CG 5 - COHEN-SUTHERLAND ALGORITHM

5. Clip lines using Cohen-Sutherland algorithm

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

#define true 1;
#define false 0;
#define bool int;
double x,y;
int xmin=50,xmax=100,ymin=50,ymax=100;
const int RIGHT=8,LEFT=2,TOP=4,BOTTOM=1;
int outcode0,outcode1,outcodeout,done,accept;

int computeoutcode(double x,double y)
{
  int code=0;
  if(y>ymax)
    code|=TOP;
  else if(y<ymin)
    code|=BOTTOM;
  if(x>xmax)
    code|=RIGHT;
  else if(x<xmin)
    code|=LEFT;
  return code;
}


void LineClip(double x0,double y0,double x1,double y1)
{
  int accept=false;
  int done=false;
  outcode0=computeoutcode(x0,y0);
  outcode1=computeoutcode(x1,y1);
  do{
    if(!(outcode0|outcode1))
    {
      accept=true;
      done=true;
    }
    else if(outcode0&outcode1)
    {
      done=true;
    }
    else
    {
      outcodeout=outcode0?outcode0:outcode1;
      if(outcodeout & TOP)
      {
        x=x0+(x1-x0)*(ymax-y0)/(y1-y0);
        y=ymax;
      }
      else if(outcodeout & BOTTOM)
      {
        x=x0+(x1-x0)*(ymin-y0)/(y1-y0);
        y=ymin;
      }
      else if(outcodeout & RIGHT)
      {
        y=y0+(y1-y0)*(xmax-x0)/(x1-x0);
        x=xmax;
      }
      else
      {
        y=y0+(y1-y0)*(xmin-x0)/(x1-x0);
        x=xmin;
      }
      if(outcodeout==outcode0)
      {
        x0=x;y0=y;outcode0=computeoutcode(x0,y0);
      }
      else
      {
        x1=x;y1=y;outcode1=computeoutcode(x1,y1);
      }
    }
  }while(!done);
  if(accept)
  {
    glPushMatrix();
    glTranslatef(100,100,0);
    glColor3f(1.0,0.0,0.0);
    glBegin(GL_LINE_LOOP);
    glVertex2i(50,50);
    glVertex2i(100,50);
    glVertex2i(100,100);
    glVertex2i(50,100);
    glEnd();
    glColor3f(1.0,0.0,1.0);
    glBegin(GL_LINES);
    glVertex2i(x0,y0);
    glVertex2i(x1,y1);
    glEnd();
    glPopMatrix();
    glFlush();
  }
}

void display()
{
  glClearColor(1,1,1,1);
  glClear(GL_COLOR_BUFFER_BIT);
  glColor3f(1.0,0.0,0.0);
  glBegin(GL_LINE_LOOP);
  glVertex2i(50,50);
  glVertex2i(100,50);
  glVertex2i(100,100);
  glVertex2i(50,100);
  glEnd();
  glColor3f(1.0,0.0,1.0);
  glBegin(GL_LINES);
  glVertex2i(60,20);
  glVertex2i(80,120);
  glVertex2i(80,20);
  glVertex2i(60,120);
  glEnd();
  LineClip(60,20,80,120);
  LineClip(80,20,60,120);
  glFlush();
}

void init()
{
  glMatrixMode(GL_PROJECTION);
  gluOrtho2D(0,300,0,300);
  glMatrixMode(GL_MODELVIEW);
}

int main(int argc,char** argv)
{
  glutInit(&argc,argv);
  glutInitDisplayMode(GLUT_SINGLE|GLUT_RGB);
  glutInitWindowPosition(0,0);
  glutInitWindowSize(500,500);
  glutCreateWindow("Cohen Sutherland line and drawing algorithm");
  init();
  glutDisplayFunc(display);
  glutMainLoop();
}

OUTPUT :

( click on image to zoom )