Fixed WGL HDC management

src/Windows/Avalonia.Win32/Interop/UnmanagedMethods.cs

@@ -1627,7 +1627,7 @@ namespace Avalonia.Win32.Interop
         public static extern bool wglDeleteContext(IntPtr context);
 
 
-        [DllImport("opengl32.dll")]
+        [DllImport("opengl32.dll", SetLastError = true)]
         public static extern bool wglMakeCurrent(IntPtr hdc, IntPtr context);
 
         [DllImport("opengl32.dll")]

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

@@ -46,7 +46,7 @@ namespace Avalonia.Win32.OpenGl
         public void Dispose()
         {
             wglDeleteContext(_context);
-            ReleaseDC(_hWnd, _dc);
+            WglDCManager.ReleaseDC(_hWnd, _dc);
             DestroyWindow(_hWnd);
             IsLost = true;
         }
@@ -72,7 +72,7 @@ namespace Avalonia.Win32.OpenGl
 
         public IntPtr CreateConfiguredDeviceContext(IntPtr hWnd)
         {
-            var dc = GetDC(hWnd);
+            var dc = WglDCManager.GetDC(hWnd);
             var fmt = _formatDescriptor;
             SetPixelFormat(dc, _pixelFormat, ref fmt);
             return dc;

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

@@ -0,0 +1,88 @@
+using System;
+using System.Collections.Generic;
+using System.Threading;
+using System.Threading.Tasks;
+using Avalonia.Win32.Interop;
+
+namespace Avalonia.Win32.OpenGl;
+
+/// <summary>
+/// 1) ReleaseDC can only happen from the same thread that has called GetDC
+/// 2) When thread exits all of its HDCs are getting destroyed
+/// 3) We need to create OpenGL render targets from thread pool threads
+///
+/// So this class hosts a dedicated thread for managing HDCs for OpenGL
+/// </summary>
+
+internal class WglDCManager
+{
+    class GetDCOp
+    {
+        public IntPtr Window;
+        public TaskCompletionSource<IntPtr> Result;
+    }
+
+    class ReleaseDCOp
+    {
+        public IntPtr Window;
+        public IntPtr DC;
+        public TaskCompletionSource<object> Result;
+    }
+
+    private static readonly Queue<object> s_Queue = new();
+    private static readonly AutoResetEvent s_Event = new(false);
+
+    static void Worker()
+    {
+        while (true)
+        {
+            s_Event.WaitOne();
+            lock (s_Queue)
+            {
+                if(s_Queue.Count == 0)
+                    continue;
+                var job = s_Queue.Dequeue();
+                if (job is GetDCOp getDc)
+                    getDc.Result.TrySetResult(UnmanagedMethods.GetDC(getDc.Window));
+                else if (job is ReleaseDCOp releaseDc)
+                {
+                    UnmanagedMethods.ReleaseDC(releaseDc.Window, releaseDc.DC);
+                    releaseDc.Result.SetResult(null);
+                }
+            }
+        }
+    }
+
+    static WglDCManager()
+    {
+        new Thread(Worker) { IsBackground = true }.Start();
+    }
+    
+    public static IntPtr GetDC(IntPtr hWnd)
+    {
+        var tcs = new TaskCompletionSource<IntPtr>();
+        lock(s_Queue)
+            s_Queue.Enqueue(new GetDCOp
+            {
+                Window = hWnd,
+                Result = tcs
+            });
+        s_Event.Set();
+        return tcs.Task.Result;
+    }
+
+    public static void ReleaseDC(IntPtr hWnd, IntPtr hDC)
+    {
+        var tcs = new TaskCompletionSource<object>();
+        lock(s_Queue)
+            s_Queue.Enqueue(new ReleaseDCOp()
+            {
+                Window = hWnd,
+                DC = hDC,
+                Result = tcs
+            });
+        s_Event.Set();
+        tcs.Task.Wait();
+        
+    }
+}

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

@@ -55,7 +55,7 @@ namespace Avalonia.Win32.OpenGl
             
             _windowClass = RegisterClassEx(ref wndClassEx);
             _bootstrapWindow = CreateOffscreenWindow();
-            _bootstrapDc = GetDC(_bootstrapWindow);
+            _bootstrapDc = WglDCManager.GetDC(_bootstrapWindow);
             _defaultPfd = new PixelFormatDescriptor
             {
                 Size = (ushort)Marshal.SizeOf<PixelFormatDescriptor>(),
@@ -132,7 +132,7 @@ namespace Avalonia.Win32.OpenGl
             using (new WglRestoreContext(_bootstrapDc, _bootstrapContext, null))
             {
                 var window = CreateOffscreenWindow();
-                var dc = GetDC(window);
+                var dc = WglDCManager.GetDC(window);
                 SetPixelFormat(dc, _defaultPixelFormat, ref _defaultPfd);
                 foreach (var version in versions)
                 {
@@ -159,7 +159,7 @@ namespace Avalonia.Win32.OpenGl
                             _defaultPixelFormat, _defaultPfd);
                 }
 
-                ReleaseDC(window, dc);
+                WglDCManager.ReleaseDC(window, dc);
                 DestroyWindow(window);
                 return null;
             }

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

@@ -37,7 +37,7 @@ namespace Avalonia.Win32.OpenGl
 
             public void Dispose()
             {
-                UnmanagedMethods.ReleaseDC(_hdc, _info.Handle);
+                WglDCManager.ReleaseDC(_info.Handle, _hdc);
             }
 
             public IGlPlatformSurfaceRenderingSession BeginDraw()

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

@@ -1,4 +1,5 @@
 using System;
+using System.Runtime.InteropServices;
 using System.Threading;
 using Avalonia.OpenGL;
 using static Avalonia.Win32.Interop.UnmanagedMethods;
@@ -22,9 +23,11 @@ namespace Avalonia.Win32.OpenGl
 
             if (!wglMakeCurrent(gc, context))
             {
+                var lastError = Marshal.GetLastWin32Error();
+                var caps = GetDeviceCaps(gc, (DEVICECAP)12);
                 if(monitor != null && takeMonitor)
                     Monitor.Exit(monitor);
-                throw new OpenGlException("Unable to make the context current");
+                throw new OpenGlException($"Unable to make the context current: {lastError}, DC valid: {caps != 0}");
             }
         }