书籍名称：HTML5-Animation-with-JavaScript
书籍源码：https://github.com/lamberta/html5-animation
1.正弦函数。x位置递增，y位置用sin生成。
这段代码是不需要ball.js的。
代码如下：
<!doctype html> <html> <head> <meta charset="utf-8"> <title>Wave 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> window.onload = function () { var canvas = document.getElementById('canvas'), context = canvas.getContext('2d'), angle = 0, range = 50, centerY = canvas.height / 2, xspeed = 1, yspeed = 0.05, xpos = 0, ypos = centerY; context.lineWidth = 2; (function drawFrame () { window.requestAnimationFrame(drawFrame, canvas); context.beginPath(); context.moveTo(xpos, ypos); //Calculate the new position. xpos += xspeed; angle += yspeed; ypos = centerY + Math.sin(angle) * range; context.lineTo(xpos, ypos); context.stroke(); }()); }; </script> </body> </html>
2.做环绕运动，就是求旋转角度对应在圆上的坐标，由下图可以看出x的值是半径r*cos（angle）,而y则为r*sin(angle)，由于canvas的坐标不同于传统的坐标系，大家自行与传统坐标系区别开。
椭圆运动则是某方向值偏大。
上代码：08-circle.html
<!doctype html> <html> <head> <meta charset="utf-8"> <title>Circle</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(), angle = 0, centerX = canvas.width / 2, centerY = canvas.height / 2, radius = 50, speed = 0.05; (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 += speed; ball.draw(context); }()); }; </script> </body> </html>
09-oval.html
<!doctype html> <html> <head> <meta charset="utf-8"> <title>Oval</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(), angle = 0, centerX = canvas.width / 2, centerY = canvas.height / 2, radiusX = 150, radiusY = 100, speed = 0.05; (function drawFrame () { window.requestAnimationFrame(drawFrame, canvas); context.clearRect(0, 0, canvas.width, canvas.height); ball.x = centerX + Math.cos(angle) * radiusX; ball.y = centerY + Math.sin(angle) * radiusY; angle += speed; ball.draw(context); }()); }; </script> </body> </html>