private void OnPainting(object sender, SKPaintSurfaceEventArgs e)
{
        var surface = e.Surface;
        var canvas = surface.Canvas;
        canvas.Clear(SKColors.White);


        var pathStroke2 = new SKPaint
        {
            IsAntialias = true,
            Style = SKPaintStyle.StrokeAndFill,
            Color = SKColors.Red,
            StrokeWidth = 5
        };

        var path2 = new SKPath { FillType = SKPathFillType.EvenOdd };
        path2.MoveTo(0, 0);
        path2.LineTo(0, 140);
        path2.MoveTo(0, 140);
        path2.LineTo(140, 140);
        path2.MoveTo(140, 140);
        path2.LineTo(0, 0);
        path2.Close();
        canvas.DrawPath(path2, pathStroke2);

    }