bool alarge = _mB < _mA;

int a = alarge ? _mB :_mA;
int b = alarge ? _mA :_mB;
int aa = a*a;
int bb = b*b;

int d2 = 0;
int d1 = 4*bb - 4*aa*b + aa;

int x = 0;
int y = b;

int deltaE = 12*bb;
int deltaSE1 = 12*bb + 8*aa - 8*aa*b;
int deltaSE2 =8*bb + 12*aa - 8*aa*b;
int deltaS = 12*aa - 8*aa*b;

int deltaSQEtoE = 8*bb;
int deltaSQEtoSE1 = 8*bb;
int deltaSQEtoSE2 = 8*bb;

int deltaSQSE1toE = 8*bb;
int deltaSQSE1toSE1 =8*bb + 8 * aa;
int deltaSQSE1toSE2 =8*bb + 8 * aa;
int deltaSQSE1toS =8 *aa;

int deltaSQSE2toSE2 =8*bb + 8 *aa;
int deltaSQSE2toS = 8 * aa;

int deltaSQStoSE2 = 8 * aa;
int deltaSQStoS = 8 * aa;

int GradX =2 * bb;
int GradY = 2*aa*b - aa;

int deltaEtoGradX = 2*bb;
int deltaSEtoGradX = 2*bb;
int deltaSEtoGradY = -aa;

 //set pixel with symmetry.
 
if (alarge) 
  DrawSymmetricalPoints(y,x,window);
else  
  DrawSymmetricalPoints(x,y,window);
  
while(GradY > GradX && y > 0){ //check if still in quadrant 1
if (d1 < 0)
{ //East
  d1 += deltaE ;
  deltaE += deltaSQEtoE;
  deltaSE1 += deltaSQEtoSE1;
  deltaSE2 += deltaSQEtoSE2;
  GradX += deltaEtoGradX;
}
else
{
   d1 += deltaSE1;
   deltaE += deltaSQSE1toE;
   deltaSE1 += deltaSQSE1toSE1;
   deltaSE2 += deltaSQSE1toSE2;
   deltaS += deltaSQSE1toS;
   GradX += deltaSEtoGradX;
   GradY += deltaSEtoGradY;
   --y;
}

++x;
if (alarge) 
  DrawSymmetricalPoints(y,x,window);
else  
  DrawSymmetricalPoints(x,y,window);

}

//bottom region.

d2 = 4*bb*x*x + 4*bb*x + bb + 4*aa*y*y - 8*aa*y + 4*aa - 4*aa*bb; //guh!

while (y > 0) { //still inside bottom region
if (d2 < 0) { //South east
    d2 += deltaSE2;
    deltaSE2 += deltaSQSE2toSE2;
    deltaS += deltaSQSE2toS;
    ++x;
} else {
    d2 += deltaS;
    deltaSE2 += deltaSQStoSE2;
    deltaS += deltaSQStoS;
}
--y;
if (alarge) 
  DrawSymmetricalPoints(y,x,window);
else  
  DrawSymmetricalPoints(x,y,window);
}