Tank shell not rotating correctly on collision

[johnc81]

Hello,

I have been trying to figure this out for a few hours and am stuck on how to get my tank shell to ricochet off walls correctly. This is what I want to happen:

This is what actually happens:

Here is my code for firing the shell:

using UnityEngine;
using System.Collections;
public class Player_Shell_Fire : MonoBehaviour
{
    public float bulletSpeed;
    private Rigidbody2D _rb2D;

    private void Start()
    {
        _rb2D = GetComponent<Rigidbody2D>();
    }

    private void OnTriggerEnter2D(Collider2D target)
    {
        _rb2D.velocity = transform.up * bulletSpeed;

        if (target.gameObject.tag == "Enemy")
        {
            Destroy(this.gameObject); // Destroy Shell
            Destroy(target.gameObject); // Destroy Enemy
        }
    }

    private void OnCollisionEnter2D(Collision2D other)
    {
        if (other.transform.CompareTag("Wall"))
        {
            CollisionWithWall(other);
        }
    }

    private void CollisionWithWall(Collision2D other)
    {
        // For Reflecting The Bullet
        Vector3 reflectedPosition = Vector3.Reflect(transform.up, other.contacts[0].normal);
        _rb2D.velocity = (reflectedPosition).normalized * bulletSpeed;

        // For Rotatating The Bullet Towards its velocity
        Vector3 dir = _rb2D.velocity;
        float angle = Mathf.Atan2(dir.y, dir.x) * Mathf.Rad2Deg;
        _rb2D.MoveRotation(angle);
    }
}

Here is my Heavy_Shell prefab:

I am using a Physics2D Material so the bounce is fine, just the rotation after the collision is wrong. I have a small circle collider at the tip of the shell.

Any assistance you can give me would be greatly appreciated because I have no idea how to sort this out.

Many Thanks,

John

[system]

Hi John
Do you want to have a smooth interpolation rotating the bullet over time?
Otherwise, you should use Rigidbody.Rotation instead of Rigidbody.MoveRotation. But I do not know, if either of them works with an angle as parameter. You should consider using quaternions.

[johnc81]

Hi,

Thank you for your reply. This can just be instant rotation to the correct angle, rather than smooth over time. Do you know of any examples I can look at for quaternions, I am not really sure how this would help or how to test? I tried changing to _rb2D.Rotation, but this does not exist.

Many Thanks,

John

[system]

Ecuse me. It’s with a lower case “r” (Unity - Scripting API: Rigidbody2D.rotation).
I just noticed that you are working on a 2D game. You’re right using angles in 2D.
So this should do it:
_rb2D.rotation += angle;

[johnc81]

Hi,

Thank you for the fast response. I made the change and this is what happens now:

As you can see the bullet reverses, but stays in a horizontal position whilst travelling along a diagonal path.

I also tried by moving the wall to the other side and firing and the bullet does not flip and travels backwards along the path:

I am really at a loss with this. In my mind it should be easy, but in reality I really underestimated this task.

Many Thanks,

John

[johnc81]

I guess one option would be to use a round shell, although I feel like this is cheating and I know there must be a way to do this properly. Am open to any ideas / tutorials about how to do this.

Many Thanks,

John

[Kurt-Dekker]

Generally Mathf.Atan2() can be used to determine a compass heading in radians, based on X and Y deltas, in this case your motion.

Mathf.Rad2Deg is a constant you can multiply by to get that heading in degrees.

Finally you can apply the rotation to the sprite object.

Putting it all together:

• get the velocity from the RB2D
• calculate the heading with Atan2
• convert it to degrees with the constant above
• rotate the tank shell to face appropriately.

Note: this presumes the original art is oriented so that heading aligns with rotation. If that is not the case, either rotate the art or make a prefab with a sub-object that is rotated so the heading aligns with rotation.