DDA circle drawing algorithm

ALGORITHM

1 .        read the radius r ,of the circle and calculate value of E

            2^n-1<=r<2ⁿ

            E=2^-n

2  .       start_x=0

             start_y=r

3          x1=start_x

            y1=start_y

4                      do

             {

                        x2=x1+Ey1

                        y2=y1-Ex2

                        [x2 represents xn+1 and x1 presents xn]

                         plot (int(x2),int(y2))

                          x1=x2;

                         y1=y2;

                        [reinitialize the current point]

             }while (y1-start_y)<E or (start_x-x1)>E

                        [check if the current  point is the starting  point or not .if current point is                                                                 not starting point repeat step 4; otherwise stop]

5.                     Stop. 

                                                C Program

 

#include<stdio.h>

#include<stdlib.h>

#include<graphics.h>

#include<math.h>

void circl(int xc,int yc,int rad)

{

int x=0,y=rad,p=1-rad;

void plot(int,int,int,int);

plot(xc,yc,x,y);

while(x<y)

{

x++;

if(p< 0)

p+=2*x+1;

else

{

y--;

p+=2*(x-y)+1;

}

plot(xc,yc,x,y);

}

}

void plot(int xc,int yc,int x,int y)

{

putpixel(xc+x,yc+y,1);

putpixel(xc-x,yc+y,1);

putpixel(xc+x,yc-y,1);

putpixel(xc-x,yc-y,1);

putpixel(xc+y,yc+x,1);

putpixel(xc-y,yc+x,1);

putpixel(xc+y,yc-x,1);

putpixel(xc-y,yc-x,1);

}

 void main()

 {

int xc,yc,r;

int gdriver=DETECT,gmode;

initgraph(&gdriver,&gmode,"T:\\BGI");

printf("Enter the center coordinates and radius\n");

scanf("%d%d%d",&xc,&yc,&r);

setbkcolor(BLACK);

setcolor(WHITE);

circl(xc,yc,r);

getch();

closegraph();

 }