A fast, easy to use, free, and community supported 2D game engine
lmauri
Member
I'm using last cocos2d release with box2d and I need to get the contact point of a collision between two bodies.
Now I've just implemented the contact listener class and I've a b2contact parameter.
From that I can retrieve the b2manifold but I'm not sure if that's correct and my question is how to get the point of contact here and how to discriminate between the contact point for each body.
It looks like the TestBed Presolve function by Simon Oliver collects contact points from the world manifold. That code is:
void PreSolve(b2Contact* contact, const b2Manifold* oldManifold) {
const b2Manifold* manifold = contact->GetManifold();
if (manifold->m_pointCount == 0)
{
return;
}
b2Fixture* fixtureA = contact->GetFixtureA();
b2Fixture* fixtureB = contact->GetFixtureB();
b2PointState state1[b2_maxManifoldPoints], state2[b2_maxManifoldPoints];
b2GetPointStates(state1, state2, oldManifold, manifold);
b2WorldManifold worldManifold;
contact->GetWorldManifold(&worldManifold);
for (int32 i = 0; i < manifold->m_pointCount && m_pointCount < k_maxContactPoints; ++i)
{
ContactPoint* cp = m_points + m_pointCount;
cp->fixtureA = fixtureA;
cp->fixtureB = fixtureB;
cp->position = worldManifold.m_points[i];
cp->normal = worldManifold.m_normal;
cp->state = state2[i];
++m_pointCount;
}
}cp->position = worldManifold.m_points[i];
cp->normal = worldManifold.m_normal;...provide the contact direction and position of colliding objects. So the trick might be to copy that into a variable and choose which contacts you want.
In my code I'm looking into user data to find out what's colliding. These are reported as fixtureA and fixtureB at the start of the code. Both need to be tested for the object you look for. With the fixture you can also get the body attached.
I hope this helps!
You must log in to post.