I’m using Box2D and rebounding a box whenever it hits the bottom or top of the screen. I’m using world positions here; the maximum is 20.0f which is the value of boundarySize:

void Game::ClampScreenY( Box* pBox)
{
    bool isColliding = false;
    auto pos = static_cast<b2Vec2>( pBox->GetPosition() );
    auto aabb = pBox->GetAABB();
    auto angle = pBox->GetAngle();


    if( aabb.upperBound.y >= boundarySize )
    {
        pos.y = boundarySize - boxSize;
        isColliding = true;
    }
    else if( aabb.lowerBound.y <= -boundarySize  )
    {
        pos.y = -boundarySize + boxSize;
        isColliding = true;
    }
    
    if( isColliding && !pBox->GetWasColliding())
    {
        auto vel = static_cast<b2Vec2>( pBox->GetVelocity() );
        vel.y *= -1;
        pBox->SetVelocity( vel );
        pBox->SetPosition( pos );
    }

    // update
    pBox->SetWasColliding( isColliding );
}

I’ve been testing this on a box with angularVelocity = 0 and angle = 0 and it works. However this rebound effect is not working for boxes that are rotating or that have an angle != 0. Why is this happening? I’m getting out of bounds drawing. There’s obviously something wrong with this math.

Angle = 0 works fine and rebounds perfectly:

Angle != 0 crashes:

The ClampScreenY function is called in the UpdateModel function I created, which is responsible for updating the logic of the game.

After the game calls the UpdateModel, it calls the ComposeFrame which draws all objects (I just have one here):

void Game::ComposeFrame()
{
       auto vertices = box->GetVertices(); // for debugging
       box->Draw();
}

The call to box->Draw() crashes when colliding with top of the window in the situation of the second image (when angle != 0). Taking a look at the 4 vertices’ values, I see that:

vertex[2] {
    x=-0.651163101 
    y=20.7524509 
}

So y > boundarySize. This shouldn’t be happening since the Clamp function was supposed to take care of this. What gives?

Maybe when I call SetPosition, it only updates the box in the next iteration?