box2dweb 学习笔记--sample讲解

 

前言:
  之前博文"台球游戏的核心算法和AI(1)" 中, 提到过想用HTML5+Box2d来编写实现一个台球游戏. 以此来对比感慨一下游戏物理引擎的巨大威力.
  做为H5+box2d的初学者, 将简单讲讲box2d的一些基础概念, 并对一个sample样例做下讲解. 权作学习笔记.

资料:
  box2d源自flash版, 后迁移到各个语言版本, box2dweb是与最新flash版本同步的js 2D物理引擎库.
  box2dweb版网址: http://code.google.com/p/box2dweb/.
  box2d官网: http://box2d.org/.

基本概念:
  世界: b2world
  box2d物体依托的世界存在, 其需指定重力向量, 以及静止物体的休眠开关.

var world = new b2World(gravity, doSleep);

  刚体: b2body
  物理世界中的具体物体, 有动态/静态物体之分.
  夹具: b2fixture
  定义物体的形状,材质属性(密度, 摩擦系数,弹性系数)等等.

代码样例:
  box2dweb库采用当前最新的Box2dWeb-2.1a.3. 该库只包含一个js文件, 并附带了样例.
  文件组织结构如下所示:
  
  我们以sample.html为例, 对box2dweb库做下简单的讲解.
  展示的效果如下:
  

  具体代码如下:

<html>
   <head>
      <title>Box2dWeb example</title>
   </head>
   <body onload="init();">
      <canvas id="canvas" width="600" height="400"></canvas>
   </body>
   <script type="text/javascript" src="Box2dWeb-2.1.a.3.min.js"></script>
   <script type="text/javascript">
      var world;
      
      function init() {
         var   b2Vec2 = Box2D.Common.Math.b2Vec2
         	,	b2BodyDef = Box2D.Dynamics.b2BodyDef
         	,	b2Body = Box2D.Dynamics.b2Body
         	,	b2FixtureDef = Box2D.Dynamics.b2FixtureDef
         	,	b2Fixture = Box2D.Dynamics.b2Fixture
         	,	b2World = Box2D.Dynamics.b2World
         	,	b2MassData = Box2D.Collision.Shapes.b2MassData
         	,	b2PolygonShape = Box2D.Collision.Shapes.b2PolygonShape
         	,	b2CircleShape = Box2D.Collision.Shapes.b2CircleShape
         	,	b2DebugDraw = Box2D.Dynamics.b2DebugDraw
            ;
         
         world = new b2World(
               new b2Vec2(0, 10)    //gravity
            ,  true                 //allow sleep
         );
         
         var fixDef = new b2FixtureDef;
         fixDef.density = 1.0;
         fixDef.friction = 0.5;
         fixDef.restitution = 0.2;
         
         var bodyDef = new b2BodyDef;
         
         //create ground
         bodyDef.type = b2Body.b2_staticBody;
         bodyDef.position.x = 9;
         bodyDef.position.y = 13;
         fixDef.shape = new b2PolygonShape;
         fixDef.shape.SetAsBox(10, 0.5);
         world.CreateBody(bodyDef).CreateFixture(fixDef);
         
         //create some objects
         bodyDef.type = b2Body.b2_dynamicBody;
         for(var i = 0; i < 10; ++i) {
            if(Math.random() > 0.5) {
               fixDef.shape = new b2PolygonShape;
               fixDef.shape.SetAsBox(
                     Math.random() + 0.1 //half width
                  ,  Math.random() + 0.1 //half height
               );
            } else {
               fixDef.shape = new b2CircleShape(
                  Math.random() + 0.1 //radius
               );
            }
            bodyDef.position.x = Math.random() * 10;
            bodyDef.position.y = Math.random() * 10;
            world.CreateBody(bodyDef).CreateFixture(fixDef);
         }
         
         //setup debug draw
         var debugDraw = new b2DebugDraw();
			debugDraw.SetSprite(document.getElementById("canvas").getContext("2d"));
			debugDraw.SetDrawScale(30.0);
			debugDraw.SetFillAlpha(0.3);
			debugDraw.SetLineThickness(1.0);
			debugDraw.SetFlags(b2DebugDraw.e_shapeBit | b2DebugDraw.e_jointBit);
			world.SetDebugDraw(debugDraw);
         
         window.setInterval(update, 1000 / 60);
      };
      
      function update() {
         world.Step(
               1 / 60   //frame-rate
            ,  10       //velocity iterations
            ,  10       //position iterations
         );
         world.DrawDebugData();
         world.ClearForces();
      };
   
   </script>
   
   
</html>

  js应该没有类似java和c#的命令空间的概念, 为避免冲突, 往往通过添加前缀名来解决, 比如box2dweb的采用b2前缀. 另一方面, 其通过简写的技巧来缩短类和函数的引用.

var b2Vec2 = Box2D.Common.Math.b2Vec2
  , b2BodyDef = Box2D.Dynamics.b2BodyDef
  , b2Body = Box2D.Dynamics.b2Body
  , b2FixtureDef = Box2D.Dynamics.b2FixtureDef
  , b2Fixture = Box2D.Dynamics.b2Fixture
  , b2World = Box2D.Dynamics.b2World
  , b2MassData = Box2D.Collision.Shapes.b2MassData
  , b2PolygonShape = Box2D.Collision.Shapes.b2PolygonShape
  , b2CircleShape = Box2D.Collision.Shapes.b2CircleShape
  , b2DebugDraw = Box2D.Dynamics.b2DebugDraw
;

  注: 通过简写来缩短类名和函数对象的引用.
  • 创建世界

world = new b2World(
  new b2Vec2(0, 10) //gravity
  , true //allow sleep
);

  • 创建地面

var bodyDef = new b2BodyDef;
//create ground
bodyDef.type = b2Body.b2_staticBody;
bodyDef.position.x = 9;
bodyDef.position.y = 13;
fixDef.shape = new b2PolygonShape;
fixDef.shape.SetAsBox(10, 0.5);
world.CreateBody(bodyDef).CreateFixture(fixDef);

  注: b2Body.b2_staticBody标示该物体为静态物体(固定物), 一个物体由b2BodyDef和b2FixtureDef来确定.
  • 创建刚体

//create some objects
bodyDef.type = b2Body.b2_dynamicBody;
for(var i = 0; i < 10; ++i) {
  if(Math.random() > 0.5) {
    fixDef.shape = new b2PolygonShape;
    fixDef.shape.SetAsBox(
      Math.random() + 0.1 //half width
      , Math.random() + 0.1 //half height
    );
  } else {
    fixDef.shape = new b2CircleShape(
      Math.random() + 0.1 //radius
    );
  }
  bodyDef.position.x = Math.random() * 10;
  bodyDef.position.y = Math.random() * 10;
  world.CreateBody(bodyDef).CreateFixture(fixDef);
}

  注: 这边随机创建了10个圆形/矩形的物体
  • box2dweb的调试器(可视化)

//setup debug draw
var debugDraw = new b2DebugDraw();
debugDraw.SetSprite(document.getElementById("canvas").getContext("2d"));
debugDraw.SetDrawScale(30.0);
debugDraw.SetFillAlpha(0.3);
debugDraw.SetLineThickness(1.0);
debugDraw.SetFlags(b2DebugDraw.e_shapeBit | b2DebugDraw.e_jointBit);
world.SetDebugDraw(debugDraw);

  注: DrawScale为物理世界和像素的比例值, 以及Sprite的canvas的2d上下文.
  • 事件驱动
  注册定时器, 定时更新. 而物理引擎的world.step函数是整个box2d的核心, 其模拟/驱动了物理世界的运行.

window.setInterval(update, 1000 / 60);

function update() {
  world.Step(
    1 / 60 //frame-rate
    , 10 //velocity iterations
    , 10 //position iterations
  );
  world.DrawDebugData();
  world.ClearForces();
};

总结:
  从这个sample代码中, 学习到了很多. 实践出真知, 希望自己作为一个html5er的初学者能快速成长.

写在最后:
  
如果你觉得这篇文章对你有帮助, 请小小打赏下. 其实我想试试, 看看写博客能否给自己带来一点小小的收益. 无论多少, 都是对楼主一种由衷的肯定.

   

posted on 2015-05-28 17:08 mumuxinfei 阅读(...) 评论(...) 编辑 收藏

公告

导航

统计

  • 随笔 - 164
  • 文章 - 0
  • 评论 - 171
  • 引用 - 0