《计算机图形学》实验四：裁剪

本博客计算机图形学系列文章索引：

地址：《计算机图形学系列相关文章索引（持续更新）》

参考教材：《计算机图形学》机械工业出版社，徐文鹏主编

实验内容：利用Cohen-Sutherland编码裁剪算法，用矩形框裁剪直线。

实验代码如下（已调试过）：

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

#pragma comment( lib, "opengl32.lib" )  
#pragma comment( lib, "glu32.lib" )    
#pragma comment( lib, "glut32.lib" )  

#define LEFT_EDGE 1
#define RIGHT_EDGE 2
#define BOTTOM_EDGE 4
#define TOP_EDGE 8
static int times=1;

//画从(x0,y0)到(x1,y1)的直线
void LineGL(int x0,int y0,int x1,int y1)
{
	glBegin(GL_LINES);
	glColor3f(1.0f,0.0f,0.0f);
	glVertex2f(x0,y0);
	glColor3f(0.0f,1.0f,0.0f);
	glVertex2f(x1,y1);
	glEnd();
}

//矩形的结构体
typedef struct Rectangle
{
	float xmin;
	float xmax;
	float ymin;
	float ymax;
} Rectan;

Rectan rect;
int x0,y0,x1,y1;

//求出坐标点的Cohen-Sutherland编码
int CompCode(int x,int y,Rectan rect)
{
	int code = 0x00;
	if (y < rect.ymin)
	{
		code=code | 4;
	}

	if (y>rect.ymax)
	{
		code = code | 8;
	}
	
	if (x>rect.xmax)
	{
		code= code | 2;
	}

	if (x<rect.xmin)
	{
		code=code | 1;
	}

	return code;
}

//裁剪直线
int cohensutherlandlineclip(Rectan rect,int& x0,int& y0,int& x1,int& y1)
{
	int accept=0,done=0;
	float x,y;
	int code0,code1,codeout;
	int x00 = x0,y00 = y0,x11 = x1,y11 = y1;

	code0= CompCode(x0,y0,rect);
	code1= CompCode(x1,y1,rect);

	//直线全部在矩形框内部，应保留
	if (!(code0 | code1))
	{
		accept=1;
		done=1;
	} 

	//直线和矩形不相交，并且划直线的两点在矩形同侧（上、下、右。左），应去掉。
	if( code0 & code1 )
	{
		done=1;
	}

	while(!done)
	{
		//直线和矩形有交点，只保留矩形内部的
		if (!(code0 | code1))
		{
			accept=1;
			done=1;
		} 
		else
		{
			if (code0 != 0)
			{
				codeout =code0;
			} 
			else
			{
				codeout =code1;
			}

			if (codeout & LEFT_EDGE)
			{
				y=y0+(y1-y0)*(rect.xmin-x0)/(x1-x0);
				x=(float)rect.xmin;
			} 
			else
			{
				if (codeout &RIGHT_EDGE)
				{
					y=y0+(y1-y0)*(rect.xmax-x0)/(x1-x0);
					x=(float)rect.xmax;
				} 
				else
				{
					if (codeout & BOTTOM_EDGE)
					{
						x=y0+(x1-x0)*(rect.ymin-y0)/(y1-y0);
						y=(float)rect.ymin;
					} 
					else
					{
						if (codeout & TOP_EDGE)
						{
							x=x0+(x1-x0)*(rect.ymax-y0)/(y1-y0);
							y=(float)rect.ymax;
						}
					}
				}
			}

			if (codeout == code0)
			{
				x0=x;
				y0=y;
				code0=CompCode(x0,y0,rect);
			} 
			else
			{
				x1=x;
				y1=y;
				code1=CompCode(x1,y1,rect);
			}
			
			//直线和矩形不相交，但是划直线的两点在矩形不同侧，这时应去掉。
			if((times<=3) && (code0 & code1))
			{
				x0=x1;
				y0=y1;
				done=1;
				accept=1;
			}
		}
	}


	if (accept)
	{
		LineGL(x0,y0,x1,y1);
	}

	return accept;
}

void myDisplay()
{
	glClear(GL_COLOR_BUFFER_BIT);
	glColor3f(1.0f,0.0f,0.0f);
	glRectf(rect.xmin,rect.ymin,rect.xmax,rect.ymax);

	LineGL(x0,y0,x1,y1);

	glFlush();
}

void Init()
{
	glClearColor(0.0,0.0,0.0,0.0);
	glShadeModel(GL_FLAT);

	rect.xmin =100;
	rect.xmax =300;
	rect.ymin=100;
	rect.ymax=300;

	x0=0;
	y0=650;
	x1=650;
	y1=0;
}

void Reshape(int w,int h)
{
	glViewport(0,0,(GLsizei)w,(GLsizei)h);
	glMatrixMode(GL_PROJECTION);
	glLoadIdentity();
	gluOrtho2D(0.0,(GLdouble)w,0.0,(GLdouble)h);
}

//按键盘上字母c裁剪，字母r恢复原状，字母x退出。
void keyboard(unsigned char key,int x,int y)
{
	switch(key)
	{
	case 'c':
		cohensutherlandlineclip(rect,x0,y0,x1,y1);
		glutPostRedisplay();
		break;
	case 'r':
		Init();
		glutPostRedisplay();
		break;
	case 'x':
		exit(0);
		break;
	default:
		break;
	}
}

int main(int argc,char* argv[])
{
	glutInit(&argc,argv);
	glutInitDisplayMode(GLUT_RGB | GLUT_SINGLE);
	glutInitWindowPosition(100,100);
	glutInitWindowSize(640,480);
	glutCreateWindow("裁剪");

	Init();
	glutDisplayFunc(myDisplay);
	glutReshapeFunc(Reshape);
	glutKeyboardFunc(keyboard);
	glutMainLoop();
	return 0;
}