Unity2D: Enemy Shooting

Question

I'm having this problem with my enemy shooting, you see I'm using raycasting to detected where my player is and once detected I want the enemy to shoot, so far I have accomplished that but however there's not delay between each Instantiated bullet!So the bullet is being constantly spawn rather than a delay in between each spawn. I've tried a whole lot of different solutions to fix this problem but nothing worked! I've tried IEnumerator, object pooling, creating a count down timer and invoke & invokerepeating but still my bullets are still being instantiated instantly without no delay. Does any one knows how to have a delay between each instantiated bullet?? Thank you!

This is my script:

public GameObject bulletPrefab;
public Transform bulletSpawn;
public Transform sightStart, sightEnd;
public bool spotted = false;

void Update()
 {     
    RayCasting ();
    Behaviours ();
 }

void RayCasting()
{
    Debug.DrawLine (sightStart.position, sightEnd.position, Color.red);
    spotted = Physics2D.Linecast (sightStart.position, sightEnd.position, 1 << LayerMask.NameToLayer("Player"));
}

void Behaviours()
{
        if (spotted == true) {
            //Invoke("Fire", cooldownTimer);
            Fire ();
    } else if (spotted == false) {
        //CancelInvoke ();
    }
}

void Fire()
{       
        GameObject bullet = (GameObject)Instantiate (bulletPrefab);
        //GameObject bullet = objectPool.GetPooledObject (); 
        bullet.transform.position = transform.position;
        bullet.GetComponent<Rigidbody2D> ().velocity = bullet.transform.up * 14;
        Destroy (bullet, 2.0f);
}

Basic Basic · Accepted Answer · 2017-05-13T17:00:11

You need to throttle the rate at which bullets are spawned. You could base it on number of frames but that's a bad approach as fire rate will vary with game performance.

A better approach is to use a variable to track how much time must elapse before we can fire again. I'll call this "Time To Next Shot" (TTNS)

Decrement TTNS by the time that has elasped.
Check if TTNS is 0 or less
If so:
- Set TTNS as appropriate for our desired rate of fire.
- Fire a shot

Something like..

private float fireRate = 3f; // Bullets/second
private float timeToNextShot; // How much longer we have to wait.

void Fire() {       
        // Subtract the time elapsed (since the last frame) from TTNS .
        timeToNextShot -= time.deltaTime;
        
        if(timeToNextShot <= 0) {
            // Reset the timer to next shot
            timeToNextShot = 1/fireRate;
            
            //.... Your code
            GameObject bullet = (GameObject)Instantiate (bulletPrefab);
            //GameObject bullet = objectPool.GetPooledObject (); 
            bullet.transform.position = transform.position;
            bullet.GetComponent<Rigidbody2D> ().velocity = bullet.transform.up * 14;
            Destroy (bullet, 2.0f);
        }
}

This does assume that you only call Fire() once per frame (Otherwise the elapsed time will be subtracted from nextShot multiple times).

I opted to do it this way (subtracting slices from a time span) rather than defining an absolute time (wait until time.elapsedTime > x) as the resolution of elapsedTime decreases over time and that approach will result in glitches after a few hours of gameplay.

Unity2D: Enemy Shooting

1 Answers