I think a couple of years ago Jules was looking to implement a method with which we could smoothly give our application windows curved corners (when using non-native titlebars). Does anyone have an idea if there was an update on this?
There’s no really easy way, but you could achieve this with a carefully constructed custom LookAndFeel class. The fillResizableWindowBackground and drawDocumentWindowTitleBar (and the buttons) are a good place to start. You then might also need to make sure all your main (rectangular) components sit within a large enough boarder if your curved corners are large.
I doubt this approach will work on Windows, however.