The author would benefit greatly from using the appropriate UI components to accomplish his goal instead of kludging a rate limiting mechanism onto his MainWindow's resize implementation.

Instead he could build a graphics scene using QGraphicsScene (http://qt-project.org/doc/qt-5.1/qtwidgets/qgraphicsscene.ht...) with a nice normalized coordinate system which logically represents the namespace size in the SSD on UI elements designed to be rectangles. Adding a view of that scene onto his window is trivial, and as an added bonus he gets the power of Qt's scene graph which will be a boon for both performance (http://blog.qt.digia.com/blog/2013/09/02/new-scene-graph-ren...) and portability. Qt will efficiently manage resizes and draw the scene optimally without overhead associated with a re-purposed widget.

His approach does achieve the desired goal and is probably appropriate in some circumstances, but in this instance he should take a step back and assess if there is a greater fundamental problem with his design.

Is there any good reference to tips on building GUI libraries? I'm doing one for a game and I'm always on the lookout for more tips on architecture and speed optimization.

Qt has layout managers. There is no need for such things.