Recommended Approach to multiple colliders

Question

I am have some difficulty with what is probably a very silly thing. I have an enemy gameobject that depending on where it is hit (collision) - either it, or the play dies. I think the simplest way to describe this is by using the classic Super Mario Bros. game as an example.

As you all know, if the player runs into the enemy - the player will lose - UNLESS he jumps on top of the enemy's head, in which case the enemy should die.

My initial idea was to create two colliders on the gameobject:

1. Blue border represents a BoxCollider2D - that if collided with - will cause player to lose (notice it is slightly lower from the top)
2. Green border represents a BoxCollider2D on a child gameobject - that if collided with - will cause the gameobject to die.

The following is a simplified version of the code I used:

    // Collider #1
    public void OnCollisionEnter2D(Collision2D collision)
    {
        // Trigger 'Game-Over' logic
    }

    // Collider #2
    public void OnCollisionEnter2D(Collision2D collision)
    {
        if (collision.gameObject.tag == "Player")
        {
            Destroy(this.gameObject);
        }
    }

This kind-of works, however momentarily after colliding with Collider #1, Collider #2 is also trigger - and while the enemy is destroyed, the player also loses.

I have been playing with the RigidBody2D values to prevent the player from entering the 2nd collider when hitting the enemy from the top - but apparently with that force / speed, the colliders may be slightly inaccurate (or maybe I'm just doing it wrong?).

I have looked into RayCasts but this seems too complex for something that me appears rather trivial (casting rays on all four sides and four vertices of the player - assuming that the player has a box collider).

What I have resorted to 'for the moment' is a a single collider with a simple piece of code that I am unhappy with, and doesn't always work:

    public void OnCollisionEnter2D(Collision2D collision)
    {
        if (collision.gameObject.tag == "Player")
        {
            float yVelocity = collision.gameObject.transform.rigidbody2D.velocity.y;

            if (yVelocity < 0)
            {
                Debug.Log("Enemy will lose..." + yVelocity);

                Destroy(this.gameObject);
            }
            else
            {
                // Trigger 'Game-Over' logic
            }
        }
    }

I'm currently working in 2D mode, but solutions for 3D mode (while maybe more complicated than necessary for my question) will also be considered.

Thanks guys.

Answer 1

as a game developer you always have many ways to solve a problem or make a gameplay. first of all i have to say you should make a polygon collider 2d fo you objects and chracters. just colliding pictures is not very good as i see you used box cilliders in your game.

a good choice can be that you attach and empty object ot you player and set its position under foots of you player and check of enemy hit that enemy dies else if enemy hit main character object, player dies.

another choice can be when o objects collide check y position of 2 objects. of player was higher he kiils, else enemy kills the player.

if you think more you will find more answers. you have to examin diffrent ways and find most efficient.

Answer 2

I think it will be easy to disable the other collider when one is triggered. You can easily enable/disable colliders with collider.enabled = true; or collider.enabled = false;

// Collider #1
public void OnCollisionEnter2D(Collision2D collision)
{
    // Trigger 'Game-Over' logic
    // collider2.enabled = false;
}

// Collider #2
public void OnCollisionEnter2D(Collision2D collision)
{
    // collider1.enabled = false;
    if (collision.gameObject.tag == "Player")
    {
        Destroy(this.gameObject);
    }
}

This way it will be pretty lightweight and easy to implement.

Answer 3

One way of implementing what you want is to put each collider in its child own game object and use the IsTouching() method.

void OnTriggerEnter2D(Collider2D other){
    if(GameObject.Find("Top Trigger").GetComponent<BoxCollider2D>().IsTouching(other)){
        Destroy(transform.gameObject)
    }
    if(GameObject.Find("Bottom Trigger").GetComponent<BoxCollider2D>().IsTouching(other)){
        Destroy(other.gameObject)
    }
}