# File lib/webby/helpers/graphviz_helper.rb, line 80
  def graphviz( *args, &block )
    opts = args.last.instance_of?(Hash) ? args.pop : {}

    text = capture_erb(&block)
    return if text.empty?

    # create a temporary file for holding any error messages
    # from the graphviz program
    err = Tempfile.new('graphviz_err')
    err.close

    defaults = ::Webby.site.graphviz
    path = opts.getopt(:path, defaults.path)
    cmd  = opts.getopt(:cmd, defaults.cmd)
    type = opts.getopt(:type, defaults.type)

    # pull the name of the graph|digraph out of the DOT script
    name = text.match(%r/\A\s*(?:strict\s+)?(?:di)?graph\s+([A-Za-z_][A-Za-z0-9_]*)\s+\{/o)[1]

    # see if the user includes any URL or href attributes
    # if so, then we need to create an imagemap
    usemap = text.match(%r/(?:URL|href)\s*=/o) != nil

    # generate the image filename based on the path, graph name, and type
    # of image to generate
    image_fn = path.nil? ? name.dup : ::File.join(path, name)
    image_fn = ::File.join('', image_fn) << '.' << type

    # create the HTML img tag
    out = "<img src=\"#{image_fn}\""

    %w[class style id alt].each do |atr|
      val = opts.getopt(atr)
      next if val.nil?
      out << " %s=\"%s\"" % [atr, val]
    end

    out << " usemap=\"\##{name}\"" if usemap
    out << " />\n"

    # generate the image map if needed
    if usemap
      IO.popen("#{cmd} -Tcmapx 2> #{err.path}", 'r+') do |io|
        io.write text
        io.close_write
        out << io.read
      end
      GraphvizHelper.error_check(err)
    end

    # generate the image using graphviz -- but first ensure that the
    # path exists
    out_dir = ::Webby.site.output_dir
    out_file = ::File.join(out_dir, image_fn)
    FileUtils.mkpath(::File.join(out_dir, path)) unless path.nil?
    cmd = "#{cmd} -T#{type} -o #{out_file} 2> #{err.path}"

    IO.popen(cmd, 'w') {|io| io.write text}
    GraphvizHelper.error_check(err)

    # put some guards around the output (specifically for textile)
    out = _guard(out)

    concat_erb(out, block.binding)
    return
  end