动画原理——图形填充
书籍名称：HTML5-Animation-with-JavaScript
书籍源码：https://github.com/lamberta/html5-animation
1.渐变填充
渐变填充有线性渐变，和径向渐变两种。因为是用法，我们直接在代码中分析会更直观
一.
<!doctype html>
<html>
<head>
<meta charset="utf-8">
<title>Gradient Fill 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>
window.onload = function () {
var canvas = document.getElementById('canvas'),
context = canvas.getContext('2d'),
pt1 = {x: 0, y: 0}, //gradient start point
pt2 = {x: 100, y: 100}, //gradient end point
//创建渐变，前pt为开始坐标，p2为结束坐标
gradient = context.createLinearGradient(pt1.x, pt1.y, pt2.x, pt2.y);
//开始颜色为白，结束颜色为红
gradient.addColorStop(0, "#ffffff");
gradient.addColorStop(1, "#ff0000");
//填充
context.fillStyle = gradient;
context.fillRect(0, 0, 100, 100);
};
</script>
</body>
</html>
二.多种颜色
<!doctype html>
<html>
<head>
<meta charset="utf-8">
<title>Gradient Fill 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>
window.onload = function () {
var canvas = document.getElementById('canvas'),
context = canvas.getContext('2d'),
pt1 = {x: 100, y: 100}, //gradient start point
pt2 = {x: 200, y: 200}, //gradient end point
gradient = context.createLinearGradient(pt1.x, pt1.y, pt2.x, pt2.y);
//white to blue to red
gradient.addColorStop(0, "#ffffff");
gradient.addColorStop(0.5, "#0000ff");
gradient.addColorStop(1, "#ff0000");
context.fillStyle = gradient;
context.fillRect(100, 100, 100, 100);
};
</script>
</body>
</html>
三.透明
<!doctype html>
<html>
<head>
<meta charset="utf-8">
<title>Gradient Fill Radial</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>
window.onload = function () {
var canvas = document.getElementById('canvas'),
context = canvas.getContext('2d'),
c1 = {x: 150, y: 150, radius: 0}, //gradient start circle
c2 = {x: 150, y: 150, radius: 50}, //gradient end circle
gradient = context.createRadialGradient(c1.x, c1.y, c1.radius,
c2.x, c2.y, c2.radius);
//all black alpha blend
gradient.addColorStop(0, "#000000");
gradient.addColorStop(1, "rgba(0, 0, 0, 0)"); //alpha required
context.fillStyle = gradient;
context.fillRect(100, 100, 100, 100);
};
</script>
</body>
</html>
