code: def __draw_block(ax, pair, block, density_scale):
          
          max_corner, min_corner = bang_visualizer.__get_rectangle_description(block, pair)
  
          belong_cluster = block.get_cluster() is not None
  
          if density_scale != 0.0:
              density_scale = bang_visualizer.__maximum_density_alpha * block.get_density() / density_scale
  
          face_color = matplotlib.colors.to_rgba('blue', alpha=density_scale)
          edge_color = matplotlib.colors.to_rgba('black', alpha=1.0)
  
          rect = patches.Rectangle(min_corner, max_corner[0] - min_corner[0], max_corner[1] - min_corner[1],
                                   fill=belong_cluster,
                                   facecolor=face_color,
                                   edgecolor=edge_color,
                                   linewidth=0.5)
          ax.add_patch(rect)
docs: !
          @brief Display BANG-block on the specified ax.
  
          @param[in] ax (Axis): Axis where block should be displayed.
          @param[in] pair (tuple): Pair of coordinate index that should be displayed.
          @param[in] block (bang_block): BANG-block that should be displayed.
          @param[in] density_scale (double): Max density to display density of the block by appropriate tone.