title: Converting mouse coordinates to label coordinates in Qt
body: <p>I'm in trouble with such issue: 
  I need to select some area with rect on my label, I'm using QRubberBand to do this, but there is one problem: I need to know coordinates of current rect on my label, so I'm in trouble with it, because mouseEvent->pos() give coordinates which starts with top left corner on mainWindow border, moreover i've rotate standard coords on label (from top left to bottom left corner, as we paint them usually). 
  <br>Anybody knows how can I do this translation? </p>