.

DoomDeathmatch.sln

@@ -8,6 +8,8 @@ Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "DoomDeathmatchConsole", "Do
 EndProject
 Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "DoomDeathmatchWPF", "DoomDeathmatchWPF\DoomDeathmatchWPF.csproj", "{B712A719-5EB3-4869-AA4A-3BFFA3B9C918}"
 EndProject
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "EngineTests", "EngineTests\EngineTests.csproj", "{CC28C26C-0998-4C13-8855-978658B8B0D6}"
+EndProject
 Global
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution
 		Debug|Any CPU = Debug|Any CPU
@@ -30,5 +32,9 @@ Global
 		{B712A719-5EB3-4869-AA4A-3BFFA3B9C918}.Debug|Any CPU.Build.0 = Debug|Any CPU
 		{B712A719-5EB3-4869-AA4A-3BFFA3B9C918}.Release|Any CPU.ActiveCfg = Release|Any CPU
 		{B712A719-5EB3-4869-AA4A-3BFFA3B9C918}.Release|Any CPU.Build.0 = Release|Any CPU
+		{CC28C26C-0998-4C13-8855-978658B8B0D6}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{CC28C26C-0998-4C13-8855-978658B8B0D6}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{CC28C26C-0998-4C13-8855-978658B8B0D6}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{CC28C26C-0998-4C13-8855-978658B8B0D6}.Release|Any CPU.Build.0 = Release|Any CPU
 	EndGlobalSection
 EndGlobal

Engine/Engine.csproj

@@ -7,14 +7,16 @@
     </PropertyGroup>
 
     <PropertyGroup Condition=" '$(Configuration)' == 'Debug' ">
-      <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
+        <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     </PropertyGroup>
 
     <ItemGroup>
-      <PackageReference Include="OpenTK" Version="4.8.2" />
-      <PackageReference Include="Serilog" Version="4.1.0" />
-      <PackageReference Include="Serilog.Enrichers.Thread" Version="4.0.0" />
-      <PackageReference Include="Serilog.Sinks.Console" Version="6.0.0" />
+        <InternalsVisibleTo Include="EngineTests" />
+        
+        <PackageReference Include="OpenTK" Version="4.8.2"/>
+        <PackageReference Include="Serilog" Version="4.1.0"/>
+        <PackageReference Include="Serilog.Enrichers.Thread" Version="4.0.0"/>
+        <PackageReference Include="Serilog.Sinks.Console" Version="6.0.0"/>
     </ItemGroup>
 
 </Project>

Engine/Scene/Component/Component.cs

@@ -1,8 +0,0 @@
-namespace Engine.Scene.Component;
-
-public abstract class Component(GameObject gameObject)
-{
-    public Guid Id { get; } = Guid.NewGuid();
-
-    public GameObject GameObject { get; } = gameObject;
-}

Engine/Scene/GameObject.cs

@@ -1,73 +0,0 @@
-using Engine.Scene.Component;
-
-namespace Engine.Scene;
-
-public sealed class GameObject
-{
-    public Guid Id { get; } = Guid.NewGuid();
-    public Transform Transform { get; }
-
-    private readonly Queue<Action> _componentActions = new();
-
-    private readonly List<Component.Component> _components = new();
-    private readonly ISet<Type> _addedComponentTypes = new HashSet<Type>();
-
-    public GameObject()
-    {
-        AddComponent<Transform>();
-        UpdateComponents();
-        
-        Transform = GetComponent<Transform>()!;
-    }
-
-    public T? GetComponent<T>() where T : Component.Component
-    {
-        if (!_addedComponentTypes.Contains(typeof(T)))
-            return null;
-
-        return _components.OfType<T>().FirstOrDefault();
-    }
-
-    public void AddComponent<T>(params object?[] args) where T : Component.Component
-    {
-        if (_addedComponentTypes.Contains(typeof(T)))
-            return;
-        
-        var newArgs = new object?[args.Length + 1];
-        newArgs[0] = this;
-        for (var i = 0; i < args.Length; i++)
-            newArgs[i + 1] = args[i];
-
-        var component = (T?)Activator.CreateInstance(typeof(T), newArgs);
-        if (component == null)
-            throw new InvalidOperationException($"Failed to create component of type {typeof(T)}");
-
-        _componentActions.Enqueue(() =>
-        {
-            _components.Add(component);
-            _addedComponentTypes.Add(typeof(T));
-        });
-    }
-
-    public void RemoveComponent<T>() where T : Component.Component
-    {
-        if (!_addedComponentTypes.Contains(typeof(T)) || typeof(T) == typeof(Transform))
-            return;
-
-        var component = GetComponent<T>();
-        if (component == null)
-            return;
-
-        _componentActions.Enqueue(() =>
-        {
-            _components.Remove(component);
-            _addedComponentTypes.Remove(typeof(T));
-        });
-    }
-
-    private void UpdateComponents()
-    {
-        while (_componentActions.TryDequeue(out var action))
-            action();
-    }
-}

Engine/src/Engine.cs

@@ -1,14 +1,8 @@
-using System.Runtime.InteropServices;
-using System.Text;
-using Engine.Renderer.Buffer;
-using Engine.Renderer.Buffer.Vertex;
-using Engine.Renderer.Shader;
-using OpenTK.Graphics.OpenGL;
+using OpenTK.Graphics.OpenGL;
 using OpenTK.Mathematics;
 using OpenTK.Windowing.Common;
 using OpenTK.Windowing.Desktop;
 using Serilog;
-using Serilog.Events;
 using Serilog.Sinks.SystemConsole.Themes;
 
 namespace Engine;
@@ -59,7 +53,7 @@ public sealed class Engine
 
         while (!_window.IsExiting)
         {
-
+            _window.Update();
         }
     }
 }

Engine/src/Renderer/Buffer/IndexBuffer.cs

@@ -15,7 +15,7 @@ public class IndexBuffer : OpenGlObject
         Handle = handle;
 
         GL.NamedBufferStorage(Handle, Count * sizeof(uint), IntPtr.Zero, flags);
-        
+
         Log.Debug("Index buffer {Handle} created with {Count} elements", Handle, Count);
     }
 

Engine/src/Renderer/Buffer/VertexArray.cs

@@ -10,7 +10,7 @@ public class VertexArray : OpenGlObject
 {
     // private IndexBuffer? _boundIndexBuffer;
     // private readonly Dictionary<int, VertexBuffer<IVertex>> _boundVertexBuffers = new();
-    
+
     public VertexArray()
     {
         GL.CreateVertexArrays(1, out int handle);
@@ -20,7 +20,7 @@ public class VertexArray : OpenGlObject
     public void BindIndexBuffer(IndexBuffer buffer)
     {
         GL.VertexArrayElementBuffer(Handle, buffer.Handle);
-        
+
         Log.Debug("Vertex array {Handle} bound to index buffer {Buffer}", Handle, buffer.Handle);
     }
 

Engine/src/Renderer/Buffer/VertexBuffer.cs

@@ -26,7 +26,7 @@ public class VertexBuffer<T> : OpenGlObject
         Handle = handle;
 
         GL.NamedBufferStorage(Handle, Count * _stride, IntPtr.Zero, flags);
-        
+
         Log.Debug("Vertex buffer {Handle} created with {Count} elements of type {Type}", Handle, Count, typeof(T).Name);
     }
 

Engine/src/Renderer/Camera/ICamera.cs

@@ -6,4 +6,5 @@ public interface ICamera
 {
     public Matrix4 View { get; }
     public Matrix4 Projection { get; }
+    public Vector2i ScreenSize { get; internal set; }
 }

Engine/src/Renderer/Camera/ScreenspaceCamera.cs

@@ -6,4 +6,5 @@ public class ScreenspaceCamera : ICamera
 {
     public Matrix4 View => Matrix4.Identity;
     public Matrix4 Projection => Matrix4.Identity;
+    public Vector2i ScreenSize { get; set; }
 }

Engine/src/Renderer/Debug.cs

@@ -1,38 +1,18 @@
 using System.Runtime.InteropServices;
-using Engine.Renderer.Pixel;
 using OpenTK.Graphics.OpenGL;
 using Serilog;
 using Serilog.Events;
 
 namespace Engine.Renderer;
 
-public class Renderer
+internal static class Debug
 {
-    internal Texture.Texture<Rgb8> TextureInternal => _framebuffer.TextureInternal;
-
-    private readonly Framebuffer.Framebuffer _framebuffer;
-    private readonly Queue<Action<Renderer>> _renderActions = new();
-
-    public Renderer(int width, int height)
-    {
-        InitializeOpenGl();
-
-        _framebuffer = new Framebuffer.Framebuffer(width, height);
-    }
-
-    private void InitializeOpenGl()
+    public static void Setup()
     {
         GL.Enable(EnableCap.DebugOutput);
         GL.DebugMessageCallback(DebugCallback, IntPtr.Zero);
-
-        GL.Enable(EnableCap.DepthTest);
-
-        GL.Enable(EnableCap.FramebufferSrgb);
-
-        GL.BlendFunc(BlendingFactor.SrcAlpha, BlendingFactor.OneMinusSrcAlpha);
-        GL.Enable(EnableCap.Blend);
     }
-    
+
     private static void DebugCallback(DebugSource source, DebugType type, int id, DebugSeverity severity, int length,
         IntPtr message, IntPtr userParam)
     {
@@ -53,7 +33,7 @@ public class Renderer
             DebugType.DebugTypeOther => "Info",
             _ => "Unknown"
         };
-        
+
         var sourcePrefix = source switch
         {
             DebugSource.DebugSourceApi => "API",
@@ -65,8 +45,7 @@ public class Renderer
             _ => "Unknown"
         };
 
-        logger.Write(
-            GetLogLevel(severity),
+        logger.Write(GetLogLevel(severity),
             "[OpenGL {TypePrefix}] [{Source}] {Message} (ID: 0x{Id:X8})",
             typePrefix,
             sourcePrefix,
@@ -86,22 +65,4 @@ public class Renderer
             _ => LogEventLevel.Debug
         };
     }
-
-    internal void Commit(Action<Renderer> renderAction)
-    {
-        _renderActions.Enqueue(renderAction);
-    }
-
-    internal void Render()
-    {
-        _framebuffer.Bind();
-        while (_renderActions.TryDequeue(out var renderAction))
-            renderAction(this);
-        _framebuffer.Unbind();
-    }
-
-    internal void Resize(int width, int height)
-    {
-        _framebuffer.Resize(width, height);
-    }
 }

Engine/src/Renderer/Framebuffer/Framebuffer.cs

@@ -29,7 +29,7 @@ public class Framebuffer : OpenGlObject
             _height = value;
         }
     }
-    
+
     public IConstTexture<Rgb8> Texture => _texture;
     internal Texture.Texture<Rgb8> TextureInternal => _texture;
 

Engine/src/Renderer/OpenGLObject.cs

@@ -15,7 +15,7 @@ public abstract class OpenGlObject
     {
         Destroy();
         Handle = -1;
-        
+
         Log.Debug("OpenGL object {Handle} destroyed", Handle);
     }
 }

Engine/src/Renderer/Renderer.cs

@@ -0,0 +1,55 @@
+using System.Runtime.InteropServices;
+using Engine.Renderer.Pixel;
+using Engine.Renderer.Shader;
+using OpenTK.Graphics.OpenGL;
+using Serilog;
+using Serilog.Events;
+
+namespace Engine.Renderer;
+
+public class Renderer
+{
+    internal Texture.Texture<Rgb8> TextureInternal => _framebuffer.TextureInternal;
+
+    private readonly Framebuffer.Framebuffer _framebuffer;
+    private readonly Queue<Action<Renderer>> _renderActions = new();
+
+    public Renderer(int width, int height)
+    {
+        InitializeOpenGl();
+
+        _framebuffer = new Framebuffer.Framebuffer(width, height);
+    }
+
+    private void InitializeOpenGl()
+    {
+#if DEBUG
+        Debug.Setup();
+#endif
+
+        GL.Enable(EnableCap.DepthTest);
+
+        GL.Enable(EnableCap.FramebufferSrgb);
+
+        GL.BlendFunc(BlendingFactor.SrcAlpha, BlendingFactor.OneMinusSrcAlpha);
+        GL.Enable(EnableCap.Blend);
+    }
+
+    internal void Commit(Action<Renderer> renderAction)
+    {
+        _renderActions.Enqueue(renderAction);
+    }
+
+    internal void Render()
+    {
+        _framebuffer.Bind();
+        while (_renderActions.TryDequeue(out var renderAction))
+            renderAction(this);
+        _framebuffer.Unbind();
+    }
+
+    internal void Resize(int width, int height)
+    {
+        _framebuffer.Resize(width, height);
+    }
+}

Engine/src/Renderer/Texture/Texture.cs

@@ -42,7 +42,7 @@ public abstract class Texture<T> : OpenGlObject, ITexture<T> where T : struct, I
         GL.CreateTextures(TextureTarget.Texture2D, 1, out int handle);
         Handle = handle;
     }
-    
+
     public void UploadPixels(int x, int y, int width, int height, T[,] pixels)
     {
         if (x < 0 || y < 0)

Engine/src/Scene/Component/BuiltIn/Camera.cs

@@ -0,0 +1,29 @@
+using Engine.Renderer.Camera;
+using OpenTK.Mathematics;
+
+namespace Engine.Scene.Component.BuiltIn;
+
+public abstract class Camera(
+    float nearPlane,
+    float farPlane
+) : Component, ICamera
+{
+    public float AspectRatio { get; private set; } = 1;
+    public float NearPlane { get; set; } = nearPlane;
+    public float FarPlane { get; set; } = farPlane;
+
+    private Vector2i _screenSize = new(1, 1);
+
+    public abstract Matrix4 View { get; }
+    public abstract Matrix4 Projection { get; }
+
+    public Vector2i ScreenSize
+    {
+        get => _screenSize;
+        set
+        {
+            _screenSize = value;
+            AspectRatio = (float)value.X / value.Y;
+        }
+    }
+}

Engine/src/Scene/Component/BuiltIn/OrthographicCamera.cs

@@ -0,0 +1,27 @@
+using OpenTK.Mathematics;
+
+namespace Engine.Scene.Component.BuiltIn;
+
+public class OrthographicCamera(
+    float nearPlane = 0.1f,
+    float farPlane = 1000f,
+    float size = 10f,
+    OrthographicCamera.Axis axis = OrthographicCamera.Axis.Y
+)
+    : Camera(nearPlane, farPlane)
+{
+    public Axis FixedAxis { get; set; } = axis;
+    public float Size { get; set; } = size;
+
+    public override Matrix4 View => GameObject.Transform.TransformMatrix.Inverted();
+
+    public override Matrix4 Projection => FixedAxis == Axis.X
+        ? Matrix4.CreateOrthographic(Size, Size / AspectRatio, NearPlane, FarPlane)
+        : Matrix4.CreateOrthographic(Size * AspectRatio, Size, NearPlane, FarPlane);
+
+    public enum Axis
+    {
+        X,
+        Y,
+    }
+}

Engine/src/Scene/Component/BuiltIn/PerspectiveCamera.cs

@@ -1,23 +1,18 @@
-using Engine.Renderer.Camera;
-using Engine.Util;
+using Engine.Util;
 using OpenTK.Mathematics;
 
-namespace Engine.Scene.Component;
+namespace Engine.Scene.Component.BuiltIn;
 
 public class PerspectiveCamera(
-    GameObject gameObject,
-    float aspectRatio,
-    float fieldOfView,
-    float nearPlane,
-    float farPlane)
-    : Component(gameObject), ICamera
+    float fieldOfView = 90.0f,
+    float nearPlane = 0.1f,
+    float farPlane = 1000f
+)
+    : Camera(nearPlane, farPlane)
 {
-    public float AspectRatio { get; set; } = aspectRatio;
     public float FieldOfView { get; set; } = fieldOfView;
-    public float NearPlane { get; set; } = nearPlane;
-    public float FarPlane { get; set; } = farPlane;
 
-    public Matrix4 View
+    public override Matrix4 View
     {
         get
         {
@@ -30,5 +25,6 @@ public class PerspectiveCamera(
         }
     }
 
-    public Matrix4 Projection => Matrix4.CreatePerspectiveFieldOfView(FieldOfView, AspectRatio, NearPlane, FarPlane);
+    public override Matrix4 Projection =>
+        Matrix4.CreatePerspectiveFieldOfView(FieldOfView, AspectRatio, NearPlane, FarPlane);
 }

Engine/src/Scene/Component/BuiltIn/Transform.cs

@@ -1,8 +1,8 @@
 using OpenTK.Mathematics;
 
-namespace Engine.Scene.Component;
+namespace Engine.Scene.Component.BuiltIn;
 
-public class Transform(GameObject gameObject) : Component(gameObject)
+public class Transform : Component
 {
     public Vector3 Position { get; set; } = Vector3.Zero;
     public Quaternion Rotation { get; set; } = Quaternion.Identity;
@@ -15,5 +15,25 @@ public class Transform(GameObject gameObject) : Component(gameObject)
 
     public Matrix4 TransformMatrix => LocalTransformMatrix * ParentTransformMatrix;
 
-    private Matrix4 ParentTransformMatrix => Matrix4.Identity;
+    private Matrix4 ParentTransformMatrix
+    {
+        get
+        {
+            var parent = GameObject.Scene?.Hierarchy.GetParent(GameObject);
+            return parent == null ? Matrix4.Identity : parent.Transform.TransformMatrix;
+        }
+    }
+
+    public Transform Clone()
+    {
+        var clone = new Transform
+        {
+            Position = Position,
+            Rotation = Rotation,
+            Scale = Scale,
+            LocalScale = LocalScale
+        };
+
+        return clone;
+    }
 }

Engine/src/Scene/Component/Component.cs

@@ -0,0 +1,45 @@
+namespace Engine.Scene.Component;
+
+public abstract class Component
+{
+    public Guid Id { get; } = Guid.NewGuid();
+
+    public GameObject GameObject { get; internal set; }
+
+    internal virtual void Awake()
+    {
+    }
+
+    internal virtual void Start()
+    {
+    }
+
+    internal virtual void Update()
+    {
+    }
+
+    internal virtual void Render()
+    {
+    }
+
+    internal virtual void Destroy()
+    {
+    }
+}
+
+public static class ComponentTypeExtensions
+{
+    internal static Type GetComponentBaseType(this Type type)
+    {
+        var baseType = type.BaseType;
+        if (baseType == null || baseType == typeof(Component))
+            return type;
+
+        while (baseType.BaseType != null && baseType.BaseType != typeof(Component))
+        {
+            baseType = baseType.BaseType;
+        }
+
+        return baseType;
+    }
+}

Engine/src/Scene/GameObject.cs

@@ -0,0 +1,136 @@
+using System.Reflection;
+using Engine.Scene.Component;
+using Engine.Scene.Component.BuiltIn;
+
+namespace Engine.Scene;
+
+public sealed class GameObject
+{
+    public Guid Id { get; } = Guid.NewGuid();
+    public Transform Transform { get; }
+
+    internal Scene? Scene { get; set; }
+
+    private readonly Queue<Action> _componentActions = new();
+
+    private readonly IList<Component.Component> _components = new List<Component.Component>();
+    private readonly ISet<Type> _addedComponentTypes = new HashSet<Type>();
+
+    public GameObject()
+    {
+        AddComponent<Transform>();
+        ProcessChanges();
+
+        Transform = GetComponent<Transform>()!;
+    }
+
+    public GameObject(Transform transform)
+    {
+        AddComponent(transform.Clone());
+        ProcessChanges();
+
+        Transform = GetComponent<Transform>()!;
+    }
+
+    public void Awake()
+    {
+        foreach (var component in _components)
+            component.Awake();
+    }
+
+    public void Start()
+    {
+        foreach (var component in _components)
+            component.Start();
+    }
+
+    public void Update()
+    {
+        foreach (var component in _components)
+            component.Update();
+    }
+
+    public void Render()
+    {
+        foreach (var component in _components)
+            component.Render();
+    }
+
+    public void Destroy()
+    {
+        foreach (var component in _components)
+            component.Destroy();
+    }
+
+    public T? GetComponent<T>() where T : Component.Component
+    {
+        return !HasComponent<T>() ? null : _components.OfType<T>().First();
+    }
+
+    public void AddComponent<T>() where T : Component.Component, new()
+    {
+        var component = new T();
+        AddComponent(component);
+    }
+
+    public void AddComponent<T>(params object?[] args) where T : Component.Component
+    {
+        var component = (T?)Activator.CreateInstance(
+            typeof(T),
+            BindingFlags.Instance | BindingFlags.Public | BindingFlags.CreateInstance |
+            BindingFlags.OptionalParamBinding,
+            null,
+            args,
+            null
+        );
+
+        if (component == null)
+            throw new InvalidOperationException($"Failed to create component of type {typeof(T)}");
+
+        AddComponent(component);
+    }
+
+    public void AddComponent<T>(T component) where T : Component.Component
+    {
+        _componentActions.Enqueue(() =>
+        {
+            if (HasComponent<T>())
+                throw new ArgumentException($"GameObject already has component of type {typeof(T)}");
+
+            component.GameObject = this;
+            _components.Add(component);
+            _addedComponentTypes.Add(typeof(T).GetComponentBaseType());
+        });
+    }
+
+    public void RemoveComponent<T>() where T : Component.Component
+    {
+        if (typeof(T) == typeof(Transform))
+            throw new ArgumentException("GameObject cannot remove Transform component");
+
+        _componentActions.Enqueue(() =>
+        {
+            if (!HasComponent<T>())
+                throw new ArgumentException($"GameObject does not have component of type {typeof(T)}");
+
+            var component = GetComponent<T>();
+            if (component == null)
+                return;
+
+            _components.Remove(component);
+            _addedComponentTypes.Remove(typeof(T));
+        });
+    }
+
+    public bool HasComponent<T>() where T : Component.Component
+    {
+        var baseType = typeof(T).GetComponentBaseType();
+        return _addedComponentTypes.Contains(baseType);
+    }
+
+    internal void ProcessChanges()
+    {
+        while (_componentActions.TryDequeue(out var action))
+            action();
+    }
+}

Engine/src/Scene/Hierarchy.cs

@@ -0,0 +1,140 @@
+using System.Collections;
+using System.Collections.Concurrent;
+using Engine.Util;
+
+namespace Engine.Scene;
+
+public class Hierarchy<T> : IEnumerable<T>
+    where T : class
+{
+    private readonly Dictionary<NullableObject<T>, IList<T>> _childrenLookup = new();
+    private readonly Dictionary<T, T?> _parentLookup = new();
+
+    private readonly ConcurrentQueue<Action> _hierarchyActions = new();
+
+    public Hierarchy()
+    {
+        _childrenLookup.Add(new NullableObject<T>(), new List<T>());
+    }
+
+    internal void ProcessChanges()
+    {
+        while (_hierarchyActions.TryDequeue(out var action))
+            action();
+    }
+
+    public void Add(T obj)
+    {
+        _hierarchyActions.Enqueue(() =>
+        {
+            if (_parentLookup.ContainsKey(obj))
+                throw new ArgumentException("Object is already added to hierarchy");
+
+            _childrenLookup.Add(obj, new List<T>());
+            _parentLookup.Add(obj, null);
+            _childrenLookup[null].Add(obj);
+        });
+    }
+
+    public void Remove(T obj)
+    {
+        foreach (var child in GetChildren(obj))
+            Remove(child);
+
+        _hierarchyActions.Enqueue(() =>
+        {
+            var parent = GetParent(obj);
+            _childrenLookup[parent].Remove(obj);
+
+            _parentLookup.Remove(obj);
+            _childrenLookup.Remove(obj);
+        });
+    }
+
+    public void AddChild(T parent, T child)
+    {
+        SetParent(child, parent);
+    }
+
+    private void SetParent(T child, T? parent)
+    {
+        if (child.Equals(parent))
+            throw new InvalidOperationException("Child cannot be parent");
+
+        _hierarchyActions.Enqueue(() =>
+        {
+            if (IsInHierarchy(child, parent))
+                throw new InvalidOperationException("Parent is a child of child");
+
+            var oldParent = GetParent(child);
+            _childrenLookup[oldParent].Remove(child);
+
+            _childrenLookup[parent].Add(child);
+            _parentLookup[child] = parent;
+        });
+    }
+
+    public bool Contains(T obj)
+    {
+        return _parentLookup.ContainsKey(obj) && _childrenLookup.ContainsKey(obj);
+    }
+
+    public T? GetParent(T child)
+    {
+        return _parentLookup.TryGetValue(child, out var parent)
+            ? parent
+            : throw new InvalidOperationException($"Child {child} is not in hierarchy");
+    }
+
+    public IEnumerable<T> GetChildren(T? obj = null)
+    {
+        return _childrenLookup.TryGetValue(obj, out var children) ? children : Enumerable.Empty<T>();
+    }
+
+    public bool IsInHierarchy(T? ancestor, T? child)
+    {
+        if (child == null) // if child is null (root), then it is not in hierarchy, as root can not have a parent
+            return false;
+
+        if (ancestor == null) // if ancestor is null (root), then child is not in hierarchy, as root is not a parent
+            return false;
+
+        if (ancestor.Equals(child))
+            return true;
+
+        var parent = GetParent(child);
+
+        if (parent == null)
+            return false;
+
+        if (ancestor.Equals(parent))
+            return true;
+
+        return IsInHierarchy(ancestor, parent);
+    }
+
+    public IEnumerable<T> GetAllChildren(T? obj = null)
+    {
+        var children = GetChildren(obj);
+
+        foreach (var child in children)
+        {
+            yield return child;
+
+            foreach (var descendant in GetAllChildren(child))
+            {
+                yield return descendant;
+            }
+        }
+    }
+
+    public IEnumerator<T> GetEnumerator()
+    {
+        return _parentLookup.Keys.GetEnumerator();
+    }
+
+    IEnumerator IEnumerable.GetEnumerator()
+    {
+        return GetEnumerator();
+    }
+}

Engine/src/Scene/Scene.cs

@@ -0,0 +1,108 @@
+using Engine.Renderer.Camera;
+using Engine.Scene.Component.BuiltIn;
+
+namespace Engine.Scene;
+
+public class Scene
+{
+    public bool IsPlaying { get; private set; }
+    public ICamera? Camera { get; private set; }
+
+    internal Hierarchy<GameObject> Hierarchy { get; } = [];
+
+    private readonly Queue<Action> _sceneActions = [];
+
+    internal void Enter()
+    {
+        if (IsPlaying)
+            throw new InvalidOperationException("Scene is already playing");
+
+        ProcessChanges();
+
+        Camera = FindFirstComponent<Camera>();
+
+        IsPlaying = true;
+    }
+
+    public T? FindFirstComponent<T>() where T : Component.Component
+    {
+        return Hierarchy.Select(gameObject => gameObject.GetComponent<T>()).OfType<T>().FirstOrDefault();
+    }
+
+    internal void Update()
+    {
+        if (!IsPlaying)
+            throw new InvalidOperationException("Scene is not playing");
+
+        ProcessChanges();
+
+        foreach (var gameObject in Hierarchy)
+            gameObject.Update();
+    }
+
+    internal void Render()
+    {
+        if (!IsPlaying)
+            throw new InvalidOperationException("Scene is not playing");
+
+        foreach (var gameObject in Hierarchy)
+        {
+            gameObject.Render();
+        }
+    }
+
+    internal void Exit()
+    {
+        if (!IsPlaying)
+            throw new InvalidOperationException("Scene is not playing");
+
+        foreach (var gameObject in Hierarchy)
+        {
+            gameObject.Destroy();
+        }
+
+        IsPlaying = false;
+    }
+
+    public void Add(GameObject gameObject)
+    {
+        Hierarchy.Add(gameObject);
+
+        _sceneActions.Enqueue(() =>
+        {
+            gameObject.Scene = this;
+
+            gameObject.Awake();
+            gameObject.Start();
+        });
+    }
+
+    public void Remove(GameObject gameObject)
+    {
+        Hierarchy.Remove(gameObject);
+
+        _sceneActions.Enqueue(() =>
+        {
+            foreach (var child in Hierarchy.GetAllChildren(gameObject))
+            {
+                child.Destroy();
+                child.Scene = null;
+            }
+
+            gameObject.Destroy();
+
+            gameObject.Scene = null;
+        });
+    }
+
+    private void ProcessChanges()
+    {
+        Hierarchy.ProcessChanges();
+
+        while (_sceneActions.TryDequeue(out var action))
+            action();
+
+        foreach (var gameObject in Hierarchy)
+            gameObject.ProcessChanges();
+    }
+}

Engine/src/Util/NullableObject.cs

@@ -0,0 +1,55 @@
+namespace Engine.Util;
+
+public readonly struct NullableObject<T>
+    where T : class
+{
+    public bool IsNull => _value == null;
+    public T? Value => _value;
+
+    private readonly T? _value;
+
+    public NullableObject()
+    {
+        _value = null;
+    }
+
+    public NullableObject(T? value)
+    {
+        _value = value;
+    }
+
+    public static implicit operator T?(NullableObject<T> nullableObject) => nullableObject.Value;
+    public static implicit operator NullableObject<T>(T? value) => new(value);
+
+    public override string ToString()
+    {
+        return _value?.ToString() ?? "null";
+    }
+
+    public override bool Equals(object? obj)
+    {
+        if (obj == null)
+            return IsNull;
+
+        if (obj is not NullableObject<T> other)
+            return false;
+
+        if (IsNull && other.IsNull)
+            return true;
+
+        return _value!.Equals(other._value);
+    }
+
+    public override int GetHashCode()
+    {
+        if (IsNull)
+            return 0;
+
+        var hashCode = _value!.GetHashCode();
+
+        if (hashCode >= 0)
+            hashCode += 1;
+
+        return hashCode;
+    }
+}

Engine/src/Window.cs

@@ -10,9 +10,9 @@ namespace Engine;
 public class Window : IPresenter<Rgb8>
 {
     public bool IsExiting => _window.IsExiting;
-    public int Width => _window.ClientSize.X;
-    public int Height => _window.ClientSize.Y;
-    
+    public int Width { get; private set; }
+    public int Height { get; private set; }
+
     private readonly Engine _engine;
     private readonly NativeWindow _window;
     private readonly bool _headless;
@@ -22,9 +22,15 @@ public class Window : IPresenter<Rgb8>
         _engine = engine;
         _window = window;
         _headless = headless;
-        
+
+        (Width, Height) = _window.ClientSize;
+
         _window.MakeCurrent();
-        _window.Resize +=  args => GL.Viewport(0, 0, args.Width, args.Height);
+        _window.Resize += args =>
+        {
+            Width = args.Width;
+            Height = args.Height;
+        };
     }
 
     public void Update()
@@ -42,30 +48,30 @@ public class Window : IPresenter<Rgb8>
             return;
 
         GL.Clear(ClearBufferMask.ColorBufferBit | ClearBufferMask.DepthBufferBit);
-        
+
         _engine.Renderer.TextureInternal.Bind();
-        
+
         GL.Enable(EnableCap.Texture2D);
         GL.Begin(PrimitiveType.Quads);
         GL.Color3(1, 1, 1);
-        
+
         GL.TexCoord2(0, 0);
         GL.Vertex2(0, 0);
-        
+
         GL.TexCoord2(1, 0);
         GL.Vertex2(1, 0);
-        
+
         GL.TexCoord2(1, 1);
         GL.Vertex2(1, 1);
-        
+
         GL.TexCoord2(0, 1);
         GL.Vertex2(0, 1);
-        
+
         GL.End();
-        
+
         GL.Disable(EnableCap.Texture2D);
         GL.Flush();
-        
+
         _engine.Renderer.TextureInternal.Unbind();
     }
 }

EngineTests/src/Scene/GameObjectTests.cs

@@ -0,0 +1,71 @@
+using Engine.Scene;
+using Engine.Scene.Component.BuiltIn;
+
+namespace EngineTests.Scene;
+
+public class GameObjectTests
+{
+    private GameObject _gameObject;
+
+    [SetUp]
+    public void Setup()
+    {
+        _gameObject = new GameObject();
+    }
+
+    [Test]
+    public void Constructor_ShouldInitializeWithTransformComponent()
+    {
+        Assert.Multiple(() =>
+        {
+            Assert.That(_gameObject.Transform, Is.Not.Null);
+            Assert.That(_gameObject.HasComponent<Transform>(), Is.True);
+        });
+    }
+
+    [Test]
+    public void AddComponent_ShouldThrowIfComponentAlreadyExists()
+    {
+        _gameObject.AddComponent<Transform>();
+
+        Assert.Throws<ArgumentException>(() => _gameObject.ProcessChanges());
+    }
+
+    [Test]
+    public void AddComponent_ShouldAddComponentToGameObject()
+    {
+        _gameObject.AddComponent<OrthographicCamera>();
+        _gameObject.ProcessChanges();
+
+        Assert.Multiple(() =>
+        {
+            Assert.That(_gameObject.GetComponent<OrthographicCamera>(), Is.Not.Null);
+            Assert.That(_gameObject.HasComponent<OrthographicCamera>(), Is.True);
+        });
+    }
+
+    [Test]
+    public void AddComponent_ShouldAddComponentToGameObjectWithArgs()
+    {
+        _gameObject.AddComponent<PerspectiveCamera>(99, 0.2f, 1001f);
+        _gameObject.ProcessChanges();
+
+        var camera = _gameObject.GetComponent<PerspectiveCamera>()!;
+
+        Assert.Multiple(() =>
+        {
+            Assert.That(camera.FieldOfView, Is.EqualTo(99));
+            Assert.That(camera.NearPlane, Is.EqualTo(0.2f));
+            Assert.That(camera.FarPlane, Is.EqualTo(1001f));
+        });
+    }
+
+    [Test]
+    public void AddComponent_ShouldThrowIfComponentBaseTypeAlreadyExists()
+    {
+        _gameObject.AddComponent<OrthographicCamera>();
+        _gameObject.AddComponent<PerspectiveCamera>();
+
+        Assert.Throws<ArgumentException>(() => _gameObject.ProcessChanges());
+    }
+}

EngineTests/src/Scene/HierarchyTests.cs

@@ -0,0 +1,566 @@
+using Engine.Scene;
+
+namespace EngineTests.Scene;
+
+public class HierarchyTests
+{
+    private Hierarchy<object> _hierarchy;
+
+    [SetUp]
+    public void Setup()
+    {
+        _hierarchy = new Hierarchy<object>();
+    }
+
+    [Test]
+    public void AddToRoot()
+    {
+        var obj = new object();
+        _hierarchy.Add(obj);
+        _hierarchy.ProcessChanges();
+
+        Assert.Multiple(() =>
+        {
+            Assert.That(_hierarchy.GetChildren().Count(), Is.EqualTo(1));
+            Assert.That(_hierarchy.GetParent(obj), Is.Null);
+        });
+    }
+
+    [Test]
+    public void AddToChild()
+    {
+        var parent = new object();
+        var child = new object();
+
+        _hierarchy.Add(parent);
+        _hierarchy.Add(child);
+
+        _hierarchy.AddChild(parent, child);
+        _hierarchy.ProcessChanges();
+
+        Assert.Multiple(() =>
+        {
+            Assert.That(_hierarchy.GetChildren(parent).Count(), Is.EqualTo(1));
+            Assert.That(_hierarchy.GetParent(parent), Is.Null);
+            Assert.That(_hierarchy.GetParent(child), Is.EqualTo(parent));
+        });
+    }
+
+    [Test]
+    public void RemoveChild()
+    {
+        var parent = new object();
+        var child = new object();
+
+        _hierarchy.Add(parent);
+        _hierarchy.Add(child);
+
+        _hierarchy.AddChild(parent, child);
+        _hierarchy.ProcessChanges();
+
+        _hierarchy.Remove(child);
+        _hierarchy.ProcessChanges();
+
+        Assert.Multiple(() =>
+        {
+            Assert.That(_hierarchy.GetChildren(parent).Count(), Is.EqualTo(0));
+            Assert.That(_hierarchy.Contains(child), Is.False);
+        });
+    }
+
+    [Test]
+    public void RemoveParentAndAllChildren()
+    {
+        var parent = new object();
+        var child1 = new object();
+        var child2 = new object();
+
+        _hierarchy.Add(parent);
+        _hierarchy.Add(child1);
+        _hierarchy.Add(child2);
+
+        _hierarchy.AddChild(parent, child1);
+        _hierarchy.AddChild(parent, child2);
+        _hierarchy.ProcessChanges();
+
+        _hierarchy.Remove(parent);
+        _hierarchy.ProcessChanges();
+
+        Assert.Multiple(() =>
+        {
+            Assert.That(_hierarchy.GetChildren().Count(), Is.EqualTo(0));
+            Assert.That(_hierarchy.Contains(child1), Is.False);
+            Assert.That(_hierarchy.Contains(child2), Is.False);
+            Assert.That(_hierarchy.Contains(parent), Is.False);
+        });
+    }
+
+    [Test]
+    public void DetectCycleInHierarchy()
+    {
+        var parent = new object();
+        var child = new object();
+
+        _hierarchy.Add(parent);
+        _hierarchy.AddChild(parent, child);
+        _hierarchy.AddChild(child, parent);
+
+        Assert.Throws<InvalidOperationException>(() => _hierarchy.ProcessChanges());
+    }
+
+    [Test]
+    public void IsInHierarchy_PositiveCase()
+    {
+        var ancestor = new object();
+        var child = new object();
+
+        _hierarchy.Add(ancestor);
+        _hierarchy.Add(child);
+
+        _hierarchy.AddChild(ancestor, child);
+        _hierarchy.ProcessChanges();
+
+        Assert.That(_hierarchy.IsInHierarchy(ancestor, child), Is.True);
+    }
+
+    [Test]
+    public void IsInHierarchy_NegativeCase()
+    {
+        var obj1 = new object();
+        var obj2 = new object();
+
+        _hierarchy.Add(obj1);
+        _hierarchy.Add(obj2);
+        _hierarchy.ProcessChanges();
+
+        Assert.That(_hierarchy.IsInHierarchy(obj1, obj2), Is.False);
+    }
+
+    [Test]
+    public void MultipleChildrenHandling()
+    {
+        var parent = new object();
+        var child1 = new object();
+        var child2 = new object();
+
+        _hierarchy.Add(parent);
+        _hierarchy.Add(child1);
+        _hierarchy.Add(child2);
+
+        _hierarchy.AddChild(parent, child1);
+        _hierarchy.AddChild(parent, child2);
+        _hierarchy.ProcessChanges();
+
+        Assert.Multiple(() =>
+        {
+            Assert.That(_hierarchy.GetChildren(parent).Count(), Is.EqualTo(2));
+            Assert.That(_hierarchy.GetParent(child1), Is.EqualTo(parent));
+            Assert.That(_hierarchy.GetParent(child2), Is.EqualTo(parent));
+        });
+    }
+
+    [Test]
+    public void GetChildren_EmptyCase()
+    {
+        var obj = new object();
+        _hierarchy.Add(obj);
+        _hierarchy.ProcessChanges();
+
+        Assert.That(_hierarchy.GetChildren(obj).Count(), Is.EqualTo(0));
+    }
+
+    [Test]
+    public void AddDuplicateObjectThrows()
+    {
+        var obj = new object();
+
+        _hierarchy.Add(obj);
+        _hierarchy.Add(obj);
+
+        Assert.Throws<ArgumentException>(() => _hierarchy.ProcessChanges());
+    }
+
+    [Test]
+    public void AddChild_ParentNotInHierarchyThrows()
+    {
+        var parent = new object();
+        var child = new object();
+
+        _hierarchy.Add(child);
+        _hierarchy.AddChild(parent, child);
+
+        Assert.Throws<InvalidOperationException>(() => _hierarchy.ProcessChanges());
+    }
+
+    [Test]
+    public void GetParent_ObjectNotInHierarchyThrows()
+    {
+        var obj = new object();
+
+        Assert.That(_hierarchy.Contains(obj), Is.False);
+    }
+
+    [Test]
+    public void NestedHierarchyTest()
+    {
+        var grandParent = new object();
+        var parent = new object();
+        var child = new object();
+
+        _hierarchy.Add(grandParent);
+        _hierarchy.Add(parent);
+        _hierarchy.Add(child);
+
+        _hierarchy.AddChild(grandParent, parent);
+        _hierarchy.AddChild(parent, child);
+        _hierarchy.ProcessChanges();
+
+        Assert.Multiple(() =>
+        {
+            Assert.That(_hierarchy.GetParent(parent), Is.EqualTo(grandParent));
+            Assert.That(_hierarchy.GetParent(child), Is.EqualTo(parent));
+            Assert.That(_hierarchy.IsInHierarchy(grandParent, child), Is.True);
+        });
+    }
+
+    [Test]
+    public void ReparentObjectTest()
+    {
+        var parent1 = new object();
+        var parent2 = new object();
+        var child = new object();
+
+        _hierarchy.Add(parent1);
+        _hierarchy.Add(parent2);
+        _hierarchy.Add(child);
+
+        _hierarchy.AddChild(parent1, child);
+        _hierarchy.ProcessChanges();
+
+        // Reparent the child to parent2
+        _hierarchy.AddChild(parent2, child);
+        _hierarchy.ProcessChanges();
+
+        Assert.Multiple(() =>
+        {
+            Assert.That(_hierarchy.GetChildren(parent1).Count(), Is.EqualTo(0));
+            Assert.That(_hierarchy.GetChildren(parent2).Count(), Is.EqualTo(1));
+            Assert.That(_hierarchy.GetParent(child), Is.EqualTo(parent2));
+        });
+    }
+
+    [Test]
+    public void RemoveRootObjectsTest()
+    {
+        var obj1 = new object();
+        var obj2 = new object();
+
+        _hierarchy.Add(obj1);
+        _hierarchy.Add(obj2);
+        _hierarchy.ProcessChanges();
+
+        _hierarchy.Remove(obj1);
+        _hierarchy.ProcessChanges();
+
+        Assert.Multiple(() =>
+        {
+            Assert.That(_hierarchy.GetChildren().Count(), Is.EqualTo(1));
+            Assert.That(_hierarchy.Contains(obj1), Is.False);
+        });
+    }
+
+    [Test]
+    public void IsInHierarchy_SelfTest()
+    {
+        var obj = new object();
+        _hierarchy.Add(obj);
+        _hierarchy.ProcessChanges();
+
+        Assert.That(_hierarchy.IsInHierarchy(obj, obj), Is.True);
+    }
+
+    [Test]
+    public void ComplexHierarchyRemovalTest()
+    {
+        var grandParent = new object();
+        var parent1 = new object();
+        var parent2 = new object();
+        var child1 = new object();
+        var child2 = new object();
+
+        _hierarchy.Add(grandParent);
+        _hierarchy.Add(parent1);
+        _hierarchy.Add(parent2);
+        _hierarchy.Add(child1);
+        _hierarchy.Add(child2);
+
+        _hierarchy.AddChild(grandParent, parent1);
+        _hierarchy.AddChild(grandParent, parent2);
+        _hierarchy.AddChild(parent1, child1);
+        _hierarchy.AddChild(parent2, child2);
+        _hierarchy.ProcessChanges();
+
+        _hierarchy.Remove(parent1);
+        _hierarchy.ProcessChanges();
+
+        Assert.Multiple(() =>
+        {
+            Assert.That(_hierarchy.GetChildren(grandParent).Count(), Is.EqualTo(1));
+            Assert.That(_hierarchy.Contains(child1), Is.False);
+            Assert.That(_hierarchy.Contains(parent1), Is.False);
+        });
+    }
+
+    [Test]
+    public void AddChild_SelfAsParentThrowsException()
+    {
+        var obj = new object();
+        _hierarchy.Add(obj);
+
+        Assert.Throws<InvalidOperationException>(() => _hierarchy.AddChild(obj, obj));
+    }
+
+    [Test]
+    public void MultiLevelReparentingTest()
+    {
+        var grandParent = new object();
+        var parent = new object();
+        var child1 = new object();
+        var child2 = new object();
+
+        _hierarchy.Add(grandParent);
+        _hierarchy.Add(parent);
+        _hierarchy.Add(child1);
+        _hierarchy.Add(child2);
+
+        // Initial hierarchy setup
+        _hierarchy.AddChild(grandParent, parent);
+        _hierarchy.AddChild(parent, child1);
+        _hierarchy.AddChild(parent, child2);
+        _hierarchy.ProcessChanges();
+
+        // Reparent child1 to child2
+        _hierarchy.AddChild(child2, child1);
+        _hierarchy.ProcessChanges();
+
+        Assert.Multiple(() =>
+        {
+            Assert.That(_hierarchy.GetChildren(parent).Count(), Is.EqualTo(1));
+            Assert.That(_hierarchy.GetParent(child1), Is.EqualTo(child2));
+            Assert.That(_hierarchy.IsInHierarchy(grandParent, child1), Is.True);
+        });
+    }
+
+    [Test]
+    public void DeepHierarchyTest()
+    {
+        const int hierarchyDepth = 100;
+        var objects = new object[hierarchyDepth];
+
+        // Create objects
+        for (var i = 0; i < hierarchyDepth; i++)
+        {
+            objects[i] = new object();
+            _hierarchy.Add(objects[i]);
+        }
+
+        // Create a deep hierarchy
+        for (var i = 1; i < hierarchyDepth; i++)
+        {
+            _hierarchy.AddChild(objects[i - 1], objects[i]);
+        }
+
+        _hierarchy.ProcessChanges();
+
+        Assert.Multiple(() =>
+        {
+            // Verify parent-child relationships
+            for (var i = 1; i < hierarchyDepth; i++)
+            {
+                Assert.That(_hierarchy.GetParent(objects[i]), Is.EqualTo(objects[i - 1]));
+                Assert.That(_hierarchy.IsInHierarchy(objects[0], objects[i]), Is.True);
+            }
+
+            // Verify children
+            for (var i = 0; i < hierarchyDepth - 1; i++)
+            {
+                var children = _hierarchy.GetChildren(objects[i]).ToList();
+                Assert.That(children, Has.Count.EqualTo(1));
+                Assert.That(children[0], Is.EqualTo(objects[i + 1]));
+            }
+        });
+    }
+
+    [Test]
+    public void RemoveFromMiddleOfHierarchyTest()
+    {
+        var grandParent = new object();
+        var parent = new object();
+        var child1 = new object();
+        var child2 = new object();
+
+        _hierarchy.Add(grandParent);
+        _hierarchy.Add(parent);
+        _hierarchy.Add(child1);
+        _hierarchy.Add(child2);
+
+        _hierarchy.AddChild(grandParent, parent);
+        _hierarchy.AddChild(parent, child1);
+        _hierarchy.AddChild(parent, child2);
+        _hierarchy.ProcessChanges();
+
+        // Remove parent, which will also remove its children
+        _hierarchy.Remove(parent);
+        _hierarchy.ProcessChanges();
+
+        Assert.Multiple(() =>
+        {
+            Assert.That(_hierarchy.GetChildren(grandParent).Count(), Is.EqualTo(0));
+            Assert.That(_hierarchy.Contains(child1), Is.False);
+            Assert.That(_hierarchy.Contains(child2), Is.False);
+            Assert.That(_hierarchy.Contains(parent), Is.False);
+        });
+    }
+
+    [Test]
+    public void ConcurrentModificationTest()
+    {
+        var parent = new object();
+        var children = Enumerable.Range(0, 10)
+            .Select(_ => new object())
+            .ToList();
+
+        _hierarchy.Add(parent);
+        children.ForEach(child => _hierarchy.Add(child));
+
+        // Simulate concurrent child additions
+        children.AsParallel().ForAll(child => { _hierarchy.AddChild(parent, child); });
+
+        _hierarchy.ProcessChanges();
+
+        Assert.That(_hierarchy.GetChildren(parent).Count(), Is.EqualTo(children.Count));
+    }
+
+    [Test]
+    public void IsInHierarchy_NullInputs()
+    {
+        Assert.Multiple(() =>
+        {
+            // Null child
+            Assert.That(_hierarchy.IsInHierarchy(new object(), null), Is.False);
+
+            // Null ancestor
+            Assert.That(_hierarchy.IsInHierarchy(null, new object()), Is.False);
+
+            // Both null
+            Assert.That(_hierarchy.IsInHierarchy(null, null), Is.False);
+        });
+    }
+
+    [Test]
+    public void IsInHierarchy_SameObject()
+    {
+        var obj = new object();
+        _hierarchy.Add(obj);
+        _hierarchy.ProcessChanges();
+
+        Assert.That(_hierarchy.IsInHierarchy(obj, obj), Is.True);
+    }
+
+    [Test]
+    public void IsInHierarchy_DirectParentChild()
+    {
+        var parent = new object();
+        var child = new object();
+
+        _hierarchy.Add(parent);
+        _hierarchy.Add(child);
+        _hierarchy.AddChild(parent, child);
+        _hierarchy.ProcessChanges();
+
+        Assert.Multiple(() =>
+        {
+            Assert.That(_hierarchy.IsInHierarchy(parent, child), Is.True);
+            Assert.That(_hierarchy.IsInHierarchy(child, parent), Is.False);
+        });
+    }
+
+    [Test]
+    public void IsInHierarchy_DeepHierarchy()
+    {
+        var grandParent = new object();
+        var parent = new object();
+        var child = new object();
+        var grandChild = new object();
+
+        _hierarchy.Add(grandParent);
+        _hierarchy.Add(parent);
+        _hierarchy.Add(child);
+        _hierarchy.Add(grandChild);
+
+        _hierarchy.AddChild(grandParent, parent);
+        _hierarchy.AddChild(parent, child);
+        _hierarchy.AddChild(child, grandChild);
+        _hierarchy.ProcessChanges();
+
+        Assert.Multiple(() =>
+        {
+            // Verify deep hierarchy relationships
+            Assert.That(_hierarchy.IsInHierarchy(grandParent, grandChild), Is.True);
+            Assert.That(_hierarchy.IsInHierarchy(parent, grandChild), Is.True);
+            Assert.That(_hierarchy.IsInHierarchy(child, grandChild), Is.True);
+
+            // Verify inverse relationships are false
+            Assert.That(_hierarchy.IsInHierarchy(grandChild, grandParent), Is.False);
+            Assert.That(_hierarchy.IsInHierarchy(grandChild, parent), Is.False);
+            Assert.That(_hierarchy.IsInHierarchy(grandChild, child), Is.False);
+        });
+    }
+
+    [Test]
+    public void IsInHierarchy_SeparateBranches()
+    {
+        var root = new object();
+        var branch1Parent = new object();
+        var branch1Child = new object();
+        var branch2Parent = new object();
+        var branch2Child = new object();
+
+        _hierarchy.Add(root);
+        _hierarchy.Add(branch1Parent);
+        _hierarchy.Add(branch1Child);
+        _hierarchy.Add(branch2Parent);
+        _hierarchy.Add(branch2Child);
+
+        _hierarchy.AddChild(root, branch1Parent);
+        _hierarchy.AddChild(root, branch2Parent);
+        _hierarchy.AddChild(branch1Parent, branch1Child);
+        _hierarchy.AddChild(branch2Parent, branch2Child);
+        _hierarchy.ProcessChanges();
+
+        Assert.Multiple(() =>
+        {
+            // Verify within same branch
+            Assert.That(_hierarchy.IsInHierarchy(root, branch1Parent), Is.True);
+            Assert.That(_hierarchy.IsInHierarchy(root, branch1Child), Is.True);
+            Assert.That(_hierarchy.IsInHierarchy(branch1Parent, branch1Child), Is.True);
+
+            // Verify between different branches
+            Assert.That(_hierarchy.IsInHierarchy(branch1Parent, branch2Child), Is.False);
+            Assert.That(_hierarchy.IsInHierarchy(branch2Parent, branch1Child), Is.False);
+        });
+    }
+
+    [Test]
+    public void IsInHierarchy_ObjectsNotInHierarchy()
+    {
+        var obj1 = new object();
+        var obj2 = new object();
+
+        _hierarchy.Add(obj1);
+        _hierarchy.Add(obj2);
+        _hierarchy.ProcessChanges();
+
+        Assert.That(_hierarchy.IsInHierarchy(obj1, obj2), Is.False);
+    }
+}