Module: Webby::Helpers::TexImgHelper

Defined in:
lib/webby/helpers/tex_img_helper.rb

Instance Method Summary collapse

Instance Method Details

#tex2img(*args, &block) ⇒ Object

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 />



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# File 'lib/webby/helpers/tex_img_helper.rb', line 39

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 = <<-TEX
    \\nonstopmode
    \\documentclass{article}
    \\usepackage[T1]{fontenc}
    \\usepackage{amsmath,amsfonts,amssymb,wasysym,latexsym,marvosym,txfonts}
    \\usepackage[pdftex]{color}
    \\pagestyle{empty}
    \\begin{document}
    \\fontsize{12}{24}
    \\selectfont
    \\color{white}
    \\pagecolor{black}
    \\[
    #{text}
    \\]
    \\end{document}
  TEX
  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