# Game Patterns

> Game Patterns with JEngine

- Skill: `jasonxudeveloper/game-patterns` (Agent Skill)
- Install (CLI): `npx skillmds@latest add jasonxudeveloper/game-patterns`
- Raw SKILL.md: https://api.skillmd.com/api/skills/jasonxudeveloper/game-patterns/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Coding & Dev Tools
- Author: jasonxudeveloper (https://skillmd.com/u/jasonxudeveloper)
- Updated: 2026-09-17
- Page: https://skillmd.com/skills/jasonxudeveloper/game-patterns

---


# Game Patterns with JEngine

Zero-GC patterns using JAction + JObjectPool with modern C# 9+ features.

## Principles

1. **Async-First:** Always use `ExecuteAsync()` (non-blocking)
2. **Zero-GC:** Use static lambdas + reference type state + object pooling
3. **Modern C#:** Target-typed new, init properties, Span<T>, in parameters

## State Classes for Zero-GC

JAction state parameters must be reference types to avoid boxing.
Pool these state objects for true zero-GC:

```csharp
// Reusable state for abilities
public sealed class AbilityState
{
    public bool CanUse { get; set; } = true;
    public float Cooldown { get; init; }
}

// Reusable state for DoT effects
public sealed class DoTState
{
    public IDamageable Target { get; set; }
    public float DamagePerTick { get; set; }
    public int TicksRemaining { get; set; }

    public void Reset()
    {
        Target = null;
        DamagePerTick = 0;
        TicksRemaining = 0;
    }
}

// Reusable state for timers
public sealed class TimerState
{
    public float Duration { get; set; }
    public float Elapsed { get; set; }
    public Action OnComplete { get; set; }

    public void Reset()
    {
        Duration = 0;
        Elapsed = 0;
        OnComplete = null;
    }
}
```

## Combat Patterns

### Ability with Cooldown (Zero-GC)
```csharp
public sealed class AbilitySystem
{
    private readonly AbilityState _state = new() { Cooldown = 2f };

    public async UniTaskVoid UseAbility()
    {
        if (!_state.CanUse) return;
        _state.CanUse = false;

        PerformAbility();

        using var action = await JAction.Create()
            .Delay(_state.Cooldown)
            .Do(static s => s.CanUse = true, _state)
            .ExecuteAsync();
    }
}
```

### Damage Over Time (Zero-GC Pooled State)
```csharp
public static class DoTSystem
{
    public static async UniTaskVoid Apply(
        IDamageable target,
        float damagePerTick,
        int ticks,
        float interval)
    {
        var state = JObjectPool.Shared<DoTState>().Rent();
        state.Target = target;
        state.DamagePerTick = damagePerTick;

        using var action = await JAction.Create()
            .Repeat(
                static s => s.Target?.TakeDamage(s.DamagePerTick),
                state,
                count: ticks,
                interval: interval)
            .ExecuteAsync();

        state.Reset();
        JObjectPool.Shared<DoTState>().Return(state);
    }
}
```

### Combo System (Zero-GC)
```csharp
public sealed class ComboState
{
    public int Count;
    public JAction ResetAction;
}

public sealed class ComboSystem : IDisposable
{
    private readonly ComboState _state = new();

    public int ComboCount => _state.Count;

    public void OnHit()
    {
        _state.ResetAction?.Cancel();
        _state.ResetAction?.Dispose();
        _state.Count++;

        _state.ResetAction = JAction.Create()
            .Delay(1.5f)
            .Do(static s => s.Count = 0, _state);

        _ = _state.ResetAction.ExecuteAsync();
    }

    /// <summary>
    /// Call from OnDestroy to prevent callbacks on destroyed objects.
    /// </summary>
    public void Dispose()
    {
        _state.ResetAction?.Cancel();
        _state.ResetAction?.Dispose();
        _state.ResetAction = null;
    }
}
```

## Spawning Patterns

### Wave Spawner (Async)
```csharp
public sealed class WaveSpawner
{
    private readonly EnemySpawner _spawner;

    // Use ReadOnlyMemory<T> for async (ReadOnlySpan<T> is a ref struct, invalid in async)
    // Access .Span inside the loop for zero-allocation iteration
    public async UniTask RunWaves(ReadOnlyMemory<WaveConfig> waves, CancellationToken ct = default)
    {
        foreach (var wave in waves.Span)
        {
            using var action = await JAction.Create()
                .Delay(wave.StartDelay)
                .Do(() => SpawnWave(wave.EnemyCount))
                .WaitUntil(() => ActiveCount == 0, timeout: 120f)
                .ExecuteAsync();

            if (action.Cancelled || ct.IsCancellationRequested) break;
        }
    }

    private void SpawnWave(int count)
    {
        for (var i = 0; i < count; i++)
        {
            var pos = GetSpawnPosition(i);
            _spawner.Spawn(in pos);
        }
    }
}
```

### Pooled Spawner (Generic, Zero-GC)
```csharp
public interface IPoolable
{
    void OnSpawn();
    void OnDespawn();
}

public sealed class PooledSpawner<T> where T : class, IPoolable, new()
{
    private readonly JObjectPool<T> _pool;

    public PooledSpawner(int maxSize = 64)
    {
        _pool = new(
            maxSize,
            onRent: static obj => obj.OnSpawn(),
            onReturn: static obj => obj.OnDespawn());
    }

    public T Spawn() => _pool.Rent();
    public void Despawn(T obj) => _pool.Return(obj);
    public void Prewarm(int count) => _pool.Prewarm(count);
    public int PooledCount => _pool.Count;
}
```

## Resource Patterns

### Health Regeneration (Zero-GC)
```csharp
public sealed class RegenState
{
    public float Current;
    public float Max;
    public float PerTick;
    public JAction Action;

    public void Cleanup()
    {
        Action?.Cancel();
        Action?.Dispose();
        Action = null;
    }
}

public static class RegenSystem
{
    public static void Start(RegenState state, float hpPerSecond)
    {
        state.Cleanup();
        state.PerTick = hpPerSecond * 0.1f;

        state.Action = JAction.Create()
            .RepeatWhile(
                static s => s.Current = MathF.Min(s.Current + s.PerTick, s.Max),
                static s => s.Current < s.Max,
                state,
                frequency: 0.1f);

        _ = state.Action.ExecuteAsync();
    }

    /// <summary>
    /// Stop regeneration. Call Cleanup() from OnDestroy to fully dispose.
    /// </summary>
    public static void Stop(RegenState state) => state.Cleanup();
}
```

## Projectile Patterns

### Bullet Manager (Zero-GC)
```csharp
public sealed class Bullet
{
    public Vector3 Position;
    public Vector3 Velocity;
    public float Damage;
    public bool Active;

    public void Reset()
    {
        Position = default;
        Velocity = default;
        Damage = 0;
        Active = false;
    }
}

public sealed class BulletManager
{
    public static BulletManager Instance { get; private set; }

    private readonly JObjectPool<Bullet> _pool = new(
        maxSize: 500,
        onReturn: static b => b.Reset());

    public void Initialize()
    {
        Instance = this;
        _pool.Prewarm(200);
    }

    public Bullet Fire(in Vector3 pos, in Vector3 dir, float speed, float damage)
    {
        var bullet = _pool.Rent();
        bullet.Position = pos;
        bullet.Velocity = dir * speed;
        bullet.Damage = damage;
        bullet.Active = true;
        return bullet;
    }

    public void Return(Bullet b) => _pool.Return(b);
}
```

### Auto-Return After Lifetime (Zero-GC)
```csharp
public sealed class BulletLifetimeState
{
    public Bullet Bullet;
    public BulletManager Manager;

    public void Reset()
    {
        Bullet = null;
        Manager = null;
    }
}

public static async UniTaskVoid FireWithLifetime(
    BulletManager manager,
    in Vector3 pos,
    in Vector3 dir,
    float speed,
    float damage,
    float lifetime)
{
    var bullet = manager.Fire(in pos, in dir, speed, damage);

    var state = JObjectPool.Shared<BulletLifetimeState>().Rent();
    state.Bullet = bullet;
    state.Manager = manager;

    using var action = await JAction.Create()
        .Delay(lifetime)
        .Do(static s => s.Manager?.Return(s.Bullet), state)
        .ExecuteAsync();

    state.Reset();
    JObjectPool.Shared<BulletLifetimeState>().Return(state);
}
```

## UI Patterns

### Delayed Tooltip (Zero-GC)
```csharp
public sealed class TooltipState
{
    public JAction Action;
    public Action ShowCallback;
    public Action HideCallback;

    public void Reset()
    {
        Action = null;
        ShowCallback = null;
        HideCallback = null;
    }
}

public sealed class TooltipTrigger : IDisposable
{
    private readonly TooltipState _state = new();

    public void OnPointerEnter(Action show, Action hide)
    {
        _state.Action?.Cancel();
        _state.Action?.Dispose();

        _state.ShowCallback = show;
        _state.HideCallback = hide;

        _state.Action = JAction.Create()
            .Delay(0.5f)
            .Do(static s => s.ShowCallback?.Invoke(), _state);

        _ = _state.Action.ExecuteAsync();
    }

    public void OnPointerExit()
    {
        _state.Action?.Cancel();
        _state.Action?.Dispose();
        _state.Action = null;
        _state.HideCallback?.Invoke();
    }

    /// <summary>
    /// Call from OnDestroy to prevent callbacks on destroyed objects.
    /// </summary>
    public void Dispose()
    {
        _state.Action?.Cancel();
        _state.Action?.Dispose();
        _state.Reset();
    }
}
```

### Typewriter Effect (Zero-GC)
```csharp
public sealed class TypewriterState
{
    public string FullText;
    public int CurrentIndex;
    public Action<string> OnUpdate;
    public StringBuilder Builder;

    public void Reset()
    {
        FullText = null;
        CurrentIndex = 0;
        OnUpdate = null;
        Builder = null;
    }
}

public static async UniTask TypeText(string content, float charDelay, Action<string> onUpdate)
{
    var state = JObjectPool.Shared<TypewriterState>().Rent();
    var sb = JObjectPool.Shared<StringBuilder>().Rent();

    state.FullText = content;
    state.CurrentIndex = 0;
    state.OnUpdate = onUpdate;
    state.Builder = sb;

    using var action = await JAction.Create()
        .Repeat(
            static s =>
            {
                if (s.CurrentIndex < s.FullText.Length)
                {
                    s.Builder.Append(s.FullText[s.CurrentIndex++]);
                    s.OnUpdate?.Invoke(s.Builder.ToString());
                }
            },
            state,
            count: content.Length,
            interval: charDelay)
        .ExecuteAsync();

    sb.Clear();
    JObjectPool.Shared<StringBuilder>().Return(sb);

    state.Reset();
    JObjectPool.Shared<TypewriterState>().Return(state);
}
```

## Best Practices

1. **Always use ExecuteAsync()** - Non-blocking, proper frame delays
2. **Always use `using var`** - Ensures JAction returns to pool
3. **Use static lambdas + state** - Avoids closure allocations
4. **State must be reference type** - Value types get boxed
5. **Pool state objects** - Use JObjectPool.Shared<T>() for state classes
6. **Reset state on return** - Clear all fields to prevent data leaks
7. **Use `in` parameters** - Avoid struct copies for Vector3, etc.
8. **Prewarm pools during loading** - Avoid runtime allocations
9. **Set timeouts** - Prevent infinite waits in production
10. **Cancel actions on disable** - Avoid callbacks on destroyed objects