[PTRun]Fixed unstable startup position after moving to PerMonitorV2 (m…

…icrosoft#33784)

## Summary of the Pull Request
Fixes an issue where PowerToys Run can sometimes start up in an
inconvenient position in a multi-monitor / multi-DPI setup.

src/modules/launcher/PowerLauncher/Helper/WindowsInteropHelper.cs

@@ -10,7 +10,6 @@
 using System.Windows.Forms;
 using System.Windows.Interop;
 using System.Windows.Media;
-using Point = System.Windows.Point;
 
 namespace PowerLauncher.Helper
 {
@@ -188,30 +187,29 @@ internal static void SetToolWindowStyle(Window win)
             _ = NativeMethods.SetWindowLong(hwnd, GWL_EX_STYLE, NativeMethods.GetWindowLong(hwnd, GWL_EX_STYLE) | WS_EX_TOOLWINDOW);
         }
 
-        /// <summary>
-        /// Transforms pixels to Device Independent Pixels used by WPF
-        /// </summary>
-        /// <param name="visual">current window, required to get presentation source</param>
-        /// <param name="unitX">horizontal position in pixels</param>
-        /// <param name="unitY">vertical position in pixels</param>
-        /// <returns>point containing device independent pixels</returns>
-        public static Point TransformPixelsToDIP(Visual visual, double unitX, double unitY)
+        public static void MoveToScreenCenter(Window window, Screen screen)
         {
-            Matrix matrix;
-            var source = PresentationSource.FromVisual(visual);
-            if (source != null)
+            var workingArea = screen.WorkingArea;
+            var matrix = GetCompositionTarget(window).TransformFromDevice;
+            var dpiX = matrix.M11;
+            var dpiY = matrix.M22;
+
+            window.Left = (dpiX * workingArea.Left) + (((dpiX * workingArea.Width) - window.Width) / 2);
+            window.Top = (dpiY * workingArea.Top) + (((dpiY * workingArea.Height) - window.Height) / 2);
+        }
+
+        private static CompositionTarget GetCompositionTarget(Visual visual)
+        {
+            var presentationSource = PresentationSource.FromVisual(visual);
+            if (presentationSource != null)
             {
-                matrix = source.CompositionTarget.TransformFromDevice;
+                return presentationSource.CompositionTarget;
             }
             else
             {
-                using (var src = new HwndSource(default))
-                {
-                    matrix = src.CompositionTarget.TransformFromDevice;
-                }
+                using var hwndSource = new HwndSource(default);
+                return hwndSource.CompositionTarget;
             }
-
-            return new Point((int)(matrix.M11 * unitX), (int)(matrix.M22 * unitY));
         }
 
         [StructLayout(LayoutKind.Sequential)]

src/modules/launcher/PowerLauncher/MainWindow.xaml.cs

@@ -411,8 +411,8 @@ private void OnMouseDown(object sender, MouseButtonEventArgs e)
 
         private void InitializePosition()
         {
-            Top = WindowTop();
-            Left = WindowLeft();
+            MoveToDesiredPosition();
+
             _settings.WindowTop = Top;
             _settings.WindowLeft = Left;
         }
@@ -434,11 +434,31 @@ private void UpdatePosition()
             }
             else
             {
-                Top = WindowTop();
-                Left = WindowLeft();
+                MoveToDesiredPosition();
             }
         }
 
+        private void MoveToDesiredPosition()
+        {
+            // Hack: After switching to PerMonitorV2, this operation seems to require a three-step operation
+            // to ensure a stable position: First move to top-left of desired screen, then centralize twice.
+            // More straightforward ways of doing this don't seem to work well for unclear reasons, but possibly related to
+            // https://github.com/dotnet/wpf/issues/4127
+            // In any case, there does not seem to be any big practical downside to doing it this way. As a bonus, it can be
+            // done in pure WPF without any native calls and without too much DPI-based fiddling.
+            // In terms of the hack itself, removing any of these three steps seems to fail in certain scenarios only,
+            // so be careful with testing!
+            var desiredScreen = GetScreen();
+
+            // Move to top-left of desired screen.
+            Top = desiredScreen.WorkingArea.Top;
+            Left = desiredScreen.WorkingArea.Left;
+
+            // Centralize twice.
+            WindowsInteropHelper.MoveToScreenCenter(this, desiredScreen);
+            WindowsInteropHelper.MoveToScreenCenter(this, desiredScreen);
+        }
+
         private void OnLocationChanged(object sender, EventArgs e)
         {
             if (_settings.RememberLastLaunchLocation)
@@ -448,28 +468,6 @@ private void OnLocationChanged(object sender, EventArgs e)
             }
         }
 
-        /// <summary>
-        /// Calculates X co-ordinate of main window top left corner.
-        /// </summary>
-        /// <returns>X co-ordinate of main window top left corner</returns>
-        private double WindowLeft()
-        {
-            var screen = GetScreen();
-            var dip1 = WindowsInteropHelper.TransformPixelsToDIP(this, screen.WorkingArea.X, 0);
-            var dip2 = WindowsInteropHelper.TransformPixelsToDIP(this, screen.WorkingArea.Width, 0);
-            var left = ((dip2.X - ActualWidth) / 2) + dip1.X;
-            return left;
-        }
-
-        private double WindowTop()
-        {
-            var screen = GetScreen();
-            var dip1 = WindowsInteropHelper.TransformPixelsToDIP(this, 0, screen.WorkingArea.Y);
-            var dip2 = WindowsInteropHelper.TransformPixelsToDIP(this, 0, screen.WorkingArea.Height);
-            var top = ((dip2.Y - SearchBox.ActualHeight) / 4) + dip1.Y;
-            return top;
-        }
-
         private Screen GetScreen()
         {
             ManagedCommon.StartupPosition position = _settings.StartupPosition;