Box2D, Contact Listener: Never calling BeginContact

Question

I've been trying to implement Box2D into this code, and I've been extremely stuck on this. I've searched high and low for an answer but could not find anything that would fix this problem. I looked at guides and tried fixes that helped other users such as doing b2World->SetAllowSleeping(false).

I start by creating the world and setting the contact listener. The World class contains the b2World, therefore I get the world and set the contact listener. To add, both pointers are stored within a scene class.

    m_World = new World();
    m_ContactListener = new ContactListener(m_World);

    m_World->GetB2World()->SetContactListener(m_ContactListener);

I return the pointer and store it in my scene just in case it will be necessary later on.

My Contact Listener class is basically just the basics that every tutorial has said. I put a few lines of code into the BeginContact() to put a break point and try to see if it's working but so far it has not been working.

Here is the ContactListener.h:

#pragma once
class ContactListener : public b2ContactListener
{
private:
    World* m_World;
public:
    ContactListener(World* aWorld);
    ~ContactListener();`

    virtual void BeginContact(b2Contact* aContact);
    virtual void EndContact(b2Contact* aContact);

    void SetWorld(World* aWorld) { m_World = aWorld; }
    World* GetWorld() { return m_World; }
};

And here is the ContactListener.cpp file: #include "pch.h"

ContactListener::ContactListener(World* aWorld)
{
    m_World = aWorld;
}

ContactListener::~ContactListener()
{

}

void ContactListener::BeginContact(b2Contact* aContact)
 {
    b2Fixture* fixtureA = aContact->GetFixtureA();
    b2Fixture* fixtureB = aContact->GetFixtureB();

    void* userDataA = fixtureA->GetUserData();
    std::string nameA = ((GameObject*)userDataA)->GetName();

    void* userDataB = fixtureB->GetUserData();
    std::string nameB = ((GameObject*)userDataB)->GetName();
}

void ContactListener::EndContact(b2Contact* aContact)
{

}

Like I said previously I added lines of code just to try and put a break point. The guides I read said to simply override the functions and everything should work. Any help with this issue would be appreciated and if you need anymore info I will gladly add any.

For the bodies, I have created two. One static and one dynamic.

Here's the function I use to create the bodies:

b2Body* World::CreateBody(b2Vec2 aPosition, float aRotation, BodyType aType,          GameObject* aOwner)
{
    b2BodyDef bodyDef;
    bodyDef.position = aPosition;
    bodyDef.angle = aRotation;

    if (aType == KinematicBody)
    {
        bodyDef.type = b2_kinematicBody;
    }
    else if (aType == DynamicBody)
    {
        bodyDef.type = b2_dynamicBody;
    }
    else
    {
        bodyDef.type = b2_staticBody;
    }

    bodyDef.userData = aOwner;

    return m_b2World->CreateBody(&bodyDef);
}

Then after I create the two bodies I was previously talking about:

    ((PlayerObject*)m_pGameObjects["Floor"])->AddBody(m_World->CreateBody(aPosBlock, aRotationBlock, World::BodyType::StaticBody, m_pGameObjects["Floor"]));
    ((PlayerObject*)m_pGameObjects["Player"])->AddBody(m_World->CreateBody(aPos, aRotation, World::BodyType::DynamicBody, m_pGameObjects["Player"]));

In your first code, you return a pointer to "temp", but temp goes out of the scope when your function exit. — lolando
I was pretty sure it did this. That's actually a backup function I wrote after looking up a different guide. My original has a contact listener pointer in the scene and then I create a new instance of it. — Temunish
As lolando said, your code shown has temp going out of scope. Please correct that and retry. If still the same results, then please edit your question to show your corrected code that you believe no longer has data being used out of scope. If it works however, please explain this fix in the answer section so this question won't show up as unanswered anymore. Thanks! — Louis Langholtz
Looks like the out-of-scope code got edited away. Cool. Now please show code that demonstrates the bodies that are created and the dynamics done with them that should be invoking the contact listener. — Louis Langholtz

Temunish Temunish · Accepted Answer · 2017-03-05T17:26:51

I took a look at my code once again and the tutorials and have figured out that my issue was missing fixtures. Just goes to prove that if you try to rush your code you'll always miss something. Thanks to everyone who had tried to help me with this issue.

Box2D, Contact Listener: Never calling BeginContact

1 Answers