剛學編程，寫了個判斷獨立點與多邊形位置關係的演算法（C#）

編程|演算法 #region Using directives

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

#endregion

namespace p_polygon
{
partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
}

public int count = 0;//頂點計數

public bool reset=false;//設複位功能標誌

private struct point//頂點結構
{
public float x, y;
}

point[] pt = new point[100];

private float Max(float x,float y)
{
return(x>y?x:y);
}

private float Min(float x, float y)
{
return (x < y ? x : y);
}

private void Judge(point[] pt)//判斷函數
{
float Px = float.Parse(textBox1.Text);
float Py = float.Parse(textBox2.Text);
float[] line = new float[99];
float linelast;
float flag = 1;//判斷在直線左右的標誌數（大於0在右，小於0在左）
bool online = false;
for (int i = 1; i < count; i++)
{
line[i - 1] = (pt[i].y - pt[i - 1].y) * Px + (pt[i - 1].x - pt[i].x) * Py +
(pt[i].x - pt[i - 1].x) * pt[i - 1].y - (pt[i].y - pt[i - 1].y) * pt[i - 1].x;
if (line[i - 1] == 0 && Px <= Max(pt[i].x, pt[i - 1].x) && Px >= Min(pt[i].x, pt[i - 1].x))
online = true;
flag *= line[i - 1];
if (i == count - 1)
{
linelast = (pt[0].y - pt[i].y) * Px + (pt[i].x - pt[0].x) * Py +
(pt[0].x - pt[i].x) * pt[i].y - (pt[0].y - pt[i].y) * pt[i].x;
flag *= linelast;
if (flag == 0)
{
if (Px <= Max(pt[i].x, pt[0].x) && Py >= Min(pt[i].x, pt[0].x))
online = true;
else
online = false;
}
}

if ((flag < 0 && online == false) || (flag == 0 && online == false))
{
MessageBox.Show("the isolated point is outside the polygon");
break;
}
else if (flag == 0 && i == count - 1 && online == true)
{
MessageBox.Show("the isolated point is on the border of the polygon");
break;
}
else if (flag > 0 && i == count - 1)
{
MessageBox.Show("the isolated point is inside the polygon");
break;
}

}


}

//複位函數
private void Resetall()
{
textBox1.Text = "";
textBox2.Text = "";
textBox3.Text = "";
textBox4.Text = "";
count = 0;
label1.Text = "0";
reset = true;
}


private void button1_Click(object sender, EventArgs e)
{
if (textBox3.Text != "" && textBox4.Text != "")
{

if (count < 100)
{
pt[count].x = float.Parse(textBox3.Text);
pt[count].y = float.Parse(textBox4.Text);
count++;
label1.Text = count.ToString();
reset = false;
}
else
MessageBox.Show("Only 100 vertexes support!");
}
else
MessageBox.Show("Please input necessary data!");
}

private void button2_Click(object sender, EventArgs e)
{
if (reset == false)
{
if (textBox1.Text != "" && textBox2.Text != "" && textBox3.Text != "" && textBox4.Text != "")
Judge(pt);
else
MessageBox.Show("Please input necessary data!");
}
else
MessageBox.Show("All data Cleared! Input again.");

}

private void button3_Click(object sender, EventArgs e)
{
Resetall();
}

private void button4_Click(object sender, EventArgs e)
{
MessageBox.Show("When you input the coordinates of vertexes,\nyou must ensure that the vertexes are ORDINAL\nand the polygon is at the RIGHT side of the line\nfrom PREVIOUS vertex to CURRENT vertex.\nOr else, there must be ERROR!\n\nPLEASE REMEMBER! Good Luck!\n\n\npoint & polygon v1.0 <<ICEBOY 2005.1.2>>",
"Attention!",MessageBoxButtons.OK,MessageBoxIcon.Information);
}
}
}