Write a program to clip a line using Cohen – Sutherland line clipping algorithm.

#include<stdio.h>

#include<conio.h>

#include<graphics.h>

#define ROUND(a)    ( (int) a+0.5 )

#define ACCEPT(a,b) (!(a|b))

#define REJECT(a,b) (a&b)

#define INSIDE(a)   (!a)

#define LEFT   0x1

#define RIGHT  0x2

#define BOTTOM 0x4

#define TOP    0x8

#define TRUE  1

#define FALSE 0

int xMin, xMax, yMin, yMax;

void clip(int, int, int, int);

char encode(int, int);

void  main()

{

   int gdriver = DETECT, gmode;

   int x1,y1,x2,y2;

   initgraph(&gdriver,&gmode,"c:\\tc\\bgi");

   cleardevice();

   clip(x1,y1,x2,y2);

   getch();

   closegraph();

}

char encode(int x, int y)

{

   char code = 0x00;

   if(x < xMin)

         code = code | LEFT;

   if(x > xMax)

         code = code | RIGHT;

   if(y < yMin)

         code = code | BOTTOM;

   if(y > yMax)

         code = code | TOP;

   return(code);

}

void clip(int x1, int y1, int x2, int y2)

{

   char code1, code2;

   int done = FALSE, draw = FALSE;

   float m;

   while( !done )

   {

         code1 = encode(x1,y1);

         code2 = encode(x2,y2);

         if( ACCEPT(code1, code2) )

         {

               done = TRUE;

               draw = TRUE;

         }

         else if( REJECT(code1, code2) )

               done = TRUE;

         else if( INSIDE(code1) )

               swap(x1,y1,x2,y2,code1,code2);

         if( x2 != x1)

               m = (float) (y2 -y1) / (x2 - x1);

         if(code1 & LEFT)

         {

               y1 = (xMin - x1) * m;

               x1 = xMin;

         }

         else if(code1 & RIGHT)

         {

               y1 = (xMax - x1) * m;

               x1 = xMax;

         }

         else if(code1 & BOTTOM)

         {

               y1 = yMin;

               x1 = (yMin - y1) / m;

         }

         else if(code1 & TOP)

         {

               y1 = yMax;

               x1 = (yMax - y1) / m;

         }

   }

   if(draw)

         line( ROUND(x1), ROUND(y1), ROUND(x2), ROUND(y2) );

}