GTK+ menu transitions possible?

I'm trying to use GTK+ 2.0 for my GUI, but I'm not sure how I could implement a menu that slides out when a button is clicked. Making a menu disappear/re-appear instantaneously would not be difficult to do as it requires a simple change to the visibility property. This app is being 开发者_开发百科developed on Windows, but I'm also planning to port it over to Linux. So any ideas on how to achieve menu transitions that work on Windows and Linux?

Maybe you can make a menu widget yourself. Last time, I made a menu widget inherited from gtk dialog. You can move the dialog anywhere you want.