Path Indicators in RadSyntaxEditor

Updated on Aug 27, 2026

Environment

Product Version	Product	Author
2021.2.615	RadSyntaxEditor for WinForms	Desislava Yordanova

Description

You can add indicators to particular lines of the RadSyntaxEditor control by using the IndicatorsMargin<T> class. This tutorial demonstrates how to achieve a Path indicator:

Solution

It is possible to construct a custom IndicatorsMargin<T>, where T is Path for example:

Defining Custom BookmarksPath Margins

C#

private void SetupBookmarksPathMargin()
{
    BookmarksPathMargin bookmarksPathMargin = new BookmarksPathMargin(this.radSyntaxEditor1.SyntaxEditorElement);
    this.radSyntaxEditor1.SyntaxEditorElement.Margins.ScrollableLeft.Insert(0, bookmarksPathMargin); 
}
/// <summary>
/// A margin holding a collection of bookmarks to highlight lines of the RadSyntaxEditor control.
/// </summary>
public class BookmarksPathMargin : IndicatorsMargin<Path>
{
    private TypeConverter stringToGeometryConverter;
    private Geometry defaultGeometry;

    /// <summary>
    /// Initializes a new instance of the <see cref="BookmarksPathMargin"/> class.
    /// </summary>
    /// <param name="syntaxEditor">The RadSyntaxEditor instance.</param>
    public BookmarksPathMargin(RadSyntaxEditorElement syntaxEditor)
        : base(syntaxEditor)
    {
        this.Background = new System.Drawing.SolidBrush(System.Drawing.Color.LightGray);

        this.stringToGeometryConverter = TypeDescriptor.GetConverter(typeof(Geometry));
        string data = "M15,5H8C6.9,5,6,5.9,6,7v3h3v11l4-3l4,3V7C17,5.9,16.1,5,15,5z M9,9H7V7c0-0.6,0.4-1,1-1h1V9z";
        var convertor = new Telerik.WinForms.Controls.SyntaxEditor.Utilities.StringToPathGeometryConverter();
        var geometry = convertor.Convert(data);
        this.defaultGeometry = geometry;
    }

    /// <summary>
    /// Called when an indicator needs to be updated. This can happen when the indicator is
    /// first created, when it is brought inside or outside of the viewport or when
    /// the EditorFontSize property of the RadSyntaxEditor or the IndicatorBrush property
    /// of the margin change.
    /// </summary>
    /// <param name="path">The Path to update.</param>
    /// <param name="lineNumber">The line number the indicator is placed on.</param>
    protected override void UpdateIndicator(Path path, int lineNumber)
    {
        if (path.Data != this.defaultGeometry)
        {
            path.Data = this.defaultGeometry;
        } 

        if (path.Width != this.Editor.EditorFontSize)
        {
            path.Width = this.Editor.EditorFontSize;
        }

        if (path.Height != this.Editor.EditorFontSize)
        {
            path.Height = this.Editor.EditorFontSize;
        }

        if (path.Fill != this.IndicatorBrush)
        {
            path.Fill = this.IndicatorBrush;
        }

        path.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;
        path.Margin = new System.Windows.Forms.Padding(-(int)(path.Width / 2f), -4, 0, 0);
    }
}

VB.NET

Private Sub SetupBookmarksPathMargin()
    Dim bookmarksPathMargin As BookmarksPathMargin = New BookmarksPathMargin(Me.RadSyntaxEditor1.SyntaxEditorElement)
    Me.RadSyntaxEditor1.SyntaxEditorElement.Margins.ScrollableLeft.Insert(0, bookmarksPathMargin)
End Sub

Public Class BookmarksPathMargin
    Inherits IndicatorsMargin(Of Path)

    Private stringToGeometryConverter As TypeConverter
    Private defaultGeometry As Geometry

    Public Sub New(ByVal syntaxEditor As RadSyntaxEditorElement)
        MyBase.New(syntaxEditor)
        Me.Background = New System.Drawing.SolidBrush(System.Drawing.Color.LightGray)
        Me.stringToGeometryConverter = TypeDescriptor.GetConverter(GetType(Geometry))
        Dim data As String = "M15,5H8C6.9,5,6,5.9,6,7v3h3v11l4-3l4,3V7C17,5.9,16.1,5,15,5z M9,9H7V7c0-0.6,0.4-1,1-1h1V9z"
        Dim convertor = New Telerik.WinForms.Controls.SyntaxEditor.Utilities.StringToPathGeometryConverter()
        Dim geometry = convertor.Convert(data)
        Me.defaultGeometry = geometry
    End Sub

    Protected Overrides Sub UpdateIndicator(ByVal path As Path, ByVal lineNumber As Integer)
        If path.Data Is Nothing Then
            path.Data = Me.defaultGeometry
        ElseIf Not path.Data.Equals(Me.defaultGeometry) Then
            path.Data = Me.defaultGeometry
        End If

        If path.Width <> Me.Editor.EditorFontSize Then
            path.Width = Me.Editor.EditorFontSize
        End If

        If path.Height <> Me.Editor.EditorFontSize Then
            path.Height = Me.Editor.EditorFontSize
        End If

        If path.Fill Is Nothing Then
            path.Fill = Me.IndicatorBrush
        ElseIf Not path.Fill.Equals(Me.IndicatorBrush) Then
            path.Fill = Me.IndicatorBrush
        End If

        path.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality
        path.Margin = New System.Windows.Forms.Padding(-CInt((path.Width / 2.0F)), -4, 0, 0)
    End Sub
End Class

See Also

• RadSyntaxEditor
• Layers
• Margins