Some hacks to reduce left/top resize jitter

src/Avalonia.Controls/Platform/ITopLevelWithWin32JitterHacks.cs

@@ -0,0 +1,13 @@
+using System;
+
+namespace Avalonia.Controls.Platform
+{
+    /// <summary>
+    /// This file is needed to represent how awesome Windows is
+    /// See https://stackoverflow.com/questions/53000291/how-to-smooth-ugly-jitter-flicker-jumping-when-resizing-windows-especially-drag for more details
+    /// </summary>
+    public interface ITopLevelWithWin32JitterHacks
+    {
+        Action Win32JitterLastFrameRepaint { get; set; }
+    }
+}

src/Avalonia.Controls/TopLevel.cs

@@ -5,6 +5,7 @@ using System;
 using System.Linq;
 using System.Reactive.Linq;
 using Avalonia.Controls.Notifications;
+using Avalonia.Controls.Platform;
 using Avalonia.Controls.Primitives;
 using Avalonia.Input;
 using Avalonia.Input.Raw;
@@ -114,6 +115,9 @@ namespace Avalonia.Controls
             impl.Resized = HandleResized;
             impl.ScalingChanged = HandleScalingChanged;
 
+            if (impl is ITopLevelWithWin32JitterHacks jitterHacks)
+                jitterHacks.Win32JitterLastFrameRepaint += HandleWin32JitterRepaint;
+
             _keyboardNavigationHandler?.SetOwner(this);
             _accessKeyHandler?.SetOwner(this);
             styler?.ApplyStyles(this);
@@ -271,6 +275,11 @@ namespace Avalonia.Controls
             Renderer?.Paint(rect);
         }
 
+        protected virtual void HandleWin32JitterRepaint()
+        {
+            Renderer?.RepaintLastFrameIfExists();
+        }
+
         /// <summary>
         /// Handles a closed notification from <see cref="ITopLevelImpl.Closed"/>.
         /// </summary>

src/Avalonia.Visuals/Rendering/DeferredRenderer.cs

@@ -31,6 +31,7 @@ namespace Avalonia.Rendering
         private volatile IRef<Scene> _scene;
         private DirtyVisuals _dirty;
         private IRef<IRenderTargetBitmapImpl> _overlay;
+        private IRef<Scene> _lastRenderedScene;
         private int _lastSceneId = -1;
         private DisplayDirtyRects _dirtyRectsDisplay = new DisplayDirtyRects();
         private IRef<IDrawOperation> _currentDraw;
@@ -129,6 +130,9 @@ namespace Avalonia.Rendering
                 var scene = _scene;
                 _scene = null;
                 scene?.Dispose();
+                scene = _lastRenderedScene;
+                _lastRenderedScene = null;
+                scene?.Dispose();
             }
 
             Stop();
@@ -176,6 +180,11 @@ namespace Avalonia.Rendering
                 Render(true);
         }
 
+        public void RepaintLastFrameIfExists()
+        {
+            Render(true, true);
+        }
+
         /// <inheritdoc/>
         public void Resized(Size size)
         {
@@ -229,7 +238,7 @@ namespace Avalonia.Rendering
 
         internal void UnitTestRender() => Render(false);
 
-        private void Render(bool forceComposite)
+        private void Render(bool forceComposite, bool doNotUpdateScene = false)
         {
             using (var l = _lock.TryLock())
             {
@@ -256,12 +265,17 @@ namespace Avalonia.Rendering
 
                         }
 
-                        var (scene, updated) = UpdateRenderLayersAndConsumeSceneIfNeeded(GetContext);
+                        var (scene, updated) =
+                            doNotUpdateScene ?
+                                (_lastRenderedScene?.Clone(), false) :
+                                UpdateRenderLayersAndConsumeSceneIfNeeded(GetContext);
 
                         using (scene)
                         {
                             if (scene?.Item != null)
                             {
+                                _lastRenderedScene?.Dispose();
+                                _lastRenderedScene = scene.Clone();
                                 var overlay = DrawDirtyRects || DrawFps;
                                 if (DrawDirtyRects)
                                     _dirtyRectsDisplay.Tick();

src/Avalonia.Visuals/Rendering/IRenderer.cs

@@ -62,6 +62,8 @@ namespace Avalonia.Rendering
         /// <param name="rect">The dirty rectangle.</param>
         void Paint(Rect rect);
 
+        void RepaintLastFrameIfExists();
+
         /// <summary>
         /// Starts the renderer.
         /// </summary>

src/Avalonia.Visuals/Rendering/ImmediateRenderer.cs

@@ -88,6 +88,11 @@ namespace Avalonia.Rendering
             SceneInvalidated?.Invoke(this, new SceneInvalidatedEventArgs((IRenderRoot)_root, rect));
         }
 
+        public void RepaintLastFrameIfExists()
+        {
+            // No-op, we don't have a saved frame
+        }
+
         /// <inheritdoc/>
         public void Resized(Size size)
         {

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

@@ -1235,23 +1235,31 @@ namespace Avalonia.Win32.Interop
         [StructLayout(LayoutKind.Sequential)]
         public struct WINDOWPOS
         {
-            public IntPtr hwnd;
+            public IntPtr hWndInsertAfter;
-            public IntPtr hwndInsertAfter;
+            public IntPtr hWnd;
-            public int x;
+            public int X;
-            public int y;
+            public int Y;
-            public int cx;
+            public int CX;
-            public int cy;
+            public int CY;
             public uint flags;
         }
 
         [StructLayout(LayoutKind.Sequential)]
-        public struct NCCALCSIZE_PARAMS
+        public struct NCCALSIZEPARAMS_ARGS
         {
-            [MarshalAs(UnmanagedType.ByValArray, SizeConst = 3)]
+            public RECT NewRect;
-            public RECT[] rgrc;
+            public RECT OldRect;
-            public WINDOWPOS lppos;
+            public RECT OldClientRect;
+            public WINDOWPOS WindowPos;
         }
-
+        
+        public struct NCCALSIZEPARAMS_RETURN
+        {
+            public RECT NewClientRect;
+            public RECT DstRect;
+            public RECT SrcRect;
+        }
+        
         public struct TRACKMOUSEEVENT
         {
             public int cbSize;

src/Windows/Avalonia.Win32/WindowImpl.cs

@@ -8,6 +8,7 @@ using System.Diagnostics.CodeAnalysis;
 using System.Reactive.Disposables;
 using System.Runtime.InteropServices;
 using Avalonia.Controls;
+using Avalonia.Controls.Platform;
 using Avalonia.Input;
 using Avalonia.Input.Raw;
 using Avalonia.OpenGL;
@@ -20,7 +21,8 @@ using static Avalonia.Win32.Interop.UnmanagedMethods;
 
 namespace Avalonia.Win32
 {
-    public class WindowImpl : IWindowImpl, EglGlPlatformSurface.IEglWindowGlPlatformSurfaceInfo
+    public unsafe class WindowImpl : IWindowImpl, EglGlPlatformSurface.IEglWindowGlPlatformSurfaceInfo,
+        ITopLevelWithWin32JitterHacks
     {
         private static readonly List<WindowImpl> s_instances = new List<WindowImpl>();
 
@@ -84,7 +86,10 @@ namespace Avalonia.Win32
 
         public Action<RawInputEventArgs> Input { get; set; }
 
+        
         public Action<Rect> Paint { get; set; }
+        
+        public Action Win32JitterLastFrameRepaint { get; set; }
 
         public Action<Size> Resized { get; set; }
 
@@ -459,12 +464,26 @@ namespace Avalonia.Win32
 
                     return IntPtr.Zero;
 
+                
                 case WindowsMessage.WM_NCCALCSIZE:
-                    if (ToInt32(wParam) == 1 && !_decorated)
+                    if (ToInt32(wParam) == 1)
                     {
-                        return IntPtr.Zero;
+                        var ncargs = *(NCCALSIZEPARAMS_ARGS*)lParam;
+                        var rv = (NCCALSIZEPARAMS_RETURN*)lParam;
+
+                        if (_decorated)
+                            DefWindowProc(_hwnd, msg, wParam, lParam);
+                        else
+                        {
+                            var x = rv->NewClientRect.left;
+                            var y = rv->NewClientRect.top;
+                            rv->DstRect = rv->SrcRect = new RECT {left = x, top = y, right = x + 1, bottom = y + 1};
+                        }
+
+                        return new IntPtr(0x0400);
                     }
                     break;
+                    
 
                 case UnmanagedMethods.WindowsMessage.WM_CLOSE:
                     bool? preventClosing = Closing?.Invoke();
@@ -661,6 +680,11 @@ namespace Avalonia.Win32
                         return IntPtr.Zero;
                     }
                     break;
+                case WindowsMessage.WM_ERASEBKGND:
+
+                    if (_decorated)
+                        return new IntPtr(1);
+                    break;
 
                 case WindowsMessage.WM_NCACTIVATE:
                     if (!_decorated)
@@ -690,6 +714,11 @@ namespace Avalonia.Win32
                     {
                         // Do nothing here, just block until the pending frame render is completed on the render thread
                     }
+                    
+                    // This is needed to fool Windows™®Ⓒ to think that we've reacted to resize in time,
+                    // so it won't do atrocities to our window 
+                    Win32JitterLastFrameRepaint?.Invoke();
+                    
                     var size = (UnmanagedMethods.SizeCommand)wParam;
 
                     if (Resized != null &&
@@ -697,6 +726,7 @@ namespace Avalonia.Win32
                          size == UnmanagedMethods.SizeCommand.Maximized))
                     {
                         var clientSize = new Size(ToInt32(lParam) & 0xffff, ToInt32(lParam) >> 16);
+
                         Resized(clientSize / Scaling);
                     }
 
@@ -782,7 +812,7 @@ namespace Avalonia.Win32
             UnmanagedMethods.WNDCLASSEX wndClassEx = new UnmanagedMethods.WNDCLASSEX
             {
                 cbSize = Marshal.SizeOf<UnmanagedMethods.WNDCLASSEX>(),
-                style = (int)(ClassStyles.CS_OWNDC | ClassStyles.CS_HREDRAW | ClassStyles.CS_VREDRAW), // Unique DC helps with performance when using Gpu based rendering
+                style = (int)(ClassStyles.CS_OWNDC),// | ClassStyles.CS_HREDRAW | ClassStyles.CS_VREDRAW), // Unique DC helps with performance when using Gpu based rendering
                 lpfnWndProc = _wndProcDelegate,
                 hInstance = UnmanagedMethods.GetModuleHandle(null),
                 hCursor = DefaultCursor,