Qt, drawing with floating point coordinates
===

I was reading http://doc-snapshot.qt-project.org/4.8/painting-concentriccircles.html and was confused how you can get more accurate circles on screen without using anti aliasing when the only difference of painting the circle is

     if (floatBased) {
         painter.drawEllipse(QRectF(-diameter / 2.0, -diameter / 2.0,
                                    diameter, diameter));
     } else {
         painter.drawEllipse(QRect(-diameter / 2, -diameter / 2,
                                   diameter, diameter));
     }

Since even the floating point version ends up at the screen at distinct pixels, I don't understand why it doesn't suffer from the "2-1-2-1" pixels distance problem. 

Is the reason of this because we may have different center points for each circle (I noticed a circle that is near on the top-left half to another circle is far from the same circle at the lower-right corner)? If so, would using the following overload of `QPainter` fix the problem with the int version?

    void drawEllipse (const QPoint & center, int rx, int ry)
