Javascript下雪特效

nkc3g4

本文来自lyz810的空间，http://hi.baidu.com/lyz810/item/1f4567768dfbd23d71442399
效果演示：http://www.lyz810.tk/lab/Snow.php
该特效适用于非IE浏览器,由于下雪由setTimeout调用,IE在setTimeout的误差过大
调用方式:lyz.snow(option)
option为json格式：
stopdiv:雪花停留元素，可选项，可以是一个HTMLElement或String,当参数为String类型时,为指定的id作为停留元素
speed:默认速度为每50ms执行一次,该参数可选项,数值类型,有效范围0~4,数值越大,速度越快,但对浏览器性能要求会越高,适当做测试,选择一个恰当的速度
num:默认雪花数100,该参数可选项,数值类型,建议不要超过200,否则大多数浏览器对CPU的开销极大,一般设置50左右即可 sym:默认为*,雪花默认样式,通常不需要更改

1. var lyz=lyz||{};
   lyz.snow=function(option){
   option=option||{};
   var G=function(id){
   return document.getElementById(id);
   }
   var g=function(id){
   if(typeof id=='string'){
   return G(id);
   }else if(typeof id=='object'){
   return id;
   }
   }
   var snowspeed=[100,80,60,40,20];
   var snowflakes = option.sym||'*';//闆姳鏍峰紡
   var drops = option.num||100;//闆姳鏁扮洰
   var stopdiv = option.stopdiv||null;
   var speed = snowspeed[option.speed]||50;
   var snowflake = new Array();
   var x = new Array();
   var y = new Array();
   var mv = new Array();
   var maxx = document.documentElement.clientWidth;
   var maxy = document.documentElement.clientHeight;
   for(i = 0; i < drops; i++){
   document.write('<div id="lyz_snow'+i+'" style="position:absolute;color:white;cursor:default">'+snowflakes+'</div>');
   snowflake[i] = G('lyz_snow'+i)
   x[i] = Math.random()*maxx-40;
   y[i] = -Math.random()*maxy;
   snowflake[i].style.left = x[i]+'px';
   snowflake[i].style.top = y[i]+'px';
   mv[i] = (Math.random()*5)+0.5;
   snowflake[i].style.fontSize = ((Math.random()-0.5)*10)+16;
   }
   var startsnow=function(){
   var stopsnow = true;
   for(i=0; i<drops; i++){
   var movex = (Math.random()-0.75)*2.5;
   if(stopdiv){
   if(x[i]<g(stopdiv).offsetLeft||x[i]>g(stopdiv).offsetLeft+g(stopdiv).offsetWidth||y[i]<g(stopdiv).offsetTop-15-window.scrollY||y[i]>g(stopdiv).offsetTop+g(stopdiv).offsetHeight-15-window.scrollY){
   x[i]+=movex;
   y[i]+=mv[i];
   stopsnow = false;
   }
   }else{
   x[i]+=movex;
   y[i]+=mv[i];
   stopsnow = false;
   }//endOfElse
   if(x[i] < 0||x[i]>maxx){
   x[i] = Math.random()*maxx-40;
   y[i] = 10;
   }
   if(y[i] > maxy-40){
   y[i] = 10;
   }
   snowflake[i].style.left = x[i]+'px';
   snowflake[i].style.top = y[i]+document.body.scrollTop+'px';
   }//endOfFor
   if(!stopsnow){
   setTimeout(startsnow,speed);
   }
   }//endOfStartSnow
   startsnow();
   }