Fix: Fixed an issue where the title bar drag region was sometimes missing

src/Files.App.CsWin32/NativeMethods.txt

@@ -160,3 +160,5 @@ IApplicationDocumentLists
 ApplicationDocumentLists
 IApplicationActivationManager
 MENU_ITEM_TYPE
+GetDpiForMonitor
+MonitorFromWindow

src/Files.App/Helpers/Win32/Win32PInvoke.Consts.cs

@@ -67,5 +67,7 @@ public static partial class Win32PInvoke
 		public const string LOCALE_NAME_USER_DEFAULT = null;
 		public const string LOCALE_NAME_INVARIANT = "";
 		public const string LOCALE_NAME_SYSTEM_DEFAULT = "!sys-default-locale";
+
+		public const int USER_DEFAULT_SCREEN_DPI = 96;
 	}
 }

src/Files.App/MainWindow.xaml.cs

@@ -9,6 +9,9 @@
 using System.Runtime.InteropServices;
 using Windows.ApplicationModel.Activation;
 using Windows.Storage;
+using Windows.Win32;
+using Windows.Win32.Graphics.Gdi;
+using Windows.Win32.UI.HiDpi;
 using IO = System.IO;
 
 namespace Files.App
@@ -339,5 +342,15 @@ x.tabItem.NavigationParameter.NavigationParameter is PaneNavigationArguments pan
 				}
 			}
 		}
+
+		public double GetDpiScale()
+		{
+			var hMonitor = PInvoke.MonitorFromWindow(
+				new(WinRT.Interop.WindowNative.GetWindowHandle(this)),
+				MONITOR_FROM_FLAGS.MONITOR_DEFAULTTONEAREST);
+
+			var res = PInvoke.GetDpiForMonitor(hMonitor, MONITOR_DPI_TYPE.MDT_EFFECTIVE_DPI, out var dpiX, out var _);
+			return res == 0 ? ((float)dpiX / Win32PInvoke.USER_DEFAULT_SCREEN_DPI) : 1;
+		}
 	}
 }

src/Files.App/UserControls/TabBar/TabBar.xaml

@@ -228,7 +228,7 @@
 					<Grid.ColumnDefinitions>
 						<ColumnDefinition Width="Auto" />
 						<ColumnDefinition Width="*" />
-						<ColumnDefinition x:Name="RightPaddingColumn" Width="0" />
+						<ColumnDefinition x:Name="RightPaddingColumn" Width="{x:Bind TitleBarWidth, Mode=OneWay}" />
 					</Grid.ColumnDefinitions>
 
 					<!--  Height is not divisble by four in order to properly align the button  -->
@@ -260,7 +260,8 @@
 						Grid.ColumnSpan="2"
 						HorizontalAlignment="Stretch"
 						VerticalAlignment="Stretch"
-						Fill="Transparent" />
+						Fill="Transparent"
+						Loaded="DragAreaRectangle_Loaded" />
 
 				</Grid>
 			</TabView.TabStripFooter>

src/Files.App/UserControls/TabBar/TabBar.xaml.cs

@@ -2,11 +2,13 @@
 // Licensed under the MIT License. See the LICENSE.
 
 using CommunityToolkit.WinUI.UI;
+using Microsoft.UI.Input;
 using Microsoft.UI.Xaml;
 using Microsoft.UI.Xaml.Controls;
 using Microsoft.UI.Xaml.Input;
 using Microsoft.UI.Xaml.Shapes;
 using Windows.ApplicationModel.DataTransfer;
+using Windows.Graphics;
 using Windows.Storage;
 using Windows.Win32;
 
@@ -28,6 +30,8 @@ public sealed partial class TabBar : BaseTabBar, INotifyPropertyChanged
 
 		private bool _lockDropOperation = false;
 
+		private static int _gap = 6;
+
 		// Starting position when dragging a tab
 		private System.Drawing.Point dragStartPoint;
 
@@ -51,6 +55,14 @@ public bool AllowTabsDrag
 		public Rectangle DragArea
 			=> DragAreaRectangle;
 
+		private GridLength _titleBarWidth;
+
+		public GridLength TitleBarWidth
+		{
+			get => _titleBarWidth;
+			set => _titleBarWidth = new((value.Value / MainWindow.Instance.GetDpiScale()) + _gap);
+		}
+
 		// Events
 
 		public static event EventHandler<TabBarItem?>? SelectedTabItemChanged;
@@ -66,12 +78,10 @@ public TabBar()
 
 			var appWindow = MainWindow.Instance.AppWindow;
 
-			double rightPaddingColumnWidth =
-				FilePropertiesHelpers.FlowDirectionSettingIsRightToLeft
+			TitleBarWidth =
+				new(FilePropertiesHelpers.FlowDirectionSettingIsRightToLeft
 					? appWindow.TitleBar.LeftInset
-					: appWindow.TitleBar.RightInset;
-
-			RightPaddingColumn.Width = new(rightPaddingColumnWidth >= 0 ? rightPaddingColumnWidth : 0);
+					: appWindow.TitleBar.RightInset);
 
 			AppearanceSettingsService.PropertyChanged += (s, e) =>
 			{
@@ -366,5 +376,17 @@ private void TabViewItem_Loaded(object sender, RoutedEventArgs e)
 				});
 			}
 		}
+
+		private void DragAreaRectangle_Loaded(object sender, RoutedEventArgs e)
+			=> HorizontalTabView.Measure(new(HorizontalTabView.ActualWidth - TabBarAddNewTabButton.Width - TitleBarWidth.Value, HorizontalTabView.ActualHeight));
+
+		public int SetTitleBarDragRegion(InputNonClientPointerSource source, SizeInt32 size, double scaleFactor, Func<UIElement, RectInt32?, RectInt32> getScaledRect)
+		{
+			var height = (int)ActualHeight;
+			var width = (int)(ActualWidth - DragArea.ActualWidth);
+
+			source.SetRegionRects(NonClientRegionKind.Passthrough, [getScaledRect(this, new RectInt32(0, 0, width, height))]);
+			return height;
+		}
 	}
 }

src/Files.App/Views/MainPage.xaml.cs

@@ -126,7 +126,9 @@ private void UserSettingsService_OnSettingChangedEvent(object? sender, SettingCh
 
 		private void HorizontalMultitaskingControl_Loaded(object sender, RoutedEventArgs e)
 		{
-			TabControl.DragArea.SizeChanged += (_, _) => MainWindow.Instance.RaiseSetTitleBarDragRegion(SetTitleBarDragRegion);
+			TabControl.DragArea.SizeChanged += (_, _) => MainWindow.Instance.RaiseSetTitleBarDragRegion(TabControl.SetTitleBarDragRegion);
+			TabControl.SizeChanged += (_, _) => MainWindow.Instance.RaiseSetTitleBarDragRegion(TabControl.SetTitleBarDragRegion);
+
 			if (ViewModel.MultitaskingControl is not TabBar)
 			{
 				ViewModel.MultitaskingControl = TabControl;
@@ -135,13 +137,6 @@ private void HorizontalMultitaskingControl_Loaded(object sender, RoutedEventArgs
 			}
 		}
 
-		private int SetTitleBarDragRegion(InputNonClientPointerSource source, SizeInt32 size, double scaleFactor, Func<UIElement, RectInt32?, RectInt32> getScaledRect)
-		{
-			var height = (int)TabControl.ActualHeight;
-			source.SetRegionRects(NonClientRegionKind.Passthrough, [getScaledRect(this, new RectInt32(0, 0, (int)(TabControl.ActualWidth + TabControl.Margin.Left - TabControl.DragArea.ActualWidth), height))]);
-			return height;
-		}
-
 		public async void TabItemContent_ContentChanged(object? sender, TabBarItemParameter e)
 		{
 			if (SidebarAdaptiveViewModel.PaneHolder is null)
@@ -279,7 +274,7 @@ protected override void OnLostFocus(RoutedEventArgs e)
 
 		private void Page_Loaded(object sender, RoutedEventArgs e)
 		{
-			MainWindow.Instance.AppWindow.Changed += (_, _) => MainWindow.Instance.RaiseSetTitleBarDragRegion(SetTitleBarDragRegion);
+			MainWindow.Instance.AppWindow.Changed += (_, _) => MainWindow.Instance.RaiseSetTitleBarDragRegion(TabControl.SetTitleBarDragRegion);
 
 			// Defers the status bar loading until after the page has loaded to improve startup perf
 			FindName(nameof(StatusBar));