fix: draw in software over remote desktop so the window has no black area

App.xaml.cs

@@ -1,4 +1,4 @@
-using System;
+using System;
 using System.Diagnostics;
 using System.IO;
 using System.IO.Compression;
@@ -68,8 +68,27 @@ namespace MmdPdf
         // Startup
         // ============================================================
 
+        // Windows reports whether we are being viewed over a remote desktop. In that case WPF's
+        // hardware compositing hands the session a surface it never repaints when the desktop is
+        // resized, which leaves the part of the window outside the original size drawn as flat
+        // black. Drawing in software costs nothing at this size and keeps the whole window painted.
+        [DllImport("user32.dll")]
+        private static extern int GetSystemMetrics(int index);
+        private const int SM_REMOTESESSION = 0x1000;
+
+        private static void UseSoftwareRenderingOnRemoteDesktops()
+        {
+            try
+            {
+                if (GetSystemMetrics(SM_REMOTESESSION) != 0)
+                    RenderOptions.ProcessRenderMode = System.Windows.Interop.RenderMode.SoftwareOnly;
+            }
+            catch { /* never let a rendering hint stop the application starting */ }
+        }
+
         protected override void OnStartup(StartupEventArgs e)
         {
+            UseSoftwareRenderingOnRemoteDesktops();
             StartupTrace.Mark("App.OnStartup entered");
             DispatcherUnhandledException                    += OnDispatcherException;
             AppDomain.CurrentDomain.UnhandledException      += OnDomainException;