Project Hasseu – Tutorial 2 – Programming Sentry Turrets

In this tutorial we are going to go through the process a making sentry turrets. Between tutorial 1 and this one, I made a simple script to spawn monster prefabs – I figured no need for me to cover this as this is much better covered other places.

Like the last one, here is the youtube video of the tutorial:

Below is the important script portion.

Here is the TurretController Script, attached to the turret prefab:

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class TurretController : MonoBehaviour
{
    // reference to bullet prefab
    public GameObject bulletPreFab;

    // firing rate s/projectile
    public float fireRate = .01f;
    public float fireCooldown = 0f;

    // holds all monsters that are in range
    List<GameObject> inRangeMonsters = new List<GameObject>();

    void Start()
    {
        
    }

    // Update is called once per frame
    void Update()
    {
        // if there are monsters in range
        if(inRangeMonsters.Count > 0)
        {
            fireCooldown += Time.deltaTime;
            while (fireCooldown >= fireRate)
            {
                FireProjectile(inRangeMonsters[0]);
                fireCooldown -= fireRate;
            }
        }
        
    }

    private void OnTriggerEnter2D(Collider2D collision)
    {
        // get game object
        GameObject go = collision.gameObject;

        // we only want to fire at monsters
        if (go.CompareTag("Monster"))
        {
            // add monster to list
            inRangeMonsters.Add(go);
        }
    }

    private void OnTriggerExit2D(Collider2D collision)
    {
        // get game object
        GameObject go = collision.gameObject;

        // if they get out of range or die
        if (go.CompareTag("Monster"))
        {
            // remove from list
            inRangeMonsters.Remove(go);
        }
    }

    private void FireProjectile(GameObject targetObject)
    {
        // create the new bullet
        GameObject newObject = Instantiate(bulletPreFab);

        // setting starting position of bullet at turret
        newObject.transform.position = this.transform.position;

        // direction to shoot (target object - turret)
        Vector2 trajectory = (Vector2)targetObject.transform.position - (Vector2)this.transform.position;

        // give trajectory to object
        newObject.GetComponent<BulletController>().SetTrajectory(trajectory);

        // convertering trajectory into rotation angle and setting
        float angle = Mathf.Atan2(trajectory.y, trajectory.x) * 360f / (2f * Mathf.PI) - 90f;

        // rotate turret
        this.transform.rotation = Quaternion.Euler(0f, 0f, angle);
    }
}

The turret pre-fab also needs a CircleCollider2d attached to it to simulate eye-sight/range. The collider will need to be marked as “Is Trigger” to allow the monster objects to pass through and trigger the functions. Additionally, set the radius of the collider to the desired range by modifying the Radius.

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