source: branches/2839_HiveProjectManagement/HeuristicLab.ExtLibs/HeuristicLab.AvalonEdit/5.0.1/AvalonEdit-5.0.1/Rendering/TextView.cs @ 15761

// Copyright (c) 2014 AlphaSierraPapa for the SharpDevelop Team
// 
// Permission is hereby granted, free of charge, to any person obtaining a copy of this
// software and associated documentation files (the "Software"), to deal in the Software
// without restriction, including without limitation the rights to use, copy, modify, merge,
// publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons
// to whom the Software is furnished to do so, subject to the following conditions:
// 
// The above copyright notice and this permission notice shall be included in all copies or
// substantial portions of the Software.
// 
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED,
// INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR
// PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE
// FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
// OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
// DEALINGS IN THE SOFTWARE.

using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.ComponentModel;
using System.ComponentModel.Design;
using System.Diagnostics;
using System.Globalization;
using System.Linq;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Controls.Primitives;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.TextFormatting;
using System.Windows.Threading;
using ICSharpCode.NRefactory.Editor;
using ICSharpCode.AvalonEdit.Document;
using ICSharpCode.AvalonEdit.Utils;

namespace ICSharpCode.AvalonEdit.Rendering
{
  /// <summary>
  /// A virtualizing panel producing+showing <see cref="VisualLine"/>s for a <see cref="TextDocument"/>.
  /// 
  /// This is the heart of the text editor, this class controls the text rendering process.
  /// 
  /// Taken as a standalone control, it's a text viewer without any editing capability.
  /// </summary>
  [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Design", "CA1001:TypesThatOwnDisposableFieldsShouldBeDisposable",
                                                   Justification = "The user usually doesn't work with TextView but with TextEditor; and nulling the Document property is sufficient to dispose everything.")]
  public class TextView : FrameworkElement, IScrollInfo, IWeakEventListener, ITextEditorComponent, IServiceProvider
  {
    #region Constructor
    static TextView()
    {
      ClipToBoundsProperty.OverrideMetadata(typeof(TextView), new FrameworkPropertyMetadata(Boxes.True));
      FocusableProperty.OverrideMetadata(typeof(TextView), new FrameworkPropertyMetadata(Boxes.False));
    }
    
    ColumnRulerRenderer columnRulerRenderer;
    CurrentLineHighlightRenderer currentLineHighlighRenderer;
    
    /// <summary>
    /// Creates a new TextView instance.
    /// </summary>
    public TextView()
    {
      services.AddService(typeof(TextView), this);
      textLayer = new TextLayer(this);
      elementGenerators = new ObserveAddRemoveCollection<VisualLineElementGenerator>(ElementGenerator_Added, ElementGenerator_Removed);
      lineTransformers = new ObserveAddRemoveCollection<IVisualLineTransformer>(LineTransformer_Added, LineTransformer_Removed);
      backgroundRenderers = new ObserveAddRemoveCollection<IBackgroundRenderer>(BackgroundRenderer_Added, BackgroundRenderer_Removed);
      columnRulerRenderer = new ColumnRulerRenderer(this);
      currentLineHighlighRenderer = new CurrentLineHighlightRenderer(this);
      this.Options = new TextEditorOptions();
      
      Debug.Assert(singleCharacterElementGenerator != null); // assert that the option change created the builtin element generators
      
      layers = new LayerCollection(this);
      InsertLayer(textLayer, KnownLayer.Text, LayerInsertionPosition.Replace);
      
      this.hoverLogic = new MouseHoverLogic(this);
      this.hoverLogic.MouseHover += (sender, e) => RaiseHoverEventPair(e, PreviewMouseHoverEvent, MouseHoverEvent);
      this.hoverLogic.MouseHoverStopped += (sender, e) => RaiseHoverEventPair(e, PreviewMouseHoverStoppedEvent, MouseHoverStoppedEvent);
    }

    #endregion
    
    #region Document Property
    /// <summary>
    /// Document property.
    /// </summary>
    public static readonly DependencyProperty DocumentProperty =
      DependencyProperty.Register("Document", typeof(TextDocument), typeof(TextView),
                                  new FrameworkPropertyMetadata(OnDocumentChanged));
    
    TextDocument document;
    HeightTree heightTree;
    
    /// <summary>
    /// Gets/Sets the document displayed by the text editor.
    /// </summary>
    public TextDocument Document {
      get { return (TextDocument)GetValue(DocumentProperty); }
      set { SetValue(DocumentProperty, value); }
    }
    
    static void OnDocumentChanged(DependencyObject dp, DependencyPropertyChangedEventArgs e)
    {
      ((TextView)dp).OnDocumentChanged((TextDocument)e.OldValue, (TextDocument)e.NewValue);
    }
    
    internal double FontSize {
      get {
        return (double)GetValue(TextBlock.FontSizeProperty);
      }
    }
    
    /// <summary>
    /// Occurs when the document property has changed.
    /// </summary>
    public event EventHandler DocumentChanged;
    
    void OnDocumentChanged(TextDocument oldValue, TextDocument newValue)
    {
      if (oldValue != null) {
        heightTree.Dispose();
        heightTree = null;
        formatter.Dispose();
        formatter = null;
        cachedElements.Dispose();
        cachedElements = null;
        TextDocumentWeakEventManager.Changing.RemoveListener(oldValue, this);
      }
      this.document = newValue;
      ClearScrollData();
      ClearVisualLines();
      if (newValue != null) {
        TextDocumentWeakEventManager.Changing.AddListener(newValue, this);
        formatter = TextFormatterFactory.Create(this);
        InvalidateDefaultTextMetrics(); // measuring DefaultLineHeight depends on formatter
        heightTree = new HeightTree(newValue, DefaultLineHeight);
        cachedElements = new TextViewCachedElements();
      }
      InvalidateMeasure(DispatcherPriority.Normal);
      if (DocumentChanged != null)
        DocumentChanged(this, EventArgs.Empty);
    }
    
    /// <summary>
    /// Recreates the text formatter that is used internally
    /// by calling <see cref="TextFormatterFactory.Create"/>.
    /// </summary>
    void RecreateTextFormatter()
    {
      if (formatter != null) {
        formatter.Dispose();
        formatter = TextFormatterFactory.Create(this);
        Redraw();
      }
    }
    
    void RecreateCachedElements()
    {
      if (cachedElements != null) {
        cachedElements.Dispose();
        cachedElements = new TextViewCachedElements();
      }
    }
    
    /// <inheritdoc cref="IWeakEventListener.ReceiveWeakEvent"/>
    protected virtual bool ReceiveWeakEvent(Type managerType, object sender, EventArgs e)
    {
      if (managerType == typeof(TextDocumentWeakEventManager.Changing)) {
        // TODO: put redraw into background so that other input events can be handled before the redraw.
        // Unfortunately the "easy" approach (just use DispatcherPriority.Background) here makes the editor twice as slow because
        // the caret position change forces an immediate redraw, and the text input then forces a background redraw.
        // When fixing this, make sure performance on the SharpDevelop "type text in C# comment" stress test doesn't get significantly worse.
        DocumentChangeEventArgs change = (DocumentChangeEventArgs)e;
        Redraw(change.Offset, change.RemovalLength, DispatcherPriority.Normal);
        return true;
      } else if (managerType == typeof(PropertyChangedWeakEventManager)) {
        OnOptionChanged((PropertyChangedEventArgs)e);
        return true;
      }
      return false;
    }
    
    bool IWeakEventListener.ReceiveWeakEvent(Type managerType, object sender, EventArgs e)
    {
      return ReceiveWeakEvent(managerType, sender, e);
    }
    #endregion
    
    #region Options property
    /// <summary>
    /// Options property.
    /// </summary>
    public static readonly DependencyProperty OptionsProperty =
      DependencyProperty.Register("Options", typeof(TextEditorOptions), typeof(TextView),
                                  new FrameworkPropertyMetadata(OnOptionsChanged));
    
    /// <summary>
    /// Gets/Sets the options used by the text editor.
    /// </summary>
    public TextEditorOptions Options {
      get { return (TextEditorOptions)GetValue(OptionsProperty); }
      set { SetValue(OptionsProperty, value); }
    }
    
    /// <summary>
    /// Occurs when a text editor option has changed.
    /// </summary>
    public event PropertyChangedEventHandler OptionChanged;
    
    /// <summary>
    /// Raises the <see cref="OptionChanged"/> event.
    /// </summary>
    protected virtual void OnOptionChanged(PropertyChangedEventArgs e)
    {
      if (OptionChanged != null) {
        OptionChanged(this, e);
      }
      
      if (Options.ShowColumnRuler)
        columnRulerRenderer.SetRuler(Options.ColumnRulerPosition, ColumnRulerPen);
      else
        columnRulerRenderer.SetRuler(-1, ColumnRulerPen);
      
      UpdateBuiltinElementGeneratorsFromOptions();
      Redraw();
    }
    
    static void OnOptionsChanged(DependencyObject dp, DependencyPropertyChangedEventArgs e)
    {
      ((TextView)dp).OnOptionsChanged((TextEditorOptions)e.OldValue, (TextEditorOptions)e.NewValue);
    }
    
    void OnOptionsChanged(TextEditorOptions oldValue, TextEditorOptions newValue)
    {
      if (oldValue != null) {
        PropertyChangedWeakEventManager.RemoveListener(oldValue, this);
      }
      if (newValue != null) {
        PropertyChangedWeakEventManager.AddListener(newValue, this);
      }
      OnOptionChanged(new PropertyChangedEventArgs(null));
    }
    #endregion
    
    #region ElementGenerators+LineTransformers Properties
    readonly ObserveAddRemoveCollection<VisualLineElementGenerator> elementGenerators;
    
    /// <summary>
    /// Gets a collection where element generators can be registered.
    /// </summary>
    public IList<VisualLineElementGenerator> ElementGenerators {
      get { return elementGenerators; }
    }
    
    void ElementGenerator_Added(VisualLineElementGenerator generator)
    {
      ConnectToTextView(generator);
      Redraw();
    }
    
    void ElementGenerator_Removed(VisualLineElementGenerator generator)
    {
      DisconnectFromTextView(generator);
      Redraw();
    }
    
    readonly ObserveAddRemoveCollection<IVisualLineTransformer> lineTransformers;
    
    /// <summary>
    /// Gets a collection where line transformers can be registered.
    /// </summary>
    public IList<IVisualLineTransformer> LineTransformers {
      get { return lineTransformers; }
    }
    
    void LineTransformer_Added(IVisualLineTransformer lineTransformer)
    {
      ConnectToTextView(lineTransformer);
      Redraw();
    }
    
    void LineTransformer_Removed(IVisualLineTransformer lineTransformer)
    {
      DisconnectFromTextView(lineTransformer);
      Redraw();
    }
    #endregion
    
    #region Builtin ElementGenerators
//    NewLineElementGenerator newLineElementGenerator;
    SingleCharacterElementGenerator singleCharacterElementGenerator;
    LinkElementGenerator linkElementGenerator;
    MailLinkElementGenerator mailLinkElementGenerator;
    
    void UpdateBuiltinElementGeneratorsFromOptions()
    {
      TextEditorOptions options = this.Options;
      
//      AddRemoveDefaultElementGeneratorOnDemand(ref newLineElementGenerator, options.ShowEndOfLine);
      AddRemoveDefaultElementGeneratorOnDemand(ref singleCharacterElementGenerator, options.ShowBoxForControlCharacters || options.ShowSpaces || options.ShowTabs);
      AddRemoveDefaultElementGeneratorOnDemand(ref linkElementGenerator, options.EnableHyperlinks);
      AddRemoveDefaultElementGeneratorOnDemand(ref mailLinkElementGenerator, options.EnableEmailHyperlinks);
    }
    
    void AddRemoveDefaultElementGeneratorOnDemand<T>(ref T generator, bool demand)
      where T : VisualLineElementGenerator, IBuiltinElementGenerator, new()
    {
      bool hasGenerator = generator != null;
      if (hasGenerator != demand) {
        if (demand) {
          generator = new T();
          this.ElementGenerators.Add(generator);
        } else {
          this.ElementGenerators.Remove(generator);
          generator = null;
        }
      }
      if (generator != null)
        generator.FetchOptions(this.Options);
    }
    #endregion
    
    #region Layers
    internal readonly TextLayer textLayer;
    readonly LayerCollection layers;
    
    /// <summary>
    /// Gets the list of layers displayed in the text view.
    /// </summary>
    public UIElementCollection Layers {
      get { return layers; }
    }
    
    sealed class LayerCollection : UIElementCollection
    {
      readonly TextView textView;
      
      public LayerCollection(TextView textView)
        : base(textView, textView)
      {
        this.textView = textView;
      }
      
      public override void Clear()
      {
        base.Clear();
        textView.LayersChanged();
      }
      
      public override int Add(UIElement element)
      {
        int r = base.Add(element);
        textView.LayersChanged();
        return r;
      }
      
      public override void RemoveAt(int index)
      {
        base.RemoveAt(index);
        textView.LayersChanged();
      }
      
      public override void RemoveRange(int index, int count)
      {
        base.RemoveRange(index, count);
        textView.LayersChanged();
      }
    }
    
    void LayersChanged()
    {
      textLayer.index = layers.IndexOf(textLayer);
    }
    
    /// <summary>
    /// Inserts a new layer at a position specified relative to an existing layer.
    /// </summary>
    /// <param name="layer">The new layer to insert.</param>
    /// <param name="referencedLayer">The existing layer</param>
    /// <param name="position">Specifies whether the layer is inserted above,below, or replaces the referenced layer</param>
    public void InsertLayer(UIElement layer, KnownLayer referencedLayer, LayerInsertionPosition position)
    {
      if (layer == null)
        throw new ArgumentNullException("layer");
      if (!Enum.IsDefined(typeof(KnownLayer), referencedLayer))
        throw new InvalidEnumArgumentException("referencedLayer", (int)referencedLayer, typeof(KnownLayer));
      if (!Enum.IsDefined(typeof(LayerInsertionPosition), position))
        throw new InvalidEnumArgumentException("position", (int)position, typeof(LayerInsertionPosition));
      if (referencedLayer == KnownLayer.Background && position != LayerInsertionPosition.Above)
        throw new InvalidOperationException("Cannot replace or insert below the background layer.");
      
      LayerPosition newPosition = new LayerPosition(referencedLayer, position);
      LayerPosition.SetLayerPosition(layer, newPosition);
      for (int i = 0; i < layers.Count; i++) {
        LayerPosition p = LayerPosition.GetLayerPosition(layers[i]);
        if (p != null) {
          if (p.KnownLayer == referencedLayer && p.Position == LayerInsertionPosition.Replace) {
            // found the referenced layer
            switch (position) {
              case LayerInsertionPosition.Below:
                layers.Insert(i, layer);
                return;
              case LayerInsertionPosition.Above:
                layers.Insert(i + 1, layer);
                return;
              case LayerInsertionPosition.Replace:
                layers[i] = layer;
                return;
            }
          } else if (p.KnownLayer == referencedLayer && p.Position == LayerInsertionPosition.Above
                     || p.KnownLayer > referencedLayer) {
            // we skipped the insertion position (referenced layer does not exist?)
            layers.Insert(i, layer);
            return;
          }
        }
      }
      // inserting after all existing layers:
      layers.Add(layer);
    }
    
    /// <inheritdoc/>
    protected override int VisualChildrenCount {
      get { return layers.Count + inlineObjects.Count; }
    }
    
    /// <inheritdoc/>
    protected override Visual GetVisualChild(int index)
    {
      int cut = textLayer.index + 1;
      if (index < cut)
        return layers[index];
      else if (index < cut + inlineObjects.Count)
        return inlineObjects[index - cut].Element;
      else
        return layers[index - inlineObjects.Count];
    }
    
    /// <inheritdoc/>
    protected override System.Collections.IEnumerator LogicalChildren {
      get {
        return inlineObjects.Select(io => io.Element).Concat(layers.Cast<UIElement>()).GetEnumerator();
      }
    }
    #endregion
    
    #region Inline object handling
    List<InlineObjectRun> inlineObjects = new List<InlineObjectRun>();
    
    /// <summary>
    /// Adds a new inline object.
    /// </summary>
    internal void AddInlineObject(InlineObjectRun inlineObject)
    {
      Debug.Assert(inlineObject.VisualLine != null);
      
      // Remove inline object if its already added, can happen e.g. when recreating textrun for word-wrapping
      bool alreadyAdded = false;
      for (int i = 0; i < inlineObjects.Count; i++) {
        if (inlineObjects[i].Element == inlineObject.Element) {
          RemoveInlineObjectRun(inlineObjects[i], true);
          inlineObjects.RemoveAt(i);
          alreadyAdded = true;
          break;
        }
      }
      
      inlineObjects.Add(inlineObject);
      if (!alreadyAdded) {
        AddVisualChild(inlineObject.Element);
      }
      inlineObject.Element.Measure(new Size(double.PositiveInfinity, double.PositiveInfinity));
      inlineObject.desiredSize = inlineObject.Element.DesiredSize;
    }
    
    void MeasureInlineObjects()
    {
      // As part of MeasureOverride(), re-measure the inline objects
      foreach (InlineObjectRun inlineObject in inlineObjects) {
        if (inlineObject.VisualLine.IsDisposed) {
          // Don't re-measure inline objects that are going to be removed anyways.
          // If the inline object will be reused in a different VisualLine, we'll measure it in the AddInlineObject() call.
          continue;
        }
        inlineObject.Element.Measure(new Size(double.PositiveInfinity, double.PositiveInfinity));
        if (!inlineObject.Element.DesiredSize.IsClose(inlineObject.desiredSize)) {
          // the element changed size -> recreate its parent visual line
          inlineObject.desiredSize = inlineObject.Element.DesiredSize;
          if (allVisualLines.Remove(inlineObject.VisualLine)) {
            DisposeVisualLine(inlineObject.VisualLine);
          }
        }
      }
    }
    
    List<VisualLine> visualLinesWithOutstandingInlineObjects = new List<VisualLine>();
    
    void RemoveInlineObjects(VisualLine visualLine)
    {
      // Delay removing inline objects:
      // A document change immediately invalidates affected visual lines, but it does not
      // cause an immediate redraw.
      // To prevent inline objects from flickering when they are recreated, we delay removing
      // inline objects until the next redraw.
      if (visualLine.hasInlineObjects) {
        visualLinesWithOutstandingInlineObjects.Add(visualLine);
      }
    }
    
    /// <summary>
    /// Remove the inline objects that were marked for removal.
    /// </summary>
    void RemoveInlineObjectsNow()
    {
      if (visualLinesWithOutstandingInlineObjects.Count == 0)
        return;
      inlineObjects.RemoveAll(
        ior => {
          if (visualLinesWithOutstandingInlineObjects.Contains(ior.VisualLine)) {
            RemoveInlineObjectRun(ior, false);
            return true;
          }
          return false;
        });
      visualLinesWithOutstandingInlineObjects.Clear();
    }

    // Remove InlineObjectRun.Element from TextLayer.
    // Caller of RemoveInlineObjectRun will remove it from inlineObjects collection.
    void RemoveInlineObjectRun(InlineObjectRun ior, bool keepElement)
    {
      if (!keepElement && ior.Element.IsKeyboardFocusWithin) {
        // When the inline element that has the focus is removed, WPF will reset the
        // focus to the main window without raising appropriate LostKeyboardFocus events.
        // To work around this, we manually set focus to the next focusable parent.
        UIElement element = this;
        while (element != null && !element.Focusable) {
          element = VisualTreeHelper.GetParent(element) as UIElement;
        }
        if (element != null)
          Keyboard.Focus(element);
      }
      ior.VisualLine = null;
      if (!keepElement)
        RemoveVisualChild(ior.Element);
    }
    #endregion
    
    #region Brushes
    /// <summary>
    /// NonPrintableCharacterBrush dependency property.
    /// </summary>
    public static readonly DependencyProperty NonPrintableCharacterBrushProperty =
      DependencyProperty.Register("NonPrintableCharacterBrush", typeof(Brush), typeof(TextView),
                                  new FrameworkPropertyMetadata(Brushes.LightGray));
    
    /// <summary>
    /// Gets/sets the Brush used for displaying non-printable characters.
    /// </summary>
    public Brush NonPrintableCharacterBrush {
      get { return (Brush)GetValue(NonPrintableCharacterBrushProperty); }
      set { SetValue(NonPrintableCharacterBrushProperty, value); }
    }
    
    /// <summary>
    /// LinkTextForegroundBrush dependency property.
    /// </summary>
    public static readonly DependencyProperty LinkTextForegroundBrushProperty =
      DependencyProperty.Register("LinkTextForegroundBrush", typeof(Brush), typeof(TextView),
                                  new FrameworkPropertyMetadata(Brushes.Blue));
    
    /// <summary>
    /// Gets/sets the Brush used for displaying link texts.
    /// </summary>
    public Brush LinkTextForegroundBrush {
      get { return (Brush)GetValue(LinkTextForegroundBrushProperty); }
      set { SetValue(LinkTextForegroundBrushProperty, value); }
    }
    
    /// <summary>
    /// LinkTextBackgroundBrush dependency property.
    /// </summary>
    public static readonly DependencyProperty LinkTextBackgroundBrushProperty =
      DependencyProperty.Register("LinkTextBackgroundBrush", typeof(Brush), typeof(TextView),
                                  new FrameworkPropertyMetadata(Brushes.Transparent));
    
    /// <summary>
    /// Gets/sets the Brush used for the background of link texts.
    /// </summary>
    public Brush LinkTextBackgroundBrush {
      get { return (Brush)GetValue(LinkTextBackgroundBrushProperty); }
      set { SetValue(LinkTextBackgroundBrushProperty, value); }
    }
    #endregion
    
    #region Redraw methods / VisualLine invalidation
    /// <summary>
    /// Causes the text editor to regenerate all visual lines.
    /// </summary>
    public void Redraw()
    {
      Redraw(DispatcherPriority.Normal);
    }
    
    /// <summary>
    /// Causes the text editor to regenerate all visual lines.
    /// </summary>
    public void Redraw(DispatcherPriority redrawPriority)
    {
      VerifyAccess();
      ClearVisualLines();
      InvalidateMeasure(redrawPriority);
    }
    
    /// <summary>
    /// Causes the text editor to regenerate the specified visual line.
    /// </summary>
    public void Redraw(VisualLine visualLine, DispatcherPriority redrawPriority = DispatcherPriority.Normal)
    {
      VerifyAccess();
      if (allVisualLines.Remove(visualLine)) {
        DisposeVisualLine(visualLine);
        InvalidateMeasure(redrawPriority);
      }
    }
    
    /// <summary>
    /// Causes the text editor to redraw all lines overlapping with the specified segment.
    /// </summary>
    public void Redraw(int offset, int length, DispatcherPriority redrawPriority = DispatcherPriority.Normal)
    {
      VerifyAccess();
      bool changedSomethingBeforeOrInLine = false;
      for (int i = 0; i < allVisualLines.Count; i++) {
        VisualLine visualLine = allVisualLines[i];
        int lineStart = visualLine.FirstDocumentLine.Offset;
        int lineEnd = visualLine.LastDocumentLine.Offset + visualLine.LastDocumentLine.TotalLength;
        if (offset <= lineEnd) {
          changedSomethingBeforeOrInLine = true;
          if (offset + length >= lineStart) {
            allVisualLines.RemoveAt(i--);
            DisposeVisualLine(visualLine);
          }
        }
      }
      if (changedSomethingBeforeOrInLine) {
        // Repaint not only when something in visible area was changed, but also when anything in front of it
        // was changed. We might have to redraw the line number margin. Or the highlighting changed.
        // However, we'll try to reuse the existing VisualLines.
        InvalidateMeasure(redrawPriority);
      }
    }
    
    /// <summary>
    /// Causes a known layer to redraw.
    /// This method does not invalidate visual lines;
    /// use the <see cref="Redraw()"/> method to do that.
    /// </summary>
    [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Usage", "CA1801:ReviewUnusedParameters", MessageId = "knownLayer",
                                                     Justification="This method is meant to invalidate only a specific layer - I just haven't figured out how to do that, yet.")]
    public void InvalidateLayer(KnownLayer knownLayer)
    {
      InvalidateMeasure(DispatcherPriority.Normal);
    }
    
    /// <summary>
    /// Causes a known layer to redraw.
    /// This method does not invalidate visual lines;
    /// use the <see cref="Redraw()"/> method to do that.
    /// </summary>
    [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Usage", "CA1801:ReviewUnusedParameters", MessageId = "knownLayer",
                                                     Justification="This method is meant to invalidate only a specific layer - I just haven't figured out how to do that, yet.")]
    public void InvalidateLayer(KnownLayer knownLayer, DispatcherPriority priority)
    {
      InvalidateMeasure(priority);
    }
    
    /// <summary>
    /// Causes the text editor to redraw all lines overlapping with the specified segment.
    /// Does nothing if segment is null.
    /// </summary>
    public void Redraw(ISegment segment, DispatcherPriority redrawPriority = DispatcherPriority.Normal)
    {
      if (segment != null) {
        Redraw(segment.Offset, segment.Length, redrawPriority);
      }
    }
    
    /// <summary>
    /// Invalidates all visual lines.
    /// The caller of ClearVisualLines() must also call InvalidateMeasure() to ensure
    /// that the visual lines will be recreated.
    /// </summary>
    void ClearVisualLines()
    {
      visibleVisualLines = null;
      if (allVisualLines.Count != 0) {
        foreach (VisualLine visualLine in allVisualLines) {
          DisposeVisualLine(visualLine);
        }
        allVisualLines.Clear();
      }
    }
    
    void DisposeVisualLine(VisualLine visualLine)
    {
      if (newVisualLines != null && newVisualLines.Contains(visualLine)) {
        throw new ArgumentException("Cannot dispose visual line because it is in construction!");
      }
      visibleVisualLines = null;
      visualLine.Dispose();
      RemoveInlineObjects(visualLine);
    }
    #endregion
    
    #region InvalidateMeasure(DispatcherPriority)
    DispatcherOperation invalidateMeasureOperation;
    
    void InvalidateMeasure(DispatcherPriority priority)
    {
      if (priority >= DispatcherPriority.Render) {
        if (invalidateMeasureOperation != null) {
          invalidateMeasureOperation.Abort();
          invalidateMeasureOperation = null;
        }
        base.InvalidateMeasure();
      } else {
        if (invalidateMeasureOperation != null) {
          invalidateMeasureOperation.Priority = priority;
        } else {
          invalidateMeasureOperation = Dispatcher.BeginInvoke(
            priority,
            new Action(
              delegate {
                invalidateMeasureOperation = null;
                base.InvalidateMeasure();
              }
            )
          );
        }
      }
    }
    #endregion
    
    #region Get(OrConstruct)VisualLine
    /// <summary>
    /// Gets the visual line that contains the document line with the specified number.
    /// Returns null if the document line is outside the visible range.
    /// </summary>
    public VisualLine GetVisualLine(int documentLineNumber)
    {
      // TODO: EnsureVisualLines() ?
      foreach (VisualLine visualLine in allVisualLines) {
        Debug.Assert(visualLine.IsDisposed == false);
        int start = visualLine.FirstDocumentLine.LineNumber;
        int end = visualLine.LastDocumentLine.LineNumber;
        if (documentLineNumber >= start && documentLineNumber <= end)
          return visualLine;
      }
      return null;
    }
    
    /// <summary>
    /// Gets the visual line that contains the document line with the specified number.
    /// If that line is outside the visible range, a new VisualLine for that document line is constructed.
    /// </summary>
    public VisualLine GetOrConstructVisualLine(DocumentLine documentLine)
    {
      if (documentLine == null)
        throw new ArgumentNullException("documentLine");
      if (!this.Document.Lines.Contains(documentLine))
        throw new InvalidOperationException("Line belongs to wrong document");
      VerifyAccess();
      
      VisualLine l = GetVisualLine(documentLine.LineNumber);
      if (l == null) {
        TextRunProperties globalTextRunProperties = CreateGlobalTextRunProperties();
        VisualLineTextParagraphProperties paragraphProperties = CreateParagraphProperties(globalTextRunProperties);
        
        while (heightTree.GetIsCollapsed(documentLine.LineNumber)) {
          documentLine = documentLine.PreviousLine;
        }
        
        l = BuildVisualLine(documentLine,
                            globalTextRunProperties, paragraphProperties,
                            elementGenerators.ToArray(), lineTransformers.ToArray(),
                            lastAvailableSize);
        allVisualLines.Add(l);
        // update all visual top values (building the line might have changed visual top of other lines due to word wrapping)
        foreach (var line in allVisualLines) {
          line.VisualTop = heightTree.GetVisualPosition(line.FirstDocumentLine);
        }
      }
      return l;
    }
    #endregion
    
    #region Visual Lines (fields and properties)
    List<VisualLine> allVisualLines = new List<VisualLine>();
    ReadOnlyCollection<VisualLine> visibleVisualLines;
    double clippedPixelsOnTop;
    List<VisualLine> newVisualLines;
    
    /// <summary>
    /// Gets the currently visible visual lines.
    /// </summary>
    /// <exception cref="VisualLinesInvalidException">
    /// Gets thrown if there are invalid visual lines when this property is accessed.
    /// You can use the <see cref="VisualLinesValid"/> property to check for this case,
    /// or use the <see cref="EnsureVisualLines()"/> method to force creating the visual lines
    /// when they are invalid.
    /// </exception>
    [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Design", "CA1065:DoNotRaiseExceptionsInUnexpectedLocations")]
    public ReadOnlyCollection<VisualLine> VisualLines {
      get {
        if (visibleVisualLines == null)
          throw new VisualLinesInvalidException();
        return visibleVisualLines;
      }
    }
    
    /// <summary>
    /// Gets whether the visual lines are valid.
    /// Will return false after a call to Redraw().
    /// Accessing the visual lines property will cause a <see cref="VisualLinesInvalidException"/>
    /// if this property is <c>false</c>.
    /// </summary>
    public bool VisualLinesValid {
      get { return visibleVisualLines != null; }
    }
    
    /// <summary>
    /// Occurs when the TextView is about to be measured and will regenerate its visual lines.
    /// This event may be used to mark visual lines as invalid that would otherwise be reused.
    /// </summary>
    public event EventHandler<VisualLineConstructionStartEventArgs> VisualLineConstructionStarting;
    
    /// <summary>
    /// Occurs when the TextView was measured and changed its visual lines.
    /// </summary>
    public event EventHandler VisualLinesChanged;
    
    /// <summary>
    /// If the visual lines are invalid, creates new visual lines for the visible part
    /// of the document.
    /// If all visual lines are valid, this method does nothing.
    /// </summary>
    /// <exception cref="InvalidOperationException">The visual line build process is already running.
    /// It is not allowed to call this method during the construction of a visual line.</exception>
    public void EnsureVisualLines()
    {
      Dispatcher.VerifyAccess();
      if (inMeasure)
        throw new InvalidOperationException("The visual line build process is already running! Cannot EnsureVisualLines() during Measure!");
      if (!VisualLinesValid) {
        // increase priority for re-measure
        InvalidateMeasure(DispatcherPriority.Normal);
        // force immediate re-measure
        UpdateLayout();
      }
      // Sometimes we still have invalid lines after UpdateLayout - work around the problem
      // by calling MeasureOverride directly.
      if (!VisualLinesValid) {
        Debug.WriteLine("UpdateLayout() failed in EnsureVisualLines");
        MeasureOverride(lastAvailableSize);
      }
      if (!VisualLinesValid)
        throw new VisualLinesInvalidException("Internal error: visual lines invalid after EnsureVisualLines call");
    }
    #endregion
    
    #region Measure
    /// <summary>
    /// Additonal amount that allows horizontal scrolling past the end of the longest line.
    /// This is necessary to ensure the caret always is visible, even when it is at the end of the longest line.
    /// </summary>
    const double AdditionalHorizontalScrollAmount = 3;
    
    Size lastAvailableSize;
    bool inMeasure;
    
    /// <inheritdoc/>
    protected override Size MeasureOverride(Size availableSize)
    {
      // We don't support infinite available width, so we'll limit it to 32000 pixels.
      if (availableSize.Width > 32000)
        availableSize.Width = 32000;
      
      if (!canHorizontallyScroll && !availableSize.Width.IsClose(lastAvailableSize.Width))
        ClearVisualLines();
      lastAvailableSize = availableSize;
      
      foreach (UIElement layer in layers) {
        layer.Measure(availableSize);
      }
      MeasureInlineObjects();
      
      InvalidateVisual(); // = InvalidateArrange+InvalidateRender
      
      double maxWidth;
      if (document == null) {
        // no document -> create empty list of lines
        allVisualLines = new List<VisualLine>();
        visibleVisualLines = allVisualLines.AsReadOnly();
        maxWidth = 0;
      } else {
        inMeasure = true;
        try {
          maxWidth = CreateAndMeasureVisualLines(availableSize);
        } finally {
          inMeasure = false;
        }
      }
      
      // remove inline objects only at the end, so that inline objects that were re-used are not removed from the editor
      RemoveInlineObjectsNow();
      
      maxWidth += AdditionalHorizontalScrollAmount;
      double heightTreeHeight = this.DocumentHeight;
      TextEditorOptions options = this.Options;
      if (options.AllowScrollBelowDocument) {
        if (!double.IsInfinity(scrollViewport.Height)) {
          heightTreeHeight = Math.Max(heightTreeHeight, Math.Min(heightTreeHeight - 50, scrollOffset.Y) + scrollViewport.Height);
        }
      }
      
      textLayer.SetVisualLines(visibleVisualLines);
      
      SetScrollData(availableSize,
                    new Size(maxWidth, heightTreeHeight),
                    scrollOffset);
      if (VisualLinesChanged != null)
        VisualLinesChanged(this, EventArgs.Empty);
      
      return new Size(Math.Min(availableSize.Width, maxWidth), Math.Min(availableSize.Height, heightTreeHeight));
    }
    
    /// <summary>
    /// Build all VisualLines in the visible range.
    /// </summary>
    /// <returns>Width the longest line</returns>
    double CreateAndMeasureVisualLines(Size availableSize)
    {
      TextRunProperties globalTextRunProperties = CreateGlobalTextRunProperties();
      VisualLineTextParagraphProperties paragraphProperties = CreateParagraphProperties(globalTextRunProperties);
      
      Debug.WriteLine("Measure availableSize=" + availableSize + ", scrollOffset=" + scrollOffset);
      var firstLineInView = heightTree.GetLineByVisualPosition(scrollOffset.Y);
      
      // number of pixels clipped from the first visual line(s)
      clippedPixelsOnTop = scrollOffset.Y - heightTree.GetVisualPosition(firstLineInView);
      // clippedPixelsOnTop should be >= 0, except for floating point inaccurracy.
      Debug.Assert(clippedPixelsOnTop >= -ExtensionMethods.Epsilon);
      
      newVisualLines = new List<VisualLine>();
      
      if (VisualLineConstructionStarting != null)
        VisualLineConstructionStarting(this, new VisualLineConstructionStartEventArgs(firstLineInView));
      
      var elementGeneratorsArray = elementGenerators.ToArray();
      var lineTransformersArray = lineTransformers.ToArray();
      var nextLine = firstLineInView;
      double maxWidth = 0;
      double yPos = -clippedPixelsOnTop;
      while (yPos < availableSize.Height && nextLine != null) {
        VisualLine visualLine = GetVisualLine(nextLine.LineNumber);
        if (visualLine == null) {
          visualLine = BuildVisualLine(nextLine,
                                       globalTextRunProperties, paragraphProperties,
                                       elementGeneratorsArray, lineTransformersArray,
                                       availableSize);
        }
        
        visualLine.VisualTop = scrollOffset.Y + yPos;
        
        nextLine = visualLine.LastDocumentLine.NextLine;
        
        yPos += visualLine.Height;
        
        foreach (TextLine textLine in visualLine.TextLines) {
          if (textLine.WidthIncludingTrailingWhitespace > maxWidth)
            maxWidth = textLine.WidthIncludingTrailingWhitespace;
        }
        
        newVisualLines.Add(visualLine);
      }
      
      foreach (VisualLine line in allVisualLines) {
        Debug.Assert(line.IsDisposed == false);
        if (!newVisualLines.Contains(line))
          DisposeVisualLine(line);
      }
      
      allVisualLines = newVisualLines;
      // visibleVisualLines = readonly copy of visual lines
      visibleVisualLines = new ReadOnlyCollection<VisualLine>(newVisualLines.ToArray());
      newVisualLines = null;
      
      if (allVisualLines.Any(line => line.IsDisposed)) {
        throw new InvalidOperationException("A visual line was disposed even though it is still in use.\n" +
                                            "This can happen when Redraw() is called during measure for lines " +
                                            "that are already constructed.");
      }
      return maxWidth;
    }
    #endregion
    
    #region BuildVisualLine
    TextFormatter formatter;
    internal TextViewCachedElements cachedElements;
    
    TextRunProperties CreateGlobalTextRunProperties()
    {
      var p = new GlobalTextRunProperties();
      p.typeface = this.CreateTypeface();
      p.fontRenderingEmSize = FontSize;
      p.foregroundBrush = (Brush)GetValue(Control.ForegroundProperty);
      ExtensionMethods.CheckIsFrozen(p.foregroundBrush);
      p.cultureInfo = CultureInfo.CurrentCulture;
      return p;
    }
    
    VisualLineTextParagraphProperties CreateParagraphProperties(TextRunProperties defaultTextRunProperties)
    {
      return new VisualLineTextParagraphProperties {
        defaultTextRunProperties = defaultTextRunProperties,
        textWrapping = canHorizontallyScroll ? TextWrapping.NoWrap : TextWrapping.Wrap,
        tabSize = Options.IndentationSize * WideSpaceWidth
      };
    }
    
    VisualLine BuildVisualLine(DocumentLine documentLine,
                               TextRunProperties globalTextRunProperties,
                               VisualLineTextParagraphProperties paragraphProperties,
                               VisualLineElementGenerator[] elementGeneratorsArray,
                               IVisualLineTransformer[] lineTransformersArray,
                               Size availableSize)
    {
      if (heightTree.GetIsCollapsed(documentLine.LineNumber))
        throw new InvalidOperationException("Trying to build visual line from collapsed line");
      
      //Debug.WriteLine("Building line " + documentLine.LineNumber);
      
      VisualLine visualLine = new VisualLine(this, documentLine);
      VisualLineTextSource textSource = new VisualLineTextSource(visualLine) {
        Document = document,
        GlobalTextRunProperties = globalTextRunProperties,
        TextView = this
      };
      
      visualLine.ConstructVisualElements(textSource, elementGeneratorsArray);
      
      if (visualLine.FirstDocumentLine != visualLine.LastDocumentLine) {
        // Check whether the lines are collapsed correctly:
        double firstLinePos = heightTree.GetVisualPosition(visualLine.FirstDocumentLine.NextLine);
        double lastLinePos = heightTree.GetVisualPosition(visualLine.LastDocumentLine.NextLine ?? visualLine.LastDocumentLine);
        if (!firstLinePos.IsClose(lastLinePos)) {
          for (int i = visualLine.FirstDocumentLine.LineNumber + 1; i <= visualLine.LastDocumentLine.LineNumber; i++) {
            if (!heightTree.GetIsCollapsed(i))
              throw new InvalidOperationException("Line " + i + " was skipped by a VisualLineElementGenerator, but it is not collapsed.");
          }
          throw new InvalidOperationException("All lines collapsed but visual pos different - height tree inconsistency?");
        }
      }
      
      visualLine.RunTransformers(textSource, lineTransformersArray);
      
      // now construct textLines:
      int textOffset = 0;
      TextLineBreak lastLineBreak = null;
      var textLines = new List<TextLine>();
      paragraphProperties.indent = 0;
      paragraphProperties.firstLineInParagraph = true;
      while (textOffset <= visualLine.VisualLengthWithEndOfLineMarker) {
        TextLine textLine = formatter.FormatLine(
          textSource,
          textOffset,
          availableSize.Width,
          paragraphProperties,
          lastLineBreak
        );
        textLines.Add(textLine);
        textOffset += textLine.Length;
        
        // exit loop so that we don't do the indentation calculation if there's only a single line
        if (textOffset >= visualLine.VisualLengthWithEndOfLineMarker)
          break;
        
        if (paragraphProperties.firstLineInParagraph) {
          paragraphProperties.firstLineInParagraph = false;
          
          TextEditorOptions options = this.Options;
          double indentation = 0;
          if (options.InheritWordWrapIndentation) {
            // determine indentation for next line:
            int indentVisualColumn = GetIndentationVisualColumn(visualLine);
            if (indentVisualColumn > 0 && indentVisualColumn < textOffset) {
              indentation = textLine.GetDistanceFromCharacterHit(new CharacterHit(indentVisualColumn, 0));
            }
          }
          indentation += options.WordWrapIndentation;
          // apply the calculated indentation unless it's more than half of the text editor size:
          if (indentation > 0 && indentation * 2 < availableSize.Width)
            paragraphProperties.indent = indentation;
        }
        lastLineBreak = textLine.GetTextLineBreak();
      }
      visualLine.SetTextLines(textLines);
      heightTree.SetHeight(visualLine.FirstDocumentLine, visualLine.Height);
      return visualLine;
    }
    
    static int GetIndentationVisualColumn(VisualLine visualLine)
    {
      if (visualLine.Elements.Count == 0)
        return 0;
      int column = 0;
      int elementIndex = 0;
      VisualLineElement element = visualLine.Elements[elementIndex];
      while (element.IsWhitespace(column)) {
        column++;
        if (column == element.VisualColumn + element.VisualLength) {
          elementIndex++;
          if (elementIndex == visualLine.Elements.Count)
            break;
          element = visualLine.Elements[elementIndex];
        }
      }
      return column;
    }
    #endregion
    
    #region Arrange
    /// <summary>
    /// Arrange implementation.
    /// </summary>
    protected override Size ArrangeOverride(Size finalSize)
    {
      EnsureVisualLines();
      
      foreach (UIElement layer in layers) {
        layer.Arrange(new Rect(new Point(0, 0), finalSize));
      }
      
      if (document == null || allVisualLines.Count == 0)
        return finalSize;
      
      // validate scroll position
      Vector newScrollOffset = scrollOffset;
      if (scrollOffset.X + finalSize.Width > scrollExtent.Width) {
        newScrollOffset.X = Math.Max(0, scrollExtent.Width - finalSize.Width);
      }
      if (scrollOffset.Y + finalSize.Height > scrollExtent.Height) {
        newScrollOffset.Y = Math.Max(0, scrollExtent.Height - finalSize.Height);
      }
      if (SetScrollData(scrollViewport, scrollExtent, newScrollOffset))
        InvalidateMeasure(DispatcherPriority.Normal);
      
      //Debug.WriteLine("Arrange finalSize=" + finalSize + ", scrollOffset=" + scrollOffset);
      
//      double maxWidth = 0;
      
      if (visibleVisualLines != null) {
        Point pos = new Point(-scrollOffset.X, -clippedPixelsOnTop);
        foreach (VisualLine visualLine in visibleVisualLines) {
          int offset = 0;
          foreach (TextLine textLine in visualLine.TextLines) {
            foreach (var span in textLine.GetTextRunSpans()) {
              InlineObjectRun inline = span.Value as InlineObjectRun;
              if (inline != null && inline.VisualLine != null) {
                Debug.Assert(inlineObjects.Contains(inline));
                double distance = textLine.GetDistanceFromCharacterHit(new CharacterHit(offset, 0));
                inline.Element.Arrange(new Rect(new Point(pos.X + distance, pos.Y), inline.Element.DesiredSize));
              }
              offset += span.Length;
            }
            pos.Y += textLine.Height;
          }
        }
      }
      InvalidateCursorIfMouseWithinTextView();
      
      return finalSize;
    }
    #endregion
    
    #region Render
    readonly ObserveAddRemoveCollection<IBackgroundRenderer> backgroundRenderers;
    
    /// <summary>
    /// Gets the list of background renderers.
    /// </summary>
    public IList<IBackgroundRenderer> BackgroundRenderers {
      get { return backgroundRenderers; }
    }
    
    void BackgroundRenderer_Added(IBackgroundRenderer renderer)
    {
      ConnectToTextView(renderer);
      InvalidateLayer(renderer.Layer);
    }
    
    void BackgroundRenderer_Removed(IBackgroundRenderer renderer)
    {
      DisconnectFromTextView(renderer);
      InvalidateLayer(renderer.Layer);
    }
    
    /// <inheritdoc/>
    protected override void OnRender(DrawingContext drawingContext)
    {
      RenderBackground(drawingContext, KnownLayer.Background);
      foreach (var line in visibleVisualLines) {
        Brush currentBrush = null;
        int startVC = 0;
        int length = 0;
        foreach (var element in line.Elements) {
          if (currentBrush == null || !currentBrush.Equals(element.BackgroundBrush)) {
            if (currentBrush != null) {
              BackgroundGeometryBuilder builder = new BackgroundGeometryBuilder();
              builder.AlignToWholePixels = true;
              builder.CornerRadius = 3;
              foreach (var rect in BackgroundGeometryBuilder.GetRectsFromVisualSegment(this, line, startVC, startVC + length))
                builder.AddRectangle(this, rect);
              Geometry geometry = builder.CreateGeometry();
              if (geometry != null) {
                drawingContext.DrawGeometry(currentBrush, null, geometry);
              }
            }
            startVC = element.VisualColumn;
            length = element.DocumentLength;
            currentBrush = element.BackgroundBrush;
          } else {
            length += element.VisualLength;
          }
        }
        if (currentBrush != null) {
          BackgroundGeometryBuilder builder = new BackgroundGeometryBuilder();
          builder.AlignToWholePixels = true;
          builder.CornerRadius = 3;
          foreach (var rect in BackgroundGeometryBuilder.GetRectsFromVisualSegment(this, line, startVC, startVC + length))
            builder.AddRectangle(this, rect);
          Geometry geometry = builder.CreateGeometry();
          if (geometry != null) {
            drawingContext.DrawGeometry(currentBrush, null, geometry);
          }
        }
      }
    }
    
    internal void RenderBackground(DrawingContext drawingContext, KnownLayer layer)
    {
      foreach (IBackgroundRenderer bg in backgroundRenderers) {
        if (bg.Layer == layer) {
          bg.Draw(this, drawingContext);
        }
      }
    }
    
    internal void ArrangeTextLayer(IList<VisualLineDrawingVisual> visuals)
    {
      Point pos = new Point(-scrollOffset.X, -clippedPixelsOnTop);
      foreach (VisualLineDrawingVisual visual in visuals) {
        TranslateTransform t = visual.Transform as TranslateTransform;
        if (t == null || t.X != pos.X || t.Y != pos.Y) {
          visual.Transform = new TranslateTransform(pos.X, pos.Y);
          visual.Transform.Freeze();
        }
        pos.Y += visual.Height;
      }
    }
    #endregion
    
    #region IScrollInfo implementation
    /// <summary>
    /// Size of the document, in pixels.
    /// </summary>
    Size scrollExtent;
    
    /// <summary>
    /// Offset of the scroll position.
    /// </summary>
    Vector scrollOffset;
    
    /// <summary>
    /// Size of the viewport.
    /// </summary>
    Size scrollViewport;
    
    void ClearScrollData()
    {
      SetScrollData(new Size(), new Size(), new Vector());
    }
    
    bool SetScrollData(Size viewport, Size extent, Vector offset)
    {
      if (!(viewport.IsClose(this.scrollViewport)
            && extent.IsClose(this.scrollExtent)
            && offset.IsClose(this.scrollOffset)))
      {
        this.scrollViewport = viewport;
        this.scrollExtent = extent;
        SetScrollOffset(offset);
        this.OnScrollChange();
        return true;
      }
      return false;
    }
    
    void OnScrollChange()
    {
      ScrollViewer scrollOwner = ((IScrollInfo)this).ScrollOwner;
      if (scrollOwner != null) {
        scrollOwner.InvalidateScrollInfo();
      }
    }
    
    bool canVerticallyScroll;
    bool IScrollInfo.CanVerticallyScroll {
      get { return canVerticallyScroll; }
      set {
        if (canVerticallyScroll != value) {
          canVerticallyScroll = value;
          InvalidateMeasure(DispatcherPriority.Normal);
        }
      }
    }
    bool canHorizontallyScroll;
    bool IScrollInfo.CanHorizontallyScroll {
      get { return canHorizontallyScroll; }
      set {
        if (canHorizontallyScroll != value) {
          canHorizontallyScroll = value;
          ClearVisualLines();
          InvalidateMeasure(DispatcherPriority.Normal);
        }
      }
    }
    
    double IScrollInfo.ExtentWidth {
      get { return scrollExtent.Width; }
    }
    
    double IScrollInfo.ExtentHeight {
      get { return scrollExtent.Height; }
    }
    
    double IScrollInfo.ViewportWidth {
      get { return scrollViewport.Width; }
    }
    
    double IScrollInfo.ViewportHeight {
      get { return scrollViewport.Height; }
    }
    
    /// <summary>
    /// Gets the horizontal scroll offset.
    /// </summary>
    public double HorizontalOffset {
      get { return scrollOffset.X; }
    }
    
    /// <summary>
    /// Gets the vertical scroll offset.
    /// </summary>
    public double VerticalOffset {
      get { return scrollOffset.Y; }
    }
    
    /// <summary>
    /// Gets the scroll offset;
    /// </summary>
    public Vector ScrollOffset {
      get { return scrollOffset; }
    }
    
    /// <summary>
    /// Occurs when the scroll offset has changed.
    /// </summary>
    public event EventHandler ScrollOffsetChanged;
    
    void SetScrollOffset(Vector vector)
    {
      if (!canHorizontallyScroll)
        vector.X = 0;
      if (!canVerticallyScroll)
        vector.Y = 0;
      
      if (!scrollOffset.IsClose(vector)) {
        scrollOffset = vector;
        if (ScrollOffsetChanged != null)
          ScrollOffsetChanged(this, EventArgs.Empty);
      }
    }
    
    ScrollViewer IScrollInfo.ScrollOwner { get; set; }
    
    void IScrollInfo.LineUp()
    {
      ((IScrollInfo)this).SetVerticalOffset(scrollOffset.Y - DefaultLineHeight);
    }
    
    void IScrollInfo.LineDown()
    {
      ((IScrollInfo)this).SetVerticalOffset(scrollOffset.Y + DefaultLineHeight);
    }
    
    void IScrollInfo.LineLeft()
    {
      ((IScrollInfo)this).SetHorizontalOffset(scrollOffset.X - WideSpaceWidth);
    }
    
    void IScrollInfo.LineRight()
    {
      ((IScrollInfo)this).SetHorizontalOffset(scrollOffset.X + WideSpaceWidth);
    }
    
    void IScrollInfo.PageUp()
    {
      ((IScrollInfo)this).SetVerticalOffset(scrollOffset.Y - scrollViewport.Height);
    }
    
    void IScrollInfo.PageDown()
    {
      ((IScrollInfo)this).SetVerticalOffset(scrollOffset.Y + scrollViewport.Height);
    }
    
    void IScrollInfo.PageLeft()
    {
      ((IScrollInfo)this).SetHorizontalOffset(scrollOffset.X - scrollViewport.Width);
    }
    
    void IScrollInfo.PageRight()
    {
      ((IScrollInfo)this).SetHorizontalOffset(scrollOffset.X + scrollViewport.Width);
    }
    
    void IScrollInfo.MouseWheelUp()
    {
      ((IScrollInfo)this).SetVerticalOffset(
        scrollOffset.Y - (SystemParameters.WheelScrollLines * DefaultLineHeight));
      OnScrollChange();
    }
    
    void IScrollInfo.MouseWheelDown()
    {
      ((IScrollInfo)this).SetVerticalOffset(
        scrollOffset.Y + (SystemParameters.WheelScrollLines * DefaultLineHeight));
      OnScrollChange();
    }
    
    void IScrollInfo.MouseWheelLeft()
    {
      ((IScrollInfo)this).SetHorizontalOffset(
        scrollOffset.X - (SystemParameters.WheelScrollLines * WideSpaceWidth));
      OnScrollChange();
    }
    
    void IScrollInfo.MouseWheelRight()
    {
      ((IScrollInfo)this).SetHorizontalOffset(
        scrollOffset.X + (SystemParameters.WheelScrollLines * WideSpaceWidth));
      OnScrollChange();
    }
    
    bool defaultTextMetricsValid;
    double wideSpaceWidth; // Width of an 'x'. Used as basis for the tab width, and for scrolling.
    double defaultLineHeight; // Height of a line containing 'x'. Used for scrolling.
    double defaultBaseline; // Baseline of a line containing 'x'. Used for TextTop/TextBottom calculation.
    
    /// <summary>
    /// Gets the width of a 'wide space' (the space width used for calculating the tab size).
    /// </summary>
    /// <remarks>
    /// This is the width of an 'x' in the current font.
    /// We do not measure the width of an actual space as that would lead to tiny tabs in
    /// some proportional fonts.
    /// For monospaced fonts, this property will return the expected value, as 'x' and ' ' have the same width.
    /// </remarks>
    public double WideSpaceWidth {
      get {
        CalculateDefaultTextMetrics();
        return wideSpaceWidth;
      }
    }
    
    /// <summary>
    /// Gets the default line height. This is the height of an empty line or a line containing regular text.
    /// Lines that include formatted text or custom UI elements may have a different line height.
    /// </summary>
    public double DefaultLineHeight {
      get {
        CalculateDefaultTextMetrics();
        return defaultLineHeight;
      }
    }
    
    /// <summary>
    /// Gets the default baseline position. This is the difference between <see cref="VisualYPosition.TextTop"/>
    /// and <see cref="VisualYPosition.Baseline"/> for a line containing regular text.
    /// Lines that include formatted text or custom UI elements may have a different baseline.
    /// </summary>
    public double DefaultBaseline {
      get {
        CalculateDefaultTextMetrics();
        return defaultBaseline;
      }
    }
    
    void InvalidateDefaultTextMetrics()
    {
      defaultTextMetricsValid = false;
      if (heightTree != null) {
        // calculate immediately so that height tree gets updated
        CalculateDefaultTextMetrics();
      }
    }
    
    void CalculateDefaultTextMetrics()
    {
      if (defaultTextMetricsValid)
        return;
      defaultTextMetricsValid = true;
      if (formatter != null) {
        var textRunProperties = CreateGlobalTextRunProperties();
        using (var line = formatter.FormatLine(
          new SimpleTextSource("x", textRunProperties),
          0, 32000,
          new VisualLineTextParagraphProperties { defaultTextRunProperties = textRunProperties },
          null))
        {
          wideSpaceWidth = Math.Max(1, line.WidthIncludingTrailingWhitespace);
          defaultBaseline = Math.Max(1, line.Baseline);
          defaultLineHeight = Math.Max(1, line.Height);
        }
      } else {
        wideSpaceWidth = FontSize / 2;
        defaultBaseline = FontSize;
        defaultLineHeight = FontSize + 3;
      }
      // Update heightTree.DefaultLineHeight, if a document is loaded.
      if (heightTree != null)
        heightTree.DefaultLineHeight = defaultLineHeight;
    }
    
    static double ValidateVisualOffset(double offset)
    {
      if (double.IsNaN(offset))
        throw new ArgumentException("offset must not be NaN");
      if (offset < 0)
        return 0;
      else
        return offset;
    }
    
    void IScrollInfo.SetHorizontalOffset(double offset)
    {
      offset = ValidateVisualOffset(offset);
      if (!scrollOffset.X.IsClose(offset)) {
        SetScrollOffset(new Vector(offset, scrollOffset.Y));
        InvalidateVisual();
        textLayer.InvalidateVisual();
      }
    }
    
    void IScrollInfo.SetVerticalOffset(double offset)
    {
      offset = ValidateVisualOffset(offset);
      if (!scrollOffset.Y.IsClose(offset)) {
        SetScrollOffset(new Vector(scrollOffset.X, offset));
        InvalidateMeasure(DispatcherPriority.Normal);
      }
    }
    
    Rect IScrollInfo.MakeVisible(Visual visual, Rect rectangle)
    {
      if (rectangle.IsEmpty || visual == null || visual == this || !this.IsAncestorOf(visual)) {
        return Rect.Empty;
      }
      // Convert rectangle into our coordinate space.
      GeneralTransform childTransform = visual.TransformToAncestor(this);
      rectangle = childTransform.TransformBounds(rectangle);
      
      MakeVisible(Rect.Offset(rectangle, scrollOffset));
      
      return rectangle;
    }
    
    /// <summary>
    /// Scrolls the text view so that the specified rectangle gets visible.
    /// </summary>
    public void MakeVisible(Rect rectangle)
    {
      Rect visibleRectangle = new Rect(scrollOffset.X, scrollOffset.Y,
                                       scrollViewport.Width, scrollViewport.Height);
      Vector newScrollOffset = scrollOffset;
      if (rectangle.Left < visibleRectangle.Left) {
        if (rectangle.Right > visibleRectangle.Right) {
          newScrollOffset.X = rectangle.Left + rectangle.Width / 2;
        } else {
          newScrollOffset.X = rectangle.Left;
        }
      } else if (rectangle.Right > visibleRectangle.Right) {
        newScrollOffset.X = rectangle.Right - scrollViewport.Width;
      }
      if (rectangle.Top < visibleRectangle.Top) {
        if (rectangle.Bottom > visibleRectangle.Bottom) {
          newScrollOffset.Y = rectangle.Top + rectangle.Height / 2;
        } else {
          newScrollOffset.Y = rectangle.Top;
        }
      } else if (rectangle.Bottom > visibleRectangle.Bottom) {
        newScrollOffset.Y = rectangle.Bottom - scrollViewport.Height;
      }
      newScrollOffset.X = ValidateVisualOffset(newScrollOffset.X);
      newScrollOffset.Y = ValidateVisualOffset(newScrollOffset.Y);
      if (!scrollOffset.IsClose(newScrollOffset)) {
        SetScrollOffset(newScrollOffset);
        this.OnScrollChange();
        InvalidateMeasure(DispatcherPriority.Normal);
      }
    }
    #endregion
    
    #region Visual element mouse handling
    /// <inheritdoc/>
    protected override HitTestResult HitTestCore(PointHitTestParameters hitTestParameters)
    {
      // accept clicks even where the text area draws no background
      return new PointHitTestResult(this, hitTestParameters.HitPoint);
    }
    
    [ThreadStatic] static bool invalidCursor;
    
    /// <summary>
    /// Updates the mouse cursor by calling <see cref="Mouse.UpdateCursor"/>, but with background priority.
    /// </summary>
    public static void InvalidateCursor()
    {
      if (!invalidCursor) {
        invalidCursor = true;
        Dispatcher.CurrentDispatcher.BeginInvoke(
          DispatcherPriority.Background, // fixes issue #288
          new Action(
            delegate {
              invalidCursor = false;
              Mouse.UpdateCursor();
            }));
      }
    }
    
    internal void InvalidateCursorIfMouseWithinTextView()
    {
      // Don't unnecessarily call Mouse.UpdateCursor() if the mouse is outside the text view.
      // Unnecessary updates may cause the mouse pointer to flicker
      // (e.g. if it is over a window border, it blinks between Resize and Normal)
      if (this.IsMouseOver)
        InvalidateCursor();
    }
    
    /// <inheritdoc/>
    protected override void OnQueryCursor(QueryCursorEventArgs e)
    {
      VisualLineElement element = GetVisualLineElementFromPosition(e.GetPosition(this) + scrollOffset);
      if (element != null) {
        element.OnQueryCursor(e);
      }
    }
    
    /// <inheritdoc/>
    protected override void OnMouseDown(MouseButtonEventArgs e)
    {
      base.OnMouseDown(e);
      if (!e.Handled) {
        EnsureVisualLines();
        VisualLineElement element = GetVisualLineElementFromPosition(e.GetPosition(this) + scrollOffset);
        if (element != null) {
          element.OnMouseDown(e);
        }
      }
    }
    
    /// <inheritdoc/>
    protected override void OnMouseUp(MouseButtonEventArgs e)
    {
      base.OnMouseUp(e);
      if (!e.Handled) {
        EnsureVisualLines();
        VisualLineElement element = GetVisualLineElementFromPosition(e.GetPosition(this) + scrollOffset);
        if (element != null) {
          element.OnMouseUp(e);
        }
      }
    }
    #endregion
    
    #region Getting elements from Visual Position
    /// <summary>
    /// Gets the visual line at the specified document position (relative to start of document).
    /// Returns null if there is no visual line for the position (e.g. the position is outside the visible
    /// text area).
    /// </summary>
    public VisualLine GetVisualLineFromVisualTop(double visualTop)
    {
      // TODO: change this method to also work outside the visible range -
      // required to make GetPosition work as expected!
      EnsureVisualLines();
      foreach (VisualLine vl in this.VisualLines) {
        if (visualTop < vl.VisualTop)
          continue;
        if (visualTop < vl.VisualTop + vl.Height)
          return vl;
      }
      return null;
    }
    
    /// <summary>
    /// Gets the visual top position (relative to start of document) from a document line number.
    /// </summary>
    public double GetVisualTopByDocumentLine(int line)
    {
      VerifyAccess();
      if (heightTree == null)
        throw ThrowUtil.NoDocumentAssigned();
      return heightTree.GetVisualPosition(heightTree.GetLineByNumber(line));
    }
    
    VisualLineElement GetVisualLineElementFromPosition(Point visualPosition)
    {
      VisualLine vl = GetVisualLineFromVisualTop(visualPosition.Y);
      if (vl != null) {
        int column = vl.GetVisualColumnFloor(visualPosition);
//        Debug.WriteLine(vl.FirstDocumentLine.LineNumber + " vc " + column);
        foreach (VisualLineElement element in vl.Elements) {
          if (element.VisualColumn + element.VisualLength <= column)
            continue;
          return element;
        }
      }
      return null;
    }
    #endregion
    
    #region Visual Position <-> TextViewPosition
    /// <summary>
    /// Gets the visual position from a text view position.
    /// </summary>
    /// <param name="position">The text view position.</param>
    /// <param name="yPositionMode">The mode how to retrieve the Y position.</param>
    /// <returns>The position in WPF device-independent pixels relative
    /// to the top left corner of the document.</returns>
    public Point GetVisualPosition(TextViewPosition position, VisualYPosition yPositionMode)
    {
      VerifyAccess();
      if (this.Document == null)
        throw ThrowUtil.NoDocumentAssigned();
      DocumentLine documentLine = this.Document.GetLineByNumber(position.Line);
      VisualLine visualLine = GetOrConstructVisualLine(documentLine);
      int visualColumn = position.VisualColumn;
      if (visualColumn < 0) {
        int offset = documentLine.Offset + position.Column - 1;
        visualColumn = visualLine.GetVisualColumn(offset - visualLine.FirstDocumentLine.Offset);
      }
      return visualLine.GetVisualPosition(visualColumn, position.IsAtEndOfLine, yPositionMode);
    }
    
    /// <summary>
    /// Gets the text view position from the specified visual position.
    /// If the position is within a character, it is rounded to the next character boundary.
    /// </summary>
    /// <param name="visualPosition">The position in WPF device-independent pixels relative
    /// to the top left corner of the document.</param>
    /// <returns>The logical position, or null if the position is outside the document.</returns>
    public TextViewPosition? GetPosition(Point visualPosition)
    {
      VerifyAccess();
      if (this.Document == null)
        throw ThrowUtil.NoDocumentAssigned();
      VisualLine line = GetVisualLineFromVisualTop(visualPosition.Y);
      if (line == null)
        return null;
      return line.GetTextViewPosition(visualPosition, Options.EnableVirtualSpace);
    }
    
    /// <summary>
    /// Gets the text view position from the specified visual position.
    /// If the position is inside a character, the position in front of the character is returned.
    /// </summary>
    /// <param name="visualPosition">The position in WPF device-independent pixels relative
    /// to the top left corner of the document.</param>
    /// <returns>The logical position, or null if the position is outside the document.</returns>
    public TextViewPosition? GetPositionFloor(Point visualPosition)
    {
      VerifyAccess();
      if (this.Document == null)
        throw ThrowUtil.NoDocumentAssigned();
      VisualLine line = GetVisualLineFromVisualTop(visualPosition.Y);
      if (line == null)
        return null;
      return line.GetTextViewPositionFloor(visualPosition, Options.EnableVirtualSpace);
    }
    #endregion
    
    #region Service Provider
    readonly ServiceContainer services = new ServiceContainer();
    
    /// <summary>
    /// Gets a service container used to associate services with the text view.
    /// </summary>
    /// <remarks>
    /// This container does not provide document services -
    /// use <c>TextView.GetService()</c> instead of <c>TextView.Services.GetService()</c> to ensure
    /// that document services can be found as well.
    /// </remarks>
    public ServiceContainer Services {
      get { return services; }
    }
    
    /// <summary>
    /// Retrieves a service from the text view.
    /// If the service is not found in the <see cref="Services"/> container,
    /// this method will also look for it in the current document's service provider.
    /// </summary>
    public virtual object GetService(Type serviceType)
    {
      object instance = services.GetService(serviceType);
      if (instance == null && document != null) {
        instance = document.ServiceProvider.GetService(serviceType);
      }
      return instance;
    }
    
    void ConnectToTextView(object obj)
    {
      ITextViewConnect c = obj as ITextViewConnect;
      if (c != null)
        c.AddToTextView(this);
    }
    
    void DisconnectFromTextView(object obj)
    {
      ITextViewConnect c = obj as ITextViewConnect;
      if (c != null)
        c.RemoveFromTextView(this);
    }
    #endregion
    
    #region MouseHover
    /// <summary>
    /// The PreviewMouseHover event.
    /// </summary>
    public static readonly RoutedEvent PreviewMouseHoverEvent =
      EventManager.RegisterRoutedEvent("PreviewMouseHover", RoutingStrategy.Tunnel,
                                       typeof(MouseEventHandler), typeof(TextView));
    /// <summary>
    /// The MouseHover event.
    /// </summary>
    public static readonly RoutedEvent MouseHoverEvent =
      EventManager.RegisterRoutedEvent("MouseHover", RoutingStrategy.Bubble,
                                       typeof(MouseEventHandler), typeof(TextView));
    
    /// <summary>
    /// The PreviewMouseHoverStopped event.
    /// </summary>
    public static readonly RoutedEvent PreviewMouseHoverStoppedEvent =
      EventManager.RegisterRoutedEvent("PreviewMouseHoverStopped", RoutingStrategy.Tunnel,
                                       typeof(MouseEventHandler), typeof(TextView));
    /// <summary>
    /// The MouseHoverStopped event.
    /// </summary>
    public static readonly RoutedEvent MouseHoverStoppedEvent =
      EventManager.RegisterRoutedEvent("MouseHoverStopped", RoutingStrategy.Bubble,
                                       typeof(MouseEventHandler), typeof(TextView));
    
    
    /// <summary>
    /// Occurs when the mouse has hovered over a fixed location for some time.
    /// </summary>
    public event MouseEventHandler PreviewMouseHover {
      add { AddHandler(PreviewMouseHoverEvent, value); }
      remove { RemoveHandler(PreviewMouseHoverEvent, value); }
    }
    
    /// <summary>
    /// Occurs when the mouse has hovered over a fixed location for some time.
    /// </summary>
    public event MouseEventHandler MouseHover {
      add { AddHandler(MouseHoverEvent, value); }
      remove { RemoveHandler(MouseHoverEvent, value); }
    }
    
    /// <summary>
    /// Occurs when the mouse had previously hovered but now started moving again.
    /// </summary>
    public event MouseEventHandler PreviewMouseHoverStopped {
      add { AddHandler(PreviewMouseHoverStoppedEvent, value); }
      remove { RemoveHandler(PreviewMouseHoverStoppedEvent, value); }
    }
    
    /// <summary>
    /// Occurs when the mouse had previously hovered but now started moving again.
    /// </summary>
    public event MouseEventHandler MouseHoverStopped {
      add { AddHandler(MouseHoverStoppedEvent, value); }
      remove { RemoveHandler(MouseHoverStoppedEvent, value); }
    }
    
    MouseHoverLogic hoverLogic;
    
    void RaiseHoverEventPair(MouseEventArgs e, RoutedEvent tunnelingEvent, RoutedEvent bubblingEvent)
    {
      var mouseDevice = e.MouseDevice;
      var stylusDevice = e.StylusDevice;
      int inputTime = Environment.TickCount;
      var args1 = new MouseEventArgs(mouseDevice, inputTime, stylusDevice) {
        RoutedEvent = tunnelingEvent,
        Source = this
      };
      RaiseEvent(args1);
      var args2 = new MouseEventArgs(mouseDevice, inputTime, stylusDevice) {
        RoutedEvent = bubblingEvent,
        Source = this,
        Handled = args1.Handled
      };
      RaiseEvent(args2);
    }
    #endregion
    
    /// <summary>
    /// Collapses lines for the purpose of scrolling. <see cref="DocumentLine"/>s marked as collapsed will be hidden
    /// and not used to start the generation of a <see cref="VisualLine"/>.
    /// </summary>
    /// <remarks>
    /// This method is meant for <see cref="VisualLineElementGenerator"/>s that cause <see cref="VisualLine"/>s to span
    /// multiple <see cref="DocumentLine"/>s. Do not call it without providing a corresponding
    /// <see cref="VisualLineElementGenerator"/>.
    /// If you want to create collapsible text sections, see <see cref="Folding.FoldingManager"/>.
    /// 
    /// Note that if you want a VisualLineElement to span from line N to line M, then you need to collapse only the lines
    /// N+1 to M. Do not collapse line N itself.
    /// 
    /// When you no longer need the section to be collapsed, call <see cref="CollapsedLineSection.Uncollapse()"/> on the
    /// <see cref="CollapsedLineSection"/> returned from this method.
    /// </remarks>
    public CollapsedLineSection CollapseLines(DocumentLine start, DocumentLine end)
    {
      VerifyAccess();
      if (heightTree == null)
        throw ThrowUtil.NoDocumentAssigned();
      return heightTree.CollapseText(start, end);
    }
    
    /// <summary>
    /// Gets the height of the document.
    /// </summary>
    public double DocumentHeight {
      get {
        // return 0 if there is no document = no heightTree
        return heightTree != null ? heightTree.TotalHeight : 0;
      }
    }
    
    /// <summary>
    /// Gets the document line at the specified visual position.
    /// </summary>
    public DocumentLine GetDocumentLineByVisualTop(double visualTop)
    {
      VerifyAccess();
      if (heightTree == null)
        throw ThrowUtil.NoDocumentAssigned();
      return heightTree.GetLineByVisualPosition(visualTop);
    }
    
    /// <inheritdoc/>
    protected override void OnPropertyChanged(DependencyPropertyChangedEventArgs e)
    {
      base.OnPropertyChanged(e);
      if (TextFormatterFactory.PropertyChangeAffectsTextFormatter(e.Property)) {
        // first, create the new text formatter:
        RecreateTextFormatter();
        // changing text formatter requires recreating the cached elements
        RecreateCachedElements();
        // and we need to re-measure the font metrics:
        InvalidateDefaultTextMetrics();
      } else if (e.Property == Control.ForegroundProperty
                 || e.Property == TextView.NonPrintableCharacterBrushProperty
                 || e.Property == TextView.LinkTextBackgroundBrushProperty
                 || e.Property == TextView.LinkTextForegroundBrushProperty)
      {
        // changing brushes requires recreating the cached elements
        RecreateCachedElements();
        Redraw();
      }
      if (e.Property == Control.FontFamilyProperty
          || e.Property == Control.FontSizeProperty
          || e.Property == Control.FontStretchProperty
          || e.Property == Control.FontStyleProperty
          || e.Property == Control.FontWeightProperty)
      {
        // changing font properties requires recreating cached elements
        RecreateCachedElements();
        // and we need to re-measure the font metrics:
        InvalidateDefaultTextMetrics();
        Redraw();
      }
      if (e.Property == ColumnRulerPenProperty) {
        columnRulerRenderer.SetRuler(this.Options.ColumnRulerPosition, this.ColumnRulerPen);
      }
      if (e.Property == CurrentLineBorderProperty) {
        currentLineHighlighRenderer.BorderPen = this.CurrentLineBorder;
      }
      if (e.Property == CurrentLineBackgroundProperty) {
        currentLineHighlighRenderer.BackgroundBrush = this.CurrentLineBackground;
      }
    }
    
    /// <summary>
    /// The pen used to draw the column ruler.
    /// <seealso cref="TextEditorOptions.ShowColumnRuler"/>
    /// </summary>
    public static readonly DependencyProperty ColumnRulerPenProperty =
      DependencyProperty.Register("ColumnRulerBrush", typeof(Pen), typeof(TextView),
                                  new FrameworkPropertyMetadata(CreateFrozenPen(Brushes.LightGray)));
    
    static Pen CreateFrozenPen(SolidColorBrush brush)
    {
      Pen pen = new Pen(brush, 1);
      pen.Freeze();
      return pen;
    }
    
    /// <summary>
    /// Gets/Sets the pen used to draw the column ruler.
    /// <seealso cref="TextEditorOptions.ShowColumnRuler"/>
    /// </summary>
    public Pen ColumnRulerPen {
      get { return (Pen)GetValue(ColumnRulerPenProperty); }
      set { SetValue(ColumnRulerPenProperty, value); }
    }
    
    /// <summary>
    /// The <see cref="CurrentLineBackground"/> property.
    /// </summary>
    public static readonly DependencyProperty CurrentLineBackgroundProperty =
      DependencyProperty.Register("CurrentLineBackground", typeof(Brush), typeof(TextView));
    
    /// <summary>
    /// Gets/Sets the background brush used by current line highlighter.
    /// </summary>
    public Brush CurrentLineBackground {
      get { return (Brush)GetValue(CurrentLineBackgroundProperty); }
      set { SetValue(CurrentLineBackgroundProperty, value); }
    }
    
    /// <summary>
    /// The <see cref="CurrentLineBorder"/> property.
    /// </summary>
    public static readonly DependencyProperty CurrentLineBorderProperty =
      DependencyProperty.Register("CurrentLineBorder", typeof(Pen), typeof(TextView));
    
    /// <summary>
    /// Gets/Sets the background brush used for the current line.
    /// </summary>
    public Pen CurrentLineBorder {
      get { return (Pen)GetValue(CurrentLineBorderProperty); }
      set { SetValue(CurrentLineBorderProperty, value); }
    }
    
    /// <summary>
    /// Gets/Sets highlighted line number.
    /// </summary>
    public int HighlightedLine {
      get { return this.currentLineHighlighRenderer.Line; }
      set { this.currentLineHighlighRenderer.Line = value; }
    }
  }
}