Adding graphs to posts in Nikola


nikola 

Update as of April 2019

This blog no longer runs on Nikola so the embedded examples do not work anymore. The method described in the post is still valid though.


I really like to teach, try to explain things in a simple manner. There is often no better way of making an explanation than visualizing it. The problem is that I really can’t draw, especially on a computer. Wouldn’t it be awesome if I could make the computer draw for me ? I found out that, unsurprisingly, there is a software for that already. The one I like is called mermaid - it renders a simple text description of a graph or diagram into an html representation. Can look something like this.

<div class="mermaid">
  graph TB subgraph one a1-->a2 end subgraph two b1-->b2 end subgraph three
  c1-->c2 end c1-->a2
</div>

This blog is rendered by Nikola hence I would like to show you how I’ve added mermaid support to my Nikola installation. I use USE_BUNDLES = False in conf.py as for it gives me more control and is more HTTP/2 friendly. With that disabled I can include mermaid’s style and js files like so (also in conf.py):

EXTRA_HEAD_DATA = """
<link rel="stylesheet" type="text/css" href="/assets/css/fontawesome.css">
<link rel="stylesheet" type="text/css" href="/assets/css/titillium.css">
<link rel="stylesheet" type="text/css" href="/assets/css/mermaid.forest.css">
"""

BODY_END = """
<script src="/assets/js/mermaid.js"></script>
<script>mermaid.initialize({startOnLoad:true, cloneCssStyles: false});</script>
"""

Where do all these files come from though ? In my case, I have a custom theme, based on zen called zen-cyplo. The assets in the sources are located under themes/zen-cyplo/assets/. Oh, and cloneCssStyles: false is there as the default of true made the different css styles on my blog clash. Finally, to use mermaid in the post do (for reStructured Text):

<div class="mermaid">
  graph TB subgraph one a1-->a2 end subgraph two b1-->b2 end subgraph three
  c1-->c2 end c1-->a2
</div>

You can click on source button located below the title of this post to see it in action. If you are interested in the build process and how all these come together - the complete sources for this blog are hosted under https://github.com/cyplo/blog

nikola 

See also