刚体(Body)：

通过世界创建的对象，物理引擎里面所有东西都是刚体

创建方式：

定义一个b2BodyDef，b2World调用createBody的方法传入此参数

定制器(Fixture)：

带有形状，密度，摩擦力等属性

创建方式：

定义一个b2FixtureDef，调用刚体的createFixture方法为刚体创建定制器（相当于附加属性），每个刚体支持添加多个Fixture；

刚体的createFixture重载了两种模式，一种是b2FixtureDef作为参数，一种是shape作为参数，效果是一样的。

形状（shape）：

刚体的形状

种类：

circle（圆形），Polygon（多边形），其他等等

基本上他们的范围是这样：world，body，fixture（刚体的多个属性）

tips：b2Vec2是2dx里面类似CGPoint的东西

 

具体看代码

1     //刚体 2     b2BodyDef testBodyDef; 3     testBodyDef.type = b2_staticBody; 4     testBodyDef.position.Set(0,0); 5      6     //底部的边缘线 7     b2EdgeShape testShape; 8     testShape.Set(b2Vec2(0,0), b2Vec2(s.width/PTM_RATIO,0)); 9     10     b2FixtureDef testFixtueDef;11     testFixtueDef.shape = &testShape;12 13     b2Body* testBody = world->CreateBody(&testBodyDef);14     testBody->CreateFixture(&testFixtueDef);15     16     //顶部边缘线17     testShape.Set(b2Vec2(0,s.height/PTM_RATIO), b2Vec2(s.width/PTM_RATIO,s.height/PTM_RATIO));18     testBody->CreateFixture(&testFixtueDef);19     20     //左边边缘线21     testShape.Set(b2Vec2(0,0), b2Vec2(0,s.height/PTM_RATIO));22     testBody->CreateFixture(&testFixtueDef);23     24     //右边边缘线25     testShape.Set(b2Vec2(s.width/PTM_RATIO,0), b2Vec2(s.width/PTM_RATIO,s.height/PTM_RATIO));26     testBody->CreateFixture(&testFixtueDef);27 28     //创建可运动的缸体29     CCPoint ballPosition = CCPointMake(200, 100);30     CCSprite* ballSprite = CCSprite::create("Ball.png");31     ballSprite->setPosition(ballPosition);32     this->addChild(ballSprite);33     34     b2BodyDef moveableBodyDef;35     moveableBodyDef.type = b2_dynamicBody;36     37     //设置刚体位置38     //刚体相对于世界的位置，坐标转换为box2d里面的坐标39     moveableBodyDef.position.Set(ballPosition.x/PTM_RATIO,ballPosition.y/PTM_RATIO);40     //把精灵放到b2BodyDef的userData里面，在update里面刷新精灵位置41     moveableBodyDef.userData = ballSprite;42     43     b2Body *moveableBody = world->CreateBody(&moveableBodyDef);44     45     //创建圆形小球46     b2CircleShape testCircleShape;47     //刚体和形状设置坐标的时候，选一个就ok48     testCircleShape.m_p.Set(0,0);49     float radius = ballSprite->getContentSize().width/(2*PTM_RATIO);50     testCircleShape.m_radius = radius;51     52     b2FixtureDef moveableFixtureDef;53     moveableFixtureDef.shape = &testCircleShape;54     moveableFixtureDef.density = 1.0f;55     moveableFixtureDef.friction = 0.3f;56     moveableBody->CreateFixture(&moveableFixtureDef);

update方法

1 void HelloWorld::update(float dt) 2 { 3     int velocityIterations = 8; 4     int positionIterations = 1; 5      6     world->Step(dt, velocityIterations, positionIterations); 7      8     //刷新精灵位置 9     for (b2Body* body = world->GetBodyList(); NULL!= body; body = body->GetNext())10     {11         if ( NULL != body->GetUserData() )12         {13             CCSprite* sprite = (CCSprite*)body->GetUserData();14             15             sprite->setPosition( CCPointMake( body->GetPosition().x * PTM_RATIO, body->GetPosition().y * PTM_RATIO) );16             sprite->setRotation( -1 * CC_RADIANS_TO_DEGREES(body->GetAngle()) );17         }    18     }19 }