Fixes #4200. ExtendedCharInfo needs be enhanced to properly deal with all codepoints

Examples/UICatalog/Properties/launchSettings.json

@@ -48,6 +48,30 @@
       "commandLineArgs": "dotnet UICatalog.dll --driver v2net",
       "distributionName": ""
     },
+    "WSL-Gnome: UICatalog": {
+      "commandName": "Executable",
+      "executablePath": "wsl",
+      "commandLineArgs": "bash -c 'while [ ! -e \"$XDG_RUNTIME_DIR/bus\" ]; do sleep 0.1; done; gnome-terminal --wait -- bash -l -c \"dotnet UICatalog.dll; exec bash\"'",
+      "distributionName": ""
+    },
+    "WSL-Gnome: UICatalog --driver NetDriver": {
+      "commandName": "Executable",
+      "executablePath": "wsl",
+      "commandLineArgs": "bash -c 'while [ ! -e \"$XDG_RUNTIME_DIR/bus\" ]; do sleep 0.1; done; gnome-terminal --wait -- bash -l -c \"dotnet UICatalog.dll --driver NetDriver; exec bash\"'",
+      "distributionName": ""
+    },
+    "WSL-Gnome: UICatalog --driver v2": {
+      "commandName": "Executable",
+      "executablePath": "wsl",
+      "commandLineArgs": "bash -c 'while [ ! -e \"$XDG_RUNTIME_DIR/bus\" ]; do sleep 0.1; done; gnome-terminal --wait -- bash -l -c \"dotnet UICatalog.dll --driver v2; exec bash\"'",
+      "distributionName": ""
+    },
+    "WSL-Gnome: UICatalog --driver v2net": {
+      "commandName": "Executable",
+      "executablePath": "wsl",
+      "commandLineArgs": "bash -c 'while [ ! -e \"$XDG_RUNTIME_DIR/bus\" ]; do sleep 0.1; done; gnome-terminal --wait -- bash -l -c \"dotnet UICatalog.dll --driver v2net; exec bash\"'",
+      "distributionName": ""
+    },
     "Benchmark All": {
       "commandName": "Project",
       "commandLineArgs": "--benchmark"

Examples/UICatalog/Scenarios/NumericUpDownDemo.cs

@@ -252,7 +252,7 @@ void IncrementOnAccept (object? o, EventArgs eventArgs)
             {
                 X = Pos.Center (),
                 Y = Pos.Bottom (_increment) + 1,
-                Increment = NumericUpDown<int>.TryConvert (1, out T? increment) ? increment : default,
+                Increment = NumericUpDown<int>.TryConvert (1, out T? increment) ? increment : default (T?),
             };
 
             _numericUpDown.ValueChanged += NumericUpDownOnValueChanged;

Examples/UICatalog/UICatalogTop.cs

@@ -166,13 +166,23 @@ View [] CreateThemeMenuItems ()
                 CheckedState = Application.Force16Colors ? CheckState.Checked : CheckState.UnChecked
             };
 
+            _force16ColorsMenuItemCb.CheckedStateChanging += (sender, args) =>
+                                                             {
+                                                                 if (Application.Force16Colors
+                                                                     && args.Result == CheckState.UnChecked
+                                                                     && !Application.Driver!.SupportsTrueColor)
+                                                                 {
+                                                                     args.Handled = true;
+                                                                 }
+                                                             };
+
             _force16ColorsMenuItemCb.CheckedStateChanged += (sender, args) =>
-            {
-                Application.Force16Colors = args.Value == CheckState.Checked;
+                                                            {
+                                                                Application.Force16Colors = args.Value == CheckState.Checked;
 
-                _force16ColorsShortcutCb!.CheckedState = args.Value;
-                Application.LayoutAndDraw ();
-            };
+                                                                _force16ColorsShortcutCb!.CheckedState = args.Value;
+                                                                Application.LayoutAndDraw ();
+                                                            };
 
             menuItems.Add (
                            new MenuItemv2
@@ -608,11 +618,22 @@ private StatusBar CreateStatusBar ()
         };
 
         _force16ColorsShortcutCb.CheckedStateChanging += (sender, args) =>
-        {
-            Application.Force16Colors = args.Result == CheckState.Checked;
-            _force16ColorsMenuItemCb!.CheckedState = args.Result;
-            Application.LayoutAndDraw ();
-        };
+                                                         {
+                                                             if (Application.Force16Colors
+                                                                 && args.Result == CheckState.UnChecked
+                                                                 && !Application.Driver!.SupportsTrueColor)
+                                                             {
+                                                                 // If the driver does not support TrueColor, we cannot disable 16 colors
+                                                                 args.Handled = true;
+                                                             }
+                                                         };
+
+        _force16ColorsShortcutCb.CheckedStateChanged += (sender, args) =>
+                                                         {
+                                                             Application.Force16Colors = args.Value == CheckState.Checked;
+                                                             _force16ColorsMenuItemCb!.CheckedState = args.Value;
+                                                             Application.LayoutAndDraw ();
+                                                         };
 
         statusBar.Add (
                        _shQuit,

Terminal.Gui/Drawing/Sixel/SixelSupportDetector.cs

@@ -20,7 +20,7 @@ public class SixelSupportDetector
     public void Detect (Action<SixelSupportResult> resultCallback)
     {
         var result = new SixelSupportResult ();
-        result.SupportsTransparency = IsWindowsTerminal () || IsXtermWithTransparency ();
+        result.SupportsTransparency = IsVirtualTerminal () || IsXtermWithTransparency ();
         IsSixelSupportedByDar (result, resultCallback);
     }
 
@@ -142,7 +142,7 @@ private static void QueueRequest (AnsiEscapeSequence req, Action<string> respons
 
     private static bool ResponseIndicatesSupport (string response) { return response.Split (';').Contains ("4"); }
 
-    private static bool IsWindowsTerminal ()
+    private static bool IsVirtualTerminal ()
     {
         return !string.IsNullOrWhiteSpace (Environment.GetEnvironmentVariable ("WT_SESSION"));
 

Terminal.Gui/Drivers/ConsoleDriver.cs

@@ -269,7 +269,7 @@ public void AddRune (Rune rune)
                         if (Contents [Row, Col - 1].Rune.GetColumns () > 1)
                         {
                             // Invalidate cell to left
-                            Contents [Row, Col - 1].Rune = Rune.ReplacementChar;
+                            Contents [Row, Col - 1].Rune = (Rune)'\0';
                             Contents [Row, Col - 1].IsDirty = true;
                         }
                     }
@@ -308,7 +308,7 @@ public void AddRune (Rune rune)
                             {
                                 // Invalidate cell to right so that it doesn't get drawn
                                 // TODO: Figure out if it is better to show a replacement character or ' '
-                                Contents [Row, Col + 1].Rune = Rune.ReplacementChar;
+                                Contents [Row, Col + 1].Rune = (Rune)'\0';
                                 Contents [Row, Col + 1].IsDirty = true;
                             }
                         }