add support for Backspace and Delete in virtual space

src/Libraries/AvalonEdit/ICSharpCode.AvalonEdit/Editing/EmptySelection.cs

@@ -56,6 +56,7 @@ namespace ICSharpCode.AvalonEdit.Editing
 					textArea.Document.Insert(textArea.Caret.Offset, newText);
 				}
 			}
+			textArea.Caret.VisualColumn = -1;
 		}
 		
 		public override int Length {

src/Libraries/AvalonEdit/ICSharpCode.AvalonEdit/Editing/Selection.cs

@@ -81,11 +81,19 @@ namespace ICSharpCode.AvalonEdit.Editing
 		
 		internal string AddSpacesIfRequired(string newText, TextViewPosition pos)
 		{
-			if (textArea.Options.EnableVirtualSpace) {
+			if (textArea.Options.EnableVirtualSpace && !string.IsNullOrEmpty(newText)) {
-				var vLine = textArea.TextView.GetOrConstructVisualLine(textArea.Document.GetLineByNumber(pos.Line));
+				var line = textArea.Document.GetLineByNumber(pos.Line);
+				string lineText = textArea.Document.GetText(line);
+				var vLine = textArea.TextView.GetOrConstructVisualLine(line);
 				int colDiff = pos.VisualColumn - vLine.VisualLength;
 				if (colDiff > 0) {
-					string additionalSpaces = new string(' ', colDiff);
+					string additionalSpaces = "";
+					if (!textArea.Options.ConvertTabsToSpaces && lineText.Trim('\t').Length == 0) {
+						int tabCount = (int)(colDiff / textArea.Options.IndentationSize);
+						additionalSpaces = new string('\t', tabCount);
+						colDiff -= tabCount * textArea.Options.IndentationSize;
+					}
+					additionalSpaces += new string(' ', colDiff);
 					return additionalSpaces + newText;
 				}
 			}

src/Libraries/AvalonEdit/ICSharpCode.AvalonEdit/Editing/SimpleSelection.cs

@@ -56,7 +56,10 @@ namespace ICSharpCode.AvalonEdit.Editing
 						if (segmentsToDelete[i].Offset == SurroundingSegment.Offset && segmentsToDelete[i].Length == SurroundingSegment.Length) {
 							newText = AddSpacesIfRequired(newText, start);
 						}
+						int vc = textArea.Caret.VisualColumn;
 						textArea.Caret.Offset = segmentsToDelete[i].EndOffset;
+						if (string.IsNullOrEmpty(newText))
+							textArea.Caret.VisualColumn = vc;
 						textArea.Document.Replace(segmentsToDelete[i], newText);
 					} else {
 						textArea.Document.Remove(segmentsToDelete[i]);
@@ -89,8 +92,8 @@ namespace ICSharpCode.AvalonEdit.Editing
 				throw new ArgumentNullException("e");
 			return Selection.Create(
 				textArea,
-				e.GetNewOffset(startOffset, AnchorMovementType.Default),
+				new TextViewPosition(textArea.Document.GetLocation(e.GetNewOffset(startOffset, AnchorMovementType.Default)), start.VisualColumn),
-				e.GetNewOffset(endOffset, AnchorMovementType.Default)
+				new TextViewPosition(textArea.Document.GetLocation(e.GetNewOffset(endOffset, AnchorMovementType.Default)), end.VisualColumn)
 			);
 		}
 		

src/Libraries/AvalonEdit/ICSharpCode.AvalonEdit/Editing/TextArea.cs

@@ -421,6 +421,9 @@ namespace ICSharpCode.AvalonEdit.Editing
 			}
 		}
 		
+		/// <summary>
+		/// Clears the current selection.
+		/// </summary>
 		public void ClearSelection()
 		{
 			this.Selection = emptySelection;

src/Libraries/AvalonEdit/ICSharpCode.AvalonEdit/Rendering/BackgroundGeometryBuilder.cs

@@ -171,8 +171,8 @@ namespace ICSharpCode.AvalonEdit.Rendering
 							}
 						}
 						if (segmentEndVC >= vl.VisualLength) {
-							double left = (segmentStartVC > vl.VisualLength ? vl.GetTextLineVisualXPosition(line, segmentStartVC) : line.Width) - scrollOffset.X;
+							double left = (segmentStartVC > vl.VisualLength ? vl.GetTextLineVisualXPosition(lastTextLine, segmentStartVC) : line.Width) - scrollOffset.X;
-							double right = (segmentEndVC == int.MaxValue ? Math.Max(((IScrollInfo)textView).ExtentWidth, ((IScrollInfo)textView).ViewportWidth) : vl.GetTextLineVisualXPosition(line, segmentEndVC)) - scrollOffset.X;
+							double right = ((segmentEndVC == int.MaxValue || line != lastTextLine) ? Math.Max(((IScrollInfo)textView).ExtentWidth, ((IScrollInfo)textView).ViewportWidth) : vl.GetTextLineVisualXPosition(lastTextLine, segmentEndVC)) - scrollOffset.X;
 							Rect extendSelection = new Rect(Math.Min(left, right), y, Math.Abs(right - left), line.Height);
 							if (!lastRect.IsEmpty) {
 								if (extendSelection.IntersectsWith(lastRect)) {