rename flags and fix win32 implementation.

samples/ControlCatalog/ViewModels/MainWindowViewModel.cs

@@ -78,12 +78,12 @@ namespace ControlCatalog.ViewModels
 
                     if(x.Item1)
                     {
-                        hints |= ExtendClientAreaChromeHints.SystemTitleBar;
+                        hints |= ExtendClientAreaChromeHints.SystemChrome;
                     }
 
                     if(x.Item2)
                     {
-                        hints |= ExtendClientAreaChromeHints.PreferSystemChromeButtons;
+                        hints |= ExtendClientAreaChromeHints.PreferSystemChrome;
                     }
 
                     ChromeHints = hints;

src/Avalonia.Controls/Platform/ExtendClientAreaChromeHints.cs

@@ -6,9 +6,9 @@ namespace Avalonia.Platform
     public enum ExtendClientAreaChromeHints
     {
         NoChrome,
-        Default = SystemTitleBar,        
-        SystemTitleBar = 0x01,
-        PreferSystemChromeButtons = 0x02,
+        Default = SystemChrome,        
+        SystemChrome = 0x01,
+        PreferSystemChrome = 0x02,
         OSXThickTitleBar = 0x08,               
     }
 }

src/Windows/Avalonia.Win32/WindowImpl.cs

@@ -694,7 +694,7 @@ namespace Avalonia.Win32
             borderCaptionThickness.left *= -1;
             borderCaptionThickness.top *= -1;
 
-            bool wantsTitleBar = _extendChromeHints.HasFlag(ExtendClientAreaChromeHints.SystemTitleBar) || _extendTitleBarHint == -1;
+            bool wantsTitleBar = _extendChromeHints.HasFlag(ExtendClientAreaChromeHints.SystemChrome) || _extendTitleBarHint == -1;
 
             if (!wantsTitleBar)
             {
@@ -711,7 +711,7 @@ namespace Avalonia.Win32
                 borderCaptionThickness.top = (int)(_extendTitleBarHint * Scaling);                
             }
 
-            margins.cyTopHeight = _extendChromeHints.HasFlag(ExtendClientAreaChromeHints.SystemTitleBar) ? borderCaptionThickness.top : 1;
+            margins.cyTopHeight = _extendChromeHints.HasFlag(ExtendClientAreaChromeHints.SystemChrome) && !_extendChromeHints.HasFlag(ExtendClientAreaChromeHints.PreferSystemChrome) ? borderCaptionThickness.top : 1;
 
             if (WindowState == WindowState.Maximized)
             {
@@ -727,7 +727,7 @@ namespace Avalonia.Win32
             return margins;
         }
 
-        private void ExtendClientArea ()
+        private void ExtendClientArea()
         {
             if (DwmIsCompositionEnabled(out bool compositionEnabled) < 0 || !compositionEnabled)
             {
@@ -735,36 +735,28 @@ namespace Avalonia.Win32
                 return;
             }
 
-            if (!_isClientAreaExtended || WindowState == WindowState.FullScreen)
+            GetWindowRect(_hwnd, out var rcClient);
+
+            // Inform the application of the frame change.
+            SetWindowPos(_hwnd,
+                         IntPtr.Zero,
+                         rcClient.left, rcClient.top,
+                         rcClient.Width, rcClient.Height,
+                         SetWindowPosFlags.SWP_FRAMECHANGED);
+
+            if (_isClientAreaExtended && WindowState != WindowState.FullScreen)
             {
-                _extendedMargins = new Thickness(0, 0, 0, 0);
-                _offScreenMargin = new Thickness();
+                var margins = UpdateExtendMargins();
+
+                DwmExtendFrameIntoClientArea(_hwnd, ref margins);
             }
             else
             {
-                GetWindowRect(_hwnd, out var rcClient);
-
-                // Inform the application of the frame change.
-                SetWindowPos(_hwnd,
-                             IntPtr.Zero,
-                             rcClient.left, rcClient.top,
-                             rcClient.Width, rcClient.Height,
-                             SetWindowPosFlags.SWP_FRAMECHANGED);
-
-                if (_isClientAreaExtended)
-                {
-                    var margins = UpdateExtendMargins();
+                var margins = new MARGINS();
+                DwmExtendFrameIntoClientArea(_hwnd, ref margins);
 
-                    DwmExtendFrameIntoClientArea(_hwnd, ref margins);
-                }
-                else
-                {
-                    var margins = new MARGINS();
-                    DwmExtendFrameIntoClientArea(_hwnd, ref margins);
-
-                    _offScreenMargin = new Thickness();
-                    _extendedMargins = new Thickness();
-                }
+                _offScreenMargin = new Thickness();
+                _extendedMargins = new Thickness();
             }
 
             ExtendClientAreaToDecorationsChanged?.Invoke(_isClientAreaExtended);
@@ -1061,7 +1053,7 @@ namespace Avalonia.Win32
         public Action<bool> ExtendClientAreaToDecorationsChanged { get; set; }
         
         /// <inheritdoc/>
-        public bool NeedsManagedDecorations => _isClientAreaExtended && _extendChromeHints.HasFlag(ExtendClientAreaChromeHints.PreferSystemChromeButtons);
+        public bool NeedsManagedDecorations => _isClientAreaExtended && _extendChromeHints.HasFlag(ExtendClientAreaChromeHints.PreferSystemChrome);
 
         /// <inheritdoc/>
         public Thickness ExtendedMargins => _extendedMargins;