下载地址：
http://www.html5tricks.com/jquery-html5-christ-snow.html
演示地址:
http://www.html5tricks.com/jquery-html5-christ-snow.html
个人的demo：
新建并且引用以下js文件：
(function($){
$.snowfall = function(element, options){
var defaults = {
flakeCount : 35,
flakeColor : '#ffffff',
flakeIndex: 999999,
minSize : 1,
maxSize : 2,
minSpeed : 1,
maxSpeed : 5,
round : false,
shadow : false,
collection : false,
collectionHeight : 40,
deviceorientation : false
},
options = $.extend(defaults, options),
random = function random(min, max){
return Math.round(min + Math.random()*(max-min));
};
$(element).data("snowfall", this);
// Snow flake object
function Flake(_x, _y, _size, _speed, _id)
{
// Flake properties
this.id = _id;
this.x = _x;
this.y = _y;
this.size = _size;
this.speed = _speed;
this.step = 0;
this.stepSize = random(1,10) / 100;
if(options.collection){
this.target = canvasCollection[random(0,canvasCollection.length-1)];
}
var flakeMarkup = $(document.createElement("div")).attr({'class': 'snowfall-flakes', 'id' : 'flake-' + this.id}).css({'width' : this.size, 'height' : this.size, 'background' : options.flakeColor, 'position' : 'absolute', 'top' : this.y, 'left' : this.x, 'fontSize' : 0, 'zIndex' : options.flakeIndex});
if($(element).get(0).tagName === $(document).get(0).tagName){
$('body').append(flakeMarkup);
element = $('body');
}else{
$(element).append(flakeMarkup);
}
this.element = document.getElementById('flake-' + this.id);
// Update function, used to update the snow flakes, and checks current snowflake against bounds
this.update = function(){
this.y += this.speed;
if(this.y > (elHeight) - (this.size + 6)){
this.reset();
}
this.element.style.top = this.y + 'px';
this.element.style.left = this.x + 'px';
this.step += this.stepSize;
if (doRatio === false) {
this.x += Math.cos(this.step);
} else {
this.x += (doRatio + Math.cos(this.step));
}
// Pileup check
if(options.collection){
if(this.x > this.target.x && this.x < this.target.width + this.target.x && this.y > this.target.y && this.y < this.target.height + this.target.y){
var ctx = this.target.element.getContext("2d"),
curX = this.x - this.target.x,
curY = this.y - this.target.y,
colData = this.target.colData;
if(colData[parseInt(curX)][parseInt(curY+this.speed+this.size)] !== undefined || curY+this.speed+this.size > this.target.height){
if(curY+this.speed+this.size > this.target.height){
while(curY+this.speed+this.size > this.target.height && this.speed > 0){
this.speed *= .5;
}
ctx.fillStyle = "#fff";
if(colData[parseInt(curX)][parseInt(curY+this.speed+this.size)] == undefined){
colData[parseInt(curX)][parseInt(curY+this.speed+this.size)] = 1;
ctx.fillRect(curX, (curY)+this.speed+this.size, this.size, this.size);
}else{
colData[parseInt(curX)][parseInt(curY+this.speed)] = 1;
ctx.fillRect(curX, curY+this.speed, this.size, this.size);
}
this.reset();
}else{
// flow to the sides
this.speed = 1;
this.stepSize = 0;
if(parseInt(curX)+1 < this.target.width && colData[parseInt(curX)+1][parseInt(curY)+1] == undefined ){
// go left
this.x++;
}else if(parseInt(curX)-1 > 0 && colData[parseInt(curX)-1][parseInt(curY)+1] == undefined ){
// go right
this.x--;
}else{
//stop
ctx.fillStyle = "#fff";
ctx.fillRect(curX, curY, this.size, this.size);
colData[parseInt(curX)][parseInt(curY)] = 1;
this.reset();
}
}
}
}
}
if(this.x > (elWidth) - widthOffset || this.x < widthOffset){
this.reset();
}
}
// Resets the snowflake once it reaches one of the bounds set
this.reset = function(){
this.y = 0;
this.x = random(widthOffset, elWidth - widthOffset);
this.stepSize = random(1,10) / 100;
this.size = random((options.minSize * 100), (options.maxSize * 100)) / 100;
this.speed = random(options.minSpeed, options.maxSpeed);
}
}
// Private vars
var flakes = [],
flakeId = 0,
i = 0,
elHeight = $(element).height(),
elWidth = $(element).width(),
widthOffset = 0,
snowTimeout = 0;
// Collection Piece ******************************
if(options.collection !== false){
var testElem = document.createElement('canvas');
if(!!(testElem.getContext && testElem.getContext('2d'))){
var canvasCollection = [],
elements = $(options.collection),
collectionHeight = options.collectionHeight;
for(var i =0; i < elements.length; i++){
var bounds = elements[i].getBoundingClientRect(),
canvas = document.createElement('canvas'),
collisionData = [];
if(bounds.top-collectionHeight > 0){
document.body.appendChild(canvas);
canvas.style.position = 'absolute';
canvas.height = collectionHeight;
canvas.width = bounds.width;
canvas.style.left = bounds.left + 'px';
canvas.style.top = bounds.top-collectionHeight + 'px';
for(var w = 0; w < bounds.width; w++){
collisionData[w] = [];
}
canvasCollection.push({element :canvas, x : bounds.left, y : bounds.top-collectionHeight, width : bounds.width, height: collectionHeight, colData : collisionData});
}
}
}else{
// Canvas element isnt supported
options.collection = false;
}
}
// ************************************************
// This will reduce the horizontal scroll bar from displaying, when the effect is applied to the whole page
if($(element).get(0).tagName === $(document).get(0).tagName){
widthOffset = 25;
}
// Bind the window resize event so we can get the innerHeight again
$(window).bind("resize", function(){
elHeight = $(element).height();
elWidth = $(element).width();
});
// initialize the flakes
for(i = 0; i < options.flakeCount; i+=1){
flakeId = flakes.length;
flakes.push(new Flake(random(widthOffset,elWidth - widthOffset), random(0, elHeight), random((options.minSize * 100), (options.maxSize * 100)) / 100, random(options.minSpeed, options.maxSpeed), flakeId));
}
// This adds the style to make the snowflakes round via border radius property
if(options.round){
$('.snowfall-flakes').css({'-moz-border-radius' : options.maxSize, '-webkit-border-radius' : options.maxSize, 'border-radius' : options.maxSize});
}
// This adds shadows just below the snowflake so they pop a bit on lighter colored web pages
if(options.shadow){
$('.snowfall-flakes').css({'-moz-box-shadow' : '1px 1px 1px #555', '-webkit-box-shadow' : '1px 1px 1px #555', 'box-shadow' : '1px 1px 1px #555'});
}
// On newer Macbooks Snowflakes will fall based on deviceorientation
var doRatio = false;
if (options.deviceorientation) {
$(window).bind('deviceorientation', function(event) {
doRatio = event.originalEvent.gamma * 0.1;
});
}
// this controls flow of the updating snow
function snow(){
for( i = 0; i < flakes.length; i += 1){
flakes[i].update();
}
snowTimeout = setTimeout(function(){snow()}, 30);
}
snow();
// Public Methods
// clears the snowflakes
this.clear = function(){
$(element).children('.snowfall-flakes').remove();
flakes = [];
clearTimeout(snowTimeout);
};
};
// Initialize the options and the plugin
$.fn.snowfall = function(options){
if(typeof(options) == "object" || options == undefined){
return this.each(function(i){
(new $.snowfall(this, options));
});
}else if (typeof(options) == "string") {
return this.each(function(i){
var snow = $(this).data('snowfall');
if(snow){
snow.clear();
}
});
}
};
})(zepto);
使用方式，请务必在页面完全加载之后使用以下代码，其他具体参数请查看演示地址的源码
$(document).snowfall({round : true, minSize: 2, maxSize:4}); // add rounded