Question

What is the best approach to create a leader line? I have tried a couple of different approaches, but with no success.

Answer

Leaders in Rhino 4.0 are defined by the ON_Leader2 class. To construct a leader, you must provide:

1. A plane, or an ON_Plane object, which defines the plane in which the leader will be located.
2. Two or more 2-D points that line in the plane that you specified above.

In the following example code, we will construct a simple leader object. The leader will reside in the world x-y plane and will have four points.

C++

  CRhinoCommand::result CCommandLeader::RunCommand( const CRhinoCommandContext& context )
  {
    // Some set of points that define the leader
    ON_3dPointArray points;
    points.Append( ON_3dPoint(1.0, 1.0, 0.0) );
    points.Append( ON_3dPoint(5.0, 1.0, 0.0) );
    points.Append( ON_3dPoint(5.0, 5.0, 0.0) );
    points.Append( ON_3dPoint(9.0, 5.0, 0.0) );


    // The plane in which the leader resides
    ON_Plane plane = ON_xy_plane;


    // Create the leader
    ON_Leader2 leader;
    leader.SetPlane( plane );


    // Add the points to the leader
    int i;
    for( i = 0; i < points.Count(); i++ )
    {
      // Make sure the points are on the plane
      ON_2dPoint p2;
      if( leader.m_plane.ClosestPointTo(points[i], &p2.x, &p2.y) )
      {
        if( leader.m_points.Count() < 1 || p2.DistanceTo(*leader.m_points.Last()) > ON_SQRT_EPSILON )
          leader.m_points.Append( p2 );
      }
    }


    // Create the leader object
    CRhinoAnnotationLeader* leader_object = new CRhinoAnnotationLeader();
    // Add our leader to the object
    leader_object->SetAnnotation( leader );


    if( context.m_doc.AddObject(leader_object) )
      context.m_doc.Redraw();
    else
      delete leader_object; // error


    return success;
  }

C# (Rhino 4)

  public override IRhinoCommand.result RunCommand(IRhinoCommandContext context)
  {
    // Some set of points that define the leader
    On3dPointArray points = new On3dPointArray();
    points.Append( 1.0, 1.0, 0.0);
    points.Append( 5.0, 1.0, 0.0);
    points.Append( 5.0, 5.0, 0.0);
    points.Append( 9.0, 5.0, 0.0);


    // Create the leader
    OnLeader2 leader = new OnLeader2();
    // Set the plane in which the leader resides
    leader.SetPlane( OnUtil.On_xy_plane );


    // Add the points to the leader
    for( int i = 0; i < points.Count(); i++ )
    {
      // Make sure the points are on the plane
      double x = 0;
      double y = 0;
      if( leader.m_plane.ClosestPointTo(points[i], ref x, ref y) )
      {
        On2dPoint p2 = new On2dPoint(x, y);
        if( leader.m_points.Count() < 1 || 
            p2.DistanceTo(leader.m_points.Last()) > OnUtil.On_SQRT_EPSILON )
          leader.m_points.Append( p2 );
      }
    }


    // Create the leader object
    MRhinoAnnotationLeader leader_object = new MRhinoAnnotationLeader();
    // Add our leader to the object
    leader_object.SetAnnotation( leader );


    if( context.m_doc.AddObject(leader_object) )
      context.m_doc.Redraw();


    return IRhinoCommand.result.success;
  }

VB.NET (Rhino 4)

  Public Overrides Function RunCommand(ByVal context As RMA.Rhino.IRhinoCommandContext) _
    As RMA.Rhino.IRhinoCommand.result
    ' Some set of points that define the leader
    Dim points As New On3dPointArray()
    points.Append(1.0, 1.0, 0.0)
    points.Append(5.0, 1.0, 0.0)
    points.Append(5.0, 5.0, 0.0)
    points.Append(9.0, 5.0, 0.0)


    ' Create the leader
    Dim leader As New OnLeader2()
    ' Set the plane in which the leader resides
    leader.SetPlane(OnUtil.On_xy_plane)


    ' Add the points to the leader
    For i As Integer = 0 To points.Count() - 1
      ' Make sure the points are on the plane
      Dim x As Double = 0
      Dim y As Double = 0
      If (leader.m_plane.ClosestPointTo(points(i), x, y)) Then
        Dim p2 As New On2dPoint(x, y)
        If (leader.m_points.Count() < 1 OrElse _
            p2.DistanceTo(leader.m_points.Last()) > OnUtil.On_SQRT_EPSILON) Then
          leader.m_points.Append(p2)
        End If
      End If
    Next


    ' Create the leader object
    Dim leader_object As New MRhinoAnnotationLeader()
    ' Add our leader to the object
    leader_object.SetAnnotation(leader)


    If (context.m_doc.AddObject(leader_object)) Then
      context.m_doc.Redraw()
    End If


    Return IRhinoCommand.result.success
  End Function