雪花飘落

function rnd(){return Math.random();}
function xRnd(){return (rnd()/10);}
function yRnd(){return (2 + 2*( .5 – rnd() ));}
var letitsnow = true;
var flakes = Array(“1.gif”,”2.gif”,”3.gif”,”4.gif”);
var numflakes = 10;
var T = 80;
var dx, xPos, yPos, am, vx, vy, obj, i;
var winwidth = 640;
var winheight = 480;
var snowID;

function sizeIt(){
window.winwidth = window.innerWidth?window.innerWidth:document.body.clientWidth;
window.winheight = window.innerHeight?window.innerHeight:document.body.clientHeight;
}

dx = new Array();
xPos = new Array();
yPos = new Array();
sway = new Array();
var swaymax = 20;
vx = new Array();
vy = new Array();
sizeIt();
document.write(“<style type=/”text/css/”>/n.flk {position:absolute;top:-100;}<//STYLE>”);
for (i = 0; i < numflakes; i++) {
var thisflake = “” + flakes[Math.floor(rnd()*flakes.length)];
dx[i] = 0;
xPos[i] = rnd()*(window.winwidth-30) +10;
yPos[i] = rnd()*window.winheight;
sway[i] = rnd()*swaymax;
vx[i] = xRnd();
vy[i] = yRnd();
document.write(“<div id=/”f”+ i +”/” class=/”flk/”><img src=/””);
document.write(thisflake + “/” border=/”0/”><//div>”);
}

function snowMove(id,left,top) {
obj = document.getElementById?document.getElementById(id).style:
document.all?document.all[id].style:
document.layers?document.layers[id]:null;
if (obj) {
obj.left=left;
obj.top=top;
}
}

function snowSwitch(s) {
if ( s == “on” ) {
if ( window.letitsnow != true ) {
window.letitsnow = true;
doSnow();
}
} else if ( s == “off” ) {
window.letitsnow = false;
hideSnow();
}
}

function hideSnow() {
for (i = 0; i < numflakes; ++ i) snowMove(“f”+i,-100,-100);
clearInterval(snowID);
}

function doSnowRun() {
if (letitsnow){
delta = (window.pageYOffset!=null)?window.pageYOffset:document.body.scrollTop;
for (i = 0; i < numflakes; ++ i) {
yPos[i] += vy[i];
if (yPos[i] > window.winheight+delta-50) {
xPos[i] = rnd()*(window.winwidth-sway[i]-30);
yPos[i] = delta;
vx[i] = xRnd();
vy[i] = yRnd();
}
dx[i] += vx[i];
snowMove(“f”+i,xPos[i]+sway[i]*Math.cos(dx[i]),yPos[i]);
}
}
}
function doSnow() {
if (letitsnow) {
doSnowRun();
snowID = setInterval(“doSnowRun()”, T);
}
}

window.letitsnow = true;
doSnow();