Box2d collisions assert error

Question

I'm using AndEngine anchor-center branch so I can't use PhysicsEditor to create bodies/fixtures since the only parser PhysicsEditor-AndEngine it's a bit out of date and doesn't support anchor-center, so I thought I could use R.U.B.E instead and it's AndEngineRubeLoaderExtension. So far so good, I can create my bodies with all their complex fixtures because RUBE will divide them into convex polygons (automatically).

The parser works great and I've my body. but I'm running into some collision errors:

A/libc﹕ jni/Box2D/Dynamics/Contacts/b2ContactSolver.cpp:72: b2ContactSolver::b2ContactSolver(b2ContactSolverDef*): assertion "pointCount > 0" failed

A/libc﹕ Fatal signal 11 (SIGSEGV) at 0xdeadbaad (code=1), thread 32158 (UpdateThread)

The body it's an airplane. If I use RUBE model I get this exception when I collide with multiple objects (the user has to catch some coins and diverge from enemies (RUBE models too)), instead, if I use a BoxBody everything works great.

Makes me wonder if it isn't related to non convex polygons witch compose the body (even though RUBE creates them correctly)... Happened to anyone?

Thanks.

EDIT: I forgot to say that I'm creating my bodies with RUBE but I'm not using the world created by RUBE when I was creating that body, so here's the code I use to create that body inside my world:

private Body createPolygonBody(PhysicsWorld pPhysicsWorld, IShape pShape, BodyDef.BodyType pBodyType, FixtureDef pFixtureDef, Jb2dJsonLoader jsonLoader, String fixtureName) {
        BodyDef boxBodyDef = new BodyDef();
        boxBodyDef.type = pBodyType;

        float[] sceneCenterCoordinates = pShape.getSceneCenterCoordinates();
        boxBodyDef.position.x = sceneCenterCoordinates[Constants.VERTEX_INDEX_X] / PhysicsConstants.PIXEL_TO_METER_RATIO_DEFAULT;
        boxBodyDef.position.y = sceneCenterCoordinates[Constants.VERTEX_INDEX_Y] / PhysicsConstants.PIXEL_TO_METER_RATIO_DEFAULT;

        Body rubeBody = jsonLoader.getBodyByName(fixtureName);
        Body boxBody = pPhysicsWorld.createBody(boxBodyDef);
        // boxBody.setTransform(rubeBody.getPosition(), rubeBody.getAngle());
        boxBody.setLinearVelocity(rubeBody.getLinearVelocity());
        boxBody.setLinearDamping(rubeBody.getLinearDamping());
        boxBody.setAngularVelocity(rubeBody.getAngularVelocity());
        boxBody.setAngularDamping(rubeBody.getAngularDamping());
        boxBody.setSleepingAllowed(rubeBody.isSleepingAllowed());
        boxBody.setAwake(rubeBody.isAwake());
        boxBody.setFixedRotation(rubeBody.isFixedRotation());
        boxBody.setBullet(rubeBody.isBullet());
        boxBody.setActive(rubeBody.isActive());
        boxBody.setMassData(rubeBody.getMassData());

        Fixture[] bodyFixtures = jsonLoader.getFixturesByName(fixtureName);
        for (int i = 0; i < bodyFixtures.length; i++) {
            FixtureDef fixtureDef = pFixtureDef;
            fixtureDef.shape = bodyFixtures[i].getShape();
            boxBody.createFixture(fixtureDef);
        }
        return boxBody;
    }

And maybe here lies the problem. Am I doing everything correct?

EDIT2: So I've replaced this code:

private void performCoinCollision(boolean coinIsBodyA, Contact contact) {
    if (coinIsBodyA) {
       contact.getFixtureA().setSensor(true);
    } else {
       contact.getFixtureB().setSensor(true);
    }
    contact.setEnabled(false);
    ...
}

with:

private void performCoinCollision(boolean coinIsBodyA, Contact contact) {
    if (coinIsBodyA) {
       elementsToBeRemoved.add(contact.getFixtureA().getBody());
    } else {
       elementsToBeRemoved.add(contact.getFixtureB().getBody());
    }
    contact.setEnabled(false);
...
}

and added this onUpdate to physicWorld:

@Override
public void onUpdate(float pSecondsElapsed) {
    if (elementsToBeRemoved != null) {
        for (Body body : elementsToBeRemoved) {
            if (body != null) {
                physicsWorld.destroyBody(body);
            }
        }
    }
    elementsToBeRemoved.clear();
}

The problem still persists.

Are all the objects made with RUBE? Does it work ok in the RUBE built-in player? — iforce2d, Aug 04 '14 at 07:32
@iforce2d yes all objects are made with RUBE and it works in the built-in player. The airplane and enemies are "complex" bodies but the coins are simple circle fixtures. — GuilhE, Aug 04 '14 at 10:01
Then if there was some fundamental problem with the shapes, I would expect the RUBE player to crash as well. Does the problem occur when you don't remove the coins from the world? You are not changing the world inside the contact listener callbacks are you? — iforce2d, Aug 04 '14 at 15:51
No I'm not changing the world and I don't remove the coins from it. When a collision is detected between airplane-coin what I do is setting the coin fixture sensor = true. Could be that? — GuilhE, Aug 04 '14 at 16:18
You should not be changing anything about the world inside the contact listener callbacks. If you are doing the sensor = true thing inside one of the callbacks, it could indeed be the problem. Easy way to find out is to try not doing it :) — iforce2d, Aug 05 '14 at 01:52
@iforce2d makes sense :) So how should I achieve this behaviour, after a coin being caught I want to deactivate its contact. What's the correct way? — GuilhE, Aug 05 '14 at 09:51
Make a note of what needs to be done, and do it after the Step has finished. — iforce2d, Aug 05 '14 at 15:49
@iforce2d thanks .setSensor(true) inside physicWorld.onUpdated works great. I'm still having a doubt (I've updated my question again) if I want to remove the body shouldn't be onUpdate too? It's failing with the same exception. — GuilhE, Aug 05 '14 at 17:56

GuilhE · Accepted Answer · 2014-08-06T09:31:25.493

I've followed iforce2d advice, which is the correct procedure, and now it's working:

private void performCoinCollision(boolean coinIsBodyA, Contact contact) {
    if (coinIsBodyA) {
       elementsToBeRemoved.add(contact.getFixtureA());
    } else {
       elementsToBeRemoved.add(contact.getFixtureB());
    }
    contact.setEnabled(false);
...
}

...

@Override
public void onUpdate(float pSecondsElapsed) {
    if (elementsToBeRemoved != null) {
        for (Fixture fixture : elementsToBeRemoved) {
             fixture.setSensor(true);
        }
    }
    elementsToBeRemoved.clear();
}

Note: in my EDIT2 I'm doing the same approach but instead of setSensor(true) I'm trying to remove the body. That approach was failing too, don't know why.

EDIT: Problem was that I was trying to destroy an already destroyed body. The solution is to make sure that elementsToBeRemoved has no duplicated bodies

Make sure elementsToBeRemoved does not contain duplicates. You can do this pretty easily by making it a set instead of a vector. — iforce2d, Aug 06 '14 at 01:11

Box2d collisions assert error

1 Answers1