Attempt to use codecogs for Latex in RSS

Refs #50

_plugins/codecogs.rb

@@ -0,0 +1,27 @@
+# Title: codecogs plugin
+# Author: Carl Boettiger, @cboettig
+# License: MIT
+#
+# A simple filter to replace mathjax-latex syntax with images of the
+# equations as rendered by codecogs.  This is useful to filter content
+# entered into the atom feed, where javascript and css-based rendering
+# of equations won't work.
+
+# Credits to Noam Ross http://www.noamross.net/blog/2012/4/4/math-in-rss-feeds.html for inspiring this approach and to
+# helpful folks on SO for the regexpr: http://stackoverflow.com/questions/13166112/ruby-regexp-to-replace-equations
+
+# Example use:
+#
+# {{ post.content | codecogs }}
+#
+
+module Jekyll
+  module ImageFilter
+    def codecogs(input)
+#    puts "generating images for equations in RSS feed with codecogs.rb"
+    desired = input.gsub(/\\\[\s*(.*?)\s*\\\]/, "<div style=\"text-align:center;\"><img src=\"http://latex.codecogs.com/png.latex?\\1\" alt=\"\\1\" /></div>")
+    desired.gsub(/\\\(\s*(.*?)\s*\\\)/, "<img src=\"http://latex.codecogs.com/png.latex?\\1\\inline\"/>")
+    end
+  end
+end
+Liquid::Template.register_filter(Jekyll::ImageFilter)

feed.xml

@@ -5,17 +5,17 @@ layout: null
 <rss version="2.0" xmlns:atom="http://www.w3.org/2005/Atom">
     <channel>
         <title>{{ site.name | xml_escape }}</title>
-        <description>{% if site.description %}{{ site.description | xml_escape }}{% endif %}</description>  
+        <description>{% if site.description %}{{ site.description | xml_escape }}{% endif %}</description>
         <link>{{ site.url }}</link>
         <atom:link href="{{ site.url }}/feed.xml" rel="self" type="application/rss+xml" />
         {% for post in site.posts limit:10 %}
         <item>
             <title>{{ post.title | xml_escape }}</title>
-            <description>{{ post.content | xml_escape }}</description>
+            <description>{{ post.content | codecogs | xml_escape }}</description>
             <pubDate>{{ post.date | date: "%a, %d %b %Y %H:%M:%S %z" }}</pubDate>
             <link>{{ site.url }}{{ post.url }}</link>
             <guid isPermaLink="true">{{ site.url }}{{ post.url }}</guid>
         </item>
         {% endfor %}
     </channel>
-</rss>
+</rss>