How to draw Bezier-Curve C#

Question

I need to draw an bezier curve. But the problem is my code bring this output:

But it should look like this:

How can i "delete" the rest of the lines. I don't know how tho draw the control polygon only on his finest Level of polyline.

    private void pb_Bezier_Paint(object sender, PaintEventArgs e)
    {
        Point P1 = new Point(10, 300);
        Point P2 = new Point(180, 50);
        Point P3 = new Point(320, 300);

        ZeichneBezier(6, P1, P2, P3, e);
    }

    private void ZeichneBezier(int n, Point P1, Point P2, Point P3, PaintEventArgs pva)
    {
        Graphics g = pva.Graphics;
        Pen kpStift = new Pen(Color.Black, 3);
        Pen bkStift = new Pen(Color.Red, 2);

        for(int i = n; i >= 0; i--)
        {
            if(i==0)
            {
                g.DrawLine(bkStift, P1, P2);
                g.DrawLine(bkStift, P2, P3);
            }
            else
            {
                Point P12 = new Point((P1.X + P2.X)/2,(P1.Y + P2.Y)/2);
                Point P23 = new Point((P2.X + P3.X)/2,(P2.Y + P3.Y)/2);
                Point P123 = new Point((P12.X + P23.X)/2,(P12.Y + P23.Y)/2);

                ZeichneBezier(n-1, P1, P12, P123, pva);
                ZeichneBezier(n-1, P123, P23, P3, pva);
            }
        }

Answer 1

Maybe this one...

    private void pb_Bezier_Paint(object sender, PaintEventArgs e)
    {
        Point P1 = new Point(10, 300);
        Point P2 = new Point(180, 50);
        Point P3 = new Point(320, 300);

        ZeichneBezier(6, P1, P2, P3, e, true);
    }

    private void ZeichneBezier(int n, Point P1, Point P2, Point P3, PaintEventArgs pva, bool initial)
    {
        Graphics g = pva.Graphics;
        Pen bkStift = new Pen(Color.Red, 2);
        Pen kpStift = new Pen(Color.Black, 3);

        if(initial)
        {
            g.DrawLine(kpStift, P1, P2);
            g.DrawLine(kpStift, P2, P3);
        }

        if (n > 0)
        {
            Point P12 = new Point((P1.X + P2.X) / 2, (P1.Y + P2.Y) / 2);
            Point P23 = new Point((P2.X + P3.X) / 2, (P2.Y + P3.Y) / 2);
            Point P123 = new Point((P12.X + P23.X) / 2, (P12.Y + P23.Y) / 2);

            ZeichneBezier(n - 1, P1, P12, P123, pva, false);
            ZeichneBezier(n - 1, P123, P23, P3, pva, false);
        }
        else
        {
            g.DrawLine(bkStift, P1, P2);
            g.DrawLine(bkStift, P2, P3);
        }
    }

Your for loop seems to be not necessary and decreases your performance.

I've added a parameter "bool initial" to decide when to draw the black lines.

Only first call of ZeichneBezier in pb_Bezier_Paint event handler should draw the lines.