How to get collision position in box2d

Question

What's the best way to get the point of collision in box2d. I'm using it with cocos2d and Objective C, but I imagine the API is similar in other languages. Using the b2ContactListener class will produce b2Contact objects, but I can't find any information on the contact position.

i think the [Demo](http://www.raywenderlich.com/606/how-to-use-box2d-for-just-collision-detection-with-cocos2d-iphone) would work for you! — Marine, Dec 23 '11 at 12:48
Thanks, I've gone through this a while back. I'm using b2Body's so detecting the collisions is still easy. — Aram Kocharyan, Dec 24 '11 at 04:48

score 0 · Answer 1 · edited Dec 23 '13 at 10:45

0

You can use the following code to get the point of collision

b2Body *bodyA = contact->GetFixtureA()->GetBody();
b2Body *bodyB = contact->GetFixtureB()->GetBody();

if ((bodyA->GetFixtureList()->GetFilterData().categoryBits == Categorybits1 || bodyA->GetFixtureList()->GetFilterData().categoryBits == categoryBits2) && (bodyB->GetFixtureList()->GetFilterData().categoryBits == categoryBits2 || bodyB->GetFixtureList()->GetFilterData().categoryBits == Categorybits1))

You can get body positions through this code.....

even i am searching how to get point of collision

edited Dec 23 '13 at 10:45

Aram Kocharyan

20,165
11
81
96

answered Dec 23 '13 at 09:33

Umesh Sharma

388
5
23

Cheers for that - I haven't really returned to this since 2011 though - hopefully it's useful to others. – Aram Kocharyan Dec 23 '13 at 10:45

score 0 · Answer 2 · answered Dec 27 '13 at 20:23

try this method

OBJECT1_CATEGORY_BITS = 0x00000001;
OBJECT2_CATEGORY_BITS = 0x00000002;

void MyContactListener::PreSolve(b2Contact *contact, const b2Manifold
*oldManifold) 
{
    b2Fixture *fixtureA = contact->GetFixtureA();
    b2Fixture *fixtureB = contact->GetFixtureB();

    b2Filter filterA = fixtureA->GetFilterData();
    b2Filter filterB = fixtureB->GetFilterData();

    if ((filterB.categoryBits == OBJECT1_CATEGORY_BITS) && (filterA.categoryBits == OBJECT2_CATEGORY_BITS))
    {
        b2Vec2 normal = contact->GetManifold()->localNormal;

        NSLog(@"pointX : %f",normal.x);
        NSLog(@"pointY : %f",normal.y);
    } 
}

How to get collision position in box2d

2 Answers2