getpointdynamicdraw

          
using Rhino;
using Rhino.Geometry;
using Rhino.Commands;
using Rhino.Input.Custom;

namespace examples_cs
{
  public class GetPointDynamicDrawCommand : Command
  {
    public override string EnglishName { get { return "csGetPointDynamicDraw"; } }

    protected override Result RunCommand(RhinoDoc doc, RunMode mode)
    {
      var gp = new GetPoint();
      gp.SetCommandPrompt("Center point");
      gp.Get();
      if (gp.CommandResult() != Result.Success)
        return gp.CommandResult();
      var center_point = gp.Point();
      if (center_point == Point3d.Unset)
        return Result.Failure;

      var gcp = new GetCircleRadiusPoint(center_point);
      gcp.SetCommandPrompt("Radius");
      gcp.ConstrainToConstructionPlane(false);
      gcp.SetBasePoint(center_point, true);
      gcp.DrawLineFromPoint(center_point, true);
      gcp.Get();
      if (gcp.CommandResult() != Result.Success)
        return gcp.CommandResult();

      var radius = center_point.DistanceTo(gcp.Point());
      var cplane = doc.Views.ActiveView.ActiveViewport.ConstructionPlane();
      doc.Objects.AddCircle(new Circle(cplane, center_point, radius));
      doc.Views.Redraw();
      return Result.Success;
    }
  }

  public class GetCircleRadiusPoint : GetPoint
  {
    private Point3d m_center_point;
 
    public GetCircleRadiusPoint(Point3d centerPoint)
    {
      m_center_point = centerPoint;
    }

    protected override void OnDynamicDraw(GetPointDrawEventArgs e)
    {
      base.OnDynamicDraw(e);
      var cplane = e.RhinoDoc.Views.ActiveView.ActiveViewport.ConstructionPlane();
      var radius = m_center_point.DistanceTo(e.CurrentPoint);
      var circle = new Circle(cplane, m_center_point, radius);
      e.Display.DrawCircle(circle, System.Drawing.Color.Black);
    }
  }
}