void DrawGraph(SKCanvas canvas, SKPaint paint, DGraph2 graph, Func <Vector2d, SKPoint> mapF)
        {
            Colorf color = Colorf.Red;

            if (Colors.ContainsKey(graph))
            {
                color = Colors[graph];
            }
            paint.Color = SkiaUtil.Color(color);

            SKPath path = SkiaUtil.ToSKPath(graph, mapF);

            paint.StrokeWidth = 2;
            canvas.DrawPath(path, paint);

            paint.StrokeWidth = 1;
            //paint.Color = SKColors.Black;
            foreach (Vector2d v in graph.Vertices())
            {
                SKPoint c = mapF(v);
                canvas.DrawCircle(c.X, c.Y, 3.0f, paint);
            }
        }