一、思路
- 有一个不停画球的方法
- 鼠标移入的时候球开始画，这个时候速度不断变化，当去了边界的时候速度变反
- 鼠标移走停止画图
二、代码
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<meta http-equiv="X-UA-Compatible" content="ie=edge">
<title>ball</title>
</head>
<body>
<canvas id="canvas" width="600" height="300"></canvas>
<script>
var canvas = document.getElementById('canvas');
var ctx = canvas.getContext('2d');
var raf;
var ball = {
x: 100,
y: 100,
vx: 5,
vy: 2,
radius: 25,
color: 'blue',
draw: function() {
ctx.beginPath();
ctx.arc(this.x, this.y, this.radius, 0, Math.PI * 2, true);
ctx.closePath();
ctx.fillStyle = this.color;
ctx.fill();
}
};
function draw() {
// 清楚画布上图形
// ctx.clearRect(0,0, canvas.width, canvas.height);
// 不清楚 半透明
ctx.fillStyle = 'rgba(255,255,255,0.3)';
ctx.fillRect(0,0,canvas.width,canvas.height);
if (ball.y + ball.vy > canvas.height || ball.y + ball.vy < 0) {
ball.vy = -ball.vy;
}
if (ball.x + ball.vx > canvas.width || ball.x + ball.vx < 0) {
ball.vx = -ball.vx;
}
ball.draw();
ball.x += ball.vx;
ball.y += ball.vy;
ball.vy *= .99;
ball.vy += .25;
raf = window.requestAnimationFrame(draw);
}
canvas.addEventListener('mouseover', function(e){
raf = window.requestAnimationFrame(draw);
});
canvas.addEventListener('mouseout', function(e){
window.cancelAnimationFrame(raf);
});
ball.draw();
</script>
</body>
</html>