C Program for BRESENHAM’S ELLIPSE DRAWING ALGORITHM

 

To draw an ellipse using Bresenham ellipse drawing algorithm.

ALGORITHM:

1.      Start

2.      Initialize the graphics mode.

3.      Get the center point as (x1,y1)

4.      Get the length of semi-major, Semi-minor axes as r1 & r2

5.      calculate t=pi/180

6.      Initialize i=0

7.      compute d= i*t

8.      compute x=x1+y1*sin(d), y=y1+r2cos(d)

9.      plot(x,y)

10.  increment i by 1

11.  Repeat steps 6 to 9 until i<360

 PROGRAM:

#include <stdio.h>

#include <conio.h>

#include <graphics.h>

#include <math.h>

#include <dos.h>

void main()

{

long int d1,d2;

int i,gd=DETECT ,gm,x,y;

long int rx,ry,rxsq,rysq,tworxsq,tworysq,dx,dy;

printf("Enter the x Radius of the ellipse");

scanf("%ld",&rx);

printf("Enter the y Radius of the ellipse");

scanf("%ld",&ry);

initgraph(&gd,&gm," ");

rxsq=rx*rx;

rysq=ry*ry;

tworxsq=2*rxsq;

tworysq=2*rysq;

x=0;

y=ry;

d1=rysq - (rxsq * ry) + (0.25 * rxsq);

dx= tworysq * x;

dy= tworxsq * y;

do

{

  putpixel(200+x,200+y,15);

  putpixel(200-x,200-y,15);

  putpixel(200+x,200-y,15);

  putpixel(200-x,200+y,15);

  if (d1 < 0)

   {

    x=x+1;

    y=y;

     dx=dx + tworysq;

     d1=d1 + dx + rysq;

     }

   else

   {

    x=x+1;

    y=y-1;

    dx= dx + tworysq;

    dy= dy - tworxsq;

    d1= d1 + dx - dy + rysq;

    }

    delay(50);

    }while (dx < dy);

   d2 = rysq * ( x + 0.5) * ( x + 0.5 ) + rxsq * (y - 1) * (y-1) - rxsq * rysq;

    do

    {

     putpixel(200+x,200+y,15);

  putpixel(200-x,200-y,15);

  putpixel(200+x,200-y,15);

  putpixel(200-x,200+y,15);

  if (d2 >0)

  {

  x=x;

  y=y-1;

  dy = dy - tworxsq;

  d2 = d2 - dy + rxsq;

  }

  else

  {

  x= x+1;

  y=y-1;

  dy=dy - tworxsq;

  dx= dx + tworysq;

  d2 = d2 + dx -dy + rxsq;

  }

  delay(50);

} while ( y> 0);

getch();

closegraph();

}

Posted in: C / C++ Program,learning