javascript雪花效果注释版

浏览数：33 / 时间：2015年06月09日

  1 (function () {
  2     // 添加事件监听器
  3     function addEvent(a, b, c) {
  4         if (a.addEventListener) a.addEventListener(b, c, false);
  5         else a.attachEvent && a.attachEvent("on" + b, c)
  6     }
  7     // 向window.onload添加执行函数
  8     function addToOnLoad(a) {
  9         if (typeof window.onload != "function") window.onload = a;
 10         else {
 11             var b = window.onload;
 12             window.onload = function () {
 13                 b();
 14                 a()
 15             }
 16         }
 17     }
 18     // scroll top ,left
 19     function getScrollDis() {
 20         var scroll = {};
 21         for (var type in {
 22             Top: "",
 23             Left: ""
 24         }) {
 25             var b = type == "Top" ? "Y" : "X";
 26             if (typeof window["page" + b + "Offset"] != "undefined") scroll[type.toLowerCase()] = window["page" + b + "Offset"];
 27             else {
 28                 // <html> 
 29                 b = document.documentElement.clientHeight ? document.documentElement : document.body;
 30                 scroll[type.toLowerCase()] = b["scroll" + type]
 31             }
 32         }
 33         return scroll;
 34     }
 35 
 36     // 获取浏览器窗口高度(不包括工具栏/滚动条)
 37     function getWinHeight() {
 38        
 39         var height = window.innerHeight || document.documentElement.clientHeight || document.body.clientHeight;
 40         return height;
 41     }
 42 
 43     //构造函数 ，模拟雪花类
 44     function SnowDot(a) {
 45         this.parent = document.body;
 46         this.createEl(this.parent, a);
 47         this.size = Math.random() * 5 + 5; // 随机设置雪花的大小
 48         this.el.style.width = Math.round(this.size) + "px";
 49         this.el.style.height = Math.round(this.size) + "px";
 50         this.maxLeft = document.body.offsetWidth - this.size;
 51         this.maxTop = document.body.offsetHeight - this.size;
 52         this.left = Math.random() * this.maxLeft;
 53         this.top = getScrollDis().top + 1;
 54         this.angle = 1.4 + 0.2 * Math.random();
 55         // PI/2 =1.57
 56         this.minAngle = 1.4;
 57         this.maxAngle = 1.6;
 58         // 角度增量
 59         this.angleDelta = 0.01 * Math.random();
 60         this.speed = 2 + Math.random()
 61     }
 62     // 原型 对象实例所共享
 63     SnowDot.prototype = {
 64         createEl: function (a, b) {
 65             this.el = document.createElement("img");
 66             this.el.setAttribute("src", b + "snow" + Math.floor(Math.random() * 4) + ".gif");
 67             this.el.style.position = "absolute";
 68             this.el.style.display = "block";
 69             this.el.style.zIndex = "99999";
 70             this.parent.appendChild(this.el)
 71         },
 72         move: function () {
 73             if (this.angle < this.minAngle || this.angle > this.maxAngle) this.angleDelta = -this.angleDelta;
 74             this.angle += this.angleDelta;
 75             // 利用正弦波 余弦波(注意波形图在 pi/2 附近的取值)
 76             this.left += this.speed * Math.cos(this.angle * Math.PI);
 77             this.top -= this.speed * Math.sin(this.angle * Math.PI);
 78             if (this.left < 0) this.left = this.maxLeft;
 79             else if (this.left > this.maxLeft) this.left = 0
 80         },
 81         draw: function () {
 82             this.el.style.top = Math.round(this.top) + "px";
 83             this.el.style.left = Math.round(this.left) + "px"
 84         },
 85         remove: function () {
 86             this.parent.removeChild(this.el);
 87             this.parent = this.el = null
 88         }
 89     }
 90 
 91     var j = false;
 92     addToOnLoad(function () {
 93         j = true
 94     });
 95 
 96     //开启/关闭 标志
 97     var f = true;
 98 
 99     // a : 雪花gif图片所在路径  
100     // b : 雪花最大数目
101     window.createSnow = function (a, b) {
102         if (j) {
103             var c = [],
104             m = setInterval(function () {
105                 // &&前的为false则后边的语句不再执行 
106                 f && b > c.length && Math.random() < b * 0.0025 && c.push(new SnowDot(a));
107                 !f && !c.length && clearInterval(m);
108                 for (var e = getScrollDis().top, n = getWinHeight(), d = c.length - 1; d >= 0; d--) {
109                     if (c[d]) {
110                         // 雪花超出指定高度 
111                         if (c[d].top > 700 || c[d].top + c[d].size + 1 > e + n) {
112                             c[d].remove();
113                             c[d] = null;
114                             c.splice(d, 1) //移除数组索引d位置开始1个元素
115                             //alert(c[d].top)
116                         } else {
117                             c[d].move();
118                             c[d].draw()
119                         }
120                     }
121                 }
122             },
123             40);
124             // 窗口滚动时 雪花移动相应的距离
125             addEvent(window, "scroll",
126             function () {
127                 for (var e = c.length - 1; e >= 0; e--) c[e].draw()
128             })
129         } else addToOnLoad(function () {
130             createSnow(a, b)
131         })
132     };
133     window.removeSnow = function () {
134         f = false
135     };
136  
137 })();