How to create a widget that independent from any window?

[Ibrahim]

I want to create a widget but it doesn't dependent with a window. Here is an example:

You see the image that we can select a region that want to record the screen. The region independent from any window. This is just an example. I ask all widgets that independent any window. How can I do it? Can I select a region from desktop screen with widget that independent window?
Thanks.

[jsulm]

@Ibrahim See https://stackoverflow.com/questions/3948441/how-to-remove-the-window-border-containing-minimize-maximize-and-close-buttons
You can create a window with

setWindowFlags( Qt::CustomizeWindowHint );