How to tilt an object(2D) after collision and the rotate continuously

Question

I am having trouble rotating and object after collision. The object only transforms to the given angle of rotation once and stops. I would like to achieve in a way that after it has collided with the player object it rotates continuously till its killed after exiting the screen. The OnCollisionEnter2D(Collision2D collision) can't achieve this.

How can I achieve it using the FixedUpdate function?

Here is the code:

namespace Assets.scripts
{
    public class Barmovementscript : MonoBehaviour
    {
        public float Tilt;

        private void FixedUpdate()
        {
        }

        // upon collision the object rotates in a clockwise direction.
        void OnCollisionEnter2D(Collision2D collision)
        {
            if (collision.collider.tag == "Player")
            {
                Tilt += Time.deltaTime * -10;
                gameObject.transform.rotation = Quaternion.Euler(0, 0, Tilt);
            }
        }
    }
}

Answer 1

Simply make the collision event change a Boolean. And rotate your object if the Boolean is true in the fixed update

Answer 2

Keep a float called, say, "spin," indicating angular velocity. In your Update method, update your Tilt with Spin, and recalculate your quaternion.

(I haven't tried to compile this.)

namespace Assets.scripts
{
    public class BarMovementScript : MonoBehaviour
    {
        // angular velocity
        public float Tilt;
        public float Spin;


        private void FixedUpdate()
        {
            if (0.f != Spin)
            {
                Tilt += Spin * Time.deltaTime;
                gameObject.transform.rotation = Quaternion.Euler(0, 0, Tilt);
            }
        }

        // upon collision the object rotates in a clockwise direction.
        void OnCollisionEnter2D(Collision2D collision)
        {
            if ("Player" == collision.collider.tag)
            {
                Spin = -10.f;
            }
        }
    }
}

For a slightly cleaner (IMHO) approach, just use Verlet integration. In FixedUpdate(), get the difference between current tilt and that in the previous frame, add it to Tilt, and update your transform:

(Again, I haven't compiled this.)

namespace Assets.scripts
{
    public class BarMovementScript : MonoBehaviour
    {
        // angular velocity
        public float Tilt;
        private float m_prevTilt;
        private float m_prevDT = 1.f / 60.f; // lame hack, assume 60FPS initially.



        private void FixedUpdate()
        {
            var dTheta = Tilt - m_prevTilt;
            var dt = Time.deltaTime;

            if (0.f != dTheta && 0.f != m_prevDT)
            {

                Tilt += dTheta * dt / m_prevDT;

                gameObject.transform.rotation = Quaternion.Euler(0, 0, Tilt);               

                m_prevTilt = Tilt;
            }

            m_prevDT = Time.deltaTime;

        }

        // upon collision the object rotates in a clockwise direction.
        void OnCollisionEnter2D(Collision2D collision)
        {
            if ("Player" == collision.collider.tag)
            {
                Tilt = Time.deltaTime * -10;
                m_prevDT = Time.deltaTime;
            }
        }
    }
}