canvas下雪效果
Demo: http://liuyanzhi08.github.io/h5/snow.html
<!DOCTYPE html>
<html>
<head>
<style type="text/css">
body {
background-color: #0c91b8;
}
</style>
</head>
<body >
<script type="text/javascript">
// Cross-browser-compliant
requestAnimationFrame = window.requestAnimationFrame ||
window.mozRequestAnimationFrame ||
window.webkitRequestAnimationFrame ||
window.msRequestAnimationFrame ||
window.oRequestAnimationFrame ||
function(callback) { setTimeout(callback, 1000 / 60); };
/**
* Snow Class
* @param {int} x
* @param {int} y
* @param {int} radius
* @param {Function} fn Formular to calculate x pos and y pos
*/
function Snow (x, y, radius, fn) {
this.x = x;
this.y = y;
this.r = radius;
this.fn = fn;
}
Snow.prototype.update = function () {
this.x = this.fn.x (this.x, this.y);
this.y = this.fn.y (this.y, this.y);
if (this.x > window.innerWidth ||
this.x < 0 ||
this.y > window.innerHeight ||
this.y < 0
){
this.x = getRandom('x');
this.y = 0;
}
}
Snow.prototype.draw = function (cxt) {
var grd = cxt.createRadialGradient (this.x, this.y, 0, this.x, this.y, this.r);
grd.addColorStop(0, "rgba(255, 255, 255, 0.9)");
grd.addColorStop(.5, "rgba(255, 255, 255, 0.5)");
grd.addColorStop(1, "rgba(255, 255, 255, 0)");
cxt.fillStyle = grd;
cxt.fillRect (this.x - this.r, this.y - this.r, this.r * 2, this.r * 2);
}
/**
* Snowlist class
* Container to hold snow objects
*/
SnowList = function () {
this.list = [];
}
SnowList.prototype.push = function (snow) {
this.list.push (snow);
}
SnowList.prototype.update = function () {
for (var i = 0, len = this.list.length; i < len; i++) {
this.list[i].update();
}
}
SnowList.prototype.draw = function (cxt) {
for (var i = 0, len = this.list.length; i < len; i++) {
this.list[i].draw (cxt);
}
}
SnowList.prototype.get = function (i) {
return this.list[i];
}
SnowList.prototype.size = function () {
return this.list.length;
}
/**
* Generate random x-pos, y-pos or fn functions
* @param {string} option x|y|fnx|fny
* @return {int|Function}
*/
function getRandom (option) {
var ret, random;
switch (option) {
case 'x':
ret = Math.random () * window.innerWidth;
break;
case 'y':
ret = Math.random () * window.innerHeight;
break;
case 'r':
ret = 2 + (Math.random () * 6);
break;
case 'fnx':
random = 27 + Math.random () * 100;
ret = function (x, y) {
return x + 0.5 * Math.sin (y / random);
};
break;
case 'fny':
random = 0.4 + Math.random () * 1.4
ret = function (x, y) {
return y + random;
};
break;
}
return ret;
}
// Start snow
function startSnow () {
// Create canvas
var canvas = document.createElement ('canvas'), cxt;
canvas.height = window.innerHeight;
canvas.width = window.innerWidth;
canvas.setAttribute ('style', 'position: fixed;left: 0;top: 0;pointer-events: none;');
canvas.setAttribute ('id', 'canvas_snow');
document.getElementsByTagName ('body')[0].appendChild (canvas);
cxt = canvas.getContext ('2d');
// Create snow objects
var snowList = new SnowList();
for(var i = 0; i < 200; i++){
var snow, randomX, randomY, randomR, randomFnx, randomFny;
randomX = getRandom ('x');
randomY = getRandom ('y');
randomR = getRandom ('r');
randomFnx = getRandom('fnx');
randomFny = getRandom('fny');
snow = new Snow (randomX, randomY, randomR, {
x: randomFnx,
y: randomFny
});
snow.draw (cxt);
snowList.push (snow);
}
// Update snow position data, and redraw them in each frame
requestAnimationFrame (function(){
cxt.clearRect (0, 0, canvas.width, canvas.height);
snowList.update ();
snowList.draw (cxt);
requestAnimationFrame (arguments.callee);
})
}
// Handle window resize
window.onresize = function () {
var canvasSnow = document.getElementById('canvas_snow');
canvasSnow.width = window.innerWidth;
canvasSnow.height = window.innerHeight;
}
// Let it snow O(∩_∩)0
startSnow ();
</script>
</body>
</html>
出处： http://blog.csdn.net/nancle/article/details/42238943