Use DrawingVisual for rendering a VisualLine. This seems to improve AvalonEdit rendering performance a lot in some scenarios.

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

@@ -33,10 +33,38 @@ namespace ICSharpCode.AvalonEdit.Rendering
 		{
 		}
 		
-		protected override void OnRender(DrawingContext drawingContext)
+		List<VisualLineDrawingVisual> visuals = new List<VisualLineDrawingVisual>();
+		
+		internal void SetVisualLines(ICollection<VisualLine> visualLines)
+		{
+			foreach (VisualLineDrawingVisual v in visuals) {
+				if (v.VisualLine.IsDisposed)
+					RemoveVisualChild(v);
+			}
+			visuals.Clear();
+			foreach (VisualLine newLine in visualLines) {
+				VisualLineDrawingVisual v = newLine.Render();
+				if (!v.IsAdded) {
+					AddVisualChild(v);
+					v.IsAdded = true;
+				}
+				visuals.Add(v);
+			}
+			InvalidateArrange();
+		}
+		
+		protected override int VisualChildrenCount {
+			get { return visuals.Count; }
+		}
+		
+		protected override Visual GetVisualChild(int index)
+		{
+			return visuals[index];
+		}
+		
+		protected override void ArrangeCore(Rect finalRect)
 		{
-			base.OnRender(drawingContext);
-			textView.RenderTextLayer(drawingContext);
+			textView.ArrangeTextLayer(visuals);
 		}
 	}
 }

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

@@ -833,7 +833,6 @@ namespace ICSharpCode.AvalonEdit.Rendering
 			MeasureInlineObjects();
 			
 			InvalidateVisual(); // = InvalidateArrange+InvalidateRender
-			textLayer.InvalidateVisual();
 			
 			double maxWidth;
 			if (document == null) {
@@ -862,6 +861,8 @@ namespace ICSharpCode.AvalonEdit.Rendering
 				}
 			}
 			
+			textLayer.SetVisualLines(visibleVisualLines);
+			
 			SetScrollData(availableSize,
 			              new Size(maxWidth, heightTreeHeight),
 			              scrollOffset);
@@ -1153,14 +1154,13 @@ namespace ICSharpCode.AvalonEdit.Rendering
 			}
 		}
 		
-		internal void RenderTextLayer(DrawingContext drawingContext)
+		internal void ArrangeTextLayer(IList<VisualLineDrawingVisual> visuals)
 		{
 			Point pos = new Point(-scrollOffset.X, -clippedPixelsOnTop);
-			foreach (VisualLine visualLine in allVisualLines) {
-				foreach (TextLine textLine in visualLine.TextLines) {
-					textLine.Draw(drawingContext, pos, InvertAxes.None);
-					pos.Y += textLine.Height;
-				}
+			foreach (VisualLineDrawingVisual visual in visuals) {
+				visual.Transform = new TranslateTransform(pos.X, pos.Y);
+				visual.Transform.Freeze();
+				pos.Y += visual.Height;
 			}
 		}
 		#endregion

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

@@ -1,6 +1,7 @@
 // Copyright (c) AlphaSierraPapa for the SharpDevelop Team (for details please see \doc\copyright.txt)
 // This code is distributed under the GNU LGPL (for details please see \doc\license.txt)
 
+using System.Windows.Media;
 using ICSharpCode.AvalonEdit.Utils;
 using System;
 using System.Collections.Generic;
@@ -424,5 +425,34 @@ namespace ICSharpCode.AvalonEdit.Rendering
 		{
 			return true;
 		}
+		
+		VisualLineDrawingVisual visual;
+		
+		internal VisualLineDrawingVisual Render()
+		{
+			if (visual == null)
+				visual = new VisualLineDrawingVisual(this);
+			return visual;
+		}
+	}
+	
+	sealed class VisualLineDrawingVisual : DrawingVisual
+	{
+		public readonly VisualLine VisualLine;
+		public readonly double Height;
+		internal bool IsAdded;
+		
+		public VisualLineDrawingVisual(VisualLine visualLine)
+		{
+			this.VisualLine = visualLine;
+			var drawingContext = RenderOpen();
+			double pos = 0;
+			foreach (TextLine textLine in visualLine.TextLines) {
+				textLine.Draw(drawingContext, new Point(0, pos), InvertAxes.None);
+				pos += textLine.Height;
+			}
+			this.Height = pos;
+			drawingContext.Close();
+		}
 	}
 }