DrawingContextのDrawLineで破線がうまく描けない

Question

前提・実現したいこと

DrawLineで線幅を変更したときに破線間隔を維持して描きたかったので、
以下のようにしたのですが、2dot以降破線になりません。

LineクラスをXamlで描いたときはうまくいくのですが、
同じようにDrawLineで描くことはできないでしょうか。

該当のソースコード

        public void DrawLines(DrawingContext dc, IEnumerable<System.Windows.Point> points, double thickness, System.Windows.Media.Color color, DashStyle dashStyle)
        {

            var myPen1 = new System.Windows.Media.Pen
            {
                Thickness = thickness,
                Brush = new SolidColorBrush(color),
                DashStyle = GetDashStyle(dashStyle, thickness)
            };
            var col = myPen1.DashStyle.Dashes;
            myPen1.Freeze();


            var tuplepoints = new List<(System.Windows.Point, System.Windows.Point)>();
            System.Windows.Point? temppoint = null;

            foreach (var point in points)
            {
                if (temppoint is System.Windows.Point pt)
                {
                    tuplepoints.Add((pt, point));
                }
                temppoint = point;
            }
            foreach (var pair in tuplepoints)
            {
                dc.DrawLine(myPen1, pair.Item1, pair.Item2);
            }
        }

        private System.Windows.Media.DashStyle GetDashStyle(DashStyle dashStyle, double thickness)
        {
            return dashStyle switch
            {
                DashStyle.Solid => DashStyles.Solid,
                DashStyle.Dot => new System.Windows.Media.DashStyle()
                {
                    Dashes = new DoubleCollection(new double[] { 2 / thickness , 2 / thickness }),
                },
                DashStyle.Dash => new System.Windows.Media.DashStyle()
                {
                    Dashes = new DoubleCollection(new double[] { 4 / thickness, 4/  thickness })
                },
                DashStyle.DashDot => new System.Windows.Media.DashStyle()
                {
                    Dashes = new DoubleCollection(new double[] { 12 / thickness, 8 / thickness, 4 / thickness, 8 / thickness }),
                    Offset = 6
                },
                DashStyle.DashDotDot => new System.Windows.Media.DashStyle()
                {
                    Dashes = new DoubleCollection(new double[] { 12 / thickness, 4 / thickness, 4 / thickness, 4 / thickness, 4 / thickness, 4 / thickness }),
                    Offset = 6
                },
                _ => throw new Exception("破線スタイルがありません")
            };
        }

        <Canvas Grid.Column="1" Background="Black">
            <Line Canvas.Left="50" Canvas.Top="150" X1="0" Y1="0" X2="300" Y2="0" Stroke="Yellow" StrokeDashArray="2,2" StrokeThickness="1"/>
            <Line Canvas.Left="50" Canvas.Top="170" X1="0" Y1="0" X2="300" Y2="0" Stroke="Yellow" StrokeDashArray="0.5,0.5" StrokeThickness="4"/>
            <Line Canvas.Left="50" Canvas.Top="190" X1="0" Y1="0" X2="300" Y2="0" Stroke="Yellow" 
        </Canvas>

Answer 1

DrawingContext自体を使ったことがないので、的外れかもしれませんが、
GetDashStyle のメソッドが変ではないでしょうか？もしかして、System.Drawing.Drawing2D.DashStyle 列挙型を使用していますか？

私の環境では以下のコードで描けました。

    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
            this.Content = new MyElment();
        }
    }

    class MyElment : FrameworkElement
    {
        protected override void OnRender(DrawingContext dc)
        {
            base.OnRender(dc);

            var pt1 = new Point(10, 10);
            var pt2 = new Point(200, 100);
            var pt3 = new Point(50, 150);

            DrawLines(dc, new[] { pt1, pt2, pt3 }, 5, Colors.Red, new DashStyle(new[] { 1d, 2d }, 0));
        }

        public void DrawLines(DrawingContext dc, IEnumerable<System.Windows.Point> points, double thickness, System.Windows.Media.Color color, DashStyle dashStyle)
        {

            var myPen1 = new System.Windows.Media.Pen
            {
                Thickness = thickness,
                Brush = new SolidColorBrush(color),
                //DashStyle = GetDashStyle(dashStyle, thickness)
                DashStyle = dashStyle
            };
            var col = myPen1.DashStyle.Dashes;
            myPen1.Freeze();


            var tuplepoints = new List<(System.Windows.Point, System.Windows.Point)>();
            System.Windows.Point? temppoint = null;

            foreach (var point in points)
            {
                if (temppoint is System.Windows.Point pt)
                {
                    tuplepoints.Add((pt, point));
                }
                temppoint = point;
            }
            foreach (var pair in tuplepoints)
            {
                dc.DrawLine(myPen1, pair.Item1, pair.Item2);
            }
        }
    }