【计算机图形学实验三——多边形的扫描转换算法】

1、多边形的扫描转换算法
2、掌握相关算法的原理及实现
3、实现算法代码，能处理任意凸多边形；
能正确处理特殊情形：交点取整、边界像素取舍等；

#include 
#include 
#include 
using namespace std;

int num; //顶点个数
struct vertex {
    float ver_x;
    float ver_y;
};
//链表的实现
typedef struct XET {
	float x;
	float dx, ymax;
	XET* next;
}AET, NET;
//结构体对于某一个点的实现
struct point {
	float x;
	float y;
};

vertex* ver;
void inputPoint() {
	cout << "请输入多边形顶点个数：   ";
	cin >> num;
	ver = (vertex*)malloc(sizeof(vertex) * num);//输入顶点以（x,y）格式
	cout << "         =======按顺序输入每个顶点的x,y值，中间以空格隔开!=========" << endl;
	cout << "         =======每输入完一个顶点，回车进入下一个顶点的输入!========" << endl;
	for (int i = 0; i < num; i++) {
		cout << "请输入第"<> ver[i].ver_x >> ver[i].ver_y;
	}
}

void Polygon() {
	int MaxY = 0;
	int i;
	for (i = 0; i < num; i++) {
		if (ver[i].ver_y > MaxY)
			MaxY = ver[i].ver_y;
	}
	//选出最大的顶点所对应的y值
	AET* pAET = new AET;
	pAET->next = NULL;

	NET* pNET[1024];
	for (i = 0; i <= MaxY; i++) {
		pNET[i] = new NET;
		pNET[i]->next = NULL;
	}//初始化扫描边的活性边表

	glClear(GL_COLOR_BUFFER_BIT);
	glColor3f(1, 0, 0); //红色
	glBegin(GL_POINTS);
	//一个点跟前面的点形成一条线段,同时跟后面一个点形成线段
	for (i = 0; i < MaxY; i++) {
		for (int j = 0; j < num; j++) {
			if (ver[j].ver_y == i) {
				if (ver[(j + 1 + num) % num].ver_y > ver[j].ver_y) {
					NET* p = new NET;
					p->x = ver[j].ver_x;
					p->ymax = ver[(j + 1 + num) % num].ver_y;
					p->dx = (ver[(j + 1 + num) % num].ver_x - ver[j].ver_x) / (ver[(j + 1 + num) % num].ver_y - ver[j].ver_y);
					p->next = pNET[i]->next;
					pNET[i]->next = p;
				}

				if (ver[(j - 1 + num) % num].ver_y > ver[j].ver_y) {
					NET* p = new NET;
					p->x = ver[j].ver_x;
					p->ymax = ver[(j - 1 + num) % num].ver_y;
					p->dx = (ver[(j - 1 + num) % num].ver_x - ver[j].ver_x) / (ver[(j - 1 + num) % num].ver_y - ver[j].ver_y);
					p->next = pNET[i]->next;
					pNET[i]->next = p;
				}
			}
		}
	}
	//把新边表net[i]中的边节点用插入排序法插入AET表，使之按照x的坐标递增顺序排序
	for (i = 0; i <= MaxY; i++) {
		NET* p = pAET->next;
		while (p) {
			p->x = p->x + p->dx;
			p = p->next;
		}
		AET* tq = pAET;
		p = pAET->next;
		tq->next = NULL;
		while (p) {
			while (tq->next && p->x >= tq->next->x)//重新排序
				tq = tq->next;
			NET* s = p->next;
			p->next = tq->next;
			tq->next = p;
			p = s;
			tq = pAET;
		}
		//遍历AET表，把配对交点的区间(左闭右开）上的像素(x,y)
		AET* q = pAET;
		p = q->next;
		while (p) {  //删掉扫描线高度等同于ymax的废弃点
			if (p->ymax == i) {
				q->next = p->next;
				delete p;
				p = q->next;
			}
			else {
				q = q->next;
				p = q->next;
			}
		}
		p = pNET[i]->next;
		q = pAET;
		while (p) {
			while (q->next && p->x >= q->next->x)
				q = q->next;
			NET* s = p->next;
			p->next = q->next;
			q->next = p;
			p = s;
			q = pAET;
		}
		p = pAET->next;
		while (p && p->next) {
			for (float j = p->x; j <= p->next->x; j++) {
				glVertex2i(static_cast(j), i);
			}
			p = p->next->next;
		}
	}
	glEnd();
	glFlush();
}
int main(int argc, char* argv) {
	glutInit(&argc, &argv);
	glutInitWindowSize(400, 300);
	glutCreateWindow("多边形的扫描转换算法");
	inputPoint();
	gluOrtho2D(0.0, 600.0, 0.0, 450.0); //设置原点在窗口左下方
	glutDisplayFunc(Polygon);//调用函数
	glutMainLoop();
}

本次实验将原点设置为窗口左下方：

gluOrtho2D(0.0, 600.0, 0.0, 450.0); //设置原点在窗口左下方

结束啦！下次实验是简单几何形体的平移、缩放、旋转等几何变换，加油！