Entity Component System (ECS)
Traditional OOP (BAD):
// Everything coupled, hard to optimize
public class Enemy : MonoBehaviour
{
public float health;
public float speed;
public Rigidbody rb;
void Update()
{
// Movement
rb.velocity = transform.forward * speed;
// AI
if (PlayerInRange()) Attack();
// Health
if (health <= 0) Die();
}
}
// Problem: 1000 enemies = 1000 Update() calls, cache misses
ECS (GOOD):
// Components are pure data
public struct Position : IComponentData
{
public float3 Value;
}
public struct Velocity : IComponentData
{
public float3 Value;
}
public struct Health : IComponentData
{
public float Current;
public float Max;
}
// Systems process components in bulk (cache-friendly)
public partial class MovementSystem : SystemBase
{
protected override void OnUpdate()
{
float deltaTime = Time.DeltaTime;
// Processes ALL entities with Position + Velocity
// in tight loop, vectorized by Burst compiler
Entities.ForEach((ref Position pos, in Velocity vel) =>
{
pos.Value += vel.Value * deltaTime;
}).ScheduleParallel();
}
}
public partial class HealthSystem : SystemBase
{
protected override void OnUpdate()
{
var ecb = new EntityCommandBuffer(Allocator.TempJob);
Entities.ForEach((Entity entity, in Health health) =>
{
if (health.Current <= 0)
{
ecb.DestroyEntity(entity);
}
}).Schedule();
ecb.Playback(EntityManager);
ecb.Dispose();
}
}
Performance comparison:
// OOP: 1000 enemies
// Update() calls: 1000/frame
// Cache misses: high (scattered objects)
// Parallelization: hard
// ECS: 1000 enemies
// System calls: 1/frame per system
// Cache misses: low (contiguous arrays)
// Parallelization: automatic with Burst
// Result: 10-100x faster for large entity counts
Data-Oriented Design
BAD (Object-Oriented):
public class Particle
{
public Vector3 position;
public Vector3 velocity;
public Color color;
public float lifetime;
public ParticleType type; // Rarely accessed
public string debugName; // Never in release
}
List<Particle> particles = new(); // Scattered in memory
void UpdateParticles()
{
foreach (var p in particles) // Cache miss on every access
{
p.position += p.velocity * Time.deltaTime;
p.lifetime -= Time.deltaTime;
}
}
GOOD (Data-Oriented):
public class ParticleSystem
{
// Structure of Arrays (SoA) - cache friendly
private Vector3[] positions;
private Vector3[] velocities;
private float[] lifetimes;
private Color[] colors;
private int count;
public ParticleSystem(int capacity)
{
positions = new Vector3[capacity];
velocities = new Vector3[capacity];
lifetimes = new float[capacity];
colors = new Color[capacity];
}
public void Update(float deltaTime)
{
// Hot data in contiguous arrays - CPU cache loves this
for (int i = 0; i < count; i++)
{
positions[i] += velocities[i] * deltaTime;
lifetimes[i] -= deltaTime;
if (lifetimes[i] <= 0)
{
RemoveParticle(i--);
}
}
}
private void RemoveParticle(int index)
{
// Swap with last element (constant time)
int last = --count;
positions[index] = positions[last];
velocities[index] = velocities[last];
lifetimes[index] = lifetimes[last];
colors[index] = colors[last];
}
}
State Machine (Production-Ready)
// Abstract state base
public abstract class State<T> where T : class
{
protected T Context { get; private set; }
public void SetContext(T context) => Context = context;
public virtual void Enter() { }
public virtual void Update() { }
public virtual void FixedUpdate() { }
public virtual void Exit() { }
}
// State machine manager
public class StateMachine<T> where T : class
{
private State<T> _current;
private readonly T _context;
public State<T> CurrentState => _current;
public StateMachine(T context, State<T> initialState)
{
_context = context;
ChangeState(initialState);
}
public void ChangeState(State<T> newState)
{
_current?.Exit();
_current = newState;
_current.SetContext(_context);
_current.Enter();
}
public void Update() => _current?.Update();
public void FixedUpdate() => _current?.FixedUpdate();
}
// Concrete states
public class PlayerIdleState : State<Player>
{
public override void Enter()
{
Context.Animator.Play("Idle");
Context.Velocity = Vector3.zero;
}
public override void Update()
{
if (Context.Input.magnitude > 0.1f)
Context.StateMachine.ChangeState(new PlayerMoveState());
if (Context.Input.Jump)
Context.StateMachine.ChangeState(new PlayerJumpState());
}
}
public class PlayerMoveState : State<Player>
{
public override void Enter()
{
Context.Animator.Play("Run");
}
public override void FixedUpdate()
{
Vector3 move = Context.Input * Context.MoveSpeed;
Context.Rigidbody.MovePosition(Context.transform.position + move * Time.fixedDeltaTime);
}
public override void Update()
{
if (Context.Input.magnitude < 0.1f)
Context.StateMachine.ChangeState(new PlayerIdleState());
if (Context.Input.Jump)
Context.StateMachine.ChangeState(new PlayerJumpState());
}
}
// Usage in Player class
public class Player : MonoBehaviour
{
public StateMachine<Player> StateMachine { get; private set; }
public Vector3 Input => new Vector3(InputX, 0, InputY);
// ... other properties
void Start()
{
StateMachine = new StateMachine<Player>(this, new PlayerIdleState());
}
void Update() => StateMachine.Update();
void FixedUpdate() => StateMachine.FixedUpdate();
}
Object Pool (Production-Ready)
// Generic object pool
public class ObjectPool<T> where T : Component
{
private readonly Queue<T> _pool = new();
private readonly T _prefab;
private readonly Transform _parent;
private readonly int _maxSize;
public ObjectPool(T prefab, int initialSize, int maxSize = 1000, Transform parent = null)
{
_prefab = prefab;
_maxSize = maxSize;
_parent = parent;
for (int i = 0; i < initialSize; i++)
_pool.Enqueue(CreateInstance());
}
public T Get(Vector3 position, Quaternion rotation)
{
T obj = _pool.Count > 0 ? _pool.Dequeue() : CreateInstance();
obj.transform.position = position;
obj.transform.rotation = rotation;
obj.gameObject.SetActive(true);
return obj;
}
public void Return(T obj)
{
if (_pool.Count >= _maxSize)
{
Object.Destroy(obj.gameObject);
return;
}
obj.gameObject.SetActive(false);
_pool.Enqueue(obj);
}
private T CreateInstance()
{
T instance = Object.Instantiate(_prefab, _parent);
instance.gameObject.SetActive(false);
return instance;
}
public void Clear()
{
while (_pool.Count > 0)
{
Object.Destroy(_pool.Dequeue().gameObject);
}
}
}
// Pooled bullet example
public class Bullet : MonoBehaviour
{
public float lifetime = 3f;
private float _spawnTime;
private ObjectPool<Bullet> _pool;
public void Initialize(ObjectPool<Bullet> pool)
{
_pool = pool;
_spawnTime = Time.time;
}
void Update()
{
if (Time.time - _spawnTime > lifetime)
_pool.Return(this);
}
void OnCollisionEnter(Collision collision)
{
// Hit something, return to pool
_pool.Return(this);
}
}
// Usage
public class Gun : MonoBehaviour
{
[SerializeField] private Bullet bulletPrefab;
private ObjectPool<Bullet> _bulletPool;
void Start()
{
_bulletPool = new ObjectPool<Bullet>(
bulletPrefab,
initialSize: 50,
maxSize: 200,
parent: transform
);
}
void Shoot()
{
Bullet bullet = _bulletPool.Get(firePoint.position, firePoint.rotation);
bullet.Initialize(_bulletPool);
bullet.GetComponent<Rigidbody>().velocity = firePoint.forward * bulletSpeed;
}
}
Observer Pattern (Event System)
// Type-safe event system
public static class GameEvents
{
// Score events
public static event Action<int> OnScoreChanged;
public static event Action<int, int> OnComboChanged; // current, max
// Health events
public static event Action<float, float> OnHealthChanged; // current, max
public static event Action OnPlayerDied;
// Game state events
public static event Action OnGameStarted;
public static event Action OnGamePaused;
public static event Action OnGameResumed;
// Invoke methods
public static void ScoreChanged(int newScore) => OnScoreChanged?.Invoke(newScore);
public static void HealthChanged(float current, float max) => OnHealthChanged?.Invoke(current, max);
public static void PlayerDied() => OnPlayerDied?.Invoke();
}
// Subscriber example
public class UIManager : MonoBehaviour
{
[SerializeField] private TextMeshProUGUI scoreText;
[SerializeField] private Slider healthBar;
[SerializeField] private GameObject gameOverPanel;
void OnEnable()
{
GameEvents.OnScoreChanged += UpdateScore;
GameEvents.OnHealthChanged += UpdateHealth;
GameEvents.OnPlayerDied += ShowGameOver;
}
void OnDisable()
{
GameEvents.OnScoreChanged -= UpdateScore;
GameEvents.OnHealthChanged -= UpdateHealth;
GameEvents.OnPlayerDied -= ShowGameOver;
}
private void UpdateScore(int score)
{
scoreText.text = $"Score: {score}";
}
private void UpdateHealth(float current, float max)
{
healthBar.value = current / max;
}
private void ShowGameOver()
{
gameOverPanel.SetActive(true);
}
}
Command Pattern (Undo/Redo)
public interface ICommand
{
void Execute();
void Undo();
}
public class MoveCommand : ICommand
{
private readonly Transform _target;
private readonly Vector3 _direction;
private Vector3 _previousPosition;
public MoveCommand(Transform target, Vector3 direction)
{
_target = target;
_direction = direction;
}
public void Execute()
{
_previousPosition = _target.position;
_target.position += _direction;
}
public void Undo()
{
_target.position = _previousPosition;
}
}
public class RotateCommand : ICommand
{
private readonly Transform _target;
private readonly float _angle;
private Quaternion _previousRotation;
public RotateCommand(Transform target, float angle)
{
_target = target;
_angle = angle;
}
public void Execute()
{
_previousRotation = _target.rotation;
_target.Rotate(Vector3.up, _angle);
}
public void Undo()
{
_target.rotation = _previousRotation;
}
}
// Command manager with undo/redo stack
public class CommandManager
{
private readonly Stack<ICommand> _undoStack = new();
private readonly Stack<ICommand> _redoStack = new();
public void ExecuteCommand(ICommand command)
{
command.Execute();
_undoStack.Push(command);
_redoStack.Clear(); // Clear redo stack on new action
}
public void Undo()
{
if (_undoStack.Count == 0) return;
ICommand command = _undoStack.Pop();
command.Undo();
_redoStack.Push(command);
}
public void Redo()
{
if (_redoStack.Count == 0) return;
ICommand command = _redoStack.Pop();
command.Execute();
_undoStack.Push(command);
}
}
// Usage in level editor
public class LevelEditor : MonoBehaviour
{
private CommandManager _commandManager = new();
void Update()
{
if (Input.GetKeyDown(KeyCode.W))
_commandManager.ExecuteCommand(new MoveCommand(selectedObject, Vector3.forward));
if (Input.GetKeyDown(KeyCode.Z))
_commandManager.Undo();
if (Input.GetKeyDown(KeyCode.Y))
_commandManager.Redo();
}
}
Service Locator
// Service locator (use sparingly, prefer dependency injection)
public static class Services
{
private static readonly Dictionary<Type, object> _services = new();
public static void Register<T>(T service) where T : class
{
_services[typeof(T)] = service;
}
public static T Get<T>() where T : class
{
if (_services.TryGetValue(typeof(T), out object service))
return service as T;
throw new Exception($"Service {typeof(T)} not registered");
}
public static bool TryGet<T>(out T service) where T : class
{
if (_services.TryGetValue(typeof(T), out object obj))
{
service = obj as T;
return true;
}
service = null;
return false;
}
}
// Register services at startup
public class GameBootstrapper : MonoBehaviour
{
void Awake()
{
Services.Register(new AudioManager());
Services.Register(new SaveManager());
Services.Register(new AnalyticsManager());
}
}
// Access from anywhere
public class Enemy : MonoBehaviour
{
void Die()
{
Services.Get<AudioManager>().PlaySound("enemy_death");
Services.Get<AnalyticsManager>().LogEvent("enemy_killed");
}
}
Architecture Layers
┌─────────────────────────────────────────┐
│ GAME LAYER │
│ ┌─────────────────────────────────┐ │
│ │ Managers │ │
│ │ - GameManager (state) │ │
│ │ - UIManager (HUD) │ │
│ │ - AudioManager (sound) │ │
│ └─────────────────────────────────┘ │
│ ┌─────────────────────────────────┐ │
│ │ Systems (ECS or domain logic) │ │
│ │ - CombatSystem │ │
│ │ - InventorySystem │ │
│ │ - QuestSystem │ │
│ └─────────────────────────────────┘ │
│ ┌─────────────────────────────────┐ │
│ │ Components (data + behavior) │ │
│ │ - Health, Weapon, AI │ │
│ └─────────────────────────────────┘ │
├─────────────────────────────────────────┤
│ ENGINE LAYER │
│ Physics | Rendering | Input | Network │
└─────────────────────────────────────────┘
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