动画原理——线性来回运动&&波动
书籍名称：HTML5-Animation-with-JavaScript
书籍源码：https://github.com/lamberta/html5-animation
1.在正选函数中，随角度的增大，sin的值徘徊在正一和负一之间。如下图。这可以用做物体的来回运动。
2.动画源码
index.html
<!doctype html> <html> <head> <meta charset="utf-8"> <title>Bobbing 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(), angle = 0, centerY = 200, range = 50, speed = 0.05; ball.x = canvas.width / 2; (function drawFrame () { window.requestAnimationFrame(drawFrame, canvas); context.clearRect(0, 0, canvas.width, canvas.height); ball.y = centerY + Math.sin(angle) * range; angle += speed; ball.draw(context); }()); }; </script> </body> </html>
style.css
/* Some HTML5 Tags */ aside, footer, header, nav, section { display: block; } /* Examples */ body { background-color: #bbb; color: #383838; } #canvas { background-color: #fff; } header { padding-bottom: 10px; } header a { color: #30f; text-decoration: none; } aside { padding-top: 6px; } /* Index page */ #index-body { background-color: #fdeba1; font-family: "Vollkorn", serif; color: #000; } #index-body a { text-decoration: none; color: #b30300; } #index-body #description, #index-body #exercises { overflow: auto; max-width: 900px; margin: 0px auto 20px auto; padding-left: 15px; padding-bottom: 15px; background-color: #fff; border-radius: 15px; } #index-body #description { margin-top: 40px; } #index-body h1 { color: #b30300; } #index-body #description h2 { margin-bottom: 0; } #index-body h1 a { text-decoration: underline; color: #b30300; } #index-body li h2, #index-body li h3, #index-body li h4 { color: #000; } #index-body li h3 { margin-bottom: 0px; } #index-body #description ul { margin: 0; padding: 0; list-style-type: none; } #index-body #description ul li { padding-bottom: 0.6em; } .container { display: table; width: 100%; height: auto; } .container .text { display:table-cell; height:100%; vertical-align:middle; } .container img { padding: 0 20px; display: block; float: right; } .container .clear { clear: both; } #exercises ul { margin: 0; padding: 4px 20px 10px 20px; } #exercises ol { margin: 0 20px 10px 0; padding: 0; list-style-type: none; } #exercises ol li { padding-top: 5px; } #exercises ol ol ol { padding-left: 60px; list-style-type: decimal-leading-zero; } #exercises ol ol ol li img, #exercises ol ol li img { margin-left: 4px; margin-bottom: -10; } #exercises h2 { margin: 10px 0 0 0; }
utils.js
/** * Normalize the browser animation API across implementations. This requests * the browser to schedule a repaint of the window for the next animation frame. * Checks for cross-browser support, and, failing to find it, falls back to setTimeout. * @param {function} callback Function to call when it's time to update your animation for the next repaint. * @param {HTMLElement} element Optional parameter specifying the element that visually bounds the entire animation. * @return {number} Animation frame request. */ if (!window.requestAnimationFrame) { window.requestAnimationFrame = (window.webkitRequestAnimationFrame || window.mozRequestAnimationFrame || window.msRequestAnimationFrame || window.oRequestAnimationFrame || function (callback) { return window.setTimeout(callback, 17 /*~ 1000/60*/); }); } /** * ERRATA: 'cancelRequestAnimationFrame' renamed to 'cancelAnimationFrame' to reflect an update to the W3C Animation-Timing Spec. * * Cancels an animation frame request. * Checks for cross-browser support, falls back to clearTimeout. * @param {number} Animation frame request. */ if (!window.cancelAnimationFrame) { window.cancelAnimationFrame = (window.cancelRequestAnimationFrame || window.webkitCancelAnimationFrame || window.webkitCancelRequestAnimationFrame || window.mozCancelAnimationFrame || window.mozCancelRequestAnimationFrame || window.msCancelAnimationFrame || window.msCancelRequestAnimationFrame || window.oCancelAnimationFrame || window.oCancelRequestAnimationFrame || window.clearTimeout); } /* Object that contains our utility functions. * Attached to the window object which acts as the global namespace. */ window.utils = {}; /** * Keeps track of the current mouse position, relative to an element. * @param {HTMLElement} element * @return {object} Contains properties: x, y, event */ window.utils.captureMouse = function (element) { var mouse = {x: 0, y: 0, event: null}, body_scrollLeft = document.body.scrollLeft, element_scrollLeft = document.documentElement.scrollLeft, body_scrollTop = document.body.scrollTop, element_scrollTop = document.documentElement.scrollTop, offsetLeft = element.offsetLeft, offsetTop = element.offsetTop; element.addEventListener('mousemove', function (event) { var x, y; if (event.pageX || event.pageY) { x = event.pageX; y = event.pageY; } else { x = event.clientX + body_scrollLeft + element_scrollLeft; y = event.clientY + body_scrollTop + element_scrollTop; } x -= offsetLeft; y -= offsetTop; mouse.x = x; mouse.y = y; mouse.event = event; }, false); return mouse; }; /** * Keeps track of the current (first) touch position, relative to an element. * @param {HTMLElement} element * @return {object} Contains properties: x, y, isPressed, event */ window.utils.captureTouch = function (element) { var touch = {x: null, y: null, isPressed: false, event: null}, body_scrollLeft = document.body.scrollLeft, element_scrollLeft = document.documentElement.scrollLeft, body_scrollTop = document.body.scrollTop, element_scrollTop = document.documentElement.scrollTop, offsetLeft = element.offsetLeft, offsetTop = element.offsetTop; element.addEventListener('touchstart', function (event) { touch.isPressed = true; touch.event = event; }, false); element.addEventListener('touchend', function (event) { touch.isPressed = false; touch.x = null; touch.y = null; touch.event = event; }, false); element.addEventListener('touchmove', function (event) { var x, y, touch_event = event.touches[0]; //first touch if (touch_event.pageX || touch_event.pageY) { x = touch_event.pageX; y = touch_event.pageY; } else { x = touch_event.clientX + body_scrollLeft + element_scrollLeft; y = touch_event.clientY + body_scrollTop + element_scrollTop; } x -= offsetLeft; y -= offsetTop; touch.x = x; touch.y = y; touch.event = event; }, false); return touch; }; /** * Returns a color in the format: '#RRGGBB', or as a hex number if specified. * @param {number|string} color * @param {boolean=} toNumber=false Return color as a hex number. * @return {string|number} */ window.utils.parseColor = function (color, toNumber) { if (toNumber === true) { if (typeof color === 'number') { return (color | 0); //chop off decimal } if (typeof color === 'string' && color[0] === '#') { color = color.slice(1); } return window.parseInt(color, 16); } else { if (typeof color === 'number') { color = '#' + ('00000' + (color | 0).toString(16)).substr(-6); //pad } return color; } }; /** * Converts a color to the RGB string format: 'rgb(r,g,b)' or 'rgba(r,g,b,a)' * @param {number|string} color * @param {number} alpha * @return {string} */ window.utils.colorToRGB = function (color, alpha) { //number in octal format or string prefixed with # if (typeof color === 'string' && color[0] === '#') { color = window.parseInt(color.slice(1), 16); } alpha = (alpha === undefined) ? 1 : alpha; //parse hex values var r = color >> 16 & 0xff, g = color >> 8 & 0xff, b = color & 0xff, a = (alpha < 0) ? 0 : ((alpha > 1) ? 1 : alpha); //only use 'rgba' if needed if (a === 1) { return "rgb("+ r +","+ g +","+ b +")"; } else { return "rgba("+ r +","+ g +","+ b +","+ a +")"; } }; /** * Determine if a rectangle contains the coordinates (x,y) within it's boundaries. * @param {object} rect Object with properties: x, y, width, height. * @param {number} x Coordinate position x. * @param {number} y Coordinate position y. * @return {boolean} */ window.utils.containsPoint = function (rect, x, y) { return !(x < rect.x || x > rect.x + rect.width || y < rect.y || y > rect.y + rect.height); }; /** * Determine if two rectangles overlap. * @param {object} rectA Object with properties: x, y, width, height. * @param {object} rectB Object with properties: x, y, width, height. * @return {boolean} */ window.utils.intersects = function (rectA, rectB) { return !(rectA.x + rectA.width < rectB.x || rectB.x + rectB.width < rectA.x || rectA.y + rectA.height < rectB.y || rectB.y + rectB.height < rectA.y); };
ball.js
function Ball (radius, color) { if (radius === undefined) { radius = 40; } if (color === undefined) { color = "#ff0000"; } this.x = 0; this.y = 0; this.radius = radius; this.rotation = 0; this.scaleX = 1; this.scaleY = 1; this.color = utils.parseColor(color); this.lineWidth = 1; } Ball.prototype.draw = function (context) { context.save(); context.translate(this.x, this.y); context.rotate(this.rotation); context.scale(this.scaleX, this.scaleY); context.lineWidth = this.lineWidth; context.fillStyle = this.color; context.beginPath(); //x, y, radius, start_angle, end_angle, anti-clockwise context.arc(0, 0, this.radius, 0, (Math.PI * 2), true); context.closePath(); context.fill(); if (this.lineWidth > 0) { context.stroke(); } context.restore(); };
3.波动实际是在上下移动的基础上x一直递增。
在原页面index.html的基础上简单修改一下就可以
<!doctype html>
<html>
<head>
<meta charset="utf-8">
<title>Bobbing 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(),
angle = 0,
centerY = 200,
range = 50,
xspeed = 1,
speed = 0.05;
ball.x = canvas.width / 2;
(function drawFrame () {
window.requestAnimationFrame(drawFrame, canvas);
context.clearRect(0, 0, canvas.width, canvas.height);
ball.x += xspeed;
ball.y = centerY + Math.sin(angle) * range;
angle += speed;
ball.draw(context);
}());
};
</script>
</body>
</html>
