<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>躁动的小球</title>
<style media="screen">
* {
margin: 0;
padding: 0;
}
html, body {
overflow: hidden;
}
/canvas {
background-color: black;
}/
</style>
</head>
<body>
<canvas id="canvas" width="300" height="300">
<p>您的浏览器不支持cavnas，请<a href="http://www.lidaze.com">点击</a>升级最新版</p>
</canvas>
</body>
<script type="text/javascript">
// 工具函数
function random(min, max) {
return parseInt(Math.random() * (max - min + 1) + min);
}
function randomColor() {
var r = random(0, 255);
var g = random(0, 255);
var b = random(0, 255);
var a = Math.random() + 0.3;
return 'rgba('+ r +', '+ g +', '+ b +', '+ a +')';
}
// 获取元素
var canvas = document.getElementById('canvas');
var ctx = canvas.getContext('2d');
// 修改canvas的宽高和屏幕一样大小
canvas.width = window.innerWidth;
canvas.height = window.innerHeight;
// 获取了canvas的宽高
var canvasWidth = canvas.width;
var canvasHeight = canvas.height;
// 创建小球的构造函数
function Ball(x, y, r, speedX, speedY, color) {
this.r = r || random(10, 30);
this.x = x || random(this.r, canvasWidth - this.r);
this.y = y || random(this.r, canvasHeight - this.r);
var sx = random(-5, 5);
this.speedX = speedX || (sx == 0 ? 1 : sx);
var sy = random(-5, 5);
this.speedY = speedY || (sy == 0 ? 1 : sy);
this.color = color || randomColor();
}
// 使用原型添加方法
Ball.prototype.draw = function () {
ctx.beginPath();
ctx.arc(this.x, this.y, this.r, 0, Math.PI * 2, false);
ctx.closePath();
ctx.fillStyle = this.color;
ctx.fill();
};
Ball.prototype.move = function () {
this.x += this.speedX;
this.y += this.speedY;
if (this.x <= this.r || this.x >= canvasWidth - this.r) {
this.speedX *= -1;
}
if (this.y <= this.r || this.y >= canvasHeight - this.r) {
this.speedY *= -1;
}
};
// 创建变量，用于保存所有的小球
var balls = [];
// 通过循环，创建对象，并放到数组中
for (var i = 0; i < 100; i++) {
var b = new Ball();
b.draw();
balls.push(b);
}
// 定时器
setInterval(function () {
ctx.clearRect(0, 0, canvasWidth, canvasHeight);
ctx.fillStyle = '#000';
ctx.fillRect(0, 0, canvasWidth, canvasHeight);
for (var i = 0; i < balls.length; i++) {
var b = balls[i];
b.move();
b.draw();
}
}, 10);
</script>
</html>
