How to recolor a specific word in AvalonEdit?

Question

I'm developing a (.NET-based) programming language and an IDE for it in WPF. I want type names to have different colors based on wheter they are reference types, value types or interfaces (just like in Visual Studio). For this I have made my compiler emit symbols containing the row, column and length of the type name in the source file. How do I implement the following method?

public static void Colorize(System.Windows.Media.Brush color, TextArea textArea, int line, int column, int length)
{

}

Answer 1

I quickly wrote this, let me know if it works

    public class HighlightedWord
    {
        public int StartIndex { get; set; }
        public int Length { get; set; }
        public int Line { get; set; }
    }

    public partial class MainWindow : Window
    {
        public static List<HighlightedWord> Words;

        public MainWindow()
        {
            InitializeComponent();
            Words = new List<HighlightedWord> 
            {
                new HighlightedWord
                {
                    StartIndex = 2,
                    Length = 5,
                    Line = 1,
                }
            };
            yourTextEditor.TextArea.TextView.LineTransformers.Add(new ColorizeAvalonEdit());
        }

    }

    public class ColorizeAvalonEdit : DocumentColorizingTransformer
    {
        protected override void ColorizeLine(DocumentLine line)
        {
            int lineStartOffset = line.Offset;
            foreach (HighlightedWord word in MainWindow.Words)
            {
                if (line.LineNumber != word.Line)
                    continue;

                if (word.StartIndex + word.Length > line.TotalLength)
                    continue;

                ChangeLinePart(
                    lineStartOffset + word.StartIndex, // startOffset
                    lineStartOffset + word.StartIndex + word.Length, // endOffset
                    (VisualLineElement element) =>
                    {
                        Typeface tf = element.TextRunProperties.Typeface;
                        element.TextRunProperties.SetTypeface(new Typeface(
                            tf.FontFamily,
                            FontStyles.Italic,
                            FontWeights.Bold,
                            tf.Stretch
                        ));
                        element.TextRunProperties.SetForegroundBrush(new SolidColorBrush(Colors.Blue));
                    }
                );
            }

        }
    }

Source: http://danielgrunwald.de/coding/AvalonEdit/rendering.php