Unity: Finding Side that a 2D Collision Occurs On - unity3d

Question

I am working on a 2D Game. I am detecting when an object collides with the player, but I am getting a little stuck trying to find which side it is colliding on. I want to be able to rotate the player to face either Left, Right, Up, or Down towards the object it collided with. How can I find which side the object collided on so that I can then rotate the player accordingly?
I am using a Rigidbody2D on the player and 2D Colliders, I am able to find the point that it collides with the player using Collider2D.ClosestPoint() but am unsure how to proceed. Thank you for the help.

Answer 1

So once you have the hit point
var hitPoint = collider.ClosestPoint();
// Instead of the transform.position the collider.bounds.center is often more accurate
var playerPosition = collider.bounds.center;
You could e.g. take the direction between those and check where it hits relative to the player like e.g.
var dir = hitPoint - playerPosition;
var angle = Vector2.SignedAngle(transform.right, dir);
// Now check the angle
if(Maths.Abs(angle) <= 45)
{
Debug.Log("hit right");
}
else if(angle > 45 && angle <= 135)
{
Debug.Log("hit top");
}
else if(angle < 45 && angle >= -135)
{
Debug.Log("hit bottom");
}
else
{
Debug.Log("hit left");
}

Answer 2

The simplest solution I see is that you first get the size of the player 2D collider with BoxCollider2D.size. Then you create a simple block of if statements to check on which side is the hit point based on the player position.
Something like this should work:
var size = collider.size;
var hitPoint = collider.ClosestPoint();
var playerPosition = transform.position;
if (hitPoint.x >= playerPosition + size.x/2)
// hit on the right
else if (hitPoint.y >= playerPosition + size.y/2)
// hit on the top
else if (hitPoint.x <= playerPosition - size.x/2)
// hit on the left
else if (hitPoint.y <= playerPosition - size.y/2)
// hit on the bottom
Note that there may be some problems in the edge cases. You reorder the if statements based on your wanted behaviour.
Hope this help.