DDA Line

/*

* THIS IS A C PROGRAM THAT IMPLEMENTS DIGITAL DIFFERENCE ANALYZER (DDA) LINE DRAWING ALGORITHM

*/

#include"compgrap.h"

void implementdda(int, int, int, int) ;

int sign(float) ;

int main(void)

{

  int x1, y1, x2, y2 ;

  initialize();                  /* basic initialization */

  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 pixel */

  setfillstyle(1, DARKGRAY) ;

  implementdda(x1, y1, x2, y2) ;   /* drawing approximated straight line by DDA algorithm */

  /* 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 DDA algorithm */

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

{

 int i, length, s1, s2 ;

 float dx, dy, x, y ;

 /* 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 or with slope = +1/-1. We keep provisions for checking whether a straight line will be

  * vertical/horizontal one or if its slope is +1 ot -1 . */

 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 or -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 */

 {

 length = max(abs(x2-x1), abs(y2-y1)) ;

 dx = (float)(x2-x1)/length ;

 dy = (float)(y2-y1)/length ;

 s1 = sign(dx);

 s2 = sign(dy) ;

 x = x1 + 0.5*s1 ;

 y = y1 + 0.5*s2 ;

 i = 1 ;

 while(i<=length)

 {

  plot(floor(x),floor(y));

  x+=dx ;

  y+=dy;

  i++;

 }

 }

}

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

 * positive, negative or zero */

int sign(float a)

{

 return a>0 ? 1:(a<0 ? -1:0) ;

}