Midpoint Circle algorithm not working for unequal center coordinates

Question

My midpoint circle algorithm C Program is given below:

#include<stdio.h>
#include<conio.h>
#include<graphics.h>
#include<math.h>

void cir(int,int,float);
void main()
{
    int gd=DETECT;
    int gm=DETECT;
    int x1,y1;
    float r;
    initgraph(&gd,&gm,"C:\\TurboC3\\BGI");
    printf("\nenter the cordinates of center: ");
    scanf("%d",&x1);
    scanf("%d",&y1);
    printf("\nenter the radius : ");
    scanf("%f",&r);
    cir(x1,y1,r);
    getch();
    closegraph();
}

void cir(int x1,int y1,float r)
{
    int x,y;
    float d;
    x=0;
    y=r;
    d=1.25-r;
    putpixel(x1+x,y1+y,RED);
    putpixel(y1+y,x1+x,RED);
    putpixel(y1+y,x1-x,RED);
    putpixel(x1+x,y1-y,RED);
    putpixel(x1-x,y1-y,RED);
    putpixel(y1-y,x1-x,RED);
    putpixel(y1-y,x1+x,RED);
    putpixel(x1-x,y1+y,RED);
    while(x<y){

        if(d<0){
            x=x+1;
            d=d+2*x+1;
        }else{
            x=x+1;
            y=y-1;
            d=d+2*(x-y)+1;
        }
        putpixel(x1+x,y1+y,RED);
        putpixel(y1+y,x1+x,RED);
        putpixel(y1+y,x1-x,RED);
        putpixel(x1+x,y1-y,RED);
        putpixel(x1-x,y1-y,RED);
        putpixel(y1-y,x1-x,RED);
        putpixel(y1-y,x1+x,RED);
        putpixel(x1-x,y1+y,RED);
    }
}

When I provide center coordinates as (200,200) the output is a perfect circle but when I provide any other coordinate where (Y<X) example (200,140) the output is not a perfect circle. Please suggest if any changes is needed in my code.

cir function implements midpoint circle algorithm. Does midpoint algorithm only works for equal center coordinates

Are you using Notepad as your code editor? Otherwise I don't see a good reason for such a flat indentation. — Eugene Sh., Sep 12 '17 at 18:49
If the arguments to putpixel() are x, y, color, then you are mixing up x and y in a lot of the calls. — Matt Timmermans, Sep 12 '17 at 19:41

I.Omar · Answer 1 · 2017-09-25T18:06:02.507

0

The result from that is inconsistent as y won't start correctly for any float and d aswell.

y=r;
d=1.25-r;

Why are you using float type in integer based algorithm and with pixel as the unit?

change

d=1.25-r;

to

d=1-r;

and all float type to int type.

as the incrementation is by 1/-1

edited Sep 25 '17 at 18:06

answered Sep 25 '17 at 17:53

I.Omar

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Midpoint Circle algorithm not working for unequal center coordinates

1 Answers1