code: def display_markers(self):
          
          for rect in self.idx_markers:
              self.scene.removeItem(rect)
          self.idx_markers = []
  
          markers = []
          if self.parent.info.markers is not None:
              if self.parent.value('marker_show'):
                  markers = self.parent.info.markers
  
          for mrk in markers:
              rect = QGraphicsRectItem(mrk['start'],
                                       BARS['markers']['pos0'],
                                       mrk['end'] - mrk['start'],
                                       BARS['markers']['pos1'])
              self.scene.addItem(rect)
  
              color = self.parent.value('marker_color')
              rect.setPen(QPen(QColor(color)))
              rect.setBrush(QBrush(QColor(color)))
              rect.setZValue(-5)
              self.idx_markers.append(rect)
docs: Mark all the markers, from the dataset.
  
          This function should be called only when we load the dataset or when
          we change the settings.