code: def __init__(self, contour_actors):
      self.__actors = contour_actors
      self.__name = "ROIs"
  
      self.__tab_id = 0
      self.__tab_ui = None
  
      self.__slider_label_opacity = build_label(text="Opacity")
  
      opacity = 1
  
      length = 450
      lw = 3
      radius = 8
      fs = 16
      tt = "{ratio:.0%}"
  
      self.__slider_opacity = ui.LineSlider2D(
          initial_value=opacity,
          max_value=1.0,
          length=length,
          line_width=lw,
          outer_radius=radius,
          font_size=fs,
          text_template=tt,
      )
  
      color_single_slider(self.__slider_opacity)
  
      self.__slider_opacity.on_change = self.__change_opacity
  
file_path: dipy/dipy/viz/horizon/tab/roi.py
imports: from dipy.utils.optpkg import optional_package
  from dipy.viz.horizon.tab import HorizonTab, build_label, color_single_slider
label_desc: Use image node_id 1 to create a new ROIsTab object from inherited base classes: HorizonTab with example: obj = ROIsTab(contour_actors)