<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Document</title>
</head>
<body>
<canvas id="canvas" style="margin:0 auto;border:1px #ddd solid">
The current browser does not support Canvas, can replace the browser a try!
</canvas>
<script>
var searchLight = {
x : 400,
y : 400,
radius : 150,
vx : Math.random() * 5 + 10,
vy : Math.random() * 5 + 10
}
window.onload = function(){
var canvas = document.getElementById('canvas');
canvas.width = 1024;
canvas.height = 768;
if(canvas.getContext('2d')){
var context = canvas.getContext('2d');
setInterval(function(){
draw(context);
update(canvas.width,canvas.height);
},40);
}else{
alert('当前游览器不支持Canvas，请更换游览器后再试！');
}
}
function draw(cxt){
var canvas = cxt.canvas;
cxt.clearRect(0,0,canvas.width,canvas.height);
cxt.save();
cxt.beginPath();
cxt.fillStyle = "#000";
cxt.fillRect(0,0,canvas.width,canvas.height)
cxt.closePath();
cxt.beginPath();
cxt.arc(searchLight.x,searchLight.y,searchLight.radius,0,Math.PI*2);
cxt.fillStyle = "#fff";
cxt.fill();
cxt.clip();
cxt.closePath();
cxt.font = "bold 150px Arial";
cxt.textAlign = "center";
cxt.textBaseline = "middle";
cxt.fillStyle = "#058";
cxt.fillText("Canvas",canvas.width/2,canvas.height/4);
cxt.fillText("Canvas",canvas.width/2,canvas.height/2);
cxt.fillText("Canvas",canvas.width/2,canvas.height * 3/4);
cxt.restore();
}
function update(canvasWidth,canvasHeight){
searchLight.x += searchLight.vx;
searchLight.y += searchLight.vy;
if(searchLight.x - searchLight.radius <= 0){
searchLight.vx = -searchLight.vx;
searchLight.x = searchLight.radius;
}
if(searchLight.x + searchLight.radius >= canvasWidth){
searchLight.vx = -searchLight.vx;
searchLight.x = canvasWidth - searchLight.radius;
}
if(searchLight.y - searchLight.radius <= 0){
searchLight.vy = -searchLight.vy;
searchLight.y = searchLight.radius;
}
if(searchLight.y + searchLight.radius >= canvasHeight){
searchLight.vy = -searchLight.vy;
searchLight.y = canvasHeight - searchLight.radius;
}
}
</script>
</body>
</html>
