First, take a look at this, which does not answer your question, but does provide some information.
http://qt-project.org/doc/qt-4.8/application-windows.html#window-geometry[
^]
ALthough I have never done this, you may need to write your own class (sub-class the class of interest) and then over-ride the move method (or is that a slot). Yes, it is a method that is called when the class is moved. I did not check the source, but, I expect that given move(x, y) and move(point), one calls the other, but I did not verify this. I am only guessing.
If you know that this will only be moved using the mouse (and not the keyboard), setMouseTracking may help, but I did not look at that in any way.