code: def html_output_graph(self, node):
      
      graph = node['graph']
      parts = node['parts']
  
      graph_hash = get_graph_hash(node)
      name = "inheritance%s" % graph_hash
      path = '_images'
      dest_path = os.path.join(setup.app.builder.outdir, path)
      if not os.path.exists(dest_path):
          os.makedirs(dest_path)
      png_path = os.path.join(dest_path, name + ".png")
      path = setup.app.builder.imgpath
  
      # Create a mapping from fully-qualified class names to URLs.
      urls = {}
      for child in node:
          if child.get('refuri') is not None:
              urls[child['reftitle']] = child.get('refuri')
          elif child.get('refid') is not None:
              urls[child['reftitle']] = '#' + child.get('refid')
  
      # These arguments to dot will save a PNG file to disk and write
      # an HTML image map to stdout.
      image_map = graph.run_dot(['-Tpng', '-o%s' % png_path, '-Tcmapx'],
                                name, parts, urls)
      return ('<img src="%s/%s.png" usemap="#%s" class="inheritance"/>%s' %
              (path, name, name, image_map))
docs: Output the graph for HTML.  This will insert a PNG with clickable
      image map.