Unity Vector3. Use and calculation principle of reflect

Calculate the reflection vector that the vector projects onto the object  

Collision simulation ：

public class test3 : MonoBehaviour
{
    Vector3 dir;
    Vector3 pos;
    private void Start()
    {
        dir = transform.right;
        pos = transform.position;
    }

    private void Update()
    {
        transform.position += dir * Time.deltaTime*4;
    }
    
    private void OnCollisionEnter2D(Collision2D collision)
    {        
        Vector2 inDirection = (transform.position - pos).normalized;
        Vector2 inNormal = collision.contacts[0].normal;
        dir = Vector2.Reflect(inDirection, inNormal);
        pos = transform.position;
    }
}

Ray simulation ：

 

    void OnDrawGizmos()
    {
#if UNITY_EDITOR
        Color prevColor = Gizmos.color;

        // Shoot a red ray from the origin to the right 
        Gizmos.color = Color.red;
        RaycastHit2D hitInfo = Physics2D.Raycast(transform.position, transform.right, Mathf.Infinity);
        Gizmos.DrawLine(transform.position, hitInfo.point);

        // The ray touches the normal of the colliding object 
        Gizmos.color = Color.green;
        Gizmos.DrawLine(hitInfo.point, hitInfo.normal * 0.2f);


        // Reflection 
        Gizmos.color = Color.blue;
        Vector2 direction = Vector2.Reflect(hitInfo.point - (Vector2)transform.position, hitInfo.normal);
        Gizmos.DrawLine(hitInfo.point, direction * 0.1f);

        Gizmos.color = prevColor;
#endif
    }