In box2d for iOS, how to find the distance between two circular bodies?

Question

I am using the following code to get the distance between two circular bodies of different radius:

distance = b2Distance(body1->GetPosition(), body2->GetPosition());

I have realized that variable distance is storing the distance between the two centers of the bodies, but not the distance between the borders. What I want is distance=0 when the two bodies are touching.

How can I do that? I've been trying this code but it fails:

b2DistanceInput *distanceInput;
distanceInput->transformA = body1->GetTransform();
distanceInput->transformB = body2->GetTransform();
b2DistanceProxy *proxyA;
proxyA->Set(fixtureBody1->GetShape(), 1);
b2DistanceProxy *proxyB;
proxyB->Set(fixtureBody2->GetShape(), 1);
distanceInput->proxyA = *proxyA;
distanceInput->proxyB = *proxyB;
b2DistanceOutput *theDistance;
b2SimplexCache *cache;
cache->count = 0;
b2Distance(theDistance, cache, distanceInput);

The getShape method is giving a bad access error within the b2box code.

Any ideas?

Thanks,

GA

Answer 1

Try use this code - it work for me:

b2DistanceInput *distanceInput = new b2DistanceInput();
b2DistanceProxy *proxyA = new b2DistanceProxy();
b2DistanceProxy *proxyB = new b2DistanceProxy();
b2SimplexCache *cache = new b2SimplexCache();
b2DistanceOutput *theDistance = new b2DistanceOutput();

proxyA->Set(fixtureBody1->GetShape(),1);
proxyB->Set(fixtureBody2->GetShape(),1);

distanceInput->transformA = body1->GetTransform();
distanceInput->transformB = body2->GetTransform();
distanceInput->proxyA = *proxyA;
distanceInput->proxyB = *proxyB;
distanceInput->useRadii = true;

cache->count = 0;

b2Distance(theDistance, cache, distanceInput);