497 lines
12 KiB
Markdown
497 lines
12 KiB
Markdown
# API Surface: OECS
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This document describes the public API surface of the OECS library. It serves
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as a contract for implementation and a reference for consumers.
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All types reside in the `OECS` namespace unless otherwise noted.
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---
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## Entity
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```csharp
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namespace OECS;
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public readonly struct Entity : IEquatable<Entity>
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{
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public static Entity Null { get; } // ID=0, Version=0
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public uint Id { get; } // lower 24-bit identifier
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public uint Version { get; } // upper 8-bit generation
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public bool IsNull { get; } // true for Entity.Null
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public bool Equals(Entity other);
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public override bool Equals(object? obj);
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public override int GetHashCode();
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public override string ToString(); // "Entity(42:v3)"
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public static bool operator ==(Entity left, Entity right);
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public static bool operator !=(Entity left, Entity right);
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}
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```
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---
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## World
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```csharp
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namespace OECS;
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public class World : IDisposable
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{
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// --- Lifecycle ---
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public World();
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// --- Entity Management ---
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public Entity CreateEntity();
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public void DestroyEntity(Entity entity);
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public bool IsAlive(Entity entity);
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// --- Component Management ---
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public void AddComponent<T>(Entity entity, T component) where T : struct;
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public void RemoveComponent<T>(Entity entity) where T : struct;
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public ref T GetComponent<T>(Entity entity) where T : struct;
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public T ReadComponent<T>(Entity entity) where T : struct;
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public bool TryGetComponent<T>(Entity entity, out T value) where T : struct;
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public bool HasComponent<T>(Entity entity) where T : struct;
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// --- Singleton ---
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public void SetSingleton<T>(T component) where T : struct;
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public ref T GetSingleton<T>() where T : struct;
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public T ReadSingleton<T>() where T : struct;
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public bool HasSingleton<T>() where T : struct;
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public void RemoveSingleton<T>() where T : struct;
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// --- Queries ---
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// See QueryExtensions for Select / FindEntity / FindEntities.
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// --- Commands ---
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public CommandQueue Commands { get; }
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public void ExecuteCommands();
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// --- Reactivity ---
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public void MarkModified<T>(Entity entity) where T : struct;
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public void PostChanges();
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public Observable<EntityChange> ObserveEntityChanges();
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public Observable<EntityChange> ObserveComponentChanges<T>()
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where T : struct;
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public Observable<EntityChange> ObserveQuery<T1>(Query<T1> query = default)
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where T1 : struct;
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public Observable<EntityChange> ObserveQuery<T1, T2>(Query<T1, T2> query = default)
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where T1 : struct where T2 : struct;
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// --- Relationships ---
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public IReadOnlyCollection<Entity> GetSources<T>(Entity target)
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where T : struct, IRelationship;
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// --- Cleanup ---
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public void Dispose();
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}
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```
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---
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## WorldQueryExtensions
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Extension methods on `World` providing `foreach`-compatible iteration and
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entity lookup. Select returns `ref struct` enumerators for zero-allocation
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iteration with `ref` access to components.
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```csharp
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namespace OECS;
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public static class WorldQueryExtensions
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{
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// Select — returns a ref struct enumerator for foreach.
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public static Select1<T1> Select<T1>(
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this World world, Query<T1> query = default) where T1 : struct;
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// Overloads for 2–6 component types:
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public static Select2<T1, T2> Select<T1, T2>(...) where T1 : struct where T2 : struct;
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// ... up to Select6<T1..T6>
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// FindEntity — returns the first matching entity or Entity.Null.
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public static Entity FindEntity<T1>(
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this World world, Query<T1> query = default) where T1 : struct;
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public static Entity FindEntity<T1, T2>(...) where T1 : struct where T2 : struct;
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public static Entity FindEntity<T1, T2, T3>(...) where T1 : struct where T2 : struct where T3 : struct;
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// FindEntities — returns all matching entities as List<Entity>.
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public static List<Entity> FindEntities<T1>(...) where T1 : struct;
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public static List<Entity> FindEntities<T1, T2>(...) where T1 : struct where T2 : struct;
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public static List<Entity> FindEntities<T1, T2, T3>(...) where T1 : struct where T2 : struct where T3 : struct;
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}
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```
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Each ref struct (Select1 through Select6) exposes:
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- `Entity Entity` — the current entity handle.
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- `ref T1 Item1`, `ref T2 Item2`, ... — read-write references to components.
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- `bool MoveNext()` — advances and returns true while items remain.
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- `GetEnumerator()` — returns `this` for `foreach` compatibility.
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- `Dispose()` — ends the iteration scope (flushes deferred mutations).
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Usage:
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```csharp
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// Simple scan: all entities with Position.
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foreach (var it in world.Select<Position>())
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{
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it.Item1.X += 1; // ref mutates component in-place
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}
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// With Without filter:
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var query = new Query<Position>().Without<Frozen>();
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foreach (var it in world.Select(query))
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{
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// it.Entity, it.Item1
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}
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// Find first entity:
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var hand = world.FindEntity<PlayerHand>();
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// Multi-component:
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foreach (var it in world.Select<Position, Velocity>())
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{
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it.Item1.X += it.Item2.X * dt;
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}
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```
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---
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## Query
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Describes a query over the ECS world. The `With` types are encoded as generic
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parameters. Optional `Without` filters are added via the fluent API.
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```csharp
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namespace OECS;
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public struct Query<T1> where T1 : struct
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{
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public Query<T1> Without<W>() where W : struct;
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}
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// Overloads for 2–6 With types:
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public struct Query<T1, T2> where T1 : struct where T2 : struct { ... }
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// ... up to Query<T1, T2, T3, T4, T5, T6>
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```
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Usage:
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```csharp
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// Two required types, one excluded:
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var query = new Query<Position, Velocity>().Without<Frozen>();
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foreach (var it in world.Select(query)) { ... }
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// Simple scan — no Without filter needed:
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foreach (var it in world.Select<Card>()) { ... }
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```
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---
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## ISystem
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A system is a unit of logic that runs during a tick. It receives the `World`
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and decides what to do — typically reading singletons, iterating queries,
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or enqueuing commands.
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```csharp
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namespace OECS;
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public interface ISystem
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{
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void Run(World world);
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}
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```
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Systems do **not** declare a query on the interface. Instead, they either
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read singletons directly (`world.ReadSingleton<T>()`) or use the
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`WorldQueryExtensions` (`Select`, `FindEntity`, `FindEntities`) with a
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`Query<T1..T6>` they build inline. This keeps the interface minimal and
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gives systems full flexibility over what they inspect at runtime.
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---
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## ITickedSystem
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An optional extension for systems that need tick metadata (delta time or
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logical tick marker).
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```csharp
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namespace OECS;
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public interface ITickedSystem : ISystem
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{
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void Run(World world, Tick tick);
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}
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```
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`SystemGroup` checks each system at runtime: if it implements
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`ITickedSystem`, the `Run(World, Tick)` overload is called; otherwise
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`Run(World)` is called. Both overloads must be implemented.
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---
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## Tick
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```csharp
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namespace OECS;
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public readonly struct Tick
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{
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public TickType Type { get; }
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public float DeltaTime { get; }
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public static Tick Timed(float deltaTime);
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public static Tick Logical();
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}
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public enum TickType
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{
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Timed,
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Logical
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}
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```
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---
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## SystemGroup
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```csharp
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namespace OECS;
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public class SystemGroup
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{
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public SystemGroup(World world);
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public void Add(ISystem system);
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public void Remove(ISystem system);
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public void RunTimed(float deltaTime);
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public void RunLogical();
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public int Count { get; }
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}
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```
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Systems execute in registration order. `SystemGroup` automatically drains
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commands and posts changes after each system and after the full tick.
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---
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## ICommand
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```csharp
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namespace OECS;
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public interface ICommand
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{
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void Execute(World world);
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}
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```
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Implementations should be `[MessagePackObject]` structs so they can be
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serialized and replayed.
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---
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## CommandQueue
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```csharp
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namespace OECS;
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public class CommandQueue
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{
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public void Enqueue<T>(T command) where T : struct, ICommand;
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public void ExecuteAll(World world);
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public void Clear();
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public void ClearErrors();
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public int Count { get; }
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public IReadOnlyList<Exception> Errors { get; }
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}
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```
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`Enqueue<T>` uses a constrained generic to avoid boxing at the call site.
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Commands enqueued during `ExecuteAll` are processed in the same drain cycle.
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---
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## IRelationship
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```csharp
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namespace OECS;
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public interface IRelationship
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{
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Entity Source { get; }
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Entity Target { get; }
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}
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```
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---
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## Relationship\<TSelf, TTarget\>
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A convenience base struct for relationship components. The type parameters are
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phantom types that differentiate relationship kinds at the type level, enabling
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type-safe queries and reverse lookups.
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```csharp
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namespace OECS;
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[MessagePackObject]
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public struct Relationship<TSelf, TTarget> : IRelationship
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where TSelf : struct where TTarget : struct
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{
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[Key(0)] public Entity Source { get; set; }
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[Key(1)] public Entity Target { get; set; }
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}
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```
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---
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## EntityChange
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```csharp
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namespace OECS;
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public readonly struct EntityChange : IEquatable<EntityChange>
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{
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public Entity Entity { get; }
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public ChangeKind Kind { get; }
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public Type? ComponentType { get; } // null for entity-level changes
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}
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public enum ChangeKind
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{
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EntityAdded,
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EntityRemoved,
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ComponentAdded,
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ComponentRemoved,
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ComponentModified
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}
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```
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---
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## WorldSerializer
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Saves and loads a `World` to/from a MessagePack stream. Components are
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serialized by their runtime type using the source-generated `ComponentRegistry`.
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```csharp
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namespace OECS;
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public static class WorldSerializer
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{
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public static void Save(World world, Stream stream);
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public static void Load(World world, Stream stream);
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}
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```
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---
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## WorldSnapshot / EntitySnapshot / ComponentEntry
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Serialization types used by `WorldSerializer`. These are public but intended
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primarily for serialization infrastructure.
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```csharp
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namespace OECS;
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[MessagePackObject]
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public class WorldSnapshot
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{
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[Key(0)] public EntitySnapshot[] Entities { get; set; }
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}
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[MessagePackObject]
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public class EntitySnapshot
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{
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[Key(0)] public uint Id { get; set; }
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[Key(1)] public uint Version { get; set; }
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[Key(2)] public ComponentEntry[] Components { get; set; }
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[IgnoreMember]
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public Entity Entity { get; }
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}
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[MessagePackObject]
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public class ComponentEntry
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{
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[Key(0)] public string TypeName { get; set; }
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[Key(1)] public byte[] Data { get; set; }
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}
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```
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---
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## Usage Example
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Components and commands should be `public record struct` types with explicit
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fields/properties (not positional syntax). See the `writing-games` skill for
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the rationale.
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```csharp
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using OECS;
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// Define components
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[MessagePackObject]
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public record struct Position
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{
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[Key(0)] public float X;
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[Key(1)] public float Y;
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}
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[MessagePackObject]
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public record struct Velocity
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{
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[Key(0)] public float X;
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[Key(1)] public float Y;
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}
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// Define a system
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public class MovementSystem : ITickedSystem
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{
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public void Run(World world) => Run(world, Tick.Logical());
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public void Run(World world, Tick tick)
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{
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float dt = tick.DeltaTime;
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foreach (var it in world.Select<Position, Velocity>())
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{
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it.Item1.X += it.Item2.X * dt;
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it.Item1.Y += it.Item2.Y * dt;
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}
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}
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}
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// Wire it up
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var world = new World();
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var group = new SystemGroup(world);
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group.Add(new MovementSystem());
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// Create entities
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var player = world.CreateEntity();
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world.AddComponent(player, new Position { X = 0, Y = 0 });
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world.AddComponent(player, new Velocity { X = 1, Y = 0 });
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// Observe changes via R3
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world.ObserveComponentChanges<Position>()
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.Subscribe(change => Console.WriteLine($"{change.Entity} moved"));
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// Run a tick
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group.RunTimed(0.016f); // ~60 FPS
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```
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---
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## Internal Types (not part of public API)
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These types are implementation details and may change without notice:
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| Type | Purpose |
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| `SparseSet<T>` | Dense/sparse array pair for component storage. |
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| `ComponentStore` | Registry of `SparseSet<T>` instances by type. |
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| `ChangeBuffer` | Accumulates `EntityChange` during system run, posts to R3 subjects. |
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| `ChangeSet` | Deduplicated change accumulator within a single batch. |
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| `RelationshipIndex` | Reverse lookup from target entity to source entities. |
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| `EntityAllocator` | Free-list + bump allocator for entity IDs. |
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| `WorldQueryExtensions` | Extension methods with ref struct iterators and entity lookup. |
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| `ComponentRegistry` | Source-generated registry of all component types for serialization. |
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| `ComponentDescriptor` | Source-generated per-type descriptor with serialize/deserialize callbacks. |
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