<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>HTML5 Canvas实现的水平线喷泉动画效果</title>
<style>
canvas {
position: absolute;
top: 0;
left: 0;
}
</style>
</head>
<body>
<canvas id=c></canvas>
<script>
var w = c.width = window.innerWidth,
h = c.height = window.innerHeight,
ctx = c.getContext('2d')
, opts = {
baseBaseSize: 20,
addedBaseSize: 10,
baseVel: 2,
addedVel: 1,
baseTime: 60,
addedTime: 20,
overTime: 5,
sliding: .99,
particleChance: .9,
particles: 250,
templateParticleColor: 'hsla(hue,80%,40%,alp)',
repaintAlpha: 'rgba(0,0,0,.1)',
startColor: .2,
fullColor: .5,
stopColor: .6,
timeToColorChange: 3
}, particles = [], tick = 0;
function Particle() {
this.reset();
}
Particle.prototype.reset = function() {
this.x = Math.pow(Math.random(), 1 / 4);
this.y = h / 2;
var color = opts.templateParticleColor.replace('hue', this.x * 360 * 2 + tick * opts.timeToColorChange);
this.baseSize = (Math.random() + this.x) / 2 * (opts.baseBaseSize + opts.addedBaseSize * Math.random());
this.gradient = ctx.createRadialGradient(0, 0, 0, 0, 0, this.baseSize / 2);
this.gradient.addColorStop(opts.startColor, color.replace('alp', 0));
this.gradient.addColorStop(opts.fullColor, color.replace('alp', 1));
this.gradient.addColorStop(opts.stopColor, color.replace('alp', 1));
this.gradient.addColorStop(1, color.replace('alp', 0));
this.vx = -(1 + Math.random() / 10 - this.x) * (opts.baseVel + Math.random() * opts.addedVel);
this.vy = Math.pow(this.x, 4) * (opts.baseVel + Math.random() * opts.addedVel) * (Math.random() < .5 ? -1 : 1);
this.x *= w / 2;
if (Math.random() < .5) {
this.x = w - this.x;
this.vx *= -1;
}
this.time = opts.baseTime + opts.addedTime * Math.random();
this.tick = this.time + opts.overTime;
}
Particle.prototype.step = function() {
var size;
if (this.tick <= this.time) {
this.x += this.vx *= opts.sliding;
this.y += this.vy *= opts.sliding;
size = Math.pow(this.tick / this.time, 1 / 2)
} else size = 1 - ((this.tick - this.time) / opts.overTime) + .000001; // only to avoid division by zero
--this.tick;
ctx.translate(this.x, this.y);
ctx.scale(size, size);
ctx.fillStyle = this.gradient;
ctx.fillRect(-this.baseSize / 2, -this.baseSize / 2, this.baseSize, this.baseSize);
ctx.scale(1 / size, 1 / size);
ctx.translate(-this.x, -this.y);
if (this.tick <= 0)
this.reset();
}
function anim() {
window.requestAnimationFrame(anim);
ctx.globalCompositeOperation = 'source-over';
ctx.fillStyle = opts.repaintAlpha;
ctx.fillRect(0, 0, w, h);
ctx.globalCompositeOperation = 'lighter';
++tick;
if (particles.length < opts.particles && Math.random() < opts.particleChance)
particles.push(new Particle);
particles.map(function(particle) {
particle.step();
});
}
ctx.fillStyle = '#222';
ctx.fillRect(0, 0, w, h);
anim();
window.addEventListener('resize', function() {
w = c.width = window.innerWidth;
h = c.height = window.innerHeight;
ctx.fillStyle = '#222';
ctx.fillRect(0, 0, w, h);
})
</script>
</body>
</html>
