var pictureSrc ="http://hieuung.tatthanh.com.vn/pic/icon/tuyet.gif"; //the location of the snowflakes
var pictureWidth = 30; //the width of the snowflakes
var pictureHeight = 30; //the height of the snowflakes
var numFlakes = 10; //the number of snowflakes
var downSpeed = 0.01; //the falling speed of snowflakes (portion of screen per 100 ms)
var lrFlakes = 10; //the speed that the snowflakes should swing from side to side

if( typeof( numFlakes ) != 'number' || Math.round( numFlakes ) != numFlakes || numFlakes < 1 ) { numFlakes = 10; }

//draw the snowflakes
for( var x = 0; x < numFlakes; x++ ) {
if( document.layers ) { //releave NS4 bug
document.write('<layer id="snFlkDiv'+x+'"><imgsrc="'+pictureSrc+'" height="'+pictureHeight+'"width="'+pictureWidth+'" alt="*" border="0"></layer>');
} else {
document.write('<div style="position:absolute;z-index: 9999;"id="snFlkDiv'+x+'"><img src="'+pictureSrc+'"height="'+pictureHeight+'" width="'+pictureWidth+'" alt="*"border="0"></div>');
}
}

//calculate initial positions (in portions of browser window size)
var xcoords = new Array(), ycoords = new Array(), snFlkTemp;
for( var x = 0; x < numFlakes; x++ ) {
xcoords[x] = ( x + 1 ) / ( numFlakes + 1 );
do { snFlkTemp = Math.round( ( numFlakes - 1 ) * Math.random() );
} while( typeof( ycoords[snFlkTemp] ) == 'number' );
ycoords[snFlkTemp] = x / numFlakes;
}

//now animate
function flakeFall() {
if( !getRefToDivNest('snFlkDiv0') ) { return; }
var scrWidth = 0, scrHeight = 0, scrollHeight = 0, scrollWidth = 0;
//find screen settings for all variations. doing this every time allows for resizing and scrolling
if( typeof( window.innerWidth ) == 'number' ) { scrWidth = window.innerWidth; scrHeight = window.innerHeight; } else {
if( document.documentElement && (document.documentElement.clientWidth ||document.documentElement.clientHeight ) ) {
scrWidth = document.documentElement.clientWidth; scrHeight = document.documentElement.clientHeight; } else {
if( document.body && ( document.body.clientWidth || document.body.clientHeight ) ) {
scrWidth = document.body.clientWidth; scrHeight = document.body.clientHeight; } } }
if( typeof( window.pageYOffset ) == 'number' ) { scrollHeight = pageYOffset; scrollWidth = pageXOffset; } else {
if( document.body && ( document.body.scrollLeft ||document.body.scrollTop ) ) { scrollHeight = document.body.scrollTop;scrollWidth = document.body.scrollLeft; } else {
if(document.documentElement && (document.documentElement.scrollLeft ||document.documentElement.scrollTop ) ) { scrollHeight =document.documentElement.scrollTop; scrollWidth =document.documentElement.scrollLeft; } }
}
//move the snowflakes to their new position
for( var x = 0; x < numFlakes; x++ ) {
if( ycoords[x] * scrHeight > scrHeight - pictureHeight ) { ycoords[x] = 0; }
var divRef = getRefToDivNest('snFlkDiv'+x); if( !divRef ) { return; }
if( divRef.style ) { divRef = divRef.style; } var oPix = document.childNodes ? 'px' : 0;
divRef.top = ( Math.round( ycoords[x] * scrHeight ) + scrollHeight ) + oPix;
divRef.left = ( Math.round( ( ( xcoords[x] * scrWidth ) - (pictureWidth / 2 ) ) + ( ( scrWidth / ( ( numFlakes + 1 ) * 4 ) ) * (Math.sin( lrFlakes * ycoords[x] ) - Math.sin( 3 * lrFlakes * ycoords[x]) ) ) ) + scrollWidth ) + oPix;
ycoords[x] += downSpeed;
}
}

//DHTML handlers
function getRefToDivNest(divName) {
if( document.layers ) { return document.layers[divName]; } //NS4
if( document[divName] ) { return document[divName]; } //NS4 also
if( document.getElementById ) { return document.getElementById(divName); } //DOM (IE5+, NS6+, Mozilla0.9+, Opera)
if( document.all ) { return document.all[divName]; } //Proprietary DOM - IE4
return false;
}

window.setInterval('flakeFall();',100);