以下是完整代码以及演示
html 代码:<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Star</title>
</head>
<body>
<canvas id="universe"></canvas>
</body>
<style>
body {
background-color: #000000;
}
#universe {
display: block;
position: fixed;
margin: 0;
padding: 0;
border: 0;
outline: 0;
left: 0;
top: 0;
width: 100%;
height: 100%;
pointer-events: none;
z-index: 1
}
</style>
<script>
window.requestAnimationFrame = window.requestAnimationFrame || window.mozRequestAnimationFrame || window
.webkitRequestAnimationFrame || window.msRequestAnimationFrame;
var starDensity = .216;
var speedCoeff = .05;
var width;
var height;
var starCount;
var circleRadius;
var circleCenter;
var first = true;
var giantColor = '180,184,240';
var starColor = '226,225,142';
var cometColor = '226,225,224';
var canva = document.getElementById('universe');
var stars = [];
windowResizeHandler();
window.addEventListener('resize', windowResizeHandler, false);
createUniverse();
function createUniverse() {
universe = canva.getContext('2d');
for (var i = 0; i < starCount; i++) {
stars[i] = new Star();
stars[i].reset();
}
draw();
}
function draw() {
universe.clearRect(0, 0, width, height);
var starsLength = stars.length;
for (var i = 0; i < starsLength; i++) {
var star = stars[i];
star.move();
star.fadeIn();
star.fadeOut();
star.draw();
}
window.requestAnimationFrame(draw);
}
function Star() {
this.reset = function() {
this.giant = getProbability(3);
this.comet = this.giant || first ? false : getProbability(10);
this.x = getRandInterval(0, width - 10);
this.y = getRandInterval(0, height);
this.r = getRandInterval(1.1, 2.6);
this.dx = getRandInterval(speedCoeff, 6 * speedCoeff) + (this.comet + 1 - 1) * speedCoeff *
getRandInterval(50, 120) + speedCoeff * 2;
this.dy = -getRandInterval(speedCoeff, 6 * speedCoeff) - (this.comet + 1 - 1) * speedCoeff *
getRandInterval(50, 120);
this.fadingOut = null;
this.fadingIn = true;
this.opacity = 0;
this.opacityTresh = getRandInterval(.2, 1 - (this.comet + 1 - 1) * .4);
this.do = getRandInterval(0.0005, 0.002) + (this.comet + 1 - 1) * .001;
};
this.fadeIn = function() {
if (this.fadingIn) {
this.fadingIn = this.opacity > this.opacityTresh ? false : true;
this.opacity += this.do;
}
};
this.fadeOut = function() {
if (this.fadingOut) {
this.fadingOut = this.opacity < 0 ? false : true;
this.opacity -= this.do / 2;
if (this.x > width || this.y < 0) {
this.fadingOut = false;
this.reset();
}
}
};
this.draw = function() {
universe.beginPath();
if (this.giant) {
universe.fillStyle = 'rgba(' + giantColor + ',' + this.opacity + ')';
universe.arc(this.x, this.y, 2, 0, 2 * Math.PI, false);
} else if (this.comet) {
universe.fillStyle = 'rgba(' + cometColor + ',' + this.opacity + ')';
universe.arc(this.x, this.y, 1.5, 0, 2 * Math.PI, false);
//comet tail
for (var i = 0; i < 30; i++) {
universe.fillStyle = 'rgba(' + cometColor + ',' + (this.opacity - (this.opacity / 20) * i) + ')';
universe.rect(this.x - this.dx / 4 * i, this.y - this.dy / 4 * i - 2, 2, 2);
universe.fill();
}
} else {
universe.fillStyle = 'rgba(' + starColor + ',' + this.opacity + ')';
universe.rect(this.x, this.y, this.r, this.r);
}
universe.closePath();
universe.fill();
};
this.move = function() {
this.x += this.dx;
this.y += this.dy;
if (this.fadingOut === false) {
this.reset();
}
if (this.x > width - (width / 4) || this.y < 0) {
this.fadingOut = true;
}
};
(function() {
setTimeout(function() {
first = false;
}, 50)
})()
}
function getProbability(percents) {
return ((Math.floor(Math.random() * 1000) + 1) < percents * 10);
}
function getRandInterval(min, max) {
return (Math.random() * (max - min) + min);
}
function windowResizeHandler() {
width = window.innerWidth;
height = window.innerHeight;
starCount = width * starDensity;
circleRadius = (width > height ? height / 2 : width / 2);
circleCenter = {
x: width / 2,
y: height / 2
}
canva.setAttribute('width', width);
canva.setAttribute('height', height);
}
</script>
</html>
