一、思路
- 绘制台球案板
- 画球方法
- 加上球移动的动作（控制透明度）
- 鼠标点击，球开始发射，匀速（实际有摩擦力，要速度减少），碰到案板要返回，速度或者说是每次位移的距离
- 鼠标移动，来放置球的位置
- 鼠标移出，停止动作
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>controlBall</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 running = false;
// 绘制边框
function drawRect() {
ctx.beginPath();
ctx.rect(0,0,canvas.width,canvas.height);
ctx.strokeStyle = '#000';
ctx.stroke();
}
var ball = {
x: 100,
y: 100,
vx: 5,
vy: 1,
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 clear() {
ctx.fillStyle = 'rgba(255,255,255,0.3)';
ctx.fillRect(0,0,canvas.width,canvas.height);
}
function draw() {
clear();
drawRect();
ball.x += ball.vx;
ball.y += ball.vy;
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();
raf = window.requestAnimationFrame(draw);
}
canvas.addEventListener('mousemove', function(e){
if (!running) {
clear();
drawRect();
ball.x = e.clientX;
ball.y = e.clientY;
ball.draw();
}
});
canvas.addEventListener('click',function(e){
if (!running) {
raf = window.requestAnimationFrame(draw);
running = true;
}
});
canvas.addEventListener('mouseout', function(e){
window.cancelAnimationFrame(raf);
running = false;
});
ball.draw();
drawRect();
</script>
</body>
</html>