Question

I have around 10 bodies in my Box2D sample app which i have created with the help of following method. But in my Update method i want get the b2FixtureDef of the bodies because i need there filter.groupIndex which is different for every body. I have the Update method as follows which loops thru all the b2Body but cant really find how to get the b2FixtureDef from b2Body??

-(void) addNewSprite:(NSString *)spriteName AtPosition:(CGPoint)p isDynamic:(BOOL)dynamic
{
    //CCNode *parent = [self getChildByTag:kTagParentNode];

PhysicsSprite *sprite = [PhysicsSprite spriteWithFile:spriteName];

[self addChild:sprite];

sprite.position = ccp( p.x, p.y);

sprite.tag = check;

// Define the dynamic body.
//Set up a 1m squared box in the physics world
b2BodyDef bodyDef;
bodyDef.type = b2_dynamicBody;  
bodyDef.position.Set(sprite.position.x/PTM_RATIO, sprite.position.y/PTM_RATIO);
bodyDef.userData = sprite;
b2Body *body = world->CreateBody(&bodyDef);

// Define another box shape for our dynamic body.
b2PolygonShape dynamicBox;
dynamicBox.SetAsBox((sprite.contentSize.width/PTM_RATIO/2)*(sprite.scaleX),
                    (sprite.contentSize.height/PTM_RATIO/2)*(sprite.scaleY));//These are mid points for our 1m box

// Define the dynamic body fixture.
b2FixtureDef fixtureDef;
fixtureDef.shape = &dynamicBox; 
fixtureDef.density = 1.0f;
fixtureDef.friction = 1.0f;
fixtureDef.userData = sprite;

switch (check)
{
    case 1:
        fixtureDef.filter.categoryBits = 0x0002;

        fixtureDef.filter.maskBits = 0x0004;
        break;
    case 2:
        fixtureDef.filter.categoryBits = 0x0004;

        fixtureDef.filter.maskBits = 0x0002;
        break;
}

body->CreateFixture(&fixtureDef);

[sprite setPhysicsBody:body];

check++;
}

-(void) update: (ccTime) dt
{
    //It is recommended that a fixed time step is used with Box2D for stability
    //of the simulation, however, we are using a variable time step here.
    //You need to make an informed choice, the following URL is useful
    //http://gafferongames.com/game-physics/fix-your-timestep/

int32 velocityIterations = 8;
int32 positionIterations = 1;

// Instruct the world to perform a single step of simulation. It is
// generally best to keep the time step and iterations fixed.
world->Step(dt, velocityIterations, positionIterations);    

for(b2Body *b = world->GetBodyList(); b; b=b->GetNext()) {    

    if (b->GetUserData() != NULL) 
    {

        //b2Fixture fixtureDef = *b->GetFixtureList();
        //b2Filter filter = fixtureDef.GetFilterData();

        // how to get b2FixtureDef from b

    }
}

Answer 1

Actually, i cannot imagine why do you need to get this info in your update method. You cannot get fixtureDef, as it is used for fixture creation only. But you can get filter data for each body fixture using GetFilterData() method. It will contain category bits, mask bits and group index.