# problem with rotation 2D

Hey,
I’m making a 2D game that has fish in it. When they reach the water surface, I want them to change their y direction so that they swim down again and gradually rotate them towards their new direction. For the ones with a positive x velocity, this works fine, but the ones swimming in the opposite direction behave in a really weird way. They turn 180 Degrees instantly and then gradually rotate to the Position they are supposed to rotate to (but take the wrong way round).

I know that I could use Quaternion.Slerp() or something similar instead of the Coroutine, but for some reason Unity always freezes when I use it and I have to restart the program, so this isn’t really an option for me.

I’d really appreciate if someone can help, I’ve been trying to fix this fo way too long…
Here is my Code:

``````// called when fish collides with the water surface
public override void SurfaceBehaviour()
{
angleOld = Mathf.Atan2(rigidbodyMovement.y, rigidbodyMovement.x) * Mathf.Rad2Deg;
float angleNew = 0f;
rigidbodyMovement.y = - rigidbodyMovement.y;
if (rigidbodyMovement.x > 0) angleNew = Mathf.Atan2(rigidbodyMovement.y, rigidbodyMovement.x) * Mathf.Rad2Deg;
else angleNew = Mathf.Atan2(-rigidbodyMovement.y, - rigidbodyMovement.x) * Mathf.Rad2Deg;
StartCoroutine("Rotate", angleNew);
ACRigidbody.velocity = new Vector2(rigidbodyMovement.x, rigidbodyMovement.y) * Time.deltaTime;
}

IEnumerator Rotate(float angleNew)
{
int counter = 100;
float Step = (angleNew - angleOld) / 100;
while (counter > 0)
{
angleOld += Step;
if (angleOld < 0)
{
angleOld += 360f;
}
else if (angleOld > 360)
{
angleOld -= 360f;
}            }
ActiveChild.transform.rotation = Quaternion.Euler(new Vector3(0f, 0f, angleOld));
counter--;
yield return new WaitForSecondsRealtime(.6f);
}

}
``````

EDIT: SOLVED!!! The problem was that I calculated angleOld in the first line of Surfacebehaviour() based on rigidbodyMovement, but if the x movement is negative and the sprite is flipped, it has to be -rigidbodyMovement

I think it has to do with your code

``````if (angleOld < 0)
{
angleOld += 360f;
}
else if (angleOld > 360)
{
angleOld -= 360f;
}}
``````

you can put it in an if statement, if(x>0)
then have else if(x<0)
and have appropriate action within, probably just rotating it the opposite direction and fixing your angle a different way.