Calculate new direction after collision

Question

The ball comes straight to the box collider of the enemy and I would need it to bounce in one of the directions marked with red arrows with same velocity and I can't figure out how to do it. alt text

  [SerializeField] private float throwForce = 10f;
     [SerializeField] private float destroyTime = 1f;
 
     Rigidbody rb;
 
     bool destroy = false;
 
     Vector3 throwDirection;
 
     private void Awake()
     {
         rb = GetComponent<Rigidbody>();
     }
     private void Start()
     {
         throwDirection = GetComponentInParent<ThrowAction>().GetThrowDirection();
         rb.AddForce(throwDirection * throwForce, ForceMode.Impulse);
     }
     private void Update()
     {
         if (destroy)
         {
             destroyTime -= Time.deltaTime;
             if(destroyTime <= 0)
             {
                 Destroy(gameObject);
             }
         }
     }
     private void OnCollisionEnter(Collision collision)
     {
         if (collision.transform.CompareTag("Enemy"))
         {
             Vector3 bounceOffset = new Vector3(4, 0, 4);
 
             int randomIndex = Random.Range(0, 2);
             switch (randomIndex)
             {
                 case 0:
                     bounceOffset *= -1;
                     break;
                 case 1:
 
                     break;
             }
             Vector3 newDirection = (collision.transform.position - (collision.transform.position + bounceOffset)).normalized;
             Vector3 currentVelocity = rb.velocity;
 
             rb.velocity = Vector3.Reflect(newDirection, currentVelocity);
             destroy = true;
         }
     }

Answer 1

Answer by Shrimpey · Jul 28, 2022 at 11:05 AM

You're really overcomplicating things. If you know that it's not like real life reflection, then you shouldn't use Vector3.Reflect(). Here's a simple example that shows the direction you want (-+45 degrees, you can add more options in array). You need to adapt it to set velocity to your rigidbody.

 private float[] possibleDegreeOffsets = { 45.0f };

 private void Awake() {
     float randomAngle = possibleDegreeOffsets[Random.Range(0, possibleDegreeOffsets.Length)];
     Vector3 newDirection = new Vector2(Mathf.Cos(randomAngle * Mathf.PI / 180), Mathf.Sin(randomAngle * Mathf.PI / 180));
     if(Random.value > 0.5f) {
         newDirection.x *= -1f;
     }
     Debug.Log(newDirection);
 }

This is made for basic up/down direction. If you need it from any direction, then just rotate the result based on normal direction.

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Calculate new direction after collision

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