ctx = canvas.getContext('2d');
    var width = masthead.clientWidth;
    var height = masthead.clientHeight;
    var i = 0;
    var active = false;
    function onResize() {
      width = masthead.clientWidth;
      height = masthead.clientHeight;
      canvas.width = width;
      canvas.height = height;
      ctx.fillStyle = '#FFF';
      var wasActive = active;
      active = width > 600;
      if (!wasActive && active)
        requestAnimFrame(update);
    }
    var Snowflake = function () {
      this.x = 0;
      this.y = 0;
      this.vy = 0;
      this.vx = 0;
      this.r = 0;
      this.reset();
    };
    Snowflake.prototype.reset = function() {
      this.x = Math.random()  width;
      this.y = Math.random()  -height;
      this.vy = 1 + Math.random()  3;
      this.vx = 0.5 - Math.random();
      this.r = 1 + Math.random()  2;
      this.o = 0.5 + Math.random()  0.5;
    };
    canvas.style.position = 'absolute';
    canvas.style.left = canvas.style. = '0';
    var snowflakes = [], snowflake;
    for (i = 0; i < COUNT; i++) {
      snowflake = new Snowflake();
      snowflakes.push(snowflake);
    }
    function update() {
      ctx.clearRect(0, 0, width, height);
      if (!active)
        return;
      for (i = 0; i < COUNT; i++) {
        snowflake = snowflakes[i];
        snowflake.y += snowflake.vy;
        snowflake.x += snowflake.vx;
        ctx.globalAlpha = snowflake.o;
        ctx.beginPath();
        ctx.arc(snowflake.x, snowflake.y, snowflake.r, 0, Math.PI  2, false);
        ctx.closePath();
        ctx.fill();
        if (snowflake.y > height) {
          snowflake.reset();
        }
      }
      requestAnimFrame(update);
    }
    // shim layer with setTimeout fallback
    window.requestAnimFrame = (function(){
      return window.requestAnimationFrame    ||
          window.webkitRequestAnimationFrame ||
          window.mozRequestAnimationFrame  ||
          function( callback ){
            window.setTimeout(callback, 1000 / 60);
          };
    })();
    onResize();
    window.addEventListener('resize', onResize, false);
    masthead.appendChild(canvas);
  })();
</script></body></html>

使用本站HTML/CSS/JS在线运行测试工具，可得到如下测试运行效果

更多关于JavaScript相关内容感兴趣的读者可查看本站专题《》、《》、《》、《》、《》、《》、《》及《》

希望本文所述对大家JavaScript程序设计有所帮助。

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