box2d之刚体，定制器笔记

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ok
48     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 }