Enemy Sight Cone

AISightCone.cs

using System.Collections;
using UnityEngine;

public class AIController : MonoBehaviour {
    [SerializeField][Range(0f, 20f)] float sightRange = 5f;
    [SerializeField][Range(0f, 1f)] float sightAngle = 0.3f;

    GameObject player;
    Vector3 headingToPlayer;
    Vector3 sightHeading;

    void Start() {
        StartCoroutine(CFindPlayer());
    }

    void Update() {
        AttackBehaviour();
    }

    private void AttackBehaviour() {
        if (IsPlayerInSight()) {
            // attack player
        } else {
            // resume patrol / guard / whatever
        }
    }

    bool IsPlayerInSight() {
        if (!player == null) return false;
        if (Vector3.Distance(transform.position, player.transform.position) > sightRange) return false;
        headingToPlayer = (player.transform.position - transform.position).normalized;
        sightHeading = transform.forward;
        if (Vector3.Dot(sightHeading, headingToPlayer) < (1 - sightAngle)) return false;
        // could also perform a raycast here to make sure that nothing is obscuring the player from sight
        return true;
    }

    void OnDrawGizmos() {
        Gizmos.color = Color.blue;
        if (IsPlayerInSight()) Gizmos.color = Color.red;
        Gizmos.DrawWireSphere(transform.position, sightRange);
        // note - these lines do not extend all the way to the edge of the wire sphere - simple fix would be normalizing and then multiplying each result by sightRange
        Gizmos.DrawLine(transform.position, transform.position + transform.forward * sightRange * (1 - sightAngle) + transform.right * sightRange * sightAngle);
        Gizmos.DrawLine(transform.position, transform.position + transform.forward * sightRange * (1 - sightAngle) - transform.right * sightRange * sightAngle);
        Gizmos.DrawLine(transform.position, transform.position + transform.forward * sightRange * (1 - sightAngle) + transform.up * sightRange * sightAngle);
        Gizmos.DrawLine(transform.position, transform.position + transform.forward * sightRange * (1 - sightAngle) - transform.up * sightRange * sightAngle);
    }

    IEnumerator CFindPlayer() {
        while (true) {
            yield return new WaitForSeconds(0.25f);
            if (player != null) continue;
            player = GameObject.FindWithTag("Player");
        }
    }
}