Fixes #4258 - Glyphs drawn at mid-point of wide glyphs don't get drawn with clipping (#4462)

* Enhanced `View.Drawing.cs` with improved comments, a new
`DoDrawComplete` method for clip region updates, and
clarified terminology. Added detailed remarks for the
`OnDrawComplete` method and `DrawComplete` event.

Refactored `ViewDrawingClippingTests` to simplify driver
setup, use target-typed `new`, and add a new test for wide
glyph clipping with bordered subviews. Improved handling of
edge cases like empty viewports and nested clips.

Added `WideGlyphs.DrawFlow.md` and
`ViewDrawingClippingTests.DrawFlow.md` to document the draw
flow, clipping behavior, and coordinate systems for both the
scenario and the test.

Commented out redundant `Driver.Clip` initialization in
`ApplicationImpl`. Added a `BUGBUG` comment in `Border` to
highlight missing redraw logic for `LineStyle` changes.

* Uncomment Driver.Clip initialization in Screen redraw

* Fixed it!

* Fixes #4258 - Correct wide glyph and border rendering

Refactored `OutputBufferImpl.AddStr` to improve handling of wide glyphs:
- Wide glyphs now modify only the first column they occupy, leaving the second column untouched.
- Removed redundant code that set replacement characters and marked cells as not dirty.
- Synchronized cursor updates (`Col` and `Row`) with the buffer lock to prevent race conditions.
- Modularized logic with helper methods for better readability and maintainability.

Updated `WideGlyphs.cs`:
- Removed dashed `BorderStyle` and added border thickness and subview for `arrangeableViewAtEven`.
- Removed unused `superView` initialization.

Enhanced tests:
- Added unit tests to verify correct rendering of borders and content at odd columns overlapping wide glyphs.
- Updated existing tests to reflect the new behavior of wide glyph handling.
- Introduced `DriverAssert.AssertDriverOutputIs` to validate raw ANSI output.

Improved documentation:
- Expanded problem description and root cause analysis in `WideGlyphBorderBugFix.md`.
- Detailed the fix and its impact, ensuring proper layering of content at any column position.

General cleanup:
- Removed unused imports and redundant code.
- Improved code readability and maintainability.

* Code cleanup

* Update Tests/UnitTestsParallelizable/ViewBase/Draw/ViewDrawingClippingTests.cs

Co-authored-by: Copilot <[email protected]>

* Update Terminal.Gui/Drivers/OutputBufferImpl.cs

Co-authored-by: Copilot <[email protected]>

* Update Tests/UnitTestsParallelizable/ViewBase/Draw/ViewDrawingClippingTests.cs

Co-authored-by: Copilot <[email protected]>

* Update Tests/UnitTestsParallelizable/ViewBase/Draw/ViewDrawingClippingTests.cs

Co-authored-by: Copilot <[email protected]>

* Fixed test slowness problem

* Simplified

* Rmoved temp .md files

* Refactor I/O handling and improve testability

Refactored `InputProcessor` and `Output` access by replacing direct property usage with `GetInputProcessor()` and `GetOutput()` methods to enhance encapsulation. Introduced `GetLastOutput()` and `GetLastBuffer()` methods for better debugging and testability.

Centralized `StringBuilder` usage in `OutputBase` implementations to ensure consistency. Improved exception handling with clearer messages. Updated tests to align with the refactored structure and added a new test for wide glyph handling.

Enhanced ANSI sequence handling and simplified cursor visibility logic to prevent flickering. Standardized method naming for consistency. Cleaned up redundant code and improved documentation for better developer clarity.

* Refactored `NetOutput`, `FakeOutput`, `UnixOutput`, and `WindowsOutput` classes to support access to `Output` and added a `IDriver.GetOutput` to acess the `IOutput`. `IOutput` now has a `GetLastOutput` method.

Simplified `DriverAssert` logic and enhanced `DriverTests` with a new test for wide glyph clipping across drivers.

Performed general cleanup, including removal of unused code, improved formatting, and adoption of modern C# practices. Added `using System.Diagnostics` in `OutputBufferImpl` for debugging.

---------

Co-authored-by: Copilot <[email protected]>

Author: tig

Examples/UICatalog/Scenarios/Keys.cs

@@ -158,7 +158,7 @@ public override void Main ()
         appKeyListView.SchemeName = "Runnable";
         win.Add (onSwallowedListView);
 
-        Application.Driver!.InputProcessor.AnsiSequenceSwallowed += (s, e) => { swallowedList.Add (e.Replace ("\x1b", "Esc")); };
+        Application.Driver!.GetInputProcessor ().AnsiSequenceSwallowed += (s, e) => { swallowedList.Add (e.Replace ("\x1b", "Esc")); };
 
         Application.KeyDown += (s, a) => KeyDownPressUp (a, "Down");
         Application.KeyUp += (s, a) => KeyDownPressUp (a, "Up");

Examples/UICatalog/Scenarios/WideGlyphs.cs

@@ -25,7 +25,7 @@ public override void Main ()
         };
 
         // Build the array of codepoints once when subviews are laid out
-        appWindow.SubViewsLaidOut += (s, e) =>
+        appWindow.SubViewsLaidOut += (s, _) =>
         {
             View? view = s as View;
             if (view is null)
@@ -34,8 +34,8 @@ public override void Main ()
             }
 
             // Only rebuild if size changed or array is null
-            if (_codepoints is null || 
-                _codepoints.GetLength (0) != view.Viewport.Height || 
+            if (_codepoints is null ||
+                _codepoints.GetLength (0) != view.Viewport.Height ||
                 _codepoints.GetLength (1) != view.Viewport.Width)
             {
                 _codepoints = new Rune [view.Viewport.Height, view.Viewport.Width];
@@ -51,7 +51,9 @@ public override void Main ()
         };
 
         // Fill the window with the pre-built codepoints array
-        appWindow.DrawingContent += (s, e) =>
+        // For detailed documentation on the draw code flow from Application.Run to this event,
+        // see WideGlyphs.DrawFlow.md in this directory
+        appWindow.DrawingContent += (s, _) =>
         {
             View? view = s as View;
             if (view is null || _codepoints is null)
@@ -73,15 +75,15 @@ public override void Main ()
             }
         };
 
-        Line verticalLineAtEven = new Line ()
+        Line verticalLineAtEven = new ()
         {
             X = 10,
             Orientation = Orientation.Vertical,
             Length = Dim.Fill ()
         };
         appWindow.Add (verticalLineAtEven);
 
-        Line verticalLineAtOdd = new Line ()
+        Line verticalLineAtOdd = new ()
         {
             X = 25,
             Orientation = Orientation.Vertical,
@@ -97,8 +99,12 @@ public override void Main ()
             Y = 5,
             Width = 15,
             Height = 5,
-            BorderStyle = LineStyle.Dashed,
+            //BorderStyle = LineStyle.Dashed,
         };
+
+        // Proves it's not LineCanvas related
+        arrangeableViewAtEven!.Border!.Thickness = new (1);
+        arrangeableViewAtEven.Border.Add(new View () { Height = Dim.Auto(), Width = Dim.Auto(), Text = "Even" });
         appWindow.Add (arrangeableViewAtEven);
 
         View arrangeableViewAtOdd = new ()
@@ -112,6 +118,70 @@ public override void Main ()
             BorderStyle = LineStyle.Dashed,
         };
         appWindow.Add (arrangeableViewAtOdd);
+
+        var superView = new View
+        {
+            CanFocus = true,
+            X = 30, // on an even column to start
+            Y = Pos.Center (),
+            Width = Dim.Auto () + 4,
+            Height = Dim.Auto () + 1,
+            BorderStyle = LineStyle.Single,
+            Arrangement = ViewArrangement.Movable | ViewArrangement.Resizable
+        };
+
+        Rune codepoint = Glyphs.Apple;
+
+        superView.DrawingContent += (s, e) =>
+                                    {
+                                        var view = s as View;
+                                        for (var r = 0; r < view!.Viewport.Height; r++)
+                                        {
+                                            for (var c = 0; c < view.Viewport.Width; c += 2)
+                                            {
+                                                if (codepoint != default (Rune))
+                                                {
+                                                    view.AddRune (c, r, codepoint);
+                                                }
+                                            }
+                                        }
+                                        e.DrawContext?.AddDrawnRectangle (view.Viewport);
+                                        e.Cancel = true;
+                                    };
+        appWindow.Add (superView);
+
+        var viewWithBorderAtX0 = new View
+        {
+            Text = "viewWithBorderAtX0",
+            BorderStyle = LineStyle.Dashed,
+            X = 0,
+            Y = 1,
+            Width = Dim.Auto (),
+            Height = 3
+        };
+
+        var viewWithBorderAtX1 = new View
+        {
+            Text = "viewWithBorderAtX1",
+            BorderStyle = LineStyle.Dashed,
+            X = 1,
+            Y = Pos.Bottom (viewWithBorderAtX0) + 1,
+            Width = Dim.Auto (),
+            Height = 3
+        };
+
+        var viewWithBorderAtX2 = new View
+        {
+            Text = "viewWithBorderAtX2",
+            BorderStyle = LineStyle.Dashed,
+            X = 2,
+            Y = Pos.Bottom (viewWithBorderAtX1) + 1,
+            Width = Dim.Auto (),
+            Height = 3
+        };
+
+        superView.Add (viewWithBorderAtX0, viewWithBorderAtX1, viewWithBorderAtX2);
+
         // Run - Start the application.
         Application.Run (appWindow);
         appWindow.Dispose ();
@@ -124,6 +194,6 @@ private Rune GetRandomWideCodepoint ()
     {
         Random random = new ();
         int codepoint = random.Next (0x4E00, 0x9FFF);
-        return new Rune (codepoint);
+        return new (codepoint);
     }
 }

Terminal.Gui/Drivers/DotNetDriver/NetOutput.cs

@@ -109,6 +109,7 @@ protected override void AppendOrWriteAttribute (StringBuilder output, Attribute
     /// <inheritdoc />
     protected override void Write (StringBuilder output)
     {
+        base.Write (output);
         try
         {
             Console.Out.Write (output);
@@ -140,7 +141,7 @@ protected override bool SetCursorPositionImpl (int col, int row)
             }
             catch (Exception)
             {
-                return false;
+                return true;
             }
         }
 

Terminal.Gui/Drivers/DriverImpl.cs

@@ -45,19 +45,19 @@ public DriverImpl (
         ISizeMonitor sizeMonitor
     )
     {
-        InputProcessor = inputProcessor;
+        _inputProcessor = inputProcessor;
         _output = output;
         OutputBuffer = outputBuffer;
         _ansiRequestScheduler = ansiRequestScheduler;
 
-        InputProcessor.KeyDown += (s, e) => KeyDown?.Invoke (s, e);
-        InputProcessor.KeyUp += (s, e) => KeyUp?.Invoke (s, e);
+        GetInputProcessor ().KeyDown += (s, e) => KeyDown?.Invoke (s, e);
+        GetInputProcessor ().KeyUp += (s, e) => KeyUp?.Invoke (s, e);
 
-        InputProcessor.MouseEvent += (s, e) =>
-                                     {
-                                         //Logging.Logger.LogTrace ($"Mouse {e.Flags} at x={e.ScreenPosition.X} y={e.ScreenPosition.Y}");
-                                         MouseEvent?.Invoke (s, e);
-                                     };
+        GetInputProcessor ().MouseEvent += (s, e) =>
+                                           {
+                                               //Logging.Logger.LogTrace ($"Mouse {e.Flags} at x={e.ScreenPosition.X} y={e.ScreenPosition.Y}");
+                                               MouseEvent?.Invoke (s, e);
+                                           };
 
         SizeMonitor = sizeMonitor;
         SizeMonitor.SizeChanged += OnSizeMonitorOnSizeChanged;
@@ -73,15 +73,18 @@ ISizeMonitor sizeMonitor
     public void Init () { throw new NotSupportedException (); }
 
     /// <inheritdoc/>
-    public void Refresh () { _output.Write (OutputBuffer); }
+    public void Refresh ()
+    {
+        _output.Write (OutputBuffer);
+    }
 
     /// <inheritdoc/>
-    public string? GetName () => InputProcessor.DriverName?.ToLowerInvariant ();
+    public string? GetName () => GetInputProcessor ().DriverName?.ToLowerInvariant ();
 
     /// <inheritdoc/>
     public virtual string GetVersionInfo ()
     {
-        string type = InputProcessor.DriverName ?? throw new ArgumentNullException (nameof (InputProcessor.DriverName));
+        string type = GetInputProcessor ().DriverName ?? throw new InvalidOperationException ("Driver name is not set.");
 
         return type;
     }
@@ -143,8 +146,12 @@ public void Dispose ()
 
     private readonly IOutput _output;
 
+    public IOutput GetOutput () => _output;
+
+    private readonly IInputProcessor _inputProcessor;
+
     /// <inheritdoc/>
-    public IInputProcessor InputProcessor { get; }
+    public IInputProcessor GetInputProcessor () => _inputProcessor;
 
     /// <inheritdoc/>
     public IOutputBuffer OutputBuffer { get; }
@@ -157,7 +164,7 @@ public void Dispose ()
 
     private void CreateClipboard ()
     {
-        if (InputProcessor.DriverName is { } && InputProcessor.DriverName.Contains ("fake"))
+        if (GetInputProcessor ().DriverName is { } && GetInputProcessor ()!.DriverName!.Contains ("fake"))
         {
             if (Clipboard is null)
             {
@@ -414,7 +421,7 @@ public bool SetCursorVisibility (CursorVisibility visibility)
     public event EventHandler<Key>? KeyUp;
 
     /// <inheritdoc/>
-    public void EnqueueKeyEvent (Key key) { InputProcessor.EnqueueKeyDownEvent (key); }
+    public void EnqueueKeyEvent (Key key) { GetInputProcessor ().EnqueueKeyDownEvent (key); }
 
     #endregion Input Events
 

Terminal.Gui/Drivers/FakeDriver/FakeOutput.cs

@@ -7,29 +7,29 @@ namespace Terminal.Gui.Drivers;
 /// </summary>
 public class FakeOutput : OutputBase, IOutput
 {
-    private readonly StringBuilder _output = new ();
+   // private readonly StringBuilder _outputStringBuilder = new ();
     private int _cursorLeft;
     private int _cursorTop;
     private Size _consoleSize = new (80, 25);
+    private IOutputBuffer? _lastBuffer;
 
     /// <summary>
     /// 
     /// </summary>
     public FakeOutput ()
     {
-        LastBuffer = new OutputBufferImpl ();
-        LastBuffer.SetSize (80, 25);
+        _lastBuffer = new OutputBufferImpl ();
+        _lastBuffer.SetSize (80, 25);
     }
 
     /// <summary>
-    ///     Gets or sets the last output buffer written.
+    ///     Gets or sets the last output buffer written. The <see cref="IOutputBuffer.Contents"/> contains
+    ///     a reference to the buffer last written with <see cref="Write(IOutputBuffer)"/>.
     /// </summary>
-    public IOutputBuffer? LastBuffer { get; set; }
+    public IOutputBuffer? GetLastBuffer () => _lastBuffer;
 
-    /// <summary>
-    ///     Gets the captured output as a string.
-    /// </summary>
-    public string Output => _output.ToString ();
+    ///// <inheritdoc cref="IOutput.GetLastOutput"/>
+    //public override string GetLastOutput () => _outputStringBuilder.ToString ();
 
     /// <inheritdoc />
     public Point GetCursorPosition ()
@@ -61,28 +61,28 @@ protected override bool SetCursorPositionImpl (int col, int row)
     /// <inheritdoc/>
     public void Write (ReadOnlySpan<char> text)
     {
-        _output.Append (text);
+//        _outputStringBuilder.Append (text);
     }
 
-    /// <inheritdoc cref="IDriver"/>
+    /// <inheritdoc cref="IOutput.Write(IOutputBuffer)"/>
     public override void Write (IOutputBuffer buffer)
     {
-        LastBuffer = buffer;
+        _lastBuffer = buffer;
         base.Write (buffer);
     }
 
+    ///// <inheritdoc/>
+    //protected override void Write (StringBuilder output)
+    //{
+    //    _outputStringBuilder.Append (output);
+    //}
+
     /// <inheritdoc cref="IDriver"/>
     public override void SetCursorVisibility (CursorVisibility visibility)
     {
         // Capture but don't act on it in fake output
     }
 
-    /// <inheritdoc/>
-    public void Dispose ()
-    {
-        // Nothing to dispose
-    }
-
     /// <inheritdoc/>
     protected override void AppendOrWriteAttribute (StringBuilder output, Attribute attr, TextStyle redrawTextStyle)
     {
@@ -123,8 +123,8 @@ protected override void AppendOrWriteAttribute (StringBuilder output, Attribute
     }
 
     /// <inheritdoc/>
-    protected override void Write (StringBuilder output)
+    public void Dispose ()
     {
-        _output.Append (output);
+        // Nothing to dispose
     }
 }

Terminal.Gui/Drivers/IDriver.cs

@@ -61,7 +61,12 @@ public interface IDriver : IDisposable
     ///     e.g. <see cref="ConsoleKeyInfo"/> into <see cref="Key"/> events
     ///     and detecting and processing ansi escape sequences.
     /// </summary>
-    IInputProcessor InputProcessor { get; }
+    IInputProcessor GetInputProcessor ();
+
+    /// <summary>
+    ///     Gets the output handler responsible for writing to the terminal.
+    /// </summary>
+    IOutput GetOutput ();
 
     /// <summary>Get the operating system clipboard.</summary>
     IClipboard? Clipboard { get; }

Terminal.Gui/Drivers/IOutput.cs

@@ -65,6 +65,12 @@ public interface IOutput : IDisposable
     /// <param name="buffer"></param>
     void Write (IOutputBuffer buffer);
 
+    /// <summary>
+    ///     Gets a string containing the ANSI escape sequences and content most recently written
+    ///     to the terminal via <see cref="Write(IOutputBuffer)"/>
+    /// </summary>
+    string GetLastOutput ();
+
     /// <summary>
     ///     Generates an ANSI escape sequence string representation of the given <paramref name="buffer"/> contents.
     ///     This is the same output that would be written to the terminal to recreate the current screen contents.