Integer Bresenham Line

/*

* THIS IS A C PROGRAM THAT IMPLEMENTS INTEGER BRESENHAM'S LINE DRAWING ALGORITHM

*/

#include"compgrap.h"

void modifiedbresenham(int, int, int, int) ;

int sign(int);

void swap(int *,int *);

int main(void)

{

  int x1, y1, x2, y2 ;

  initialize();                  /* basic initialisation */

  printf("\n Enter the coordinates of the first point:  ");

  scanf("%d%d",&x1,&y1) ;

  printf("\n Enter the coordinates of the second point:  ");

  scanf("%d%d",&x2,&y2) ;

  clrscr();

  cleardevice() ;

  /* creating a grid */

  creategrid(DARKGRAY, DARKGRAY) ;

  /* setting shading style and highlight color of a cell */

  setfillstyle(1, DARKGRAY) ;

 

/* drawing approximated straight line by Integer Bresenham Line Rasterisation algorithm */

  modifiedbresenham(x1, y1, x2, y2) ;  

  /* drawing an actual line segment from (x1,y1) to (x2,y2) */

  setcolor(WHITE);

  drawline(x1, y1, x2, y2) ;

 

   getch();

   closegraph();            /* closing the graph */

   return 0;

 }

/* Implementation of Modified Integer Bresenham Line Rasterisation algorithm */

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

{

 int i, x, y, dx, dy, e, s1, s2, inter ;

 /* since drawing straight lines should be very rapid, we skip the overhead of

  * computing the pixels, when the straight line will be an exact horizontal or

  * vertical one. We keep provisions for checking whether a straight line will be

  * vertical or horizontal one. */

 if(y1==y2)         {           /* for a horizontal line */

            x = min(x1, x2);

            y = y1;

            while(x<=max(x1,x2))

            {

                        plot(x,y);

                        x+=1;

        }

 }

 else if(x1==x2)                          {                       /* for a vertical line */

            y = min(y1, y2);

            x = x1;

            while(y<=max(y1,y2))

            {

                        plot(x,y);

                        y+=1;

            }

 }

 else if(abs(x2-x1)==abs(y2-y1)) {                       /* for lines with slopes +1 and -1 */

             x=x1;

             y=y1;

             do

             {

                         plot(x,y);

                         x+=sign(x2-x1);

                         y+=sign(y2-y1);

             }while(x!=x2 && y!=y2);

             plot(x,y);

 }

 else                 {           /* for straight lines with other slopes */

  x = x1 ;

  y = y1 ; 

  s1 = sign(x2-x1);

  s2 = sign(y2-y1);

  dx = abs(x2 - x1) ;

  dy = abs(y2 - y1) ;

  if(dy>dx) {

              swap(&dx,&dy) ;

              inter = 1;

  }

  else

              inter = 0;

  e = 2*dy - dx ;

  for(i=1; i<=dx; i++)     {

              plot(x,y);

              while(e>=0)    {

                          if(inter==1)

                                      x+=s1;

                          else

                                      y+=s2;

                          e-=2*dx;

              }

              if(inter==1)

                          y+=s2;

              else

                          x+=s1;

              e+=2*dy ;

  }

 }

}

/* function returns +1, -1 or 0 according as the argument is

 * positive, negative or zero */

int sign(int a)

{

 return a>0 ? 1:(a<0 ? -1:0) ;

}

void swap(int *a, int *b)

{

            int temp = *a;

            *a = *b;

            *b = temp;

}