Possible to create a n"inlet" in a dialog?

I designed some dialog windows in photoshop for our application. This design features a small triangle inlet in the mainwindow (or widget, or dialog....).

See my quickly made example:
http://i.imgur.com/JLlwmio.jpg
(note, this is NOT the design)


Is it possible to create such an effect within QT?

yes. try QWidget::setMask

If you remove window decorations then most likely yes.