CQ: Displaying the correct gap size using different dpi

Author: XTorLukas

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.cs

@@ -60,7 +60,7 @@ public Rectangle DragArea
 		public GridLength TitleBarWidth
 		{
 			get => _titleBarWidth;
-			set => _titleBarWidth = new(value.Value + _gap);
+			set => _titleBarWidth = new((value.Value / MainWindow.Instance.GetDpiScale()) + _gap);
 		}
 
 		// Events