【计算机图形学】c++ OpenGL Sutherlang-Hodgman 多边形裁剪

源代码

// 多边形裁剪.cpp : 定义控制台应用程序的入口点。
//

#include "stdafx.h"
#include<GL/glut.h>
#include<iostream>
#include<stdio.h>
#include<stdlib.h>

//Sutherlang-Hodgman多边形裁剪
typedef struct
{
	float x, y;
}wcPt2D;

typedef enum
{
	Left, Right, Bottom, Top
}Boundary;

int Inside(wcPt2D p, Boundary b, wcPt2D wMin, wcPt2D wMax)
{
	switch (b)
	{
	case Left:
		if (p.x<wMin.x) return (false);
		break;
	case Right:
		if (p.x>wMax.x) return (false);
		break;
	case Bottom:
		if (p.y<wMin.y) return (false);
		break;
	case Top:
		if (p.y>wMax.y) return (false);
		break;
	}
	return true;
}

int Cross(wcPt2D p1, wcPt2D p2, Boundary b, wcPt2D wMin, wcPt2D wMax)
{
	if (Inside(p1, b, wMin, wMax) == Inside(p2, b, wMin, wMax))
		return (false);
	else
		return true;
}

wcPt2D Intersect(wcPt2D p1, wcPt2D p2, Boundary b, wcPt2D	wMin, wcPt2D wMax)
{
	wcPt2D iPt;
	float m;
	if (p1.x != p2.x) m = (p2.y - p1.y) / (p2.x - p1.x);
	switch (b){
	case Left:
		iPt.x = wMin.x;
		iPt.y = p2.y + (wMin.x - p2.x)*m;
		break;
	case Right:
		iPt.x = wMax.x;
		iPt.y = p2.y + (wMax.x - p2.x)*m;
		break;
	case Bottom:
		iPt.y = wMin.y;
		if (p1.x != p2.x)iPt.x = p2.x + (wMin.y - p2.y) / m;
		else iPt.x = p2.x;
		break;
	case Top:
		iPt.y = wMax.y;
		if (p1.x != p2.x) iPt.x = p2.x + (wMax.y - p2.y) / m;
		else iPt.x = p2.x;
		break;
	}
	return iPt;
}
int edgeCliper(Boundary b, wcPt2D wMin, wcPt2D wMax, wcPt2D *pIn, int cnt, wcPt2D *pOut)
{
	wcPt2D s;
	int i, Outcnt = 0;
	s = pIn[0];
	for (i = 1; i <= cnt; i++)
	{
		if (!Inside(s, b, wMin, wMax) && Inside(pIn[i], b, wMin, wMax))
		{
			pOut[Outcnt] = Intersect(s, pIn[i], b, wMin, wMax);
			Outcnt++;
			pOut[Outcnt] = pIn[i];
			Outcnt++;
		}
		else if (Inside(s, b, wMin, wMax) && Inside(pIn[i], b, wMin, wMax))
		{
			pOut[Outcnt] = pIn[i];
			Outcnt++;
		}
		else if (Inside(s, b, wMin, wMax) && (!Inside(pIn[i], b, wMin, wMax)))
		{
			pOut[Outcnt] = Intersect(s, pIn[i], b, wMin, wMax);
			Outcnt++;
		}
		s = pIn[i];
	}
	return (Outcnt);
}

void  init(void)
{
	glClearColor(1.0, 1.0, 1.0, 0.0);
	glMatrixMode(GL_PROJECTION);
	glLoadIdentity();
	gluOrtho2D(-400.0, 400.0, -300.0, 300.0);
}

void ClipPolygonSuthHodg(void)
{
	glClear(GL_COLOR_BUFFER_BIT);
	glMatrixMode(GL_MODELVIEW);
	int i, cnt, Outcnt, b;
	wcPt2D points[7] = { { -300, -100 },{ -300, 150 }, { -100, 150 }, { 100, 100 }, { 100, 0 }, { 0, -100 },{ -300, -100 }};
	cnt = 7;
	wcPt2D pOut[28], pIn[28];
	wcPt2D wMin = { -200, 0 }, wMax = { 50, 200 };
	for (i = 0; i<4 * cnt; i++)
	{
		pIn[i].x = 0.0;
		pIn[i].y = 0.0;
		pOut[i].x = 0.0;
		pOut[i].y = 0.0;
	}
	for (i = 0; i <= cnt; i++) pIn[i] = points[i];
	glColor3f(0.0, 0.0, 0.0);
	glBegin(GL_LINE_LOOP);
	glVertex2f(wMin.x, wMin.y);
	glVertex2f(wMax.x, wMin.y);
	glVertex2f(wMax.x, wMax.y);
	glVertex2f(wMin.x, wMax.y);
	glEnd();
	glLineWidth(2.0);
	glBegin(GL_LINE_LOOP);
	for (i = 0; i<cnt; i++)
		glVertex2f(pIn[i].x, pIn[i].y);
	glEnd();
	for (b = 0; b<4; b++)
	{
		Outcnt = edgeCliper(Boundary(b), wMin, wMax, pIn, cnt, pOut);
		for (i = 0; i<Outcnt; i++)
			pIn[i] = pOut[i];
		pIn[Outcnt] = pOut[0];
		cnt = Outcnt;
	}
	glColor3f(1.0, 0.0, 0.0);
	glBegin(GL_LINE_LOOP);
	for (i = 0; i<cnt; i++)
		glVertex2f(pOut[i].x, pOut[i].y);
	glEnd();
	glFlush();
}
void main(int argc, char **argv)
{
	glutInit(&argc, argv);
	glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB);
	glutInitWindowPosition(50, 100);
	glutInitWindowSize(800, 600);
	glutCreateWindow("An Example OpenGL Program");
	init();
	glutDisplayFunc(ClipPolygonSuthHodg);
	glutMainLoop();
}

运行结果