HTML5游戏开发系列教程8(译)

原文地址：http://www.script-tutorials.com/html5-game-development-lesson-8/

这是我们最新一篇HTML5游戏开发系列文章。我们将继续使用canvas来进行HTML5游戏开发系列的文章。这次我将展示在你的项目中，如何使用Box2D的创建物体。Box2D是一个非常流行的开源物理引擎对于那些需要模拟2D物体的应用来说。在游戏开发中，2D物理引擎是个非常热门的话题。有了物理引擎的帮助，再设定环境和简单的规则，我们可以很容易的创建好玩的游戏。

准备：

首先，你应该这里下载Box2d库。

第一步：HTML

这次我们必须引用所有必需的库文件到我们项目中。

index.html

 <!DOCTYPE html>
 <html lang="en">
     <head>
         <meta charset="utf-8" />
         <title>HTML5 Game Development - Lesson 8 | Script Tutorials</title>
         <link href="css/main.css" rel="stylesheet" type="text/css" />
 
         <script src="js/protoclass.js"></script>
         <script src="js/jquery-1.6.min.js"></script>
 
         <!-- box2djs 文档上说，加载顺序很重要，所以直接从box2d提供的index.html中copy过来-->
         <script src='js/box2d/common/b2Settings.js'></script>
         <script src='js/box2d/common/math/b2Vec2.js'></script>
         <script src='js/box2d/common/math/b2Mat22.js'></script>
         <script src='js/box2d/common/math/b2Math.js'></script>
         <script src='js/box2d/collision/b2AABB.js'></script>
         <script src='js/box2d/collision/b2Bound.js'></script>
         <script src='js/box2d/collision/b2BoundValues.js'></script>
         <script src='js/box2d/collision/b2Pair.js'></script>
         <script src='js/box2d/collision/b2PairCallback.js'></script>
         <script src='js/box2d/collision/b2BufferedPair.js'></script>
         <script src='js/box2d/collision/b2PairManager.js'></script>
         <script src='js/box2d/collision/b2BroadPhase.js'></script>
         <script src='js/box2d/collision/b2Collision.js'></script>
         <script src='js/box2d/collision/Features.js'></script>
         <script src='js/box2d/collision/b2ContactID.js'></script>
         <script src='js/box2d/collision/b2ContactPoint.js'></script>
         <script src='js/box2d/collision/b2Distance.js'></script>
         <script src='js/box2d/collision/b2Manifold.js'></script>
         <script src='js/box2d/collision/b2OBB.js'></script>
         <script src='js/box2d/collision/b2Proxy.js'></script>
         <script src='js/box2d/collision/ClipVertex.js'></script>
         <script src='js/box2d/collision/shapes/b2Shape.js'></script>
         <script src='js/box2d/collision/shapes/b2ShapeDef.js'></script>
         <script src='js/box2d/collision/shapes/b2BoxDef.js'></script>
         <script src='js/box2d/collision/shapes/b2CircleDef.js'></script>
         <script src='js/box2d/collision/shapes/b2CircleShape.js'></script>
         <script src='js/box2d/collision/shapes/b2MassData.js'></script>
         <script src='js/box2d/collision/shapes/b2PolyDef.js'></script>
         <script src='js/box2d/collision/shapes/b2PolyShape.js'></script>
         <script src='js/box2d/dynamics/b2Body.js'></script>
         <script src='js/box2d/dynamics/b2BodyDef.js'></script>
         <script src='js/box2d/dynamics/b2CollisionFilter.js'></script>
         <script src='js/box2d/dynamics/b2Island.js'></script>
         <script src='js/box2d/dynamics/b2TimeStep.js'></script>
         <script src='js/box2d/dynamics/contacts/b2ContactNode.js'></script>
         <script src='js/box2d/dynamics/contacts/b2Contact.js'></script>
         <script src='js/box2d/dynamics/contacts/b2ContactConstraint.js'></script>
         <script src='js/box2d/dynamics/contacts/b2ContactConstraintPoint.js'></script>
         <script src='js/box2d/dynamics/contacts/b2ContactRegister.js'></script>
         <script src='js/box2d/dynamics/contacts/b2ContactSolver.js'></script>
         <script src='js/box2d/dynamics/contacts/b2CircleContact.js'></script>
         <script src='js/box2d/dynamics/contacts/b2Conservative.js'></script>
         <script src='js/box2d/dynamics/contacts/b2NullContact.js'></script>
         <script src='js/box2d/dynamics/contacts/b2PolyAndCircleContact.js'></script>
         <script src='js/box2d/dynamics/contacts/b2PolyContact.js'></script>
         <script src='js/box2d/dynamics/b2ContactManager.js'></script>
         <script src='js/box2d/dynamics/b2World.js'></script>
         <script src='js/box2d/dynamics/b2WorldListener.js'></script>
         <script src='js/box2d/dynamics/joints/b2JointNode.js'></script>
         <script src='js/box2d/dynamics/joints/b2Joint.js'></script>
         <script src='js/box2d/dynamics/joints/b2JointDef.js'></script>
         <script src='js/box2d/dynamics/joints/b2DistanceJoint.js'></script>
         <script src='js/box2d/dynamics/joints/b2DistanceJointDef.js'></script>
         <script src='js/box2d/dynamics/joints/b2Jacobian.js'></script>
         <script src='js/box2d/dynamics/joints/b2GearJoint.js'></script>
         <script src='js/box2d/dynamics/joints/b2GearJointDef.js'></script>
         <script src='js/box2d/dynamics/joints/b2MouseJoint.js'></script>
         <script src='js/box2d/dynamics/joints/b2MouseJointDef.js'></script>
         <script src='js/box2d/dynamics/joints/b2PrismaticJoint.js'></script>
         <script src='js/box2d/dynamics/joints/b2PrismaticJointDef.js'></script>
         <script src='js/box2d/dynamics/joints/b2PulleyJoint.js'></script>
         <script src='js/box2d/dynamics/joints/b2PulleyJointDef.js'></script>
         <script src='js/box2d/dynamics/joints/b2RevoluteJoint.js'></script>
         <script src='js/box2d/dynamics/joints/b2RevoluteJointDef.js'></script>
 
         <script src="js/script.js"></script>
     </head>
     <body>
         <header>
             <h2>HTML5 Game Development - Lesson 8</h2>
             <a href="http://www.script-tutorials.com/html5-game-development-lesson-8/" class="stuts">Back to original tutorial on <span>Script Tutorials</span></a>
         </header>
         <div class="container">
             <canvas id="game" width="800" height="600"></canvas>
         </div>
     </body>
 </html>

第二步：CSS

css/main.css

这次就不打算显示出CSS文件的内容了，因为仅仅只是些页面布局样式。你可以在源代码包里找到该文件。

第三步：JS

js/jquery-2.0.0.min.js 和 js/protoclass.js

上面两个js文件都在源代码包里。下面的js文件是最重要的，是我们游戏的主要代码。

js/script.js

 var canvas, ctx;
 var canvasWidth;
 var canvasHeight;
 var world;
 var iBorder = 5;
 
 //随机产生介于x和y之间的数
 function getRand(x, y) {
     return Math.floor(Math.random() * y) + x;
 }
 
 $(function() {
     world = createWorld();
 
     canvas = document.getElementById('game');
     ctx = canvas.getContext('2d');
     canvasWidth = parseInt(canvas.width);
     canvasHeight = parseInt(canvas.height);
 
     createGround(canvasWidth / 2, canvasHeight - iBorder, canvasWidth / 2, iBorder, 0);
     createGround(iBorder, canvasHeight / 2, iBorder, canvasHeight / 2, 0);   //左边界
     createGround(canvasWidth - iBorder, canvasHeight / 2, iBorder, canvasHeight / 2, 0);  //右边界
 
     addObjects();
 
     frame();
 });
 
 function addObjects() {
     var iVar = getRand(1, 2);
 
     if (iVar == 1) {  //圆圈
         var x = getRand(100, 600);
         var y = 0;
         var r = getRand(10, 40);
         createCircleAt(x, y, r);
     } else if(iVar == 2) {  //方块
         var x = getRand(100, 600);
         var y = 0;
         var w = getRand(5, 40);
         var h = getRand(5, 40);
         createBoxAt(x, y, w, h);
     }
 
     setTimeout(addObjects, 500);
 }
 
 function frame() {
     world.Step(1.0 / 60, 1);
     ctx.clearRect(0, 0, canvasWidth, canvasHeight);
 
     drawWorld(world, ctx);
 
     setTimeout(frame, 10);
 }
 
 function createWorld() {
     //创建世界边界
     var worldAABB = new b2AABB();
     worldAABB.minVertex.Set(-1000, -1000);  //上限
     worldAABB.maxVertex.Set(1000, 1000);    //下限
 
     //确定重力
     var gravity = new b2Vec2(0, 200);
 
     //不允许引擎睡眠
     var doSleep = false;
 
     return new b2World(worldAABB, gravity, doSleep);
 }
 
 function createGround(x, y, width, height, rotation) {
     var groundSd = new b2BoxDef();
     groundSd.extents.Set(width, height);
     groundSd.restitution = 0.4;   //弹性
 
     var groundBd = new b2BodyDef();
     groundBd.AddShape(groundSd);
     groundBd.position.Set(x, y);
     groundBd.rotation = rotation * Math.PI / 180;  //角度
     return world.CreateBody(groundBd);
 }
 
 function createBoxAt(x, y, w, h) {
     var boxSd = new b2BoxDef();
     boxSd.density = 1.0;  //密度
     boxSd.friction = 1.0;   //摩擦力
     boxSd.restitution = .5;   //弹性
     boxSd.extents.Set(w, h);
 
     var boxBd = new b2BodyDef();
     boxBd.AddShape(boxSd);
     boxBd.position.Set(x, y);
     return world.CreateBody(boxBd);
 }
 
 function createCircleAt(x, y, r) {
     var boxSd = new b2CircleDef();
     boxSd.density = 1.0;
     boxSd.friction = 1.0;
     boxSd.restitution = .5;
     boxSd.radius = r;
 
     var boxBd = new b2BodyDef();
     boxBd.AddShape(boxSd);
     boxBd.position.Set(x, y);
     return world.CreateBody(boxBd);
 }
 
 function drawWorld(world, context) {
     //循环的绘制出世界里的物体
     for (var b = world.m_bodyList; b != null; b = b.m_next) {
         for (var s = b.GetShapeList(); s != null; s = s.GetNext()) {
             drawShape(s, context);
         }
     }
 }
 
 function drawShape(shape, context) {
     context.strokeStyle = '#0000ff';
     context.fillStyle = 'rgba(100, 100, 255, 0.8)';
     context.beginPath();
 
     switch (shape.m_type) {
         case b2Shape.e_circleShape:
             var circle = shape;
             var pos = circle.m_position;
             var r = circle.m_radius;
             var segments = 16.0;
             var theta = 0.0;
             var dtheta = 2.0 * Math.PI / segments;
             context.moveTo(pos.x + r, pos.y);
             for (var i = 0; i < segments; i++) {
                 var d = new b2Vec2(r * Math.cos(theta), r * Math.sin(theta));
                 var v = b2Math.AddVV(pos, d);
                 context.lineTo(v.x, v.y);
                 theta += dtheta;
             }
             context.lineTo(pos.x + r, pos.y);
             context.moveTo(pos.x, pos.y);
             var ax = circle.m_R.col1;
             var pos2 = new b2Vec2(pos.x + r * ax.x, pos.y + r * ax.y);
             context.lineTo(pos2.x, pos2.y);
             break;
         case b2Shape.e_polyShape:
             var poly = shape;
             var tV = b2Math.AddVV(poly.m_position, b2Math.b2MulMV(poly.m_R, poly.m_vertices[0]));
             context.moveTo(tV.x, tV.y);
             for (var i = 0; i < poly.m_vertexCount; i++) {
                 var v = b2Math.AddVV(poly.m_position, b2Math.b2MulMV(poly.m_R, poly.m_vertices[i]));
                 context.lineTo(v.x, v.y);
             }
             context.lineTo(tV.x, tV.y);
             break;
     }
     context.fill();
     context.stroke();
 }

我已经在很多地方添加了注释，希望这些代码很容易理解。

结论：

就是这样了，你已经用HTML5和Box2D完成了这次的教程，恭喜！

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