4-3 Weapon Pickup Points

今天要來介紹撿拾地面的武器的機制～玩家經過放置在地上的武器後，會自動更換成玩家手中的武器。首先，在場景中製作一個空白的GameObject。

取名為Weapon Pickup。

拉進Project視窗中變成Prefab。

新增一個Script名為Weapon Pickup Point，並拉進Weapon Pickup的Prefab中。

接著先向大家介紹WeaponPickPoint中比較特別的程式碼，ExecuteInEditMode，在Class名稱之前加上這段程式碼後，Unity便會在編輯模式中自動執行Update內部的程式碼，執行的時機為編輯中有一些變動時，比如用滑鼠點擊不同的物件就會觸發。

如下圖，我們撰寫產生武器在場景中的程式。

好的！以下提供大家WeaponPickUp.cs的完整程式碼：

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using RPG.Character;

namespace RPG.Weapons{
 // 在編輯模式執行程式碼
 [ExecuteInEditMode]
 public class WeaponPickupPoint : MonoBehaviour {

  [SerializeField] Weapon weaponConfig;
  [SerializeField] AudioClip pickupSFX;

  AudioSource audioSource;

  void Start () {
   audioSource = GetComponent ();
  }
  
  void Update () {
   // 判斷要在編輯模式下才執行程式
   if (!Application.isPlaying) {
    DestroyChildren ();
    InstantiateWeapon ();
   }
  }

  void DestroyChildren(){
   foreach (Transform child in transform) {
    DestroyImmediate (child.gameObject);
   }
  }

  // 產生預覽用的武器物件於場景中
  void InstantiateWeapon(){
   GameObject weapon = weaponConfig.GetWeaponPrefab();
   weapon.transform.position = Vector3.zero;
   Instantiate (weapon, gameObject.transform);
  }

  // 觸發Trigger時更換玩家的武器
  void OnTriggerEnter(){
   FindObjectOfType ().PutWeaponInHand(weaponConfig);
   audioSource.PlayOneShot (pickupSFX);
  }
 }
}

撰寫好後，請將拉入素材進相關參數，Weapon Config要放進一個武器，Pickup SFX要放進撿拾武器的音效。接著，再請大家新增一個Box Collider，勾選Is Trigger，然後請大家調整Box Collider的位置與武器對應，當玩家觸發到Trigger時便會更換玩家手中的武器。

再新增一個Audio Source，用來播放撿拾武器的音效。

 再來，我們要修改Player.cs內更換武器的機制，原先於Player.cs中已撰寫了一個方法PutWeaponInHand，只要稍加修改後便能拿來利用。

 好的，以下提供Player.cs完整程式碼：

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.Assertions;
using UnityEngine.SceneManagement;
using RPG.CameraUI; // TODO consider re-wiring
using RPG.Core;
using RPG.Weapons;

namespace RPG.Character{
 public class Player : MonoBehaviour, IDamageable {

  [SerializeField] float maxHealthPoints = 100f;
  [SerializeField] float baseDamage = 50f;
  [SerializeField] AnimatorOverrideController animatorOverrideController;
  [SerializeField] Weapon currentWeaponConfig;
  [SerializeField] AbilityConfig[] abilities;
  [SerializeField] AudioClip[] damageSounds;
  [SerializeField] AudioClip[] deathSounds;
  [Range(.1f, 1.0f)] [SerializeField] float criticalHitChance = 0.1f;
  [SerializeField] float criticalHitMultiplier = 2.5f;
  [SerializeField] ParticleSystem criticalHitParticle;

  // 定義Trigger的字串常數
  const string DEATH_TRIGGER = "Death";
  const string ATTACK_TRIGGER = "Attack";
  const string DEFAULT_ATTACK = "DEFAULT ATTACK";

  float lastHitTime;
  float currentHealthPoint;
  Enemy currentEnemy;
  CameraRaycaster cameraRaycaster;
  AbilityBehaviour[] abilityBehaviour;
  AudioSource audioSource;
  Animator animator;
  GameObject weaponInUse;

  public float healthAsPercentage{
   get{ return currentHealthPoint / maxHealthPoints; }
  }

  void Start(){
   audioSource = GetComponent ();

   RegisterForMouseClcik ();
   SetCurrentMaxHealth ();
   PutWeaponInHand (currentWeaponConfig);
   OverrideAnimatorController ();
   AttachSpecialAbility();
  }

  void Update(){
   if (healthAsPercentage > Mathf.Epsilon) {
    ScanForAbilityKeyDown ();
   }
  }

  private void ScanForAbilityKeyDown(){
   for (int keyIndex = 1; keyIndex <= abilities.Length; keyIndex++) {
    if (Input.GetKeyDown (keyIndex.ToString())) {
     AttemptSpecialAbility (keyIndex);
    }
   }
  }

  private void AttachSpecialAbility(){
   abilityBehaviour = new AbilityBehaviour[abilities.Length];
   for (int i = 0; i < abilities.Length; i++) {
    // 儲存ISpecialAbility物件
    abilityBehaviour[i] = abilities [i].AttachAbilityTo (gameObject);
   }
  }

  private void OverrideAnimatorController(){
   // 取得Animator物件
   animator = GetComponent ();
   // 將人物的Animator取代為我們剛剛新增的Player Animator Override
   animator.runtimeAnimatorController = animatorOverrideController;
   // Player Animator Override中有一預設的DEFAULT ATTACK，將其取代成Weapon物件中的Animation
   // 亦即人物的Animation將會依據不同的Weapon物件，而使用有不同的動畫
   animatorOverrideController [DEFAULT_ATTACK] = currentWeaponConfig.GetAnimClip ();
  }

  public void PutWeaponInHand(Weapon weaponToUse){
   currentWeaponConfig = weaponToUse;
   // 先移除之前手持的武器
   Destroy(weaponInUse);
   GameObject weaponPrefab = weaponToUse.GetWeaponPrefab ();
   // 生成武器時，將會放置到指定的GameObject之下，此處為WeaponSocket之下
   // 故可將WeaponSocket設置成玩家的右手或左手
   GameObject weaponSocket = RequestDominantHand();
   weaponInUse = Instantiate (weaponPrefab, weaponSocket.transform);
   // 將武器放置到正確的位置，並有正確的方向
   weaponInUse.transform.localPosition = currentWeaponConfig.gripTransform.localPosition;
   weaponInUse.transform.localRotation = currentWeaponConfig.gripTransform.localRotation;
  }

  private GameObject RequestDominantHand(){
   // 從Children中尋找包含DominantHand的物件
   DominantHand[] dominantHand = GetComponentsInChildren ();
   // 計算取得有DominantHand的物件的數量
   int numberOfDominantHands = dominantHand.Length;
   // 確保該數量不為0
   Assert.AreNotEqual (numberOfDominantHands, 0, "No DominantHand found on player, please add one");
   // 確保該數量不要大於1
   Assert.IsFalse (numberOfDominantHands > 1, "Multiple Dominant script on Player, please remove one");
   // 傳回屬於該DominantHand的GameObject
   return dominantHand [0].gameObject;
  }

  private void SetCurrentMaxHealth(){
   currentHealthPoint = maxHealthPoints;
  }

  private void RegisterForMouseClcik(){
   cameraRaycaster = FindObjectOfType ();
   // 註冊滑鼠碰到敵人的事件
   cameraRaycaster.onMouseOverEnemy += OnMouseOverEnemy;
  }

  void OnMouseOverEnemy(Enemy enemy){
   currentEnemy = enemy;

   if (Input.GetMouseButtonDown (0) && IsTargetInRange (enemy.gameObject)) {
    AttackTarget ();
   }else if (Input.GetMouseButtonDown (1)) {
    // 0為使用第一個技能 
    AttemptSpecialAbility(0);
   }
  }

  private void AttemptSpecialAbility(int abilityIndex){
   Energy energyComponent = GetComponent ();
   // 取得技能需要的能量消耗量
   float energyCost = abilities [abilityIndex].GetEnergyCost ();

   if (energyComponent.IsEnergyAvailable (energyCost)) {
    energyComponent.ConsumeEnergy (energyCost);
    // 發動技能，並傳入Player的baseDamage
    AbilityParams abilityParams = new AbilityParams (currentEnemy, baseDamage);
    abilityBehaviour [abilityIndex].Use(abilityParams);
   }

  }

  private void AttackTarget(){
   // 確認本次攻擊時間離上一次攻擊時間須大於minTimeBetweenHits，相當於技能冷卻時間
   if ( (Time.time - lastHitTime > currentWeaponConfig.GetMinTimeBetweenHits())) {
    // 每次攻擊前都重設武器的攻擊動畫
    OverrideAnimatorController();
    // 呼叫Trigger啟動攻擊動畫
    animator.SetTrigger(ATTACK_TRIGGER);
    // 呼叫攻擊Target的方法
    currentEnemy.TakeDamage(CalculateDamage());
    // 紀錄目前攻擊的時間
    lastHitTime = Time.time;
   }
  }

  private float CalculateDamage(){
   // 產生隨機值，比較該值是否小於致命一擊的機率
   bool isCriticalHit = Random.Range (0f, 1f) <= criticalHitChance;
   float damageBeforeCritical = baseDamage + currentWeaponConfig.GetAdditionalDamage ();
   if (isCriticalHit) {
    // 播放致命一擊的特效
    criticalHitParticle.Play ();
    // 回傳攻擊力乘上致命一擊的乘率
    return damageBeforeCritical * criticalHitMultiplier;
   } else {
    return damageBeforeCritical;
   }
  }

  // 確認敵人是否在範圍技的攻擊範圍內
  private bool IsTargetInRange(GameObject target){
   float distanceToTarget = (target.transform.position - transform.position).magnitude;
   return distanceToTarget <= currentWeaponConfig.GetMaxAttackRange();
  }

  public void TakeDamage(float damage){
   // Math.Clamp可以確保數值運算後不會低於最小值或者高於最大值
   currentHealthPoint = Mathf.Clamp (currentHealthPoint - damage, 0f, maxHealthPoints);
   // 隨機播放受傷的音效
   audioSource.clip = damageSounds [Random.Range (0, damageSounds.Length)];
   audioSource.Play ();
   bool playerDies = currentHealthPoint <= 0;
   if (playerDies) {
    StartCoroutine (KillPlayer ());
   }
  }

  public void Heal(float points){
   currentHealthPoint = Mathf.Clamp (currentHealthPoint + points, 0f, maxHealthPoints);
  }

  IEnumerator KillPlayer(){
   // 播放死亡音效
   audioSource.clip = deathSounds [Random.Range (0, deathSounds.Length)];
   audioSource.Play ();
   // 播放死亡動畫
   animator.SetTrigger(DEATH_TRIGGER);
   // 等待一段時間（依音效長度而定）
   yield return new WaitForSecondsRealtime(audioSource.clip.length);
   // 重載關卡
   SceneManager.LoadScene(0);
  }
 }
}

 完成！讓我們來看看實際效果如何，於編輯模式中如下圖，會顯示該武器的模型在場景中。

執行遊戲看看，玩家手中拿的還是原本的劍。

經過地面上的鋤頭後，玩家手中的武器成功更換為鋤頭了！