Стрелка с расширяемой основой

    public class GeometryContainer : OnPropertyChangedClass
    {
        public static SizeChangedEventHandler SizeChanged { get; }
            = (object sender, SizeChangedEventArgs e) =>
        {
             Grid grid = (Grid)sender;
             GeometryContainer geometryContainer = (GeometryContainer)grid.Resources["geometryContainer"];
             geometryContainer.Width = grid.ActualWidth;
             geometryContainer.Height = grid.ActualHeight;
 
             // Прямоугольник тела стрелки
             geometryContainer.Rect = new Rect(0, geometryContainer.Height * 0.25, geometryContainer.Width - geometryContainer.Length, geometryContainer.Height * 0.5);
 
             // Вершины треугольника стрелки
             geometryContainer.ArrowheadTop = new Point(geometryContainer.Width - geometryContainer.Length, 0);
             geometryContainer.ArrowheadBottom = new Point(geometryContainer.Width - geometryContainer.Length, geometryContainer.Height);
             geometryContainer.ArrowheadRight = new Point(geometryContainer.Width, geometryContainer.Height * 0.5);
        };
 
 
        private double _length;
        private double _width;
        private double _height;
        private Rect _rect;
        private Point _arrowheadTop;
        private Point _arrowheadBottom;
        private Point _arrowheadRight;
 
        public double Length { get => _length; set => SetProperty(ref _length, value); }
        public double Width { get => _width; set => SetProperty(ref _width, value); }
        public double Height { get => _height; set => SetProperty(ref _height, value); }
        public Rect Rect { get => _rect; set => SetProperty(ref _rect, value); }
        public Point ArrowheadTop { get => _arrowheadTop; set => SetProperty(ref _arrowheadTop, value); }
        public Point ArrowheadBottom { get => _arrowheadBottom; set => SetProperty(ref _arrowheadBottom, value); }
        public Point ArrowheadRight { get => _arrowheadRight; set => SetProperty(ref _arrowheadRight, value); }
    }