AvalonEdit: add support for layers (gives users more control about z-order than adorners).

Fixed bugs in text drag+drop.

git-svn-id: svn://svn.sharpdevelop.net/sharpdevelop/trunk@3842 1ccf3a8d-04fe-1044-b7c0-cef0b8235c61

src/Libraries/AvalonEdit/ICSharpCode.AvalonEdit/Document/NewLineFinder.cs

@@ -67,5 +67,20 @@ namespace ICSharpCode.AvalonEdit.Document
 			b.Append(input, lastEndOffset, input.Length - lastEndOffset);
 			return b.ToString();
 		}
+		
+		/// <summary>
+		/// Gets the newline sequence used in the document at the specified line.
+		/// </summary>
+		public static string GetNewLineFromDocument(TextDocument document, int lineNumber)
+		{
+			DocumentLine line = document.GetLineByNumber(lineNumber);
+			if (line.DelimiterLength == 0) {
+				if (lineNumber > 1)
+					line = document.GetLineByNumber(lineNumber - 1);
+				else
+					return Environment.NewLine;
+			}
+			return document.GetText(line.Offset + line.Length, line.DelimiterLength);
+		}
 	}
 }

src/Libraries/AvalonEdit/ICSharpCode.AvalonEdit/Gui/Caret.cs

@@ -23,7 +23,7 @@ namespace ICSharpCode.AvalonEdit.Gui
 	{
 		readonly TextArea textArea;
 		readonly TextView textView;
-		CaretAdorner caretAdorner;
+		CaretLayer caretAdorner;
 		bool visible;
 		
 		internal Caret(TextArea textArea)
@@ -32,8 +32,8 @@ namespace ICSharpCode.AvalonEdit.Gui
 			this.textView = textArea.TextView;
 			position = new TextViewPosition(1, 1, 0);
 			
-			caretAdorner = new CaretAdorner(textView);
+			caretAdorner = new CaretLayer(textView);
-			textView.Adorners.Add(caretAdorner);
+			textView.InsertLayer(caretAdorner, KnownLayer.Caret, LayerInsertionPosition.Replace);
 			textView.VisualLinesChanged += TextView_VisualLinesChanged;
 			textView.ScrollOffsetChanged += TextView_ScrollOffsetChanged;
 		}

src/Libraries/AvalonEdit/ICSharpCode.AvalonEdit/Gui/CaretLayer.cs

@@ -14,19 +14,15 @@ using ICSharpCode.AvalonEdit.Utils;
 
 namespace ICSharpCode.AvalonEdit.Gui
 {
-	sealed class CaretAdorner : FrameworkElement
+	sealed class CaretLayer : Layer
 	{
-		TextView textView;
 		bool isVisible;
 		Rect caretRectangle;
 		
 		DoubleAnimationUsingKeyFrames blinkAnimation;
 		
-		public CaretAdorner(TextView textView)
+		public CaretLayer(TextView textView) : base(textView, KnownLayer.Caret)
 		{
-			this.textView = textView;
-			this.IsHitTestVisible = false;
-			
 			blinkAnimation = new DoubleAnimationUsingKeyFrames();
 			blinkAnimation.KeyFrames.Add(new DiscreteDoubleKeyFrame(1, KeyTime.FromPercent(0)));
 			blinkAnimation.KeyFrames.Add(new DiscreteDoubleKeyFrame(0, KeyTime.FromPercent(0.5)));
@@ -66,11 +62,6 @@ namespace ICSharpCode.AvalonEdit.Gui
 			BeginAnimation(OpacityProperty, null);
 		}
 		
-		protected override Size MeasureOverride(Size constraint)
-		{
-			return caretRectangle.Size;
-		}
-		
 		protected override void OnRender(DrawingContext drawingContext)
 		{
 			base.OnRender(drawingContext);

src/Libraries/AvalonEdit/ICSharpCode.AvalonEdit/Gui/EditingCommandHandler.cs

@@ -55,25 +55,12 @@ namespace ICSharpCode.AvalonEdit.Gui
 		{
 			TextArea textArea = GetTextArea(target);
 			if (textArea != null && textArea.Document != null) {
-				string newLine = GetLineDelimiter(textArea.Document, textArea.Caret.Line);
+				string newLine = NewLineFinder.GetNewLineFromDocument(textArea.Document, textArea.Caret.Line);
 				textArea.ReplaceSelectionWithText(newLine);
 				textArea.Caret.BringCaretToView();
 				args.Handled = true;
 			}
 		}
-		
-		static string GetLineDelimiter(TextDocument document, int lineNumber)
-		{
-			DocumentLine line = document.GetLineByNumber(lineNumber);
-			if (line.DelimiterLength == 0) {
-				// TODO: add line delimiter setting
-				if (lineNumber > 1)
-					line = document.GetLineByNumber(lineNumber - 1);
-				else
-					return Environment.NewLine;
-			}
-			return document.GetText(line.Offset + line.Length, line.DelimiterLength);
-		}
 		#endregion
 		
 		#region Tab
@@ -234,7 +221,7 @@ namespace ICSharpCode.AvalonEdit.Gui
 			TextArea textArea = GetTextArea(target);
 			if (textArea != null && textArea.Document != null) {
 				// convert text back to correct newlines for this document
-				string newLine = GetLineDelimiter(textArea.Document, textArea.Caret.Line);
+				string newLine = NewLineFinder.GetNewLineFromDocument(textArea.Document, textArea.Caret.Line);
 				string text = NewLineFinder.NormalizeNewLines(Clipboard.GetText(), newLine);
 				textArea.ReplaceSelectionWithText(text);
 				textArea.Caret.BringCaretToView();

src/Libraries/AvalonEdit/ICSharpCode.AvalonEdit/Gui/FoldingSection.cs

@@ -6,8 +6,8 @@
 // </file>
 
 using System;
-using ICSharpCode.AvalonEdit.Document;
 using System.Windows.Threading;
+using ICSharpCode.AvalonEdit.Document;
 
 namespace ICSharpCode.AvalonEdit.Gui
 {

src/Libraries/AvalonEdit/ICSharpCode.AvalonEdit/Gui/IBackgroundRenderer.cs

@@ -11,13 +11,23 @@ using System.Windows.Media;
 namespace ICSharpCode.AvalonEdit.Gui
 {
 	/// <summary>
-	/// Background renderers allow drawing behind the text layer.
+	/// Background renderers draw in the background of a known layer.
+	/// You can use background renderers to draw non-interactive elements on the TextView
+	/// without introducing new UIElements.
 	/// </summary>
+	/// <remarks>Background renderer will draw only if their associated known
+	/// layer chooses to draw them. For example, background renderers in the caret
+	/// layer will be invisible when the caret is hidden.</remarks>
 	public interface IBackgroundRenderer
 	{
+		/// <summary>
+		/// Gets the layer on which this background renderer should draw.
+		/// </summary>
+		KnownLayer Layer { get; }
+		
 		/// <summary>
 		/// Causes the background renderer to draw.
 		/// </summary>
-		void Draw(DrawingContext dc);
+		void Draw(DrawingContext drawingContext);
 	}
 }

src/Libraries/AvalonEdit/ICSharpCode.AvalonEdit/Gui/InlineObjectRun.cs

@@ -43,7 +43,7 @@ namespace ICSharpCode.AvalonEdit.Gui
 				throw new ArgumentNullException("context");
 			
 			// remove inline object if its already added, can happen e.g. when recreating textrun for word-wrapping
-			context.TextView.RemoveInlineObject(this.Element);
+			context.TextView.textLayer.RemoveInlineObject(this.Element);
 			
 			return new InlineObjectRun(1, this.TextRunProperties, this.Element);
 		}

src/Libraries/AvalonEdit/ICSharpCode.AvalonEdit/Gui/Layer.cs

@@ -0,0 +1,48 @@
+// <file>
+//     <copyright see="prj:///doc/copyright.txt"/>
+//     <license see="prj:///doc/license.txt"/>
+//     <author name="Daniel Grunwald"/>
+//     <version>$Revision$</version>
+// </file>
+
+using System;
+using System.Diagnostics;
+using System.Windows;
+using System.Windows.Media;
+
+namespace ICSharpCode.AvalonEdit.Gui
+{
+	/// <summary>
+	/// Base class for known layers.
+	/// </summary>
+	class Layer : UIElement
+	{
+		protected readonly TextView textView;
+		protected readonly KnownLayer knownLayer;
+		
+		public Layer(TextView textView, KnownLayer knownLayer)
+		{
+			Debug.Assert(textView != null);
+			this.textView = textView;
+			this.knownLayer = knownLayer;
+			
+			this.IsHitTestVisible = false;
+		}
+		
+		protected override GeometryHitTestResult HitTestCore(GeometryHitTestParameters hitTestParameters)
+		{
+			return null;
+		}
+		
+		protected override HitTestResult HitTestCore(PointHitTestParameters hitTestParameters)
+		{
+			return null;
+		}
+		
+		protected override void OnRender(DrawingContext drawingContext)
+		{
+			base.OnRender(drawingContext);
+			textView.RenderBackground(drawingContext, knownLayer);
+		}
+	}
+}

src/Libraries/AvalonEdit/ICSharpCode.AvalonEdit/Gui/LayerPosition.cs

@@ -0,0 +1,95 @@
+// <file>
+//     <copyright see="prj:///doc/copyright.txt"/>
+//     <license see="prj:///doc/license.txt"/>
+//     <author name="Daniel Grunwald"/>
+//     <version>$Revision$</version>
+// </file>
+
+using System;
+using System.Windows;
+
+namespace ICSharpCode.AvalonEdit.Gui
+{
+	/// <summary>
+	/// An enumeration of well-known layers.
+	/// </summary>
+	public enum KnownLayer
+	{
+		/// <summary>
+		/// This layer is in the background.
+		/// There is no UIElement to represent this layer, it is directly drawn in the TextView.
+		/// It is invalid to replace the background layer or insert
+		/// </summary>
+		/// <remarks>This layer is below the Selection layer.</remarks>
+		Background,
+		/// <summary>
+		/// This layer contains the selection rectangle.
+		/// </summary>
+		/// <remarks>This layer is between the Background and the Text layers.</remarks>
+		Selection,
+		/// <summary>
+		/// This layer contains the text and inline UI elements.
+		/// </summary>
+		/// <remarks>This layer is between the Selection and the Caret layers.</remarks>
+		Text,
+		/// <summary>
+		/// This layer contains the blinking caret.
+		/// </summary>
+		/// <remarks>This layer is above the Text layer.</remarks>
+		Caret
+	}
+	
+	/// <summary>
+	/// Specifies where a new layer is inserted, in relation to an old layer.
+	/// </summary>
+	public enum LayerInsertionPosition
+	{
+		/// <summary>
+		/// The new layer is inserted below the specified layer.
+		/// </summary>
+		Below,
+		/// <summary>
+		/// The new layer replaces the specified layer. The old layer is removed
+		/// from the <see cref="TextView.Layers"/> collection.
+		/// </summary>
+		Replace,
+		/// <summary>
+		/// The new layer is inserted above the specified layer.
+		/// </summary>
+		Above
+	}
+	
+	sealed class LayerPosition : IComparable<LayerPosition>
+	{
+		internal static readonly DependencyProperty LayerPositionProperty =
+			DependencyProperty.RegisterAttached("LayerPosition", typeof(LayerPosition), typeof(LayerPosition));
+		
+		public static void SetLayerPosition(UIElement layer, LayerPosition value)
+		{
+			layer.SetValue(LayerPositionProperty, value);
+		}
+		
+		public static LayerPosition GetLayerPosition(UIElement layer)
+		{
+			return (LayerPosition)layer.GetValue(LayerPositionProperty);
+		}
+		
+		internal readonly KnownLayer KnownLayer;
+		internal readonly LayerInsertionPosition Position;
+		
+		public LayerPosition(KnownLayer knownLayer, LayerInsertionPosition position)
+		{
+			this.KnownLayer = knownLayer;
+			this.Position = position;
+		}
+		
+		public int CompareTo(LayerPosition other)
+		{
+			int r = this.KnownLayer.CompareTo(other.KnownLayer);
+			if (r != 0)
+				return r;
+			else
+				return this.Position.CompareTo(other.Position);
+		}
+	}
+}

src/Libraries/AvalonEdit/ICSharpCode.AvalonEdit/Gui/SelectionColorizer.cs

@@ -6,17 +6,12 @@
 // </file>
 
 using System;
-using System.Linq;
 using System.Windows;
-using System.Windows.Media;
-using System.Windows.Media.TextFormatting;
-
 using ICSharpCode.AvalonEdit.Document;
-using ICSharpCode.AvalonEdit.Utils;
 
 namespace ICSharpCode.AvalonEdit.Gui
 {
-	sealed class SelectionColorizer : ColorizingTransformer, IBackgroundRenderer
+	sealed class SelectionColorizer : ColorizingTransformer
 	{
 		TextArea textArea;
 		
@@ -49,21 +44,5 @@ namespace ICSharpCode.AvalonEdit.Gui
 					});
 			}
 		}
-		
-		public void Draw(DrawingContext dc)
-		{
-			BackgroundGeometryBuilder geoBuilder = new BackgroundGeometryBuilder();
-			geoBuilder.AddSegments(textArea.TextView, textArea.Selection.Segments);
-			PathGeometry geometry = geoBuilder.CreateGeometry();
-			if (geometry != null) {
-				SolidColorBrush lightHighlightBrush = new SolidColorBrush(SystemColors.HighlightColor);
-				lightHighlightBrush.Opacity = 0.7;
-				lightHighlightBrush.Freeze();
-				Pen pen = new Pen(SystemColors.HighlightBrush, 1);
-				//pen.LineJoin = PenLineJoin.Round;
-				pen.Freeze();
-				dc.DrawGeometry(lightHighlightBrush, pen, geometry);
-			}
-		}
 	}
 }

src/Libraries/AvalonEdit/ICSharpCode.AvalonEdit/Gui/SelectionLayer.cs

@@ -0,0 +1,51 @@
+// <file>
+//     <copyright see="prj:///doc/copyright.txt"/>
+//     <license see="prj:///doc/license.txt"/>
+//     <author name="Daniel Grunwald"/>
+//     <version>$Revision$</version>
+// </file>
+
+using System;
+using System.Windows;
+using System.Windows.Media;
+
+namespace ICSharpCode.AvalonEdit.Gui
+{
+	sealed class SelectionLayer : Layer, IWeakEventListener
+	{
+		readonly TextArea textArea;
+		
+		public SelectionLayer(TextArea textArea) : base(textArea.TextView, KnownLayer.Selection)
+		{
+			this.textArea = textArea;
+			TextViewWeakEventManager.VisualLinesChanged.AddListener(textView, this);
+		}
+		
+		public bool ReceiveWeakEvent(Type managerType, object sender, EventArgs e)
+		{
+			if (managerType == typeof(TextViewWeakEventManager.VisualLinesChanged)) {
+				InvalidateVisual();
+				return true;
+			}
+			return false;
+		}
+		
+		protected override void OnRender(DrawingContext drawingContext)
+		{
+			base.OnRender(drawingContext);
+			
+			BackgroundGeometryBuilder geoBuilder = new BackgroundGeometryBuilder();
+			geoBuilder.AddSegments(textView, textArea.Selection.Segments);
+			PathGeometry geometry = geoBuilder.CreateGeometry();
+			if (geometry != null) {
+				SolidColorBrush lightHighlightBrush = new SolidColorBrush(SystemColors.HighlightColor);
+				lightHighlightBrush.Opacity = 0.7;
+				lightHighlightBrush.Freeze();
+				Pen pen = new Pen(SystemColors.HighlightBrush, 1);
+				//pen.LineJoin = PenLineJoin.Round;
+				pen.Freeze();
+				drawingContext.DrawGeometry(lightHighlightBrush, pen, geometry);
+			}
+		}
+	}
+}

src/Libraries/AvalonEdit/ICSharpCode.AvalonEdit/Gui/SelectionMouseHandler.cs

@@ -6,15 +6,15 @@
 // </file>
 
 using System;
-using System.Collections.Generic;
 using System.Diagnostics;
 using System.Linq;
+using System.Runtime.InteropServices;
 using System.Windows;
 using System.Windows.Input;
+using System.Windows.Threading;
 
 using ICSharpCode.AvalonEdit.Document;
 using ICSharpCode.AvalonEdit.Utils;
-using System.Windows.Threading;
 
 namespace ICSharpCode.AvalonEdit.Gui
 {
@@ -107,6 +107,7 @@ namespace ICSharpCode.AvalonEdit.Gui
 		{
 			try {
 				e.Effects = GetEffect(e);
+				textArea.Caret.Show();
 			} catch (Exception ex) {
 				OnDragException(ex);
 			}
@@ -147,6 +148,8 @@ namespace ICSharpCode.AvalonEdit.Gui
 		void textArea_DragLeave(object sender, DragEventArgs e)
 		{
 			e.Handled = true;
+			if (!textArea.IsKeyboardFocusWithin)
+				textArea.Caret.Hide();
 		}
 		
 		[System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Design", "CA1031:DoNotCatchGeneralExceptionTypes")]
@@ -164,6 +167,10 @@ namespace ICSharpCode.AvalonEdit.Gui
 							e.Effects = DragDropEffects.None;
 						} else {
 							Debug.WriteLine("Drop: insert at " + start);
+							
+							string newLine = NewLineFinder.GetNewLineFromDocument(textArea.Document, textArea.Caret.Line);
+							text = NewLineFinder.NormalizeNewLines(text, newLine);
+							
 							// Mark the undo group with the currentDragDescriptor, if the drag
 							// is originating from the same control. This allows combining
 							// the undo groups when text is moved.
@@ -225,8 +232,10 @@ namespace ICSharpCode.AvalonEdit.Gui
 			textArea.ReleaseMouseCapture();
 			
 			string text = textArea.Selection.GetText(textArea.Document);
-			DataObject dataObject = new DataObject();
+			text = NewLineFinder.NormalizeNewLines(text, Environment.NewLine);
-			dataObject.SetText(text);
+			DataObject dataObject = new DataObject(text);
+			// we cannot use DataObject.SetText - then we cannot drag to SciTe
+			// (but dragging to Word works in both cases)
 			
 			DragDropEffects allowedEffects = DragDropEffects.All;
 			var deleteOnMove = textArea.Selection.Segments.Select(s => new AnchorSegment(textArea.Document, s)).ToList();
@@ -234,9 +243,16 @@ namespace ICSharpCode.AvalonEdit.Gui
 			object dragDescriptor = new object();
 			this.currentDragDescriptor = dragDescriptor;
 			
+			DragDropEffects resultEffect;
+			try {
 				Debug.WriteLine("DoDragDrop with allowedEffects=" + allowedEffects);
-			DragDropEffects resultEffect = DragDrop.DoDragDrop(textArea, dataObject, allowedEffects);
+				resultEffect = DragDrop.DoDragDrop(textArea, dataObject, allowedEffects);
 				Debug.WriteLine("DoDragDrop done, resultEffect=" + resultEffect);
+			} catch (COMException ex) {
+				// ignore COM errors - don't crash on badly implemented drop targets
+				Debug.WriteLine("DoDragDrop failed: " + ex.ToString());
+				return;
+			}
 			
 			this.currentDragDescriptor = null;
 			

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

@@ -72,9 +72,8 @@ namespace ICSharpCode.AvalonEdit
 			                	Margin = new Thickness(2, 0, 2, 0)
 			                });
 			
-			SelectionColorizer sc = new SelectionColorizer(this);
+			textView.LineTransformers.Add(new SelectionColorizer(this));
-			textView.LineTransformers.Add(sc);
+			textView.InsertLayer(new SelectionLayer(this), KnownLayer.Selection, LayerInsertionPosition.Replace);
-			textView.BackgroundRenderer.Add(sc);
 			
 			caret = new Caret(this);
 			this.CommandBindings.Add(new CommandBinding(ApplicationCommands.Undo, ExecuteUndo, CanExecuteUndo));

src/Libraries/AvalonEdit/ICSharpCode.AvalonEdit/Gui/TextLayer.cs

@@ -0,0 +1,107 @@
+// <file>
+//     <copyright see="prj:///doc/copyright.txt"/>
+//     <license see="prj:///doc/license.txt"/>
+//     <author name="Daniel Grunwald"/>
+//     <version>$Revision$</version>
+// </file>
+
+using System;
+using System.Collections.Generic;
+using System.Windows;
+using System.Windows.Media;
+
+namespace ICSharpCode.AvalonEdit.Gui
+{
+	/// <summary>
+	/// The control that contains the text.
+	/// 
+	/// This control is used to allow other UIElements to be placed inside the TextView but
+	/// behind the text.
+	/// The text rendering process (VisualLine creation) is controlled by the TextView, this
+	/// class simply displays the created Visual Lines.
+	/// </summary>
+	/// <remarks>
+	/// This class does not contain any input handling and is invisible to hit testing. Input
+	/// is handled by the TextView.
+	/// This allows UIElements that are displayed behind the text, but still can react to mouse input.
+	/// </remarks>
+	sealed class TextLayer : Layer
+	{
+		public TextLayer(TextView textView) : base(textView, KnownLayer.Text)
+		{
+		}
+		
+		protected override void OnRender(DrawingContext drawingContext)
+		{
+			base.OnRender(drawingContext);
+			textView.RenderTextLayer(drawingContext);
+		}
+		
+		#region Inline object handling
+		internal List<InlineObjectRun> inlineObjects = new List<InlineObjectRun>();
+		
+		/// <summary>
+		/// Adds a new inline object.
+		/// </summary>
+		internal void AddInlineObject(InlineObjectRun inlineObject)
+		{
+			inlineObjects.Add(inlineObject);
+			AddVisualChild(inlineObject.Element);
+			inlineObject.Element.Measure(new Size(double.PositiveInfinity, double.PositiveInfinity));
+		}
+		
+		List<VisualLine> visualLinesWithOutstandingInlineObjects = new List<VisualLine>();
+		
+		internal 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.
+			visualLinesWithOutstandingInlineObjects.Add(visualLine);
+		}
+		
+		internal void RemoveInlineObjectsNow()
+		{
+			inlineObjects.RemoveAll(
+				ior => {
+					if (visualLinesWithOutstandingInlineObjects.Contains(ior.VisualLine)) {
+						ior.VisualLine = null;
+						RemoveVisualChild(ior.Element);
+						return true;
+					}
+					return false;
+				});
+			visualLinesWithOutstandingInlineObjects.Clear();
+		}
+		
+		/// <summary>
+		/// Removes the inline object that displays the specified UIElement.
+		/// </summary>
+		internal void RemoveInlineObject(UIElement element)
+		{
+			inlineObjects.RemoveAll(
+				ior => {
+					if (ior.Element == element) {
+						ior.VisualLine = null;
+						RemoveVisualChild(ior.Element);
+						return true;
+					}
+					return false;
+				});
+		}
+		
+		/// <inheritdoc/>
+		protected override int VisualChildrenCount {
+			get { return inlineObjects.Count; }
+		}
+		
+		/// <inheritdoc/>
+		protected override Visual GetVisualChild(int index)
+		{
+			return inlineObjects[index].Element;
+		}
+		#endregion
+	}
+}

src/Libraries/AvalonEdit/ICSharpCode.AvalonEdit/Gui/TextView.cs

@@ -8,6 +8,7 @@
 using System;
 using System.Collections.Generic;
 using System.Collections.ObjectModel;
+using System.ComponentModel;
 using System.Diagnostics;
 using System.Globalization;
 using System.Linq;
@@ -46,10 +47,12 @@ namespace ICSharpCode.AvalonEdit.Gui
 		/// </summary>
 		public TextView()
 		{
+			textLayer = new TextLayer(this);
 			elementGenerators.CollectionChanged += delegate { Redraw(); };
 			lineTransformers.CollectionChanged += delegate { Redraw(); };
 			backgroundRenderer.CollectionChanged += delegate { InvalidateVisual(); };
-			adorners = new UIElementCollection(this, this);
+			layers = new UIElementCollection(this, this);
+			InsertLayer(textLayer, KnownLayer.Text, LayerInsertionPosition.Replace);
 		}
 		#endregion
 		
@@ -122,7 +125,7 @@ namespace ICSharpCode.AvalonEdit.Gui
 		}
 		#endregion
 		
-		#region Collection Properties
+		#region ElementGenerators+LineTransformers Properties
 		readonly ObservableCollection<VisualLineElementGenerator> elementGenerators = new ObservableCollection<VisualLineElementGenerator>();
 		
 		/// <summary>
@@ -140,14 +143,75 @@ namespace ICSharpCode.AvalonEdit.Gui
 		public ObservableCollection<IVisualLineTransformer> LineTransformers {
 			get { return lineTransformers; }
 		}
+		#endregion
+		
+		#region Layers
+		internal readonly TextLayer textLayer;
+		readonly UIElementCollection layers;
 		
-		readonly UIElementCollection adorners;
+		/// <summary>
+		/// Gets the list of layers displayed in the text view.
+		/// </summary>
+		public UIElementCollection Layers {
+			get { return layers; }
+		}
 		
 		/// <summary>
-		/// Gets a collection where text view adorners can be added.
+		/// Inserts a new layer at a position specified relative to an existing layer.
 		/// </summary>
-		public UIElementCollection Adorners {
+		/// <param name="layer">The new layer to insert.</param>
-			get { return adorners; }
+		/// <param name="referencedLayer">The existing layer</param>
+		/// <param name="position">Specifies whether</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; }
+		}
+		
+		/// <inheritdoc/>
+		protected override Visual GetVisualChild(int index)
+		{
+			return layers[index];
 		}
 		#endregion
 		
@@ -242,7 +306,7 @@ namespace ICSharpCode.AvalonEdit.Gui
 			foreach (TextLine textLine in visualLine.TextLines) {
 				textLine.Dispose();
 			}
-			RemoveInlineObjects(visualLine);
+			textLayer.RemoveInlineObjects(visualLine);
 		}
 		#endregion
 		
@@ -395,13 +459,17 @@ namespace ICSharpCode.AvalonEdit.Gui
 				ClearVisualLines();
 			lastAvailableSize = availableSize;
 			
-			RemoveInlineObjectsNow();
+			textLayer.RemoveInlineObjectsNow();
+			
+			foreach (UIElement layer in layers) {
+				layer.Measure(availableSize);
+			}
+			InvalidateVisual(); // = InvalidateArrange+InvalidateRender
+			textLayer.InvalidateVisual();
 			
 			if (document == null)
 				return Size.Empty;
 			
-			InvalidateVisual(); // = InvalidateArrange+InvalidateRender
-			
 			double maxWidth;
 			inMeasure = true;
 			try {
@@ -410,7 +478,7 @@ namespace ICSharpCode.AvalonEdit.Gui
 				inMeasure = false;
 			}
 			
-			RemoveInlineObjectsNow();
+			textLayer.RemoveInlineObjectsNow();
 			
 			SetScrollData(availableSize,
 			              new Size(maxWidth, heightTree.TotalHeight),
@@ -569,76 +637,6 @@ namespace ICSharpCode.AvalonEdit.Gui
 		}
 		#endregion
 		
-		#region Inline object handling
-		List<InlineObjectRun> inlineObjects = new List<InlineObjectRun>();
-		
-		/// <summary>
-		/// Adds a new inline object.
-		/// </summary>
-		internal void AddInlineObject(InlineObjectRun inlineObject)
-		{
-			inlineObjects.Add(inlineObject);
-			AddVisualChild(inlineObject.Element);
-			inlineObject.Element.Measure(new Size(double.PositiveInfinity, double.PositiveInfinity));
-		}
-		
-		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.
-			visualLinesWithOutstandingInlineObjects.Add(visualLine);
-		}
-		
-		void RemoveInlineObjectsNow()
-		{
-			inlineObjects.RemoveAll(
-				ior => {
-					if (visualLinesWithOutstandingInlineObjects.Contains(ior.VisualLine)) {
-						ior.VisualLine = null;
-						RemoveVisualChild(ior.Element);
-						return true;
-					}
-					return false;
-				});
-			visualLinesWithOutstandingInlineObjects.Clear();
-		}
-		
-		/// <summary>
-		/// Removes the inline object that displays the specified UIElement.
-		/// </summary>
-		public void RemoveInlineObject(UIElement element)
-		{
-			inlineObjects.RemoveAll(
-				ior => {
-					if (ior.Element == element) {
-						ior.VisualLine = null;
-						RemoveVisualChild(ior.Element);
-						return true;
-					}
-					return false;
-				});
-		}
-		
-		/// <inheritdoc/>
-		protected override int VisualChildrenCount {
-			get { return inlineObjects.Count + adorners.Count; }
-		}
-		
-		/// <inheritdoc/>
-		protected override Visual GetVisualChild(int index)
-		{
-			if (index < inlineObjects.Count)
-				return inlineObjects[index].Element;
-			else
-				return adorners[index - inlineObjects.Count];
-		}
-		#endregion
-		
 		#region Arrange
 		/// <summary>
 		/// Arrange implementation.
@@ -663,7 +661,7 @@ namespace ICSharpCode.AvalonEdit.Gui
 			
 //			double maxWidth = 0;
 			
-			foreach (UIElement adorner in adorners) {
+			foreach (UIElement adorner in layers) {
 				adorner.Arrange(new Rect(new Point(0, 0), finalSize));
 			}
 			
@@ -675,7 +673,7 @@ namespace ICSharpCode.AvalonEdit.Gui
 						foreach (var span in textLine.GetTextRunSpans()) {
 							InlineObjectRun inline = span.Value as InlineObjectRun;
 							if (inline != null && inline.VisualLine != null) {
-								Debug.Assert(inlineObjects.Contains(inline));
+								Debug.Assert(textLayer.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));
 							}
@@ -695,7 +693,7 @@ namespace ICSharpCode.AvalonEdit.Gui
 		readonly ObservableCollection<IBackgroundRenderer> backgroundRenderer = new ObservableCollection<IBackgroundRenderer>();
 		
 		/// <summary>
-		/// Gets a collection where line transformers can be registered.
+		/// Gets the list of background renderers.
 		/// </summary>
 		public ObservableCollection<IBackgroundRenderer> BackgroundRenderer {
 			get { return backgroundRenderer; }
@@ -704,8 +702,20 @@ namespace ICSharpCode.AvalonEdit.Gui
 		/// <inheritdoc/>
 		protected override void OnRender(DrawingContext drawingContext)
 		{
-			foreach (IBackgroundRenderer r in backgroundRenderer)
+			RenderBackground(drawingContext, KnownLayer.Background);
-				r.Draw(drawingContext);
+		}
+		
+		internal void RenderBackground(DrawingContext drawingContext, KnownLayer layer)
+		{
+			foreach (IBackgroundRenderer bg in backgroundRenderer) {
+				if (bg.Layer == layer) {
+					bg.Draw(drawingContext);
+				}
+			}
+		}
+		
+		internal void RenderTextLayer(DrawingContext drawingContext)
+		{
 			Point pos = new Point(-scrollOffset.X, -clippedPixelsOnTop);
 			foreach (VisualLine visualLine in allVisualLines) {
 				foreach (TextLine textLine in visualLine.TextLines) {

src/Libraries/AvalonEdit/ICSharpCode.AvalonEdit/Gui/VisualLineTextSource.cs

@@ -46,7 +46,7 @@ namespace ICSharpCode.AvalonEdit.Gui
 						InlineObjectRun inlineRun = run as InlineObjectRun;
 						if (inlineRun != null) {
 							inlineRun.VisualLine = VisualLine;
-							TextView.AddInlineObject(inlineRun);
+							TextView.textLayer.AddInlineObject(inlineRun);
 						}
 						return run;
 					}

src/Libraries/AvalonEdit/ICSharpCode.AvalonEdit/ICSharpCode.AvalonEdit.csproj

@@ -106,7 +106,7 @@
     </Compile>
     <Compile Include="Gui\AbstractMargin.cs" />
     <Compile Include="Gui\Caret.cs" />
-    <Compile Include="Gui\CaretAdorner.cs">
+    <Compile Include="Gui\CaretLayer.cs">
       <DependentUpon>Caret.cs</DependentUpon>
     </Compile>
     <Compile Include="Gui\CaretNavigationCommandHandler.cs">
@@ -125,6 +125,12 @@
     </Compile>
     <Compile Include="Gui\IBackgroundRenderer.cs" />
     <Compile Include="Gui\IReadOnlySectionProvider.cs" />
+    <Compile Include="Gui\Layer.cs">
+      <DependentUpon>TextView.cs</DependentUpon>
+    </Compile>
+    <Compile Include="Gui\LayerPosition.cs">
+      <DependentUpon>TextView.cs</DependentUpon>
+    </Compile>
     <Compile Include="Gui\NoReadOnlySections.cs">
       <DependentUpon>IReadOnlySectionProvider.cs</DependentUpon>
     </Compile>
@@ -132,9 +138,15 @@
     <Compile Include="Gui\SelectionColorizer.cs">
       <DependentUpon>Selection.cs</DependentUpon>
     </Compile>
+    <Compile Include="Gui\SelectionLayer.cs">
+      <DependentUpon>Selection.cs</DependentUpon>
+    </Compile>
     <Compile Include="Gui\SelectionMouseHandler.cs">
       <DependentUpon>Selection.cs</DependentUpon>
     </Compile>
+    <Compile Include="Gui\TextLayer.cs">
+      <DependentUpon>TextView.cs</DependentUpon>
+    </Compile>
     <Compile Include="Gui\TextSegmentReadOnlySectionProvider.cs">
       <DependentUpon>IReadOnlySectionProvider.cs</DependentUpon>
     </Compile>