If you remember, right after we created the world, we called its SetContactListener function and passed in a reference to GameWorld. We could do this because our GameWorld class inherits not only from CCLayer, but also from b2ContactListener. As a result of this, GameWorld can receive information about any and all pairs of fixtures colliding by implementing the BeginContact function as follows:
void GameWorld::BeginContact(b2Contact *contact)
{
b2Body* body_a = contact->GetFixtureA()->GetBody();
b2Body* body_b = contact->GetFixtureB()->GetBody();
// only need to observe collisions that involve GameObjects
if(body_a->GetUserData() == NULL || body_b->GetUserData() == NULL)
{
return;
}
// identify type of the objects involved in the collision
EGameObjectType game_object_a_type =
((GameObject*)body_a->GetUserData())->GetType();
EGameObjectType game_object_b_type =
((GameObject*)body_b->GetUserData())->GetType...