原文地址：http://www.script-tutorials.com/html5-game-development-lesson-1/
以后的每篇文章都会加入一些新的东西。在这篇里我们创建了一个有7个顶点的图形，并在这些顶点上画圆圈，这样我们能通过拖动圆圈来改变顶点的位置。
我们用半透明的颜色来填充该图形。对于刚开始来说，这样就足够了。
第一步：HTML
index.html
<!DOCTYPE html> <html lang="en"> <head> <meta charset="utf-8" /> <title>HTML5 Game step 1 (demo) | Script Tutolials</title> <link href="css/main.css" rel="stylesheet" type="text/css" /> <!--[if lt IE 9]> <script src="http://html5shiv.googlecode.com/svn/trunk/html5.js"></script> <![endif]--> <script type="text/javascript" src="js/jquery-2.0.0.min.js"></script> <script type="text/javascript" src="js/script.js"></script> </head> <body> <div class="container"> <canvas id="scene" width="800" height="600"></canvas> </div> <footer> <h2>HTML5 Game step 1</h2> <a href="http://www.script-tutorials.com/htm5-game-development-lesson-1" class="stuts">Back to original tutorial on <span>Script Tutorials</span></a> </footer> </body> </html>
第二步：CSS
css/main.css
/* general styles */
* {
margin: 0;
padding: 0;
}
body {
background-color:#bababa;
background-image:-webkit-radial-gradient(600px 300px, circle, #ffffff, #bababa 60%);
background-image: -moz-radial-gradient(600px 300px, circle, #ffffff, #bababa 60%);
background-image: -o-radial-gradient(600px 300px, circle, #ffffff, #bababa 60%);
background-image: radial-gradient(600px 300px, circle, #ffffff, #bababa 60%);
color:#fff;
font:14px/1.3 Arial,sans-serif;
min-height:1000px;
}
.container {
100%;
}
.container > * {
display:block;
margin:50px auto;
}
footer {
background-color:#212121;
bottom:0;
box-shadow: 0 -1px 2px #111111;
display:block;
height:70px;
left:0;
position:fixed;
100%;
z-index:100;
}
footer h2{
font-size:22px;
font-weight:normal;
left:50%;
margin-left:-400px;
padding:22px 0;
position:absolute;
540px;
}
footer a.stuts,a.stuts:visited{
border:none;
text-decoration:none;
color:#fcfcfc;
font-size:14px;
left:50%;
line-height:31px;
margin:23px 0 0 110px;
position:absolute;
top:0;
}
footer .stuts span {
font-size:22px;
font-weight:bold;
margin-left:5px;
}
h3 {
text-align:center;
}
/* tutorial styles */
#scene {
background-image:url(../images/01.jpg);
position:relative;
}
第三步：JS
js/jquery-1.5.2.min.js
在这个示例中我们使用jQuery，jQuery可以很方便的绑定不同的事件(比如鼠标事件).script.js是最重要的文件，因为它处理了所有的逻辑。
(原文中用了jquery-1.5.2.min.js,而我自己的例子用了jquery-2.0.0.min.js,所以代码中有些小区别)
js/script.js
var canvas, ctx;
var circles = [];
var selectedCircle;
var hoveredCircle = -1;
/**
* @brief 创建圆圈对象
*
* @param x 横坐标
* @param y 纵坐标
* @param radius 半径
*
* @return
*/
function Circle(x, y, radius) {
this.x = x;
this.y = y;
this.radius = radius;
}
/**
* @brief 清空canvas
*
* @return
*/
function clear() {
ctx.clearRect(0, 0, ctx.canvas.width, ctx.canvas.height);
}
/**
* @brief 画圆圈
*
* @param ctx
* @param x
* @param y
* @param radius
*
* @return
*/
function drawCircle(ctx, x, y, radius) {
ctx.fillStyle = 'rgba(255, 35, 55, 1.0)';
ctx.beginPath();
ctx.arc(x, y, radius, 0, Math.PI * 2, true);
ctx.closePath();
ctx.fill();
}
/**
* @brief 画整个canvas
*
* @return
*/
function drawScene() {
clear(); //清除canvas
ctx.beginPath(); //定制图形开始
ctx.fillStyle = 'rgba(255, 110, 110, 0.5)';
ctx.moveTo(circles[0].x, circles[0].y);
for (var i = 0; i < circles.length; i++) {
ctx.lineTo(circles[i].x, circles[i].y);
}
ctx.closePath(); //定制图形结束
ctx.fill(); //填充定制的图形
ctx.lineWidth = 5;
ctx.strokeStyle = 'rgba(0, 0, 255, 0.5)';
ctx.stroke(); //画边
for (var i = 0; i < circles.length; i++) { //画所有的圆圈
drawCircle(ctx, circles[i].x, circles[i].y, (hoveredCircle == i) ? 25 : 15);
}
}
//初始化
$(function() {
canvas = document.getElementById('scene');
ctx = canvas.getContext('2d');
var circleRadius = 15;
var width = canvas.width;
var height = canvas.height;
var circlesCount = 7; //将会随机的画7个圆圈
for (var i = 0; i < circlesCount; i++) {
var x = Math.random() * width;
var y = Math.random() * height;
circles.push(new Circle(x, y, circleRadius));
}
// 绑定鼠标按下事件(拖动)
$('#scene').mousedown(function(e) {
var canvasPosition = $(this).offset();
var mouseX = e.originalEvent.layerX || 0; //这里原文使用的是e.layerX, 具体原因详见:http://blog.jquery.com/2011/11/03/jquery-1-7-released/
var mouseY = e.originalEvent.layerY || 0;
for (var i = 0; i < circles.length; i++) { //判断鼠标按下点坐标在那个圆圈里面
var circleX = circles[i].x;
var circleY = circles[i].y;
var radius = circles[i].radius;
if (Math.pow(mouseX - circleX, 2) + Math.pow(mouseY - circleY, 2) < Math.pow(radius, 2)) {
selectedCircle = i;
break;
}
}
});
//绑定鼠标移动事件，使可以拖动被选中的圆圈
$('#scene').mousemove(function(e) {
var mouseX = e.originalEvent.layerX || 0;
var mouseY = e.originalEvent.layerY || 0;
if (selectedCircle != undefined) {
var canvasPosition = $(this).offset();
var radius = circles[selectedCircle].radius;
circles[selectedCircle] = new Circle(mouseX, mouseY, radius); //改变被选中圆圈的位置
}
hoveredCircle = undefined;
for (var i = 0; i < circles.length; i++) { //检查所有的圆圈，判断鼠标按下点是否在圆圈内
var circleX = circles[i].x;
var circleY = circles[i].y;
var radius = circles[i].radius;
if (Math.pow(mouseX - circleX, 2) + Math.pow(mouseY - circleY, 2) < Math.pow(radius, 2)) {
hoveredCircle = i;
break;
}
}
});
//鼠标释放事件，用来清除标记selectedCircle
$('#scene').mouseup(function() {
selectedCircle = undefined;
});
//循环画
setInterval(drawScene, 30);
});