# File lib/bundler/graph.rb, line 20
    def viz(output_file, show_gem_versions = false, show_dependency_requirements = false)
      require 'graphviz'
      populate

      graph_viz = GraphViz::new('Gemfile', {:concentrate => true, :normalize => true, :nodesep => 0.55})
      graph_viz.edge[:fontname] = graph_viz.node[:fontname] = 'Arial, Helvetica, SansSerif'
      graph_viz.edge[:fontsize] = 12

      viz_nodes = {}

      # populate all of the nodes
      nodes.each do |name, node|
        label = name.dup
        label << "\n#{node.version}" if show_gem_versions
        options = { :label => label }
        options.merge!( USER_OPTIONS ) if node.is_user
        viz_nodes[name] = graph_viz.add_node( name, options )
      end

      group_nodes = {}
      @groups.each do |name, dependencies|
        group_nodes[name] = graph_viz.add_node(name.to_s, { :shape => 'box3d', :fontsize => 16 }.merge(USER_OPTIONS))
        dependencies.each do |dependency|
          options = { :weight => 2 }
          if show_dependency_requirements && (dependency.requirement.to_s != ">= 0")
            options[:label] = dependency.requirement.to_s
          end
          graph_viz.add_edge( group_nodes[name], viz_nodes[dependency.name], options )
        end
      end

      @groups.keys.select { |group| group != :default }.each do |group|
        graph_viz.add_edge( group_nodes[group], group_nodes[:default], { :weight => 2 } )
      end

      viz_nodes.each do |name, node|
        nodes[name].dependencies.each do |dependency|
          options = { }
          if nodes[dependency.name].is_user
            options[:constraint] = false
          end
          if show_dependency_requirements && (dependency.requirement.to_s != ">= 0")
            options[:label] = dependency.requirement.to_s
          end

          graph_viz.add_edge( node, viz_nodes[dependency.name], options )
        end
      end

      graph_viz.output( :png => output_file )
    end