计算机图形学——编码裁剪

版权声明：本文为博主原创文章，未经博主允许不得转载。 https://blog.csdn.net/cd1202/article/details/72887816

要求：利用编码裁剪（Cohen-Sutherland）法裁剪《计算机图形学基础》（第二版）（p183  图6-40）所示线段。

#include<GL/glut.h>  
#include<stdio.h>  
#include<stdlib.h>  
  
#define LEFT_EDGE 1  
#define RIGHT_EDGE 2  
#define BOTTOM_EDGE 4  
#define TOP_EDGE 8  
  
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();                                                
}                                                          
  
struct Rectangle  
{  
    float xmin,xmax,ymin,ymax;  
};  
  
Rectangle rect;  
int x0,y0,x1,y1;  
  
int CompCode(int x,int y,Rectangle 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;
}  
  
int cohensutherlandlineclip(Rectangle rect,int &x0,int &y0,int &x1,int &y1)  
{  
    int accept,done;  
    float x,y;  
    accept=0;  
    done=0;        
    int total=0,flag=0;       
    int code0,code1,codeout;  
    code0=CompCode(x0,y0,rect);  
    printf("code0=%d\n",code0);  
    code1=CompCode(x1,y1,rect);  
    printf("code1=%d\n",code1);  
    do{  
        if(!(code0|code1))       
        {  
            accept=1;  
            done=1;  
        }  
        else if(code0 & code1)  
        {  
            done=1;flag=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=x0+(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);  
            }  
            total++;  
            if(total>2)              
            {  
                done=1;flag=1;  
            }  
        }         
    }while(!done);  
      
    if(accept)          
        LineGL(x0,y0,x1,y1);  
    else  
    {  
        x0=0;y=0;x1=0;y1=0;  
        LineGL(x0,y0,x1,y1);  
    }  
          
    return accept;  
}  
  
void myDisplay()  
{  
    glClear(GL_COLOR_BUFFER_BIT);  
    glColor3f(1.0f,1.0f,1.0f);  
    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=200;  //设置坐标系  原坐标应为（0,0）（2,0）（0,2）（2,2）改为（200,200）（400,200）（200,400）（400,400）
    rect.xmax=400;  
    rect.ymin=200;  
    rect.ymax=400;  
  
    x0=100,y0=0,x1=500,y1=500;    //为方便看，将原坐标（-1，-2）改为（100,0），（3，3）改为（500,500）
}  
  
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);  //定义窗口大小
}  
 
int main(int argc,char *argv[])  
{  
    glutInit(&argc,argv);  
    glutInitDisplayMode(GLUT_RGB|GLUT_SINGLE);  
    glutInitWindowPosition(100,100);  
    glutInitWindowSize(640,480);  
    glutCreateWindow("Cohen-Sutherland");   
    Init();  
    glutDisplayFunc(myDisplay);  
    glutReshapeFunc(Reshape);  
    glutMainLoop();  
      
    return 0;  
}