Just a very simple QWidget based app. On a Macbook Pro with retina display, in QtCreator, I created a QToolButton on a widget. Then added a resource file called "icon@2x.png" as its icon. The png file is 80x80, I named it with "@2x" as required by Qt. I set the icon size for the QToolButton as 40x40. Everything looks fine in Qt Creator designer. The icon on the QToolButton looks nice and crispy clear on the retina display. But when I compile and run the app, the icon looks blurry in the actual running app. How could this happen?