Make WglDCManager to also manage offscreen windows

src/Windows/Avalonia.Win32/OpenGl/WglContext.cs

@@ -48,7 +48,7 @@ namespace Avalonia.Win32.OpenGl
         {
             wglDeleteContext(_context);
             WglDCManager.ReleaseDC(_hWnd, _dc);
-            DestroyWindow(_hWnd);
+            WglDCManager.DestroyWindow(_hWnd);
             IsLost = true;
         }
 

src/Windows/Avalonia.Win32/OpenGl/WglDCManager.cs

@@ -1,5 +1,6 @@
 using System;
 using System.Collections.Generic;
+using System.Runtime.InteropServices;
 using System.Threading;
 using System.Threading.Tasks;
 using Avalonia.Win32.Interop;
@@ -28,9 +29,22 @@ internal class WglDCManager
         public IntPtr DC;
         public TaskCompletionSource<object> Result;
     }
+    
+    class CreateWindowOp
+    {
+        public TaskCompletionSource<IntPtr> Result;
+    }
+
+    class DestroyWindowOp
+    {
+        public IntPtr Window;
+        public TaskCompletionSource<object> Result;
+    }
 
     private static readonly Queue<object> s_Queue = new();
     private static readonly AutoResetEvent s_Event = new(false);
+    private static readonly ushort s_WindowClass;
+    private static readonly UnmanagedMethods.WndProc s_wndProcDelegate = WndProc;
 
     static void Worker()
     {
@@ -49,12 +63,41 @@ internal class WglDCManager
                     UnmanagedMethods.ReleaseDC(releaseDc.Window, releaseDc.DC);
                     releaseDc.Result.SetResult(null);
                 }
+                else if (job is CreateWindowOp createWindow)
+                    createWindow.Result.TrySetResult(UnmanagedMethods.CreateWindowEx(
+                        0,
+                        s_WindowClass,
+                        null,
+                        (int)UnmanagedMethods.WindowStyles.WS_OVERLAPPEDWINDOW,
+                        0,
+                        0,
+                        640,
+                        480,
+                        IntPtr.Zero,
+                        IntPtr.Zero,
+                        IntPtr.Zero,
+                        IntPtr.Zero));
+                else if (job is DestroyWindowOp destroyWindow)
+                {
+                    UnmanagedMethods.DestroyWindow(destroyWindow.Window);
+                    destroyWindow.Result.TrySetResult(null);
+                }
             }
         }
     }
 
     static WglDCManager()
     {
+        var wndClassEx = new UnmanagedMethods.WNDCLASSEX
+        {
+            cbSize = Marshal.SizeOf<UnmanagedMethods.WNDCLASSEX>(),
+            hInstance = UnmanagedMethods.GetModuleHandle(null),
+            lpfnWndProc = s_wndProcDelegate,
+            lpszClassName = "AvaloniaGlWindow-" + Guid.NewGuid(),
+            style = (int)UnmanagedMethods.ClassStyles.CS_OWNDC
+        };
+            
+        s_WindowClass = UnmanagedMethods.RegisterClassEx(ref wndClassEx);
         new Thread(Worker)
         {
             IsBackground = true,
@@ -62,6 +105,25 @@ internal class WglDCManager
         }.Start();
     }
     
+        
+    
+    static IntPtr WndProc(IntPtr hWnd, uint msg, IntPtr wParam, IntPtr lParam)
+    {
+        return UnmanagedMethods.DefWindowProc(hWnd, msg, wParam, lParam);
+    }
+    
+    public static IntPtr CreateOffscreenWindow()
+    {
+        var tcs = new TaskCompletionSource<IntPtr>();
+        lock(s_Queue)
+            s_Queue.Enqueue(new CreateWindowOp()
+            {
+                Result = tcs
+            });
+        s_Event.Set();
+        return tcs.Task.Result;
+    }
+    
     public static IntPtr GetDC(IntPtr hWnd)
     {
         var tcs = new TaskCompletionSource<IntPtr>();
@@ -87,6 +149,19 @@ internal class WglDCManager
             });
         s_Event.Set();
         tcs.Task.Wait();
+    }
+    
+    public static void DestroyWindow(IntPtr hWnd)
+    {
+        var tcs = new TaskCompletionSource<object>();
+        lock(s_Queue)
+            s_Queue.Enqueue(new DestroyWindowOp()
+            {
+                Window = hWnd,
+                Result = tcs
+            });
+        s_Event.Set();
+        tcs.Task.Wait();
         
     }
 }

src/Windows/Avalonia.Win32/OpenGl/WglDisplay.cs

@@ -1,6 +1,7 @@
 using System;
 using System.Runtime.InteropServices;
 using Avalonia.OpenGL;
+using Avalonia.Threading;
 using Avalonia.Win32.Interop;
 using static Avalonia.Win32.Interop.UnmanagedMethods;
 using static Avalonia.Win32.OpenGl.WglConsts;
@@ -9,8 +10,6 @@ namespace Avalonia.Win32.OpenGl
     internal class WglDisplay
     {
         private static bool? _initialized;
-        private static ushort _windowClass;
-        private static readonly WndProc _wndProcDelegate = WndProc;
         private static readonly DebugCallbackDelegate _debugCallback = DebugCallback;
 
         private static IntPtr _bootstrapContext;
@@ -44,17 +43,8 @@ namespace Avalonia.Win32.OpenGl
         }
         static bool InitializeCore()
         {
-            var wndClassEx = new WNDCLASSEX
-            {
-                cbSize = Marshal.SizeOf<WNDCLASSEX>(),
-                hInstance = GetModuleHandle(null),
-                lpfnWndProc = _wndProcDelegate,
-                lpszClassName = "AvaloniaGlWindow-" + Guid.NewGuid(),
-                style = (int)ClassStyles.CS_OWNDC
-            };
-            
-            _windowClass = RegisterClassEx(ref wndClassEx);
-            _bootstrapWindow = CreateOffscreenWindow();
+            Dispatcher.UIThread.VerifyAccess();
+            _bootstrapWindow = WglDCManager.CreateOffscreenWindow();
             _bootstrapDc = WglDCManager.GetDC(_bootstrapWindow);
             _defaultPfd = new PixelFormatDescriptor
             {
@@ -105,17 +95,11 @@ namespace Avalonia.Win32.OpenGl
                 DescribePixelFormat(_bootstrapDc, formats[0], Marshal.SizeOf<PixelFormatDescriptor>(), ref _defaultPfd);
                 _defaultPixelFormat = formats[0];
             }
-
-
+            
             wglMakeCurrent(IntPtr.Zero, IntPtr.Zero);
             return true;
         }
-        
-        static IntPtr WndProc(IntPtr hWnd, uint msg, IntPtr wParam, IntPtr lParam)
-        {
-            return DefWindowProc(hWnd, msg, wParam, lParam);
-        }
-        
+
         private static void DebugCallback(int source, int type, int id, int severity, int len, IntPtr message, IntPtr userparam)
         {
             var err = Marshal.PtrToStringAnsi(message, len);
@@ -131,7 +115,7 @@ namespace Avalonia.Win32.OpenGl
 
             using (new WglRestoreContext(_bootstrapDc, _bootstrapContext, null))
             {
-                var window = CreateOffscreenWindow();
+                var window = WglDCManager.CreateOffscreenWindow();
                 var dc = WglDCManager.GetDC(window);
                 SetPixelFormat(dc, _defaultPixelFormat, ref _defaultPfd);
                 foreach (var version in versions)
@@ -165,25 +149,12 @@ namespace Avalonia.Win32.OpenGl
                 }
 
                 WglDCManager.ReleaseDC(window, dc);
-                DestroyWindow(window);
+                WglDCManager.DestroyWindow(window);
                 return null;
             }
         }
 
 
-        static IntPtr CreateOffscreenWindow() =>
-            CreateWindowEx(
-                0,
-                _windowClass,
-                null,
-                (int)WindowStyles.WS_OVERLAPPEDWINDOW,
-                0,
-                0,
-                640,
-                480,
-                IntPtr.Zero, 
-                IntPtr.Zero,
-                IntPtr.Zero,
-                IntPtr.Zero);
+
     }
 }