判断点到线的关系

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

namespace cac
{
    public partial class Form1 : Form
    {
        Graphics g;
        int m_judgetype = 0;
        int m_drawtype = 0;
        int pointNum = 0;
        Pen m_pen = new Pen(Color.Red , 2);
        Point[] ptArray = new Point[2];

        public Form1()
        {
            InitializeComponent();
        }

        private void pointlineToolStripMenuItem_Click(object sender, EventArgs e)
        {
            m_judgetype = 1;
            m_drawtype = 2;