I'm sorry if that's not so obvious to me. The user wants to click and drag a zoom region (that might have a max vertical or horizontal extent depending on the modifier). That sure sounds like a rectangle selection to me and not a point selection, but maybe I'm not understanding what a point selection means. The picker in the bode example doesn't look like what I'm after because it isn't zooming on a region selected by the user.

I have read the docs on mouse/key events but I have found nothing that describes how to add a shift modifier to the mouse drag event and how to hook in code that will make the rectangle maximize in vertical or horizontal directions. I tried implementing widgetMouseMoveEvent in my zoomer (which derives from QwtPlotZoomer). I can get the modifier and have tried creating a new event based on the original one but with changed position and no modifier and then I call QwtPlotZoomer::widgetMouseMoveEvent(event). But this doesn't work. Even if all I do is create a copy of the event (using the copy constructor), it still doesn't work, so obviously there is something in the event that isn't getting copied.

Thanks.