private void InitializeComponent() {
   this.Loaded += OnLoad;
   this.MouseDown += OnMouseDown;
   this.MouseMove += OnMouseMove;
   this.MouseUp += OnMouseUp;
   locus = new Path();
   locus.Fill = new SolidColorBrush(Color.FromArgb(1, 255, 255, 255));
   locus.Stroke = Brushes.Red;
   locus.StrokeThickness = 1;
   locus.IsManipulationEnabled = true;
  }

  void OnMouseUp(object sender, System.Windows.Input.MouseButtonEventArgs e) {
   ispath = false;
  }

  void OnMouseMove(object sender, System.Windows.Input.MouseEventArgs e) {
   if(ispath){
    endpoint = e.GetPosition(this);
    locus.Data = DrawingRect(startpoint,endpoint);
   }
  }

  void OnMouseDown(object sender, System.Windows.Input.MouseButtonEventArgs e) {
   if(!this.Children.Contains(locus)) this.Children.Add(locus);
   if (locus.Data != null) locus.Data = null;
   startpoint = e.GetPosition(this);
   ispath = true;
  }

  void OnLoad(object sender, System.Windows.RoutedEventArgs e) {
   this.Background = new SolidColorBrush(Color.FromArgb(35, 255, 255, 255));
  }

  private PathGeometry DrawingRect(Point beginpoint, Point closepoint) {
   PathGeometry result = new PathGeometry(); 
   PathFigure figure = new PathFigure();
   figure.IsClosed = true;
   figure.StartPoint = beginpoint;
   PathSegmentCollection pathSegmentCollection = new PathSegmentCollection();
   PathFigureCollection pathFigureCollection = new PathFigureCollection();  
   LineSegment m1 = new LineSegment();
   m1.Point = new Point(closepoint.X, beginpoint.Y);
   LineSegment m2 = new LineSegment();
   m2.Point = closepoint;
   LineSegment m3 = new LineSegment();
   m3.Point = new Point(beginpoint.X, closepoint.Y);
   pathSegmentCollection.Add(m1);
   pathSegmentCollection.Add(m2);
   pathSegmentCollection.Add(m3);
   figure.Segments = pathSegmentCollection;
   pathFigureCollection.Add(figure);
   result.Figures = pathFigureCollection;

   return result();
  }

  private Path locus;
  private bool ispath = false;
  private Point startpoint;
  private Point endpoint;
 }
}