ContactPoint2D.contacts[0].normal returns sometimes returns different value that breaks my game.

[Batka]

Hi,

I have a 2d game where the ball (Player) bounces from obstacles like a laser using Vector2.Reflect.

I tried everything, and through the debugger I noticed that sometimes ContactPoint2D.contacts[0].normal returns a different value.

So, with this function, I reflect the ball:

void ReflectBall(ContactPoint2D contact, Vector2 ballDirection)
		{
			Vector2 inDirection = Vector2.Reflect(ballDirection, contact.normal);
			float rot = Mathf.Atan2(inDirection.y, inDirection.x) * Mathf.Rad2Deg;
			_transform.eulerAngles = new Vector3(0, 0, rot);

		}

And now, using the debugger, I see that the normal of the contact point is x(0.5) y(-0.9)

Now I set the debugger to break only when the normal does not equal that value (0.5, -0.9).
And I tested on the same game object, hitting it on the same spot:

Here is the object with it’s collider:

Screenshot

as well its physics components:

Screenshot

Now here is the OnCollisionEnter function:

 void OnCollisionEnter2D(Collision2D col)
        {
			Vector2 forward = _transform.right;
			// ball hit bound of gamefield, level is going to reset
			if (col.gameObject.layer == LayerMask.NameToLayer(Constants.LayerBounds))
            {
				shouldResetTransform = true;
                Reset(false);
			}

            //if ball hit on figure
            else
            {				
				string tag = col.gameObject.tag;
				if (tag.Equals("Normal") || tag.Equals("Hard") || tag.Equals("NotDisappear"))
				{
					ContactPoint2D contact = col.contacts[0];
					ReflectBall(contact, forward);
					OnHitResponse(col.gameObject);
				}

			}
        }

OnHitResponse() is a heavy function, but it’s called after RefflectBall().

I’d really appreciate any ideas. Thanks

[MelvMay]

For starters, something is very odd with that normal as it’s supposed to be normalized and (0.5, -0.9) clearly isn’t.

Ensure that you’re using continuous collision detection otherwise you can be penetrating the other collider.

Also, changing the Transform of a GameObject that uses a Dynamic body-type Rigidbody2D is bad behaviour. If you want to modify the rotation of a Rigidbody2D then set its rotation property i.e. let the Rigidbody2D type drive the Transform, not the other way around.