title: What is the difference between a QWindow and QWidget
body: <p>The Qt 5.0 provides a new <code>QWindow</code> class. While the documentation on this class is quite comprehensive, I am failing to see how exactly the <code>QWindow</code> is different from the <code>QWidget</code> class, and in which cases you would prefer the former. Both provide a handy way of visualising all sorts of things to the screen, both can use <code>QPainter</code> for drawing, and both have a way to interact with OpenGL. </p>
  
  <p>In the <a href="http://qt-project.org/doc/qt-5.0/qtgui/qwindow.html#details">API description</a>, it says that:</p>
  
  <blockquote>
    <p>An application will typically use QWidget or QQuickView for its UI, and not QWindow directly. </p>
  </blockquote>
  
  <p>So that doesn't seem to be an advantage for the window. Moreover, it states:</p>
  
  <blockquote>
    <p>Windows can potentially use a lot of memory. A usual measurement is width times height times color depth. A window might also include multiple buffers to support double and triple buffering, as well as depth and stencil buffers. </p>
  </blockquote>
  
  <p>Which doesn't seem to be in favour of using the <code>QWindow</code>. So in what cases would you use it?</p>