title: QDialog with transparent background color
body: <p>I want to make the background of a <code>QDialog</code> transparent so that I can see through the window. I'm asking because I want to use a semi-transparent background image that creates a "rounded corner window" illusion. Using <code>setOpacity</code> is not an option for me because I want all widgets to remain at full opacity.</p>
  
  <p>Is there a way to achieve this without resorting to native OS APIs?</p>