Fix cross-process DPI scaling: send WM_DPICHANGED with explicit DPI to embedded window

Co-authored-by: BornToBeRoot <16019165+BornToBeRoot@users.noreply.github.com>

Author: Copilot

Source/NETworkManager.Utilities/NativeMethods.cs

@@ -40,7 +40,7 @@ public enum WindowShowStyle : uint
     public enum WM : uint
     {
         SYSCOMMAND = 0x0112,
-        DPICHANGED_AFTERPARENT = 0x02E3
+        DPICHANGED = 0x02E0
     }
 
     #endregion
@@ -77,6 +77,9 @@ public static extern IntPtr SetWindowPos(IntPtr hWnd, IntPtr hWndInsertAfter, in
     [DllImport("user32.dll", CharSet = CharSet.Auto)]
     public static extern IntPtr SendMessage(IntPtr hWnd, uint Msg, IntPtr wParam, IntPtr lParam);
 
+    [DllImport("user32.dll", CharSet = CharSet.Auto)]
+    public static extern bool PostMessage(IntPtr hWnd, uint Msg, IntPtr wParam, IntPtr lParam);
+
     [DllImport("user32.dll", SetLastError = true)]
     public static extern bool MoveWindow(IntPtr hWnd, int x, int y, int cx, int cy, bool repaint);
 

Source/NETworkManager/Controls/PowerShellControl.xaml.cs

@@ -23,11 +23,19 @@ private void WindowGrid_SizeChanged(object sender, SizeChangedEventArgs e)
 
     private void WindowsFormsHost_DpiChanged(object sender, DpiChangedEventArgs e)
     {
-        if (IsConnected && _appWin != IntPtr.Zero)
-            NativeMethods.SendMessage(_appWin, (uint)NativeMethods.WM.DPICHANGED_AFTERPARENT, IntPtr.Zero,
-                IntPtr.Zero);
-
+        // Resize first so the embedded window is physically on the new monitor,
+        // then post WM_DPICHANGED with the explicit new DPI in wParam so the
+        // embedded process rescales its fonts without relying on a cross-process
+        // GetDpiForWindow() call (which is unreliable after SetParent across processes).
         ResizeEmbeddedWindow();
+
+        if (IsConnected && _appWin != IntPtr.Zero)
+        {
+            var dpiX = (int)e.NewDpi.PixelsPerInchX;
+            var dpiY = (int)e.NewDpi.PixelsPerInchY;
+            var wParam = new IntPtr(unchecked((int)(uint)((dpiX & 0xFFFF) | ((dpiY & 0xFFFF) << 16))));
+            NativeMethods.PostMessage(_appWin, (uint)NativeMethods.WM.DPICHANGED, wParam, IntPtr.Zero);
+        }
     }
 
     #endregion

Source/NETworkManager/Controls/PuTTYControl.xaml.cs

@@ -24,11 +24,19 @@ private void WindowGrid_SizeChanged(object sender, SizeChangedEventArgs e)
 
     private void WindowsFormsHost_DpiChanged(object sender, DpiChangedEventArgs e)
     {
-        if (IsConnected && _appWin != IntPtr.Zero)
-            NativeMethods.SendMessage(_appWin, (uint)NativeMethods.WM.DPICHANGED_AFTERPARENT, IntPtr.Zero,
-                IntPtr.Zero);
-
+        // Resize first so the embedded window is physically on the new monitor,
+        // then post WM_DPICHANGED with the explicit new DPI in wParam so the
+        // embedded process rescales its fonts without relying on a cross-process
+        // GetDpiForWindow() call (which is unreliable after SetParent across processes).
         ResizeEmbeddedWindow();
+
+        if (IsConnected && _appWin != IntPtr.Zero)
+        {
+            var dpiX = (int)e.NewDpi.PixelsPerInchX;
+            var dpiY = (int)e.NewDpi.PixelsPerInchY;
+            var wParam = new IntPtr(unchecked((int)(uint)((dpiX & 0xFFFF) | ((dpiY & 0xFFFF) << 16))));
+            NativeMethods.PostMessage(_appWin, (uint)NativeMethods.WM.DPICHANGED, wParam, IntPtr.Zero);
+        }
     }
 
     #endregion