C# Bezier Curve

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;

namespace CSharpBezierCurve
{
    public partial class Form1 : Form
    {
        private Point[] controlPoint = new Point[4];
        private int controlPointCount = 0;
        public Form1()
        {
            InitializeComponent();
        }


        private void drawControlLine(Graphics g) {
            Pen p = new Pen(Color.Green);
            if (!controlPoint[0].IsEmpty && !controlPoint[1].IsEmpty)
                g.DrawLine(p, controlPoint[0], controlPoint[1]);
            if (!controlPoint[1].IsEmpty && !controlPoint[2].IsEmpty)
                g.DrawLine(p, controlPoint[1], controlPoint[2]);
            if (!controlPoint[2].IsEmpty && !controlPoint[3].IsEmpty)
                g.DrawLine(p, controlPoint[2], controlPoint[3]);
        }

        private void drawBezierCurve(Graphics g) {
            Pen p = new Pen(Color.Aqua);
            g.DrawBezier(p, controlPoint[0], controlPoint[1], controlPoint[2], controlPoint[3]);
        }

        private void panel1_MouseDown(object sender, MouseEventArgs e)
        {
            if (controlPointCount == 4) return;
            controlPoint[controlPointCount++] = new Point(e.X, e.Y);
            Pen p = new Pen(Color.Red);
            Panel panel = (Panel)sender;
            Graphics g = panel.CreateGraphics();
            g.DrawRectangle(p, e.X, e.Y, 2, 2);
            drawControlLine(g);
            if (controlPointCount == 4) drawBezierCurve(g);
        }

        private void button1_Click(object sender, EventArgs e)
        {
            controlPoint = null;
            controlPoint = new Point[4];
            controlPointCount = 0;
            panel1.Invalidate();

        }

    }
}