动画原理——旋转
书籍名称：HTML5-Animation-with-JavaScript
书籍源码：https://github.com/lamberta/html5-animation1
1.简单旋转
利用三角函数进行旋转
01-rotate-1.html
<!doctype html>
<html>
<head>
<meta charset="utf-8">
<title>Rotate 1</title>
<link rel="stylesheet" href="../include/style.css">
</head>
<body>
<header>
Example from <a href="http://amzn.com/1430236655?tag=html5anim-20"><em>Foundation HTML5 Animation with JavaScript</em></a>
</header>
<canvas id="canvas" width="400" height="400"></canvas>
<script src="../include/utils.js"></script>
<script src="./classes/ball.js"></script>
<script>
window.onload = function () {
var canvas = document.getElementById('canvas'),
context = canvas.getContext('2d'),
ball = new Ball(),
vr = 0.05,
angle = 0,
radius = 150,
centerX = canvas.width / 2,
centerY = canvas.height / 2;
(function drawFrame () {
window.requestAnimationFrame(drawFrame, canvas);
context.clearRect(0, 0, canvas.width, canvas.height);
ball.x = centerX + Math.cos(angle) * radius;
ball.y = centerY + Math.sin(angle) * radius;
angle += vr;
ball.draw(context);
}());
};
</script>
</body>
</html>
2.高级旋转
这种方法是根据当前的角度和坐标，计算下一帧的角度和坐标
02-rotate-2.html
<!doctype html>
<html>
<head>
<meta charset="utf-8">
<title>Rotate 2</title>
<link rel="stylesheet" href="../include/style.css">
</head>
<body>
<header>
Example from <a href="http://amzn.com/1430236655?tag=html5anim-20"><em>Foundation HTML5 Animation with JavaScript</em></a>
</header>
<canvas id="canvas" width="400" height="400"></canvas>
<script src="../include/utils.js"></script>
<script src="./classes/ball.js"></script>
<script>
window.onload = function () {
var canvas = document.getElementById('canvas'),
context = canvas.getContext('2d'),
ball = new Ball(),
vr = 0.05,
cos = Math.cos(vr),
sin = Math.sin(vr),
centerX = canvas.width / 2,
centerY = canvas.height / 2;
ball.x = Math.random() * canvas.width;
ball.y = Math.random() * canvas.height;
(function drawFrame () {
window.requestAnimationFrame(drawFrame, canvas);
context.clearRect(0, 0, canvas.width, canvas.height);
var x1 = ball.x - centerX,
y1 = ball.y - centerY,
x2 = cos * x1 - sin * y1,
y2 = cos * y1 + sin * x1;
ball.x = centerX + x2;
ball.y = centerY + y2;
ball.draw(context);
}());
};
</script>
</body>
</html>
多个物体
03-rotate-3.html
<!doctype html>
<html>
<head>
<meta charset="utf-8">
<title>Rotate 3</title>
<link rel="stylesheet" href="../include/style.css">
</head>
<body>
<header>
Example from <a href="http://amzn.com/1430236655?tag=html5anim-20"><em>Foundation HTML5 Animation with JavaScript</em></a>
</header>
<canvas id="canvas" width="400" height="400"></canvas>
<aside>Move mouse left or right on canvas element.</aside>
<script src="../include/utils.js"></script>
<script src="./classes/ball.js"></script>
<script>
window.onload = function () {
var canvas = document.getElementById('canvas'),
context = canvas.getContext('2d'),
mouse = utils.captureMouse(canvas),
balls = [],
numBalls = 10,
vr = 0.05,
centerX = canvas.width / 2,
centerY = canvas.height / 2,
cos, sin; //accessible by move and drawFrame
for (var ball, i = 0; i < numBalls; i++) {
ball = new Ball();
ball.x = Math.random() * canvas.width;
ball.y = Math.random() * canvas.height;
balls.push(ball);
}
function move (ball) {
var x1 = ball.x - centerX,
y1 = ball.y - centerY,
x2 = cos * x1 - sin * y1,
y2 = cos * y1 + sin * x1;
ball.x = centerX + x2;
ball.y = centerY + y2;
}
function draw (ball) {
ball.draw(context);
}
(function drawFrame () {
window.requestAnimationFrame(drawFrame, canvas);
context.clearRect(0, 0, canvas.width, canvas.height);
var angle = (mouse.x - centerX) * 0.0005;
cos = Math.cos(angle);
sin = Math.sin(angle);
balls.forEach(move);
balls.forEach(draw);
}());
};
</script>
</body>
</html>
3.在有角度的情况下反弹
