Creat Ellipsis

[RedCali]

// portted the algorithm found at
// http://homepage.smc.edu/kennedy_john/belipse.pdf
// by John Kennedy

  long X, Y;
  long XChange, YChange;
  long EllipseError;
  long TwoASquare,TwoBSquare;
  long StoppingX, StoppingY;
  TwoASquare = 2*XRadius*XRadius;
  TwoBSquare = 2*YRadius*YRadius;
  X = XRadius;
  Y = 0;
  XChange = YRadius*YRadius*(1-2*XRadius);
  YChange = XRadius*XRadius;
  EllipseError = 0;
  StoppingX = TwoBSquare*XRadius;
  StoppingY = 0;

  while ( StoppingX >=StoppingY ) //first set of points,y'>-1
  {
    Plot4EllipsePoints(CX,CY,X,Y,color); 
    Y++;
    StoppingY=StoppingY+ TwoASquare;
    EllipseError = EllipseError+ YChange;
    YChange=YChange+TwoASquare;
    if ((2*EllipseError + XChange) > 0 ) {
      X--;
      StoppingX=StoppingX- TwoBSquare;
      EllipseError=EllipseError+ XChange;
      XChange=XChange+TwoBSquare;
    }
  }
  //{ first point set is done; start the 2nd set of points }

  Y = YRadius;
  X = 0;
  YChange = XRadius*XRadius*(1-2*YRadius);
  XChange = YRadius*YRadius;
  EllipseError = 0;
  StoppingY = TwoASquare*YRadius;
  StoppingX = 0;
  while ( StoppingY >=StoppingX ) //{2nd set of points, y'< -1}
  {
    Plot4EllipsePoints(CX,CY,X,Y,color); 
    X++;
    StoppingX=StoppingX + TwoBSquare;
    EllipseError=EllipseError+ XChange;
    XChange=XChange+TwoBSquare;
    if ((2*EllipseError + YChange) > 0 ) {
      Y--;
      StoppingY=StoppingY- TwoASquare;
      EllipseError=EllipseError+ YChange;
      YChange=YChange+TwoASquare;
    }
  }
}; //{procedure PlotEllipse}

void Plot4EllipsePoints(long CX,long  CY, long X, long Y, int color){
  GLCD.SetDot(CX+X, CY+Y, color); //{point in quadrant 1}
  GLCD.SetDot(CX-X, CY+Y, color); //{point in quadrant 2}
  GLCD.SetDot(CX-X, CY-Y, color); //{point in quadrant 3}
  GLCD.SetDot(CX+X, CY-Y, color); //{point in quadrant 4}
}

[RedCali]

https://github.com/thegeek82000/openGLCD/blob/master/glcd.cpp