changing box2d body shapes dynamically

Question

Is it possible to change the shape of a Box2d b2Body dynamically? I want to do this to achieve the following.

i). Increasing the radius of a circle shape at a certain rate

ii). Changing the dimensions of a bounding box for a sprite to match the changing animation frames.

Concord

You can't change the shape of box2d b2body dynamically, but you can achieve that by destroying and recreating the b2body. – Shrewmouse

you only need to recreate the fixture, not the whole body – Presswork

Yes my mistak, i was about to say but wrote b2body. You just have to recreate fixture only. – Shrewmouse

@LearnCocos2D: +1 for an example on this. – Concord

Answer 1

   float radius;
   radius = 1;

Create body:

b2BodyDef bodyDef;
bodyDef.type = b2_dynamicBody;
bodyDef.position.Set(300/PTM_RATIO, 150/PTM_RATIO);
body = world->CreateBody(&bodyDef);

b2CircleShape circleShape;
circleShape.m_radius = radius;

b2FixtureDef fixtureDef;
fixtureDef.shape = &circleShape;
fixtureDef.density = 1;
fixtureDef.friction = 0.3f;
body ->CreateFixture(&fixtureDef);

In your touch method:

  - (void)ccTouchesEnded:(NSSet *)touches withEvent:(UIEvent *)event
   {  

    if (body != NULL) {

    b2Fixture *fixtureA = body->GetFixtureList();
    body->DestroyFixture(fixtureA);

    b2CircleShape circleShape;
    circleShape.m_radius = radius + 0.3; 

    b2FixtureDef fixtureDef;
    fixtureDef.shape = &circleShape;
    fixtureDef.density = 1;
    fixtureDef.friction = 0.3f;
    body->CreateFixture(&fixtureDef);

    radius = radius + 0.3;

   }

With every touch body will become bigger for 0.3.

Syncytium