<html>
<head>
<title>Gamedev Canvas Workshop - lesson 3: bounce off the walls</title>
<style>* { padding: 0; margin: 0; } canvas { background: #eee; display: block; margin: 0 auto; }</style>
</head>
<body>
<canvas height="320" id="myCanvas" width="480"></canvas>
<script>
var canvas = document.getElementById("myCanvas");
var ctx = canvas.getContext("2d");
var ballRadius = 10;
var x = canvas.width/2;
var y = canvas.height-30;
var dx = 2; (控制球飛的速度)
var dy = -2;
function drawBall() {
ctx.beginPath();
ctx.arc(x, y, ballRadius, 0, Math.PI*2);
ctx.fillStyle = "#0095DD";
ctx.fill();
ctx.closePath();
}
function draw() {
ctx.clearRect(0, 0, canvas.width, canvas.height);
drawBall();
if(x + dx > canvas.width-ballRadius || x + dx < ballRadius) {
dx = -dx;
}
if(y + dy > canvas.height-ballRadius || y + dy < ballRadius) {
dy = -dy;
}
x += dx; (避免讓球飛出框外)
y += dy;
}
setInterval(draw, 10);
</script>
</body>
</html>
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