/*
SG C Tools 1.2

(C) 1993 Steve Goldsmith
All Rights Reserved

Compiled with HI-TECH C 3.09 (CP/M-80).
*/

#include <hitech.h>
#include <vdc.h>

/* plot circle points in eights.  (y >> 1) and (x >> 1) used to help correct */
/* aspect ratio. */

void circlepointsvdc(int XC, int YC, int X, int Y)
{
  setpixvdc(XC+X,YC+(Y >> 1));
  setpixvdc(XC-X,YC+(Y >> 1));
  setpixvdc(XC+X,YC-(Y >> 1));
  setpixvdc(XC-X,YC-(Y >> 1));
  setpixvdc(XC+Y,YC+(X >> 1));
  setpixvdc(XC-Y,YC+(X >> 1));
  setpixvdc(XC+Y,YC-(X >> 1));
  setpixvdc(XC-Y,YC-(X >> 1));
}

/* draw circle using bresenham's algorithm */

void circlevdc(int XC, int YC, int R)
{
  int P, X, Y;

  X = 0;          /* select first point as (x,y) = (0,r) */
  Y = R;
  P = 3-(R << 1);
  while(X < Y)
  {
    circlepointsvdc(XC,YC,X,Y);
    if(P < 0)
      P += (X << 2)+6;      /* next point (x+1,y) */
    else
    {
      P += ((X-Y) << 2)+10; /* next point (x+1,y-1) */
      Y--;
    }
    X++;
  }
  if(X == Y)
    circlepointsvdc(XC,YC,X,Y);
}