545 lines
14 KiB
Markdown
545 lines
14 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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// --- Singleton entity ---
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public static Entity SingletonEntity { get; } // ID=1, Version=1
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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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public QueryBuilder Query();
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// --- Query Execution ---
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public void ForEach<T1>(
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QueryDescriptor query,
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ForEachAction<T1> action) where T1 : struct;
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// Overloads for 2–6 component types:
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public void ForEach<T1, T2>(QueryDescriptor, ForEachAction<T1, T2>)
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where T1 : struct where T2 : struct;
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public void ForEach<T1, T2, T3>(QueryDescriptor, ForEachAction<T1, T2, T3>)
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where T1 : struct where T2 : struct where T3 : struct;
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public void ForEach<T1, T2, T3, T4>(QueryDescriptor, ForEachAction<T1, T2, T3, T4>)
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where T1 : struct where T2 : struct where T3 : struct where T4 : struct;
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public void ForEach<T1, T2, T3, T4, T5>(QueryDescriptor, ForEachAction<T1, T2, T3, T4, T5>)
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where T1 : struct where T2 : struct where T3 : struct where T4 : struct where T5 : struct;
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public void ForEach<T1, T2, T3, T4, T5, T6>(QueryDescriptor, ForEachAction<T1, T2, T3, T4, T5, T6>)
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where T1 : struct where T2 : struct where T3 : struct where T4 : struct where T5 : struct where T6 : struct;
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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(QueryDescriptor query);
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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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## ForEachAction Delegates
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Custom delegate types for query iteration with `ref` parameters. The built-in
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`Action<...>` delegates do not support `ref` parameters.
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```csharp
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namespace OECS;
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public delegate void ForEachAction<T1>(Entity entity, ref T1 c1) where T1 : struct;
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public delegate void ForEachAction<T1, T2>(Entity entity, ref T1 c1, ref T2 c2)
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where T1 : struct where T2 : struct;
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public delegate void ForEachAction<T1, T2, T3>(Entity entity, ref T1 c1, ref T2 c2, ref T3 c3)
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where T1 : struct where T2 : struct where T3 : struct;
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public delegate void ForEachAction<T1, T2, T3, T4>(Entity entity, ref T1 c1, ref T2 c2, ref T3 c3, ref T4 c4)
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where T1 : struct where T2 : struct where T3 : struct where T4 : struct;
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public delegate void ForEachAction<T1, T2, T3, T4, T5>(Entity entity, ref T1 c1, ref T2 c2, ref T3 c3, ref T4 c4, ref T5 c5)
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where T1 : struct where T2 : struct where T3 : struct where T4 : struct where T5 : struct;
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public delegate void ForEachAction<T1, T2, T3, T4, T5, T6>(Entity entity, ref T1 c1, ref T2 c2, ref T3 c3, ref T4 c4, ref T5 c5, ref T6 c6)
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where T1 : struct where T2 : struct where T3 : struct where T4 : struct where T5 : struct where T6 : struct;
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```
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---
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## EntityIterator
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Extension methods on `World` for `foreach`-style iteration over queries.
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Returns `ref struct` iterators that support zero-allocation iteration with
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`ref` access to components.
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Two sets of overloads: one accepting an explicit `QueryDescriptor` for
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filtering with `Without<T>`, and one without for simple "has component" scans.
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```csharp
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namespace OECS;
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public static class EntityIterator
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{
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// With explicit QueryDescriptor (supports Without<T> filters).
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public static Select1<T1> Select<T1>(
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this World world, QueryDescriptor query) where T1 : struct;
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public static Select2<T1, T2> Select<T1, T2>(
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this World world, QueryDescriptor query)
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where T1 : struct where T2 : struct;
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public static Select3<T1, T2, T3> Select<T1, T2, T3>(
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this World world, QueryDescriptor query)
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where T1 : struct where T2 : struct where T3 : struct;
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// Without QueryDescriptor — iterates all entities with the given component(s).
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public static Select1<T1> Select<T1>(
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this World world) where T1 : struct;
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public static Select2<T1, T2> Select<T1, T2>(
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this World world)
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where T1 : struct where T2 : struct;
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public static Select3<T1, T2, T3> Select<T1, T2, T3>(
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this World world)
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where T1 : struct where T2 : struct where T3 : struct;
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}
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```
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The singletons `CurrentEntity`, `Current1`, `Current2`, `Current3` are
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exposed on the ref struct iterators directly. Usage:
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```csharp
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// Simple scan: all entities with PlayerHand.
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using var iter = world.Select<PlayerHand>();
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while (iter.MoveNext())
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{
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Console.WriteLine(iter.CurrentEntity);
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}
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// With query filter:
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var query = world.Query().With<Position>().Without<Frozen>().Build();
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using var iter2 = world.Select<Position>(query);
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while (iter2.MoveNext())
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{
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iter2.Current1.X += 1;
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}
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```
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---
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## QueryBuilder
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```csharp
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namespace OECS;
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public class QueryBuilder
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{
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public QueryBuilder With<T>() where T : struct;
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public QueryBuilder Without<T>() where T : struct;
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public QueryDescriptor Build();
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}
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```
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---
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## QueryDescriptor
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```csharp
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namespace OECS;
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public class QueryDescriptor
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{
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public IReadOnlySet<Type> With { get; }
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public IReadOnlySet<Type> Without { get; }
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}
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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 iterator /
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`ForEach` API with a `QueryDescriptor` they build internally. This keeps
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the interface minimal and gives systems full flexibility over what they
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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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```csharp
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using OECS;
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// Define components
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[MessagePackObject]
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public 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 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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private readonly QueryDescriptor _query;
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public MovementSystem(World world)
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{
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_query = world.Query()
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.With<Position>()
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.With<Velocity>()
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.Build();
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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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world.ForEach(_query, (Entity entity, ref Position pos, ref Velocity vel) =>
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{
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pos.X += vel.X * dt;
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pos.Y += vel.Y * dt;
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world.MarkModified<Position>(entity);
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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(world));
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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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| `QueryExecutor` | Query iteration logic with smallest-set driver optimization. |
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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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