主要包括：

• 简单形状的物体，如矩形、圆、多边形
• 复杂的由多个形状组成的物体
• 结合点，如连接多个物体的旋转结合点
• 接触监听器

一、简单形状的物体

1. 矩形
   1. function createRectangularBody(){
      var bodyDef = new b2BodyDef;
      bodyDef.type = b2Body.b2_dynamicBody;
      bodyDef.position.x = 40/scale;
      bodyDef.position.y = 100/scale;
      var fixtureDef = new b2FixtureDef;
      fixtureDef.density = 1.0;
      fixtureDef.friction = 0.5;
      fixtureDef.restitution = 0.3;
      fixtureDef.shape = new b2PolygonShape;
      fixtureDef.shape.SetAsBox(30/scale,50/scale);
      var body = world.CreateBody(bodyDef);
      var fixture = body.CreateFixture(fixtureDef);
      }
2. 圆
   1. function createCircularBody(){
      var bodyDef = new b2BodyDef;
      bodyDef.type = b2Body.b2_dynamicBody;
      bodyDef.position.x = 5;
      bodyDef.position.y = 3.3;
      var fixtureDef = new b2FixtureDef;
      fixtureDef.density = 1.0;
      fixtureDef.friction = 0.5;
      fixtureDef.restitution = 0.7;
      fixtureDef.shape = new b2CircleShape(1);
      var body = world.CreateBody(bodyDef);
      var fixture = body.CreateFixture(fixtureDef);
      }
3. 多边形

function createSimplePolygonBody(){

var bodyDef = new b2BodyDef;

bodyDef.type = b2Body.b2_dynamicBody;

bodyDef.position.x = 8;

bodyDef.position.y = 1.66;

var fixtureDef = new b2FixtureDef;

fixtureDef.density = 1.0;

fixtureDef.friction = 0.5;

fixtureDef.restitution = 0.2;

fixtureDef.shape = new b2PolygonShape;

//必须按顺时针方向创建一个顶点数组

var points = [

new b2Vec2(0,0),

new b2Vec2(40/scale,50/scale),

new b2Vec2(50/scale,100/scale),

new b2Vec2(-50/scale,100/scale),

new b2Vec2(-40/scale,50/scale),

]

//调用SetAsArray来使用顶点数组定义形状

fixtureDef.shape.SetAsArray(points,points.length);

var body= world.CreateBody(bodyDef);

var fixture = body.CreateFixture(fixtureDef);

}

二、复杂的由多个形状组成的物体

function createComplexBody(){

var bodyDef = new b2BodyDef;

bodyDef.type = b2Body.b2_dynamicBody;

bodyDef.position.x = 11.5;

bodyDef.position.y = 2;

var body = world.CreateBody(bodyDef);

//创建第一个载具并为物体添加圆形状

var fixtureDef = new b2FixtureDef;

fixtureDef.density = 1.0;

fixtureDef.friction = 0.5;

fixtureDef.restitution = 0.7;

fixtureDef.shape = new b2CircleShape(40/scale);

body.CreateFixture(fixtureDef);

//创建第二个载具并为物体添加多边形

fixtureDef.shape = new b2PolygonShape;

var points = [

new b2Vec2(0,0),

new b2Vec2(40/scale,50/scale),

new b2Vec2(50/scale,100/scale),

new b2Vec2(-50/scale,100/scale),

new b2Vec2(-40/scale,50/scale),

];

fixtureDef.shape.SetAsArray(points,points.length);

body.CreateFixture(fixtureDef);

}

三、结合点

function createRevoluteJoint(){

//定义第一个物体

var bodyDef1 = new b2BodyDef;

bodyDef1.type = b2Body.b2_dynamicBody;

bodyDef1.position.x = 16;

bodyDef1.position.y = 1.6;

var body1 = world.CreateBody(bodyDef1);

//创建第一个载具并向物体添加矩形形状

var fixtureDef1 = new b2FixtureDef;

fixtureDef1.density = 1.0;

fixtureDef1.friction = 0.5;

fixtureDef1.restitution = 0.5;

fixtureDef1.shape = new b2PolygonShape;

fixtureDef1.shape.SetAsBox(1.6,0.3);

body1.CreateFixture(fixtureDef1);

//定义第二个物体

var bodyDef2 = new b2BodyDef;

bodyDef2.type = b2Body.b2_dynamicBody;

bodyDef2.position.x = 15.5;

bodyDef2.position.y = 1.6;

var body2 = world.CreateBody(bodyDef2);

//创建第二个载具并向物体添加多边形形状

var fixtureDef2 = new b2FixtureDef;

fixtureDef2.density = 1.0;

fixtureDef2.friction = 0.5;

fixtureDef2.restitution = 0.5;

fixtureDef2.shape = new b2PolygonShape;

var points = [

new b2Vec2(0,0),

new b2Vec2(40/scale,50/scale),

new b2Vec2(50/scale,100/scale),

new b2Vec2(-50/scale,100/scale),

new b2Vec2(-40/scale,50/scale),

];

fixtureDef2.shape.SetAsArray(points,points.length);

body2.CreateFixture(fixtureDef2);

//创建结合点连接body1 and body2

var jointDef = new b2RevoluteJointDef;

var jointCenter = new b2Vec2(15.5,1.6);

jointDef.Initialize(body1,body2,jointCenter);

world.CreateJoint(jointDef);

}

四、接触监听器

var specialBody;

function createSpecialBody(){

var bodyDef = new b2BodyDef;

bodyDef.type = b2Body.b2_dynamicBody;

bodyDef.position.x = 15;

bodyDef.position.y = 0;

specialBody = world.CreateBody(bodyDef);

specialBody.SetUserData({name:'special',life:250});

//创建载具并添加圆形状

var fixtureDef = new b2FixtureDef;

fixtureDef.density = 1.0;

fixtureDef.friction = 0.5;

fixtureDef.restitution = 0.5;

fixtureDef.shape = new b2CircleShape(1);

var fixture = specialBody.CreateFixture(fixtureDef);

}

b2ContactListener有四个事件

• BeginContact（）：物体开始接触时调用
• EndContact（）：结束接触时调用
• PostSolve（）：求解器完成后调用，进行碰撞检测时很有用
• PreSolve（）：在求解器求解前调用

function listenForContact(){

var listener = new Box2D.Dynamics.b2ContactListener;

listener.PostSolve = function(contact,impulse){

var body1 = contact.GetFixtureA().GetBody();

var body2 = contact.GetFixtureB().GetBody();

//如果接触的两个物体都具有生命值，则减少生命值

if(body1==specialBody||body2==specialBody){

var impulseAlongNormal = impulse.normalImpulses[0];

specialBody.GetUserData().life -= impulseAlongNormal;

console.log(impulseAlongNormal,'碰撞后生命值：',specialBody.GetUserData().life);

}

};

world.SetContactListener(listener);

}