Module Webby::Helpers::TexImgHelper
In: lib/webby/helpers/tex_img_helper.rb

Methods

tex2img  

Public Instance methods

The +tex2img+ method converts a a section of mathematical TeX script into an image and embeds the resulting image into the page. The TeX engine must be installed on your system along with the ImageMagick convert program.

Options can be passed to the TeX engine via attributes in the +tex2img+ method.

   <% tex2img( "wave_eq", :path => "images", :alt => "wave equation" ) do -%>
     $\psi_{tot}(x,-t_0,r) = \frac{1}{(2\pi)^2} \int\!\!\!\int
     \tilde\Psi_{tot}\left(k_x,\frac{c}{2}\sqrt{k_x^2 + k_r^2},r=0\right)$
   <% end -%>

The supported TeX options are the following:

   :path         : where generated images will be stored
                   [default is "/"]
   :type         : the type of image to generate (png, jpeg, gif)
                   [default is png]
   :bg           : the background color of the image (color name,
                   TeX color spec, or #aabbcc) [default is white]
   :fg           : the foreground color of the image (color name,
                   TeX color spec, or #aabbcc) [default is black]
   :resolution   : the desired resolution in dpi (HxV)
                   [default is 150x150]

   the following options are passed as-is to the generated <img /> tag
   :style    : CSS styles to apply to the <img />
   :class    : CSS class to apply to the <img />
   :id       : HTML identifier
   :alt      : alternate text for the <img />

[Source]

# File lib/webby/helpers/tex_img_helper.rb, line 59
  def tex2img( *args, &block )
    opts = args.last.instance_of?(Hash) ? args.pop : {}
    name = args.first
    raise 'TeX graphics must have a name' if name.nil?

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

    defaults = ::Webby.site.tex2img
    path = opts.getopt(:path, defaults.path)
    type = opts.getopt(:type, defaults.type)
    bg   = opts.getopt(:bg, defaults.bg)
    fg   = opts.getopt(:fg, defaults.fg)
    res  = opts.getopt(:resolution, defaults.resolution)

    # fix color escaping
    fg = fg =~ %r/^[a-zA-Z]+$/ ? fg : "\"#{fg}\""
    bg = bg =~ %r/^[a-zA-Z]+$/ ? bg : "\"#{bg}\""

    # 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

    # generate the image using convert -- 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?

    tex = "\\\\nonstopmode\n\\\\documentclass{article}\n\\\\usepackage[T1]{fontenc}\n\\\\usepackage{amsmath,amsfonts,amssymb,wasysym,latexsym,marvosym,txfonts}\n\\\\usepackage[pdftex]{color}\n\\\\pagestyle{empty}\n\\\\begin{document}\n\\\\fontsize{12}{24}\n\\\\selectfont\n\\\\color{white}\n\\\\pagecolor{black}\n\\\\[\n\#{text}\n\\\\]\n\\\\end{document}\n"
    tex.gsub!(%r/\n\s+/, "\n").strip!

    # make a temporarty directory to store all the TeX files
    pwd = Dir.pwd
    tmpdir = ::Webby::MkTemp.mktempdir('tex2img_XXXXXX')

    begin
      Dir.chdir(tmpdir)
      File.open('out.tex', 'w') {|fd| fd.puts tex}
      dev_null = test(?e, "/dev/null") ? "/dev/null" : "NUL:"

      %x[pdflatex -interaction=batchmode out.tex &> #{dev_null}]

      convert =  "\\( -density #{res} out.pdf -trim +repage \\) "
      convert << "\\( -clone 0 -negate -background #{fg} -channel A -combine \\) "
      convert << "\\( -clone 0 -background #{bg} -channel A -combine \\) "
      convert << "-delete 0 -compose dst-over -composite #{out_file}"
      %x[convert #{convert} &> #{dev_null}]
    ensure
      Dir.chdir(pwd)
      FileUtils.rm_rf(tmpdir) if test(?e, tmpdir)
    end

    # generate the HTML img tag to insert back into the document
    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 << " />\n"

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

    concat_erb(out, block.binding)
    return
  end

[Validate]