Add scene graph draft

Ghost.Engine/Core/Scene.cs

@@ -1,88 +1,39 @@
 using Ghost.Entities;
+using Misaki.HighPerformance.LowLevel.Buffer;
+using Misaki.HighPerformance.LowLevel.Collections;
 
 namespace Ghost.Engine.Core;
 
 /// <summary>
-/// Represents a lightweight handle to a loaded scene.
+/// Represents a runtime scene - a collection of entities with the same SceneID.
 /// </summary>
-/// <remarks>
-/// A Scene is a collection of entities tagged with a unique SceneID component.
-/// The Scene class provides a convenient handle to interact with all entities
-/// belonging to a particular scene within a World.
-/// </remarks>
-public sealed class Scene : IDisposable, IEquatable<Scene>
+public readonly struct Scene : IEquatable<Scene>
 {
-    private static short s_nextSceneID = 0;
-
-    private readonly World _world;
     private readonly short _id;
-    private readonly string _name;
-    private bool _isDisposed;
 
     /// <summary>
-    /// Gets the world this scene belongs to.
-    /// </summary>
-    public World World => _world;
-
-    /// <summary>
-    /// Gets the unique identifier for this scene.
+    /// Gets the unique identifier of this scene.
     /// </summary>
     public short ID => _id;
 
     /// <summary>
-    /// Gets the name of this scene.
+    /// Gets whether this scene is valid.
     /// </summary>
-    public string Name => _name;
+    public bool IsValid => _id >= 0;
 
     /// <summary>
-    /// Creates a new scene handle.
+    /// Gets an invalid scene instance.
     /// </summary>
-    /// <param name="world">The world this scene belongs to.</param>
-    /// <param name="name">The name of the scene.</param>
-    internal Scene(World world, string name)
-    {
-        _world = world;
-        _id = s_nextSceneID++;
-        _name = name;
-    }
+    public static Scene Invalid => new(-1);
 
-    /// <summary>
-    /// Creates a new scene handle with a specific ID.
-    /// </summary>
-    /// <param name="world">The world this scene belongs to.</param>
-    /// <param name="id">The scene ID.</param>
-    /// <param name="name">The name of the scene.</param>
-    internal Scene(World world, short id, string name)
+    internal Scene(short id)
     {
-        _world = world;
         _id = id;
-        _name = name;
-
-        // Update next ID if necessary
-        if (id >= s_nextSceneID)
-        {
-            s_nextSceneID = (short)(id + 1);
-        }
     }
 
-    ~Scene()
+    public bool Equals(Scene other)
     {
-        Dispose();
-    }
-
-    public bool Equals(Scene? other)
-    {
-        if (other is null)
-        {
-            return false;
-        }
-
-        if (ReferenceEquals(this, other))
-        {
-            return true;
-        }
-
-        return _world.Equals(other._world) && _id == other._id;
+        return _id == other._id;
     }
 
     public override bool Equals(object? obj)
@@ -92,36 +43,117 @@ public sealed class Scene : IDisposable, IEquatable<Scene>
 
     public override int GetHashCode()
     {
-        return HashCode.Combine(_world, _id);
+        return _id.GetHashCode();
+    }
+
+    public static bool operator ==(Scene left, Scene right)
+    {
+        return left.Equals(right);
+    }
+
+    public static bool operator !=(Scene left, Scene right)
+    {
+        return !left.Equals(right);
     }
 
     public override string ToString()
     {
-        return $"Scene: {_name} (ID: {_id})";
-    }
-
-    public static bool operator ==(Scene? left, Scene? right)
-    {
-        if (left is null)
-        {
-            return right is null;
-        }
-        return left.Equals(right);
-    }
-
-    public static bool operator !=(Scene? left, Scene? right)
-    {
-        return !(left == right);
-    }
-
-    public void Dispose()
-    {
-        if (_isDisposed)
-        {
-            return;
-        }
-
-        _isDisposed = true;
-        GC.SuppressFinalize(this);
+        return $"Scene {{ ID: {_id} }}";
+    }
+}
+
+/// <summary>
+/// Manages scenes within a world.
+/// </summary>
+/// <remarks>
+/// This is a minimal runtime representation. All metadata (like scene names) 
+/// should be stored in editor-only classes (SceneNode).
+/// </remarks>
+public class SceneManager
+{
+    private readonly World _world;
+    private short _nextSceneID;
+
+    internal SceneManager(World world)
+    {
+        _world = world;
+        _nextSceneID = 0;
+    }
+
+    /// <summary>
+    /// Creates a new scene in the world.
+    /// </summary>
+    /// <returns>The created scene.</returns>
+    public Scene CreateScene()
+    {
+        var scene = new Scene(_nextSceneID++);
+        return scene;
+    }
+
+    /// <summary>
+    /// Destroys all entities belonging to the specified scene.
+    /// </summary>
+    /// <param name="scene">The scene to unload.</param>
+    public void UnloadScene(Scene scene)
+    {
+        // Build query for entities with SceneID
+        var builder = new QueryBuilder();
+        builder.WithAll([ComponentTypeID<Components.SceneID>.Value]);
+        var queryID = builder.Build(_world);
+        ref var query = ref _world.ComponentManager.GetEntityQueryReference(queryID);
+
+        using var scope = AllocationManager.CreateStackScope();
+        var entitiesToDestroy = new UnsafeList<Entity>(128, scope.AllocationHandle);
+
+        // Iterate through all matching entities
+        foreach (var chunk in query.GetChunkIterator())
+        {
+            var entities = chunk.GetEntities();
+            var sceneIDs = chunk.GetComponentData<Components.SceneID>();
+
+            for (var i = 0; i < chunk.Count; i++)
+            {
+                if (sceneIDs[i].id == scene.ID)
+                {
+                    entitiesToDestroy.Add(entities[i]);
+                }
+            }
+        }
+
+        _world.EntityManager.DestroyEntities(entitiesToDestroy.AsSpan());
+    }
+
+    /// <summary>
+    /// Gets all entities belonging to the specified scene.
+    /// </summary>
+    /// <param name="scene">The scene to query.</param>
+    /// <param name="entities">Span to store the entities.</param>
+    /// <returns>The number of entities written to the span.</returns>
+    public int GetSceneEntities(Scene scene, Span<Entity> entities)
+    {
+        // Build query for entities with SceneID
+        var builder = new QueryBuilder();
+        builder.WithAll([ComponentTypeID<Components.SceneID>.Value]);
+        var queryID = builder.Build(_world);
+        ref var query = ref _world.ComponentManager.GetEntityQueryReference(queryID);
+
+        var index = 0;
+
+        // Iterate through all matching entities
+        foreach (var chunk in query.GetChunkIterator())
+        {
+            var chunkEntities = chunk.GetEntities();
+            var sceneIDs = chunk.GetComponentData<Components.SceneID>();
+
+            for (var i = 0; i < chunk.Count && index < entities.Length; i++)
+            {
+                if (sceneIDs[i].id == scene.ID)
+                {
+                    entities[index++] = chunkEntities[i];
+                }
+            }
+        }
+
+        return index;
     }
 }