anchor.diff:    wp = 1.0 / ((m[3] * x) + (m[7] * y) + m[15]);
     xp = ((m[0] * x) + (m[4] * y) + m[12]) * wp;
     yp = ((m[1] * x) + (m[5] * y) + m[13]) * wp;
  -  print('$xp,$yp');
     minX = math.min(minX, xp);
     maxX = math.max(maxX, xp);
     minY = math.min(minY, yp);
  
positive.code:   double wp = 1.0 / ((m[3] * x) + (m[7] * y) + m[15]);
    double xp = ((m[0] * x) + (m[4] * y) + m[12]) * wp;
    double yp = ((m[1] * x) + (m[5] * y) + m[13]) * wp;
    print('$xp,$yp');
    minX = math.min(minX, xp);
    maxX = math.max(maxX, xp);
    minY = math.min(minY, yp);
  
negative.code:   wp = 1.0 / ((m[3] * x) + (m[7] * y) + m[15]);
    xp = ((m[0] * x) + (m[4] * y) + m[12]) * wp;
    yp = ((m[1] * x) + (m[5] * y) + m[13]) * wp;
    minX = math.min(minX, xp);
    maxX = math.max(maxX, xp);
    minY = math.min(minY, yp);
  