Top Down 2D: How to make a game perimeter that keeps objects inside

Questions & Answers
1

I’m attempting to make a (very simple to begin with) top-down game in 2D wherein the player (using arrow keys) is able to move around an enclosed polygonal area of the game. I’m having trouble ensuring that all parts of the area’s perimeter (made of a polygonal collider) are impenetrable (areas near corners tend not to be for some reason). Code below:

public float speed = 40f;
public bool heTouchedTheButt = false; //test whether the player is colliding with the perimeter

void OnCollisionEnter2D(Collision2D coll) {

	if (coll.gameObject.name == "Perimeter")
		heTouchedTheButt = true;
}

void OnCollisionExit2D(Collision2D coll) {
	
	if (coll.gameObject.name == "Perimeter")
		heTouchedTheButt = false;
}

void FixedUpdate (){
	if (!heTouchedTheButt) {
		if (Input.GetKey (KeyCode.LeftArrow)) {
			transform.position += Vector3.left * speed * Time.deltaTime;
		}
		if (Input.GetKey (KeyCode.RightArrow)) {
			transform.position += Vector3.right * speed * Time.deltaTime;
		}
		if (Input.GetKey (KeyCode.UpArrow)) {
			transform.position += Vector3.up * speed * Time.deltaTime;
		}
		if (Input.GetKey (KeyCode.DownArrow)) {
			transform.position += Vector3.down * speed * Time.deltaTime;
		}
	} else if (heTouchedTheButt) {
		if (Input.GetKey (KeyCode.RightArrow)) {
			transform.position += Vector3.left * speed * Time.deltaTime;
		}
		if (Input.GetKey (KeyCode.LeftArrow)) {
			transform.position += Vector3.right * speed * Time.deltaTime;
		}
		if (Input.GetKey (KeyCode.DownArrow)) {
			transform.position += Vector3.up * speed * Time.deltaTime;
		}
		if (Input.GetKey (KeyCode.UpArrow)) {
			transform.position += Vector3.down * speed * Time.deltaTime;
		}
	}
}

I figured setting the keys to be inversed when the player is in contact with the perimeter would allow them to come out of contact, but this appears to work only some of the time. Other times, the controls get stuck in the inverse and others allow the player to go right past the boundary as if it weren’t there. I feel like there’s a more efficient way to set up this boundary, and I appreciate any insight on how to make this easier.

2

Hi cecilfuel95,

You are probably encountering this problem because you are assigning transform.position. This is actually more like teleporting rather than moving. So if transform.position += Vector3.down * speed * Time.deltaTime happens to be on the other side of the collider, Unity dosent have a problem teleporting it to that position.

If I was you, I would give the game object your moving a Rigidbody or Rigidbody2D. And then do something like:

public float speed;

private Rigidbody2D rigidbody;

private void Awake()
{
    rigidbody = GetComponent<Rigidbody2D>();
}

private void FixedUpdate()
{
    if(Input.GetKey(KeyCode.RightArrow))
    {
        rigidbody.velocity = (Vector2.right * speed);
    }
}

Since this involves physics, use FixedUpdate(). You don’t have to worry about Time.deltaTime here. Let me know if that works out for you.