代码描述：
<!doctype html>
<html lang="en">
<head>
<meta charset="utf-8">
<title>canvas运动</title>
<style>
</style>
</head>
<body>
<canvas width="500" height="300" style="border:1px solid black" id="canvas"></canvas>
<script>
var canvas = document.getElementById(‘canvas‘);
var ctx = canvas.getContext("2d");
var father = {};
father.children = [];
/*
* 增加孩子
*/
father.add = function (child) {
father.children.push(child);
}
/*
* 矩形类
*/
function Rect (x, y, w, h, style) {
this.x = x;
this.y = y;
this.w = w;
this.h = h;
this.style = style;
father.add(this);
this.render = function () {
}
}
// 生成一个随机位置、随机方向、随机速度、
// 随机颜色的矩形
function random () {
var x = Math.random() * 400;
var y = Math.random() * 200;
var w = Math.random() * 40 + 20;
var h = Math.random() * 40 + 20;
var colorr = Math.ceil(Math.random() * 256) - 1;//Math.ceil向正取整数
var colorg = Math.ceil(Math.random() * 256) - 1;
var colorb = Math.ceil(Math.random() * 256) - 1;
var color = "rgba("+colorr+","+colorg+","+colorb+",1)";
var t = new Rect(x,y,w,h,color);
t.dx = Math.ceil(Math.random()*2) - 1;
t.dy = Math.ceil(Math.random()*2) - 1;
t.speed = Math.ceil(Math.random()*3);
t.render = function () {
// left
if (this.dx == 0) {
this.x -= this.speed ;
if (this.x < 0) {
this.dx = 1;
this.x = 0;
};
// right
}else{
this.x += this.speed;
if (this.x > canvas.width - this.w) {
this.dx = 0;
this.x = canvas.width - this.w;
};
}
// 上
if (this.dy == 0) {
this.y -= this.speed ;
if (this.y < 0) {
this.dy = 1;
this.y = 0;
};
// 下
}else{
this.y += this.speed;
if (this.y > canvas.height - this.h) {
this.dy = 0;
this.y = canvas.height - this.h;
};
}
ctx.fillStyle = this.style;
ctx.fillRect(this.x,this.y,this.w,this.h);
}
}
// 生成10个随机矩形
for (var i = 0; i < 20; i++) {
random();
};
// 主时间轴计时器，控制所有对象的绘制
setInterval(function () {
ctx.clearRect(0,0,canvas.width,canvas.height);
for (var i = 0; i < father.children.length; i++) {
ctx.save();
father.children[i].render();
ctx.restore();
};
},10);
</script>
</body>
</html>