When the user resizes a window by dragging a corner or edge of the
window I want to be able to control how big or small the resulting
window is. In the worst case I have to wait until the user releases
the mouse and then I can resize the window...but that's not what I
want. I want to control the minimum and maximum size of the window
*as the user drages the border*.

I know it's easy to do this in native Windows programming.