feat: switch default backend to Silk.NET OpenGL

- OpenGLRenderContext: Initialize() + CreateOpenGL() for non-blocking
- OpenGLWindow: Initialize() instead of Run(), CreateGL() method
- Program.cs: default backend is now 'opengl', SwapBuffers per frame
- ImGui guarded: only initialized for RaylibRenderer, ObjectManipulator
  checks _imGuiAvailable before calling ImGui.GetIO()
- 66/66 tests, 145 FPS with OpenGL backend

imgui.ini

@@ -14,7 +14,7 @@ Size=250,398
 Collapsed=0
 
 [Window][Inspector]
-Pos=36,302
+Pos=112,297
 Size=300,425
 Collapsed=0
 

src/CortexEngine.App/CortexEngine.App.csproj

@@ -26,6 +26,7 @@
     <ProjectReference Include="..\Engine.Graphics.Vulkan\Engine.Graphics.Vulkan.csproj" />
     <ProjectReference Include="..\Engine.AI\Engine.AI.csproj" />
     <ProjectReference Include="..\Engine.Physics\Engine.Physics.csproj" />
+    <ProjectReference Include="..\Engine.Graphics.OpenGL\Engine.Graphics.OpenGL.csproj" />
   </ItemGroup>
 
   <ItemGroup>

src/CortexEngine.App/ObjectManipulator.cs

@@ -28,10 +28,14 @@ public sealed class ObjectManipulator
     /// Process input for object picking and dragging.
     /// Returns true if input was consumed (ImGui should be ignored).
     /// </summary>
+    private bool _imGuiAvailable;
+
+    public void SetImGuiAvailable(bool available) => _imGuiAvailable = available;
+
     public bool ProcessInput(World world, Camera camera, IInputState input)
     {
         // Skip if ImGui is capturing mouse
-        if (ImGuiNET.ImGui.GetIO().WantCaptureMouse)
+        if (_imGuiAvailable && ImGuiNET.ImGui.GetIO().WantCaptureMouse)
         {
             _isDragging = false;
             return false;

src/CortexEngine.App/Program.cs

@@ -11,6 +11,7 @@ using Engine.Core;
 using Engine.Core.Components;
 using Engine.Graphics;
 using Engine.Graphics.Loaders;
+using Engine.Graphics.OpenGL;
 using Engine.Graphics.RaylibBackend;
 using Engine.Graphics.Vulkan;
 using Engine.Physics;
@@ -43,19 +44,22 @@ class Program
 
             RaylibBackendRegistrar.EnsureRegistered();
             VulkanBackendRegistrar.EnsureRegistered();
-            using var renderContext = RenderBackendFactory.Create("raylib", 1280, 720, enableValidation: false);
+            OpenGLBackendRegistrar.EnsureRegistered();
+            using var renderContext = RenderBackendFactory.Create("opengl", 1280, 720, enableValidation: false);
             var window = renderContext.Window;
             var input = window.Input;
             using var renderer = renderContext.CreateRenderer();
 
-            // ImGui editor layer
-            var imGuiLayer = new ImGuiLayer();
+            // ImGui editor layer (Raylib only)
+            ImGuiLayer? imGuiLayer = null;
             var objectManipulator = new ObjectManipulator();
-            if (!cameraTour)
+            objectManipulator.SetImGuiAvailable(false);
+            if (!cameraTour && renderer is RaylibRenderer rlRenderer)
             {
+                imGuiLayer = new ImGuiLayer();
                 imGuiLayer.Initialize();
-                if (renderer is RaylibRenderer rlRenderer)
-                    rlRenderer.ImGuiLayer = imGuiLayer;
+                rlRenderer.ImGuiLayer = imGuiLayer;
+                objectManipulator.SetImGuiAvailable(true);
             }
 
             var (modelPath, mcpPort) = ParseArgs(args);
@@ -283,15 +287,18 @@ class Program
                 }
 
                 // Feed frame data to ImGui before rendering.
-                imGuiLayer.SetFrameData(world, timing, currentFps);
+                if (imGuiLayer != null)
+                    imGuiLayer.SetFrameData(world, timing, currentFps);
 
-                // Sync selection between manipulator and ImGui
-                if (objectManipulator.IsDragging && !string.IsNullOrEmpty(objectManipulator.SelectedEntityName))
-                    imGuiLayer.SetSelectedEntity(objectManipulator.SelectedEntityName);
+            objectManipulator.SetImGuiAvailable(imGuiLayer != null);
 
                 renderer.RenderWorld(world);
                 queue.CompletePendingScreenshots();
 
+                // Swap buffers for OpenGL backend
+                if (renderContext is OpenGLRenderContext glCtx2)
+                    glCtx2.SwapBuffers();
+
                 frames++;
                 if (timing.TotalTime - lastFpsTime >= 1.0)
                 {
@@ -303,7 +310,7 @@ class Program
             }
 
             Console.WriteLine("Shutting down...");
-            imGuiLayer.Dispose();
+            imGuiLayer?.Dispose();
 #if !RELEASE_AOT
             if (mcpApp != null)
                 await mcpApp.StopAsync();

src/Engine.Graphics.OpenGL/OpenGLRenderContext.cs

@@ -1,7 +1,9 @@
 using Engine.Core;
 using Engine.Graphics;
 using Silk.NET.OpenGL;
+using Silk.NET.Windowing;
 using SilkWindow = Silk.NET.Windowing.IWindow;
+using CoreIWindow = Engine.Core.IWindow;
 
 namespace Engine.Graphics.OpenGL;
 
@@ -12,16 +14,15 @@ public sealed class OpenGLRenderContext : IRenderContext
     private OpenGLRenderer? _renderer;
     private bool _disposed;
 
-    public IWindow Window => _window;
+    public CoreIWindow Window => _window;
 
     public OpenGLRenderContext(int width, int height, bool enableValidation = false)
     {
         _window = new OpenGLWindow("Cortex Engine (OpenGL)", width, height);
-    }
-
-    public void OnLoad()
-    {
-        _gl = _window.SilkView.CreateOpenGL();
+        // Initialize() triggers the Load callback which creates the GL context
+        _window.SilkView.Initialize();
+        // After Initialize, CreateOpenGL should work
+        _gl = _window.CreateGL();
         _window.OnLoad();
     }
 
@@ -31,10 +32,9 @@ public sealed class OpenGLRenderContext : IRenderContext
         return _renderer;
     }
 
-    public void Resize(int width, int height)
-    {
-        _renderer?.SetScreenSize(width, height);
-    }
+    public void Resize(int width, int height) => _renderer?.SetScreenSize(width, height);
+
+    public void SwapBuffers() => _window.SilkView.SwapBuffers();
 
     public void Dispose()
     {

src/Engine.Graphics.OpenGL/OpenGLWindow.cs

@@ -2,6 +2,7 @@ using System;
 using System.Collections.Generic;
 using Engine.Core;
 using Silk.NET.Input;
+using Silk.NET.OpenGL;
 using Silk.NET.Windowing;
 using SilkWindow = Silk.NET.Windowing.IWindow;
 
@@ -31,6 +32,8 @@ public sealed class OpenGLWindow : Engine.Core.IWindow, IDisposable
 
         _silkWindow = Window.Create(options);
         _silkWindow.Closing += () => _shouldClose = true;
+        // Initialize without Run() — enables non-blocking event loop
+        _silkWindow.Initialize();
     }
 
     public void OnLoad()
@@ -39,6 +42,8 @@ public sealed class OpenGLWindow : Engine.Core.IWindow, IDisposable
         _input.Initialize(inputContext);
     }
 
+    public GL CreateGL() => _silkWindow.CreateOpenGL();
+
     public void PumpEvents() => _silkWindow.DoEvents();
     public void Close() => _shouldClose = true;
     public string[] GetRequiredVulkanExtensions() => Array.Empty<string>();