Using AvalonEdit (WPF Text Editor)

// Copyright (c) 2009 Daniel Grunwald
// 
// 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.IO;
using System.Text.RegularExpressions;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Media;
using System.Windows.Media.Imaging;

using ICSharpCode.AvalonEdit.Document;
using ICSharpCode.AvalonEdit.Rendering;

namespace AvalonEdit.Sample
{
	/// <summary>
	/// This class can be used to embed images inside AvalonEdit like this: <img src="Images/Save.png"/>
	/// </summary>
	public class ImageElementGenerator : VisualLineElementGenerator
	{
		readonly static Regex imageRegex = new Regex(@"<img src=""([\.\/\w\d]+)""/?>",
		                                             RegexOptions.IgnoreCase);
		readonly string basePath;
		
		public ImageElementGenerator(string basePath)
		{
			if (basePath == null)
				throw new ArgumentNullException("basePath");
			this.basePath = basePath;
		}
		
		Match FindMatch(int startOffset)
		{
			// fetch the end offset of the VisualLine being generated
			int endOffset = CurrentContext.VisualLine.LastDocumentLine.EndOffset;
			TextDocument document = CurrentContext.Document;
			string relevantText = document.GetText(startOffset, endOffset - startOffset);
			return imageRegex.Match(relevantText);
		}
		
		/// <summary>
		/// Gets the first offset >= startOffset where the generator wants to construct
		/// an element.
		/// Return -1 to signal no interest.
		/// </summary>
		public override int GetFirstInterestedOffset(int startOffset)
		{
			Match m = FindMatch(startOffset);
			return m.Success ? (startOffset + m.Index) : -1;
		}
		
		/// <summary>
		/// Constructs an element at the specified offset.
		/// May return null if no element should be constructed.
		/// </summary>
		public override VisualLineElement ConstructElement(int offset)
		{
			Match m = FindMatch(offset);
			// check whether there's a match exactly at offset
			if (m.Success && m.Index == 0) {
				BitmapImage bitmap = LoadBitmap(m.Groups[1].Value);
				if (bitmap != null) {
					Image image = new Image();
					image.Source = bitmap;
					image.Width = bitmap.PixelWidth;
					image.Height = bitmap.PixelHeight;
					// Pass the length of the match to the 'documentLength' parameter
					// of InlineObjectElement.
					return new InlineObjectElement(m.Length, image);
				}
			}
			return null;
		}
		
		BitmapImage LoadBitmap(string fileName)
		{
			// TODO: add some kind of cache to avoid reloading the image whenever the
			// VisualLine is reconstructed
			try {
				string fullFileName = Path.Combine(basePath, fileName);
				if (File.Exists(fullFileName)) {
					BitmapImage bitmap = new BitmapImage(new Uri(fullFileName));
					bitmap.Freeze();
					return bitmap;
				}
			} catch (ArgumentException) {
				// invalid filename syntax
			} catch (IOException) {
				// other IO error
			}
			return null;
		}
	}
}