2D C++ Box collision response

[wrymn]

Hi, I am really big noob and I cannot really write this part of code.
I need to write collision detection response on 2D box colliders(AABB), so no rotation involved.

Here is my function, please could you incorportate collision response into it? I`ve been trying for past 5 hours and nothing.

void BoxCollider::BoxVsBox(Collider* collider)
	{
		UpdateColliderSize();//Function will just update width and height variable of collider

		//Get other Box collider
		BoxCollider* otherBoxCollider = dynamic_cast<BoxCollider*>(collider);
		otherBoxCollider->UpdateColliderSize();

		//Check if colliders collide
		if (gameObject->transform->position.x + width > otherBoxCollider->gameObject->transform->position.x &&
			gameObject->transform->position.x < otherBoxCollider->gameObject->transform->position.x + otherBoxCollider->width &&
			gameObject->transform->position.y + height > otherBoxCollider->gameObject->transform->position.y &&
			gameObject->transform->position.y < otherBoxCollider->gameObject->transform->position.y + otherBoxCollider->height)
		{

                      //We have a collision, need collision response for both objects here, so both move from each others side depends on collision depth
                }
}

Thanks.

[CodeWriter]

.

[dhayden]

To make code easier to read and write, consider using references. When doing this, I like to add the comment //shorthand to make it clear why I'm creating the reference. Your example could be rewritten like this:

Position & gamePos(gameObject->transform->position); // shorthand
Position & otherPos(otherBoxCollider->gameObject->transform->position) //shorthand
if (gamePos.x + width > otherPos.x &&
    gamePos.x < otherPos.x +otherBoxCollider->width &&
    gamePos.y + height > otherPos.y &&
    gamePos.y < otherPos.y + otherBoxCollider->height) ....

Your code will fail if one box is contained completely within the other. It's easier to write code that detects if the boxes *don't* intersect. Then just invert it to see if they *do* intersect.

Two boxes b1 and b2 don't intersect if:

b1.top < b2.bottom // b1 below b2
|| b2.top < b1.bottom // b2 below b1
|| b1.right < b2.left // b2 to the right of b1
|| b2.right < b1.left // b1 to the right of b2 

When translating this to your code, be sure to consider off-by-one errors.

[wrymn]

Thanks you dhayden, this is really helpfull when I will be structuring my code.

At least I won`t have to do this for example:

otherBoxCollider->gameObject->transform->position.x

but rather with dots as in other langauges.

otherBoxCollider.gameObject.transform.position.x

Also, it is better to have more reference variables or pointer variables? Because I always just use pointsers e.g.

GameObject* gameObject;
GameObject* parent;
Transform* transform;
Scene* scene;

Or is it better to have references rather? It`s true I wouldn`t have to use ->. When is it appropriate for variable to be rather reference than pointer?

[dhayden]

If you know it won't be null then use a reference.