Fixes #3823 - Upgrades TextView to use View's modern scrolling infrastructure

Terminal.Gui/Views/TextInput/TextView.cs

@@ -770,7 +770,13 @@ public int LeftColumn
                 return;
             }
 
-            _leftColumn = Math.Max (Math.Min (value, Maxlength - 1), 0);
+            int clampedValue = Math.Max (Math.Min (value, Maxlength - 1), 0);
+            _leftColumn = clampedValue;
+
+            if (IsInitialized && Viewport.X != _leftColumn)
+            {
+                Viewport = Viewport with { X = _leftColumn };
+            }
         }
     }
 
@@ -966,7 +972,16 @@ public override string Text
     public int TopRow
     {
         get => _topRow;
-        set => _topRow = Math.Max (Math.Min (value, Lines - 1), 0);
+        set
+        {
+            int clampedValue = Math.Max (Math.Min (value, Lines - 1), 0);
+            _topRow = clampedValue;
+
+            if (IsInitialized && Viewport.Y != _topRow)
+            {
+                Viewport = Viewport with { Y = _topRow };
+            }
+        }
     }
 
     /// <summary>
@@ -1004,6 +1019,13 @@ public bool WordWrap
                 _model = _wrapManager.Model;
             }
 
+            // Update horizontal scrollbar AutoShow based on WordWrap
+            if (IsInitialized)
+            {
+                HorizontalScrollBar.AutoShow = !_wordWrap;
+                UpdateContentSize ();
+            }
+
             SetNeedsDraw ();
         }
     }
@@ -1777,6 +1799,12 @@ public virtual void OnContentsChanged ()
 
         ProcessInheritsPreviousScheme (CurrentRow, CurrentColumn);
         ProcessAutocomplete ();
+
+        // Update content size when content changes
+        if (IsInitialized)
+        {
+            UpdateContentSize ();
+        }
     }
 
     /// <inheritdoc/>
@@ -2139,12 +2167,22 @@ public void ScrollTo (int idx, bool isRow = true)
         if (isRow)
         {
             _topRow = Math.Max (idx > _model.Count - 1 ? _model.Count - 1 : idx, 0);
+
+            if (IsInitialized && Viewport.Y != _topRow)
+            {
+                Viewport = Viewport with { Y = _topRow };
+            }
         }
         else if (!_wordWrap)
         {
             int maxlength =
                 _model.GetMaxVisibleLine (_topRow, _topRow + Viewport.Height, TabWidth);
             _leftColumn = Math.Max (!_wordWrap && idx > maxlength - 1 ? maxlength - 1 : idx, 0);
+
+            if (IsInitialized && Viewport.X != _leftColumn)
+            {
+                Viewport = Viewport with { X = _leftColumn };
+            }
         }
 
         SetNeedsDraw ();
@@ -2342,6 +2380,12 @@ private void Adjust ()
             need = true;
         }
 
+        // Sync Viewport with the internal scroll position
+        if (IsInitialized && (_leftColumn != Viewport.X || _topRow != Viewport.Y))
+        {
+            Viewport = new Rectangle (_leftColumn, _topRow, Viewport.Width, Viewport.Height);
+        }
+
         if (need)
         {
             if (_wrapNeeded)
@@ -4652,12 +4696,72 @@ private void TextView_Initialized (object sender, EventArgs e)
         App?.Popover?.Register (ContextMenu);
         KeyBindings.Add (ContextMenu.Key, Command.Context);
 
+        // Configure ScrollBars to use modern View scrolling infrastructure
+        ConfigureScrollBars ();
+
         OnContentsChanged ();
     }
+
+    /// <summary>
+    ///     Configures the ScrollBars to work with the modern View scrolling system.
+    /// </summary>
+    private void ConfigureScrollBars ()
+    {
+        // Subscribe to ViewportChanged to sync internal scroll fields
+        ViewportChanged += TextView_ViewportChanged;
+
+        // Vertical ScrollBar: AutoShow enabled by default as per requirements
+        VerticalScrollBar.AutoShow = true;
+
+        // Horizontal ScrollBar: AutoShow tracks WordWrap as per requirements
+        HorizontalScrollBar.AutoShow = !WordWrap;
+    }
+
+    private void TextView_ViewportChanged (object? sender, DrawEventArgs e)
+    {
+        // Sync internal scroll position fields with Viewport
+        // Only update if values actually changed to prevent infinite loops
+        if (_topRow != Viewport.Y)
+        {
+            _topRow = Viewport.Y;
+        }
+
+        if (_leftColumn != Viewport.X)
+        {
+            _leftColumn = Viewport.X;
+        }
+    }
+
+    /// <summary>
+    ///     Updates the content size based on the text model dimensions.
+    /// </summary>
+    private void UpdateContentSize ()
+    {
+        int contentHeight = Math.Max (_model.Count, 1);
+
+        // For horizontal size: if word wrap is enabled, content width equals viewport width
+        // Otherwise, calculate the maximum line width (but only if we have a reasonable viewport)
+        int contentWidth;
+
+        if (_wordWrap)
+        {
+            // Word wrap: content width follows viewport width
+            contentWidth = Math.Max (Viewport.Width, 1);
+        }
+        else
+        {
+            // No word wrap: calculate max line width
+            // Cache the current value to avoid recalculating on every call
+            contentWidth = Math.Max (_model.GetMaxVisibleLine (0, _model.Count, TabWidth), 1);
+        }
+
+        SetContentSize (new Size (contentWidth, contentHeight));
+    }
 
     private void TextView_LayoutComplete (object? sender, LayoutEventArgs e)
     {
         WrapTextModel ();
+        UpdateContentSize ();
         Adjust ();
     }