Rename OffSetBackground to GetViewportClipping

The method calculates viewport clipping caused by the view extending

beyond the SuperView's boundaries, not anything related to 'background'.

- Renamed OffSetBackground() -> GetViewportClipping()

- Updated XML documentation to accurately describe clipping behavior

- Fixed incorrect terminology (background -> viewport clipping)

- Updated TextView.Drawing.cs to use renamed method

This is a legacy naming issue. The term 'background' was misleading

as it has nothing to do with background colors or rendering.

The method returns negative offsets when the viewport extends beyond

the SuperView, representing how much is clipped.

Build successful, all 163 tests pass

Terminal.Gui/Views/TextInput/TextView/TextView.Drawing.cs

@@ -95,7 +95,7 @@ public partial class TextView
 
         SetAttributeForRole (Enabled ? VisualRole.Editable : VisualRole.Disabled);
 
-        (int width, int height) offB = OffSetBackground ();
+        (int width, int height) offB = GetViewportClipping ();
         int right = Viewport.Width + offB.width;
         int bottom = Viewport.Height + offB.height;
         var row = 0;

Terminal.Gui/Views/TextInput/TextView/TextView.Utilities.cs

@@ -8,9 +8,9 @@ public partial class TextView
     ///     This method handles both horizontal and vertical scrolling, word wrap considerations, and syncs
     ///     the internal scroll fields with the Viewport property.
     /// </summary>
-    private void Adjust ()
+    private void AdjustScrollPosition ()
     {
-        (int width, int height) offB = OffSetBackground ();
+        (int width, int height) offB = GetViewportClipping ();
         List<Cell> line = GetCurrentLine ();
         bool need = NeedsDraw || _wrapNeeded || !Used;
         (int size, int length) tSize = TextModel.DisplaySize (line, -1, -1, false, TabWidth);
@@ -87,7 +87,7 @@ public partial class TextView
 
     /// <summary>
     ///     INTERNAL: Determines if a redraw is needed based on selection state, word wrap needs, and Used flag.
-    ///     If a redraw is needed, calls <see cref="Adjust"/>; otherwise positions the cursor and updates
+    ///     If a redraw is needed, calls <see cref="AdjustScrollPosition"/>; otherwise positions the cursor and updates
     ///     the unwrapped cursor position.
     /// </summary>
     private void DoNeededAction ()
@@ -99,7 +99,7 @@ public partial class TextView
 
         if (NeedsDraw)
         {
-            Adjust ();
+            AdjustScrollPosition ();
         }
         else
         {
@@ -109,12 +109,12 @@ public partial class TextView
     }
 
     /// <summary>
-    ///     INTERNAL: Calculates the offset from the viewport edges caused by the background extending
-    ///     beyond the SuperView's boundaries. Returns negative width and height offsets if the viewport
-    ///     extends beyond the SuperView.
+    ///     INTERNAL: Calculates the viewport clipping caused by the view extending beyond the SuperView's boundaries.
+    ///     Returns negative width and height offsets when the viewport extends beyond the SuperView, representing
+    ///     how much of the viewport is clipped.
     /// </summary>
-    /// <returns>A tuple containing the width and height offsets.</returns>
-    private (int width, int height) OffSetBackground ()
+    /// <returns>A tuple containing the width and height clipping offsets (negative when clipped).</returns>
+    private (int width, int height) GetViewportClipping ()
     {
         var w = 0;
         var h = 0;