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在OpenGL环境下, 运用Sutherland_Hodheman算法实现多边形裁剪

程序员文章站 2024-03-16 19:50:22
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#在OpenGL环境下, 运用Sutherland_Hodheman算法实现多边形裁剪

Sutherland_Hodheman算法基本思想是:简单得通过单一边或面的剪裁实现对多边形的裁剪;原多边形和每次裁剪所生成的多边形将逐次对裁剪窗口的每一条边进行裁剪。

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

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, Ocnt = 0;
	s = pIn[0];
	for (i = 1; i <= cnt; i++)
	{
		if (!inside(s, b, wMin, wMax) && inside(pIn[i], b, wMin, wMax))
		{
			pOut[Ocnt] = intersect(s, pIn[i], b, wMin, wMax);
			Ocnt++;
			pOut[Ocnt] = pIn[i];
			Ocnt++;
		}
		else if (inside(s, b, wMin, wMax) && inside(pIn[i], b, wMin, wMax))
		{
			pOut[Ocnt] = pIn[i];
			Ocnt++;
		}
		else if (inside(s, b, wMin, wMax) && (!inside(pIn[i], b, wMin, wMax)))
		{
			pOut[Ocnt] = intersect(s, pIn[i], b, wMin, wMax);
			Ocnt++;
		}
		s = pIn[i];
	}
	return (Ocnt);
}

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, Ocnt, b;
	wcPt2D points[7] = { {-300,-100},{-300,90},{-100,150},{-80,130},{90,160},{130,0},{0,-150} };
	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++)
	{
		Ocnt = edgeCliper(Boundary(b), wMin, wMax, pIn, cnt, pOut);
		for (i = 0; i < Ocnt; i++)
			pIn[i] = pOut[i];
		pIn[Ocnt] = pOut[0];
		cnt = Ocnt;
	}
	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(600, 600);
	glutCreateWindow("Sutherland-hodgman Clips Example");
	init();
	glutDisplayFunc(ClipPolygonSuthHodg);
	glutMainLoop();
}

OpenGL 环境下,运行Sutherland_Hodheman算法实现多边形裁剪

相关标签: opengl c++ 算法

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