<!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 canvas = document.getElementById('canvas');
var context = canvas.getContext('2d');
var balls = []; window.onload = function(){
// var canvas = document.getElementById('canvas'); canvas.width = 1024;
canvas.height = 768; if(canvas.getContext('2d')){
// var context = canvas.getContext('2d'); for(var i=0;i<10;i++){
var aBall = {
x : Math.random()*canvas.width,
y : Math.random()*canvas.height,
r : Math.random()*50+20
};
balls[i] = aBall;
} draw();
canvas.addEventListener("mouseup",detect); }else{
alert('当前游览器不支持Canvas，请更换游览器后再试！');
}
} function draw(){
for(var i = 0;i<balls.length;i++){
context.beginPath();
context.arc(balls[i].x,balls[i].y,balls[i].r,0,Math.PI*2);
context.fillStyle = "#058";
context.fill();
}
} function detect(event){
var x = event.clientX - canvas.getBoundingClientRect().left;
var y = event.clientY - canvas.getBoundingClientRect().top; for(var i=0;i<balls.length;i++){
context.beginPath();
context.arc(balls[i].x,balls[i].y,balls[i].r,0,Math.PI*2); if(context.isPointInPath(x,y)){
context.fillStyle = "red";
context.fill();
}
}
} </script>
</body>
<script>
/*总结 //判断事件是不是在canvas内
context.isPointInPath(x,y) */
</script>
</html>