ヴァンサバ風ゲームの作り方#4｜一番近い敵を狙って自動で攻撃しよう

using UnityEngine;
using UnityEngine.Pool;

// こげたお菓子の敵。スライムちゃんを追いかけ、遠くに離れたらプールに戻る
[RequireComponent(typeof(Rigidbody2D))]
public class Enemy : MonoBehaviour
{
    [SerializeField] private float moveSpeed = 1.5f;      // 1秒に進むマス数
    [SerializeField] private float despawnDistance = 22f; // これより離れたら引っ込む
    [SerializeField] private float keepDistance = 0.5f;   // これ以上は近づかない
    [SerializeField] private int maxHp = 10;              // 体力

    private Rigidbody2D body;
    private Transform target;
    private IObjectPool<Enemy> pool;
    private int hp;

    private void Awake()
    {
        body = GetComponent<Rigidbody2D>();
    }

    // 出てくるときに、EnemySpawnerから呼んでもらう
    public void Spawn(Vector2 position, Transform newTarget, IObjectPool<Enemy> newPool)
    {
        transform.position = position;
        target = newTarget;
        pool = newPool;
        hp = maxHp; // 使い回すので、体力を戻しておく
    }

    // 攻撃が当たったときに、武器のほうから呼んでもらう
    public void TakeDamage(int damage)
    {
        if (hp <= 0) // もう倒れている（同じ瞬間に2発当たったとき用）
        {
            return;
        }

        hp -= damage;
        if (hp <= 0)
        {
            pool.Release(this);
        }
    }

    private void FixedUpdate()
    {
        if (target == null)
        {
            return;
        }

        Vector2 toTarget = (Vector2)target.position - body.position;
        float distance = toTarget.magnitude;

        // 真上に乗ってしまわないよう、一定の距離まで近づいたら止まる
        body.linearVelocity = distance > keepDistance ? toTarget.normalized * moveSpeed : Vector2.zero;

        if (distance > despawnDistance)
        {
            pool.Release(this);
        }
    }
}

using UnityEngine;
using UnityEngine.Pool;

// 投げた計量スプーン。まっすぐ飛んで、当たった敵にダメージを与える
[RequireComponent(typeof(Rigidbody2D))]
public class Spoon : MonoBehaviour
{
    [SerializeField] private float speed = 8f;  // 1秒に進むマス数
    [SerializeField] private int damage = 10;   // 当たったときに減らす体力
    [SerializeField] private float life = 3f;   // 何秒で消えるか

    private Rigidbody2D body;
    private IObjectPool<Spoon> pool;
    private float timer;
    private bool used; // 1回使ったら、それ以上は当たらない

    private void Awake()
    {
        body = GetComponent<Rigidbody2D>();
    }

    // 投げるときに、SpoonThrowerから呼んでもらう
    public void Throw(Vector2 position, Vector2 direction, IObjectPool<Spoon> newPool)
    {
        transform.position = position;
        transform.right = direction; // 飛ぶ向きに回転させる
        body.linearVelocity = direction * speed;
        pool = newPool;
        timer = 0f;
        used = false;
    }

    private void Update()
    {
        if (used)
        {
            return;
        }

        timer += Time.deltaTime;
        if (timer >= life)
        {
            used = true;
            pool.Release(this); // 当たらないまま飛んでいったら引っ込める
        }
    }

    private void OnTriggerEnter2D(Collider2D other)
    {
        if (used)
        {
            return;
        }
        if (!other.TryGetComponent(out Enemy enemy))
        {
            return;
        }

        used = true;
        enemy.TakeDamage(damage);
        pool.Release(this);
    }
}

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

// 一定間隔で、一番近い敵に計量スプーンを投げる
public class SpoonThrower : MonoBehaviour
{
    [SerializeField] private Spoon spoonPrefab;
    [SerializeField] private float interval = 1f;      // 何秒に1本投げるか
    [SerializeField] private float searchRadius = 10f; // 何マス以内の敵を狙うか
    [SerializeField] private LayerMask enemyLayer;

    private ObjectPool<Spoon> pool;
    private ContactFilter2D filter;
    private readonly List<Collider2D> found = new List<Collider2D>();
    private float timer;

    private void Awake()
    {
        filter = new ContactFilter2D
        {
            useLayerMask = true,
            layerMask = enemyLayer,
            useTriggers = true, // 敵の当たり判定はIs Triggerなので、これが必要
        };

        pool = new ObjectPool<Spoon>(
            createFunc: () => Instantiate(spoonPrefab, transform.parent),
            actionOnGet: spoon => spoon.gameObject.SetActive(true),
            actionOnRelease: spoon => spoon.gameObject.SetActive(false),
            actionOnDestroy: spoon => { if (spoon != null) Destroy(spoon.gameObject); },
            defaultCapacity: 20,
            maxSize: 200);
    }

    private void Update()
    {
        timer += Time.deltaTime;
        if (timer < interval)
        {
            return;
        }
        timer -= interval;

        Transform nearest = FindNearestEnemy();
        if (nearest == null) // 近くに敵がいないときは投げない
        {
            return;
        }

        Vector2 toEnemy = (Vector2)nearest.position - (Vector2)transform.position;
        if (toEnemy.sqrMagnitude < 0.0001f) // 真上にいるときは向きが決められない
        {
            return;
        }

        Vector2 direction = toEnemy.normalized;
        Spoon spoon = pool.Get();
        spoon.Throw(transform.position, direction, pool);
    }

    // まわりの敵を集めて、一番近いものを返す
    private Transform FindNearestEnemy()
    {
        Physics2D.OverlapCircle(transform.position, searchRadius, filter, found);

        Transform nearest = null;
        float nearestDistance = float.MaxValue;
        foreach (Collider2D collider in found)
        {
            float distance = ((Vector2)collider.transform.position - (Vector2)transform.position).sqrMagnitude;
            if (distance < nearestDistance)
            {
                nearestDistance = distance;
                nearest = collider.transform;
            }
        }
        return nearest;
    }
}