code: def recalculate(self):
          
          # recalculate the scene geometry
          scene = self.scene()
          w = self.calculateSceneWidth()
          scene.setSceneRect(0, 0, w, self.height())
          
          # recalculate the item layout
          spacing = self.spacing()
          x = self.width() / 4.0
          y = self.height() / 2.0
          for item in self.items():
              pmap = item.pixmap()
              item.setPos(x, y - pmap.height() / 1.5)
              x += pmap.size().width() + spacing
docs: Recalcualtes the slider scene for this widget.