[Qt-interest] How to make a widget show as a animation mode?

[Kermit Mei]

Hello, I find want to implement a widget shown in a MainWindow.
Before the widget be shown on MainWindow, it must do some animation act,
for example, move from left to right, or up to down, move a roll or
shake, just like the Buttons on qt-demo program shows.

I had looked qtdemo's source code, but I haven't found the base
principle, Use  QGraphicsItemAnimation?  I hope you can give me some
hints to help me understand it.

Thanks:P
Fun!