Question

I am writing a GameActivity of a swinging pendulum (in AndEngine).

While applying CollisionHandler, this will produce a series of collision events in the instead of one?? Actually, I’d like it is executed once only when sprites collide.

My case: when the movingBall collides with the mLeftWall, it called 5 times of onCollision(); It was abnormal, I expected only one time.

Should I use ContactListener instead and register with PhysicsWorld? Here’s my Code:

MyGameActivity.java:

/** List of objects to check collision of any animating objects. E.g: walls  */
private ArrayList<IShape> mCollidingTargetList = new ArrayList<IShape>();

/** user-defined collision handler */
PendulumCollisionCallback collideActionCallback = new PendulumCollisionCallback();

@Override
public Scene onCreateScene() 
{
    final Scene scene = super.onCreateScene();

    final VertexBufferObjectManager vertexBufferObjectManager = this.getVertexBufferObjectManager();

    //Create walls
    mWallLeft = new Rectangle(0, 0, 2, mCameraHeight, vertexBufferObjectManager);
    mWallRight = new Rectangle(mCameraWidth - 2, 0, 2, mCameraHeight, vertexBufferObjectManager);
    PhysicsFactory.createBoxBody(mPhyscisWorld, mWallLeft, BodyType.StaticBody, mWallFixtureDef);
    PhysicsFactory.createBoxBody(mPhyscisWorld, mWallRight, BodyType.StaticBody, mWallFixtureDef);
    scene.attachChild(mWallLeft);
    scene.attachChild(mWallRight);

    //Create movingBall - the pendulum ball
    final AnimatedSprite movingBall = new AnimatedSprite(mCenterX, mCenterY, this.mCircleFaceTextureRegion, this.getVertexBufferObjectManager());
    final Body ballBody = PhysicsFactory.createCircleBody(this.mPhysicsWorld, movingBall, BodyType.DynamicBody, mObjectFixtureDef);
    movingBall.setUserData(ballBody); // for getting the body attached with UI

    //..... Stuff to create anchorBody and RevoluteJoint with the movingBall

    //list of bodies where sprites collide
    this.mCollidingTargetList.add(mWallLeft);
    this.mCollidingTargetList.add(mWallRight);

    //Manage user-defined collision handler: movingBall collides with walls
    CollisionHandler pendulumCollideHandler = new CollisionHandler(collideActionCallback, movingBall, mCollidingTargetList);
    scene.registerUpdateHandler(pendulumCollideHandler);

    return scene;
}

PendulumCollisionCallback.java:

public class PendulumCollisionCallback implements ICollisionCallback
{
    public PendulumCollisionCallback()
    { }

    /**
     * @param animatedShape
     *      Entity to check collision with other targets
     * @param pTargetShape
     *      Target to check the collision
     * @return <code>true</code> to proceed, <code>false</code> to stop further collosion-checks.
     */
    @Override
    public boolean onCollision(IShape animatedShape, IShape pTargetShape) 
    {
        String pendulPos = String.format("Pendul:x=%f, y=%f", animatedShape.getX(), animatedShape.getY());      
        Log.d("COLLIDE", pendulPos);
        return false;
    }
}

Answer 1

I found the issue. This is because of separated Physics Handler and Scene’s UpdateHandler work sequence.

While PhysicsWorld is still controlling body collision, the body is still moving forward for a few frames => so that the position of UI sprite (attached with this body) is in junction with colliding object. During these frames, the updateHandler produces collision events by CallbackHandler.

The solution is a tricky method of adding Boolean flag which is set at first colliding and unset when finish colliding (though this is not nice).

P/S: my frame rate observed form FPSLogger is ~88,9 FPS.