CODEWITHSUNDEEP
c++openglbox2dcollision-detection
Vector
Vector

Reputation: 172

Box2D: program crashes on destroying a b2Body

I am learning collision detection and callbacks with box2D. I am trying to implement a very simple thing but my program crashes. I want to destroy b2Body* Drop_object after it gets collided with another Body.

This is how I have created it:

b2Body* addDropObj(int x,int y,int w,int h,bool dyn=true)
{
b2BodyDef bodydef;  
bodydef.position.Set(x*P2M,y*P2M);   //Setting body position
if(dyn)
{
        bodydef.type=b2_dynamicBody;  // dynamic body means body will move

}

Drop_object=world->CreateBody(&bodydef);        //Creating box2D body

b2PolygonShape shape;            //Creating shape object
shape.SetAsBox(P2M*w,P2M*h);


dropFixture.shape=&shape;
dropFixture.density=1.0;
dropFixture.restitution = 0.7; 
Drop_object->CreateFixture(&dropFixture);
return Drop_object;
}

Calling in Timer function:

    void Timer(int t)
    {

   if (mCounter == 0)
   {
            // rand() % 100 - random value in range 0 - 99
        addBrick(rand() % 100 + 100, 0,10,10);

        mCounter = rand() % MAX_DELAY;
    }
    mCounter--;

        world->Step(1.0/30.0,8,3);

        glutPostRedisplay();
        glutTimerFunc(1000/30,Timer,1);

    }

Destroying In display Function

if(hide)                 //hide is a global boolean variable initialized to false
{
world->DestroyBody(Drop_object);
hide = false;
}

And finally the Begincontact function:

    void Callback::BeginContact(b2Contact* contact)
    {


    std::cout << "Begin Contact" << std::endl;

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



    if((bodyA == Key_char && bodyB ==  Drop_object) || (bodyA == Drop_object && bodyB     ==  Key_char))
    {   

        score++;
        std::cout << score << std::endl;
    }

    hide= true;

}

It takes me to the b2World DestroyBody method with an arrow pointing at

je = je->next

Upvotes: 1

Views: 441

Answers (1)

Pavel
Pavel

Reputation: 2554

You are setting hide to true in any call of BeginContact. I think, you mean this:

if((bodyA == Key_char && bodyB ==  Drop_object) || (bodyA == Drop_object && bodyB     ==  Key_char))
{   

    score++;
    std::cout << score << std::endl;
    hide= true; 
}

And, as recomendation:

world->DestroyBody(Drop_object);
Drop_object = nullptr; // To avoid future errors

Answer to comment: I think some bodies do not vanish after collision because you are using one varible for all generated bodies. Suggest next sequence:

1) Drop_object=world->CreateBody(&bodydef);
2) Drop_object=world->CreateBody(&bodydef); // First object still falling
3) world->DestroyBody(Drop_object); // Second object contacted, and destoryed
// First object will never be destroyed

Upvotes: 2

Related Questions