From af8acfce0dbab0864affb5bc8ee4e45bc8c9f4a9 Mon Sep 17 00:00:00 2001
From: Dariusz Komosinski <darek.komosinski@gmail.com>
Date: Thu, 9 Jul 2020 21:49:34 +0200
Subject: [PATCH 1/2] Prevent crashes caused by null locked framebuffer.

---
 src/Windows/Avalonia.Win32/FramebufferManager.cs | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/src/Windows/Avalonia.Win32/FramebufferManager.cs b/src/Windows/Avalonia.Win32/FramebufferManager.cs
index 87c5a1bb02..f4c3a80799 100644
--- a/src/Windows/Avalonia.Win32/FramebufferManager.cs
+++ b/src/Windows/Avalonia.Win32/FramebufferManager.cs
@@ -17,16 +17,18 @@ namespace Avalonia.Win32
 
         public ILockedFramebuffer Lock()
         {
-            UnmanagedMethods.RECT rc;
-            UnmanagedMethods.GetClientRect(_hwnd, out rc);
-            var width = rc.right - rc.left;
-            var height = rc.bottom - rc.top;
-            if ((_fb == null || _fb.Size.Width != width || _fb.Size.Height != height) && width > 0 && height > 0)
+            UnmanagedMethods.GetClientRect(_hwnd, out var rc);
+
+            var width = Math.Max(1, rc.right - rc.left);
+            var height = Math.Max(1, rc.bottom - rc.top);
+
+            if ((_fb == null || _fb.Size.Width != width || _fb.Size.Height != height))
             {
                 _fb?.Deallocate();
                 _fb = null;
                 _fb = new WindowFramebuffer(_hwnd, new PixelSize(width, height));
             }
+
             return _fb;
         }
     }

From 1d94f80f7f4392479e1311992db610d89d79100d Mon Sep 17 00:00:00 2001
From: Dariusz Komosinski <darek.komosinski@gmail.com>
Date: Thu, 9 Jul 2020 23:00:46 +0200
Subject: [PATCH 2/2] Dispose window framebuffers.

---
 src/Shared/PlatformSupport/StandardRuntimePlatform.cs | 10 +++++++---
 src/Windows/Avalonia.Win32/FramebufferManager.cs      |  8 +++++++-
 src/Windows/Avalonia.Win32/WindowImpl.cs              |  2 ++
 3 files changed, 16 insertions(+), 4 deletions(-)

diff --git a/src/Shared/PlatformSupport/StandardRuntimePlatform.cs b/src/Shared/PlatformSupport/StandardRuntimePlatform.cs
index 03832d3063..d574732e3d 100644
--- a/src/Shared/PlatformSupport/StandardRuntimePlatform.cs
+++ b/src/Shared/PlatformSupport/StandardRuntimePlatform.cs
@@ -86,11 +86,15 @@ namespace Avalonia.Shared.PlatformSupport
 #if DEBUG
                 if (Thread.CurrentThread.ManagedThreadId == GCThread?.ManagedThreadId)
                 {
-                    lock(_lock)
+                    lock (_lock)
+                    {
                         if (!IsDisposed)
+                        {
                             Console.Error.WriteLine("Native blob disposal from finalizer thread\nBacktrace: "
-                                                    + Environment.StackTrace
-                                                    + "\n\nBlob created by " + _backtrace);
+                                                 + Environment.StackTrace
+                                                 + "\n\nBlob created by " + _backtrace);
+                        }
+                    }
                 }
 #endif
                 DoDispose();
diff --git a/src/Windows/Avalonia.Win32/FramebufferManager.cs b/src/Windows/Avalonia.Win32/FramebufferManager.cs
index f4c3a80799..6969a49dad 100644
--- a/src/Windows/Avalonia.Win32/FramebufferManager.cs
+++ b/src/Windows/Avalonia.Win32/FramebufferManager.cs
@@ -5,7 +5,7 @@ using Avalonia.Win32.Interop;
 
 namespace Avalonia.Win32
 {
-    class FramebufferManager : IFramebufferPlatformSurface
+    class FramebufferManager : IFramebufferPlatformSurface, IDisposable
     {
         private readonly IntPtr _hwnd;
         private WindowFramebuffer _fb;
@@ -31,5 +31,11 @@ namespace Avalonia.Win32
 
             return _fb;
         }
+
+        public void Dispose()
+        {
+            _fb?.Deallocate();
+            _fb = null;
+        }
     }
 }
diff --git a/src/Windows/Avalonia.Win32/WindowImpl.cs b/src/Windows/Avalonia.Win32/WindowImpl.cs
index 6e9cb81b11..0ee1342d27 100644
--- a/src/Windows/Avalonia.Win32/WindowImpl.cs
+++ b/src/Windows/Avalonia.Win32/WindowImpl.cs
@@ -389,6 +389,8 @@ namespace Avalonia.Win32
                 UnregisterClass(_className, GetModuleHandle(null));
                 _className = null;
             }
+
+            _framebuffer.Dispose();
         }
 
         public void Invalidate(Rect rect)