OpenGL-学习之路-简单多边形显示 及 多边形类型判断 和 凹多边形的切割 （待更新）

内容：

1.鼠标输入顶点，建立多边形数据结构。

2.判断多边形类型。

3.若是凹多边形，则切割成多个凸多边形。

首先，多边形数据结构：

#include <iostream>
using namespace std;

struct PolygonNode
{
public:
	int x;  //点x坐标
	int y;  //点y坐标
	int SeqNode;  //记录序号，从零开始

	PolygonNode * next;

	PolygonNode(int xPos, int yPos)
	{
		x = xPos;
		y = yPos;
		next = NULL;
	}
	~PolygonNode();

};

class Polygon
{
public:
	PolygonNode *first;
	PolygonNode *last;
	PolygonNode *current;

	int numNode;  //记录顶点数
	int concave;  //记录第几个顶点为凹角

	Polygon()
	{
		last = current = NULL;
	}

	void InsertNode(int xPos, int yPos);  //插入顶点
	void RemoveNode();  //移除顶点
	void pCurrentGoto(int n);  //current指针指向第n个顶点
	int CrossProduct(int n);  //向量叉乘，从第n个顶点起始的向量叉乘于下一个向量
};

void Polygon::InsertNode(int xPos, int yPos)
{
	PolygonNode * newNode = new PolygonNode(xPos, yPos);
	//空链表
	if (current == NULL)
	{
		first = last = current = newNode;
		numNode = 1;
		last->SeqNode = 0;
	}
	else
	{
		last->next = newNode;
		newNode->next = first;
		last = newNode;
		last->SeqNode = numNode;
		numNode++;
	}
};

void Polygon::RemoveNode()
{
	//链头
	if (current == first)
	{
		first = last->next = current->next;
		current->next = NULL;
		current = first;
	}
	//链尾
	else if (current == last)
	{
		pCurrentGoto(current->SeqNode - 1);
		cur