Converts math formula (written in TeX language) into PNG file via Google Chart API.

texmath2png.rb

# -*- coding: utf-8 -*-
require 'date'
require 'uri'
require 'net/http'

USAGE = <<EOL
  Converts math formula (written in TeX language) into PNG file via Google Chart API.
  USAGE: $ ruby #{__FILE__} "Formula_in_TeX_language"
  ex.) ruby chartapi.rb "x = \\frac{-b\\pm\\sqrt{b^2-4ac}}{2a}"
EOL

class FormulaImage

  # Ref.: Mathematical Formulas - Infographics — Google Developers
  #       https://developers.google.com/chart/infographics/docs/formulas
  ROOT_URL = "https://chart.googleapis.com/chart?cht=tx&chl="

  def initialize( formula )
    @query_url = ROOT_URL + URI.escape(formula, Regexp.new("[^#{URI::PATTERN::UNRESERVED}]"))
    @image = nil
  end

  def fetch
    uri = URI.parse(@query_url)
    http = Net::HTTP.new(uri.host, uri.port)
    http.use_ssl = true
    http.verify_mode = OpenSSL::SSL::VERIFY_NONE
    request = Net::HTTP::Get.new(uri.request_uri)

    resp = http.request(request)

    @image = resp.body
  end

  def save( filename = nil )
    filename = "Formula-#{Time.now.to_datetime}.png" if filename == nil
    File.open( filename, "wb", :encoding => "BINARY" ) do |file|
      file.write( @image )
    end
  end

  def as_img_tag
    "<img src=\"#{@query_url}\" />"
  end

end

if __FILE__ == $0
  if ARGV.length == 0
    puts USAGE
    exit
  end
  formula_image = FormulaImage.new( ARGV[0] )
  formula_image.fetch
  formula_image.save
  puts formula_image.as_img_tag
end