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readme2tex

Renders LaTeX for Github Readmes

$$
\huge\text{Hello \LaTeX}
$$

\begin{tikzpicture}
\newcounter{density}
\setcounter{density}{20}
    \def\couleur{blue}
    \path[coordinate] (0,0)  coordinate(A)
                ++( 60:6cm) coordinate(B)
                ++(-60:6cm) coordinate(C);
    \draw[fill=\couleur!\thedensity] (A) -- (B) -- (C) -- cycle;
    \foreach \x in {1,...,15}{%
        \pgfmathsetcounter{density}{\thedensity+10}
        \setcounter{density}{\thedensity}
        \path[coordinate] coordinate(X) at (A){};
        \path[coordinate] (A) -- (B) coordinate[pos=.15](A)
                            -- (C) coordinate[pos=.15](B)
                            -- (X) coordinate[pos=.15](C);
        \draw[fill=\couleur!\thedensity] (A)--(B)--(C)--cycle;
    }
\end{tikzpicture}

Make sure that pdflatex is installed on your system.


readme2tex is a Python script that "texifies" your readme. It takes in Github Markdown and replaces anything enclosed between dollar signs with rendered $\text{\LaTeX}$.

In addition, while other Github TeX renderers tend to give a jumpy look to the compiled text,

readme2tex ensures that inline mathematical expressions are properly aligned with the rest of the text to give a more natural look to the document. For example, this formula $\frac{dy}{dx}$ is preprocessed so that it lines up at the correct baseline for the text. This is the one salient feature of this package compared to the others out there.

Installation

Make sure that you have Python 2.7 or above and pip installed. In addition, you'll need to have the programs latex and dvisvgm on your PATH. In addition, you'll need to pre-install the geometry package in $\text{\LaTeX}$.

To install readme2tex, you'll need to run

sudo pip install readme2tex

or, if you want to try out the bleeding edge,

git clone https://github.com/leegao/readme2tex
cd readme2tex
python setup.py develop

To compile INPUT.md and render all of its formulas, run

python -m readme2tex --output README.md INPUT.md

If you want to do this automatically for every commit of INPUT.md, you can use the --add-git-hook command once to set up the post-commit hook, like so

git stash --include-untracked
git branch svgs # if this isn't already there

python -m readme2tex --output README.md --branch svgs --usepackage tikz INPUT.md --add-git-hook

# modify INPUT.md

git add INPUT.md
git commit -a -m "updated readme"

git stash pop

and every git commit that touches INPUT.md from now on will allow you to automatically run readme2tex on it, saving you from having to remember how readme2tex works. The caveat is that if you use a GUI to interact with git, things might get a bit wonky. In particular, readme2tex will just assume that you're fine with all of the changes and won't prompt you for verification like it does on the terminal.

You can uninstall the hook by deleting .git/hooks/post-commit. See python -m readme2tex --help for a list of what you can do in readme2tex.

Examples:

Here's a display level formula

$$
\frac{n!}{k!(n-k)!} = {n \choose k}
$$

The code that was used to render this formula is just

$$
\frac{n!}{k!(n-k)!} = {n \choose k}
$$

Note: you can escape $ so that they don't render.

Here's an inline formula.

It is well known that if $ax^2 + bx + c =0$, then $x = \frac{-b \pm \sqrt{b^2- 4ac}}{2a}$.

The code that was used to render this is:

It is well known that if $ax^2 + bx + c = 0$, then $x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a}$.

Notice that the formulas line up with the baseline of the text, even when the height of these two images are different.

Sometimes, you might run into formulas that are bottom-heavy, like $x^2\sum\limits_{3^{n^{n^{n}}}}$. Here, readme2tex can compute the correct offset to align this formula to the baseline of your paragraph of text as well.

Tikz (Courtesy of http://www.texample.net/)

Did you notice the picture at the top of this page? That was also generated by $\text{\LaTeX}$. readme2tex is capable of handling Tikz code. For reference, the picture

\begin{tikzpicture}
\newcounter{density}
\setcounter{density}{20}
    \def\couleur{red}
    \path[coordinate] (0,0)  coordinate(A)
                ++( 60:6cm) coordinate(B)
                ++(-60:6cm) coordinate(C);
    \draw[fill=\couleur!\thedensity] (A) -- (B) -- (C) -- cycle;
    \foreach \x in {1,...,15}{%
        \pgfmathsetcounter{density}{\thedensity+10}
        \setcounter{density}{\thedensity}
        \path[coordinate] coordinate(X) at (A){};
        \path[coordinate] (A) -- (B) coordinate[pos=.15](A)
                            -- (C) coordinate[pos=.15](B)
                            -- (X) coordinate[pos=.15](C);
        \draw[fill=\couleur!\thedensity] (A)--(B)--(C)--cycle;
    }
\end{tikzpicture}

is given by the tikz code

\begin{tikzpicture}
\newcounter{density}
\setcounter{density}{20}
    \def\couleur{red}
    \path[coordinate] (0,0)  coordinate(A)
                ++( 60:6cm) coordinate(B)
                ++(-60:6cm) coordinate(C);
    \draw[fill=\couleur!\thedensity] (A) -- (B) -- (C) -- cycle;
    \foreach \x in {1,...,15}{%
        \pgfmathsetcounter{density}{\thedensity+10}
        \setcounter{density}{\thedensity}
        \path[coordinate] coordinate(X) at (A){};
        \path[coordinate] (A) -- (B) coordinate[pos=.15](A)
                            -- (C) coordinate[pos=.15](B)
                            -- (X) coordinate[pos=.15](C);
        \draw[fill=\couleur!\thedensity] (A)--(B)--(C)--cycle;
    }
\end{tikzpicture}

We can see a few other examples, such as this graphical proof of the Pythagorean Theorem.

\begin{tikzpicture}
\newcommand{\pythagwidth}{3cm}
\newcommand{\pythagheight}{2cm}
  \coordinate [label={below right:$A$}] (A) at (0, 0);
  \coordinate [label={above right:$B$}] (B) at (0, \pythagheight);
  \coordinate [label={below left:$C$}] (C) at (-\pythagwidth, 0);

  \coordinate (D1) at (-\pythagheight, \pythagheight + \pythagwidth);
  \coordinate (D2) at (-\pythagheight - \pythagwidth, \pythagwidth);

  \draw [very thick] (A) -- (C) -- (B) -- (A);

  \newcommand{\ranglesize}{0.3cm}
  \draw (A) -- ++ (0, \ranglesize) -- ++ (-\ranglesize, 0) -- ++ (0, -\ranglesize);

  \draw [dashed] (A) -- node [below] {$b$} ++ (-\pythagwidth, 0)
            -- node [right] {$b$} ++ (0, -\pythagwidth)
            -- node [above] {$b$} ++ (\pythagwidth, 0)
            -- node [left]  {$b$} ++ (0, \pythagwidth);

  \draw [dashed] (A) -- node [right] {$c$} ++ (0, \pythagheight)
            -- node [below] {$c$} ++ (\pythagheight, 0)
            -- node [left]  {$c$} ++ (0, -\pythagheight)
            -- node [above] {$c$} ++ (-\pythagheight, 0);

  \draw [dashed] (C) -- node [above left]  {$a$} (B)
                     -- node [below left]  {$a$} (D1)
                     -- node [below right] {$a$} (D2)
                     -- node [above right] {$a$} (C);
\end{tikzpicture}

How about a few snowflakes?

\begin{center}
\usetikzlibrary{lindenmayersystems}

\pgfdeclarelindenmayersystem{A}{
    \rule{F -> FF[+F][-F]}
}

\pgfdeclarelindenmayersystem{B}{
    \rule{F -> ffF[++FF][--FF]}
}

\pgfdeclarelindenmayersystem{C}{
    \symbol{G}{\pgflsystemdrawforward}
    \rule{F -> F[+F][-F]FG[+F][-F]FG}
}

\pgfdeclarelindenmayersystem{D}{
    \symbol{G}{\pgflsystemdrawforward}
    \symbol{H}{\pgflsystemdrawforward}
    \rule{F -> H[+HG][-HG]G}
    \rule{G -> HF}
}

\tikzset{
    type/.style={l-system={#1, axiom=F,order=3,step=4pt,angle=60},
      blue, opacity=0.4, line width=.5mm, line cap=round   
    },
}

\newcommand\drawsnowflake[2][scale=0.2]{
    \tikz[#1]
    \foreach \a in {0,60,...,300}  {
    \draw[rotate=\a,#2] l-system;
    };
}

\foreach \width in {.2,.4,...,.8} 
{  \drawsnowflake[scale=0.3]{type=A, line width=\width mm} }

\foreach \width in {.2,.4,...,.8} 
{  \drawsnowflake[scale=0.38]{type=A, l-system={angle=90}, line width=\width mm} }    

\foreach \width in {.2,.4,...,.8} 
{  \drawsnowflake[scale=0.3]{type=B, line width=\width mm} }

\foreach \width in {.2,.4,...,.8} 
{  \drawsnowflake{type=B, l-system={angle=30}, line width=\width mm} }

\drawsnowflake[scale=0.24]{type=C, l-system={order=2}, line width=0.2mm}
\drawsnowflake[scale=0.25]{type=C, l-system={order=2}, line width=0.4mm}
\drawsnowflake[scale=0.25]{type=C, l-system={order=2,axiom=fF}, line width=0.2mm}
\drawsnowflake[scale=0.32]{type=C, l-system={order=2,axiom=---fff+++F}, line width=0.2mm}

\drawsnowflake[scale=0.38]{type=D, l-system={order=4,angle=60,axiom=GF}, line width=0.7mm}
\drawsnowflake[scale=0.38]{type=D, l-system={order=4,angle=60,axiom=GfF}, line width=0.7mm}
\drawsnowflake[scale=0.38]{type=D, l-system={order=4,angle=60,axiom=FG}, line width=0.7mm}
\drawsnowflake[scale=0.38]{type=D, l-system={order=4,angle=60,axiom=FfG}, line width=0.7mm}
\end{center}

Usage

python -m readme2tex --output README.md [READOTHER.md]

It will then look for a file called readother.md and compile it down to a readable Github-ready document.

In addition, you can specify other arguments to render.py, such as:

  • --readme READOTHER.md The raw readme to process. Defaults to READOTHER.md.
  • --output README.md The processed readme.md file. Defaults to README_GH.md.
  • --usepackage tikz Addition packages to use during $\text{\LaTeX}$ compilation. You can specify this multiple times.
  • --svgdir svgs/ The directory to store the output svgs. The default is svgs/
  • --branch master Experimental Which branch to store the svgs into, the default is just master.
  • --username username Your github username. This is optional, and render.py will try to infer this for you.
  • --project project The current github project. This is also optional.
  • --nocdn Ticking this will use relative paths for the output images. Defaults to False.
  • --htmlize Ticking this will output a md.html file so you can preview what the output looks like. Defaults to False.
  • --valign Ticking this will use the valign trick (detailed below) instead. See the caveats section for tradeoffs.
  • --rerender Ticking this will force a recompilation of all $\text{\LaTeX}$ formulas even if they are already cached.
  • --bustcache Ticking this will ensure that Github renews its image cache. Github may sometimes take up to an hour for changed images to reappear. This is usually not necessary unless you've made stylistic changes.
  • --add-git-hook Ticking this will generate a post-commit hook for git that runs readme2tex with the rest of the specified arguments after each git commit.
  • --pngtrick Ticking this will generate png files instead of svgs for the formulas.

My usual workflow is to create a secondary branch just for the compiled svgs. You can accomplish this via

python -m readme2tex --branch svgs --output README.md

However, be careful with this command, since it will switch over to the svgs branch without any input from you.

Relative Paths

If you're on a private repository or you want to, for whatever reason, use relative paths to resolve your images, you can do so by using the combination

python -m readme2tex --branch master --nocdn --pngtrick ...

which will output pngs relative to your README.md.

Due to security considerations, Github will not resolve svgs relatively, which means that private repositories will be locked out of the usual svg workflow. Using the --branch master --nocdn --pngtrick combination will get around this restriction.

Troubleshooting

Tikz

If your Tikz drawings don't show up, there's a good chance that you either don't have Ghostscript installed or dvisvgm isn't picking it up for whatever reason. This is most likely to happen on some installations of TexLive on OSX.

Check to see if ps is included in the list when you run

# dvisvgm -l
bgcolor    background color special
color      complete support of color specials
dvisvgm    special set for embedding raw SVG snippets
em         line drawing statements of the emTeX special set
html       hyperref specials
pdf        pdfTeX font map specials
ps         dvips PostScript specials <<<
tpic       TPIC specials

If not, try installing it (either apt-get, yum, or brew). Furthermore, if you are on OSX, make sure to add the following to your ~/.bash_profile

export LIBGS=/usr/local/lib/libgs.dylib

where /usr/local/lib/libgs.dylib is the location where libgs.dylib is installed.

I'm seeing weird formatting from time to time.

Make sure that if you have a <p>...</p> tag somewhere, you leave at least one blank line after the closing tag.

I ran --add-git-hook, but the post-commit hook isn't running after committing.

chmod +x .git/hooks/post-commit

I raw readme2tex and got strange image srcs or got images that won't resolve

Try running readme2tex with

python -m readme2tex ... --username GITHUB_USERNAME  --project PROJECT_NAME

I ran readme2tex and got a traceback somewhere.

Unfortunately, this script still has a few kinks and bugs that I need to iron out. In the mean time, if the pypi releases aren't working for you, you should switch over to the development version to see if the bugs have been squashed:

git clone https://github.com/leegao/readme2tex
cd readme2tex
python setup.py develop

Technical Tricks

How can you tell where the baseline of an image is?

By prepending every inline formula with an anchor. During post-processing, we can isolate the anchor, which is fixed at the baseline, and crop it out. It's super clowny, but it does the job.

Caveats

Github does not allow you to pass in custom style attributes to your images. While this is useful for security purposes, it makes it incredibly difficult to ensure that images will align correctly to the text. readme2tex circumvents this using one of two tricks:

  1. In Chrome, the attribute valign=offset works for img tags as well. This allows us to shift the image directly. Unfortunately, this is not supported within any of the other major browsers, therefore this mode is not enabled by default.
  2. In every (reasonably modern) browser, the align=middle attribute will vertically center an image. However, the definition of the vertical "center" is different. In particular, for Chrome, Firefox, (and probably Safari), that center is the exact middle of the image. For IE and Edge however, the center is about 5 pixels (the height of a lower-case character) above the exact center. Since this looks great for non-IE browsers, and reasonably good on Edge, this is the default rendering method. The trick here is to pad either the top or the bottom of the image with extra spaces until the baseline of the formula is at the center. For most formulas, this works great. However, if you have a tall formula, like $\frac{~}{\sum\limits_{x^{x^{x^{x}}}}^{x^{x^{x^{x}}}} f(x)}$, you'll notice that there might be a lot of slack vertical spacing between these lines. If this is a deal-breaker for you, you can always try the --valign True mode. For most inline formulas, this is usually a non-issue.

How to compile this document

Make sure that you have the tikz and the xcolor packages installed locally.

python -m readme2tex --usepackage "tikz" --usepackage "xcolor" --output README.md --branch svgs

and of course

python -m readme2tex --usepackage "tikz" --usepackage "xcolor" --output README.md --branch svgs --add-git-hook

For the png relative mode, use

python -m readme2tex --usepackage "tikz" --usepackage "xcolor" --output README.md --branch master --nocdn --pngtrick

\begin{tikzpicture}[scale=0.25, line join=bevel]
% \a and \b are two macros defining characteristic
% dimensions of the Penrose triangle.		
\pgfmathsetmacro{\a}{2.5}
\pgfmathsetmacro{\b}{0.9}

\tikzset{%
  apply style/.code     = {\tikzset{#1}},
  triangle_edges/.style = {thick,draw=black}
}

\foreach \theta/\facestyle in {%
    0/{triangle_edges, fill = gray!50},
  120/{triangle_edges, fill = gray!25},
  240/{triangle_edges, fill = gray!90}%
}{
  \begin{scope}[rotate=\theta]
    \draw[apply style/.expand once=\facestyle]
      ({-sqrt(3)/2*\a},{-0.5*\a})                     --
      ++(-\b,0)                                       --
        ({0.5*\b},{\a+3*sqrt(3)/2*\b})                -- % higher point	
        ({sqrt(3)/2*\a+2.5*\b},{-.5*\a-sqrt(3)/2*\b}) -- % rightmost point
      ++({-.5*\b},-{sqrt(3)/2*\b})                    -- % lower point
        ({0.5*\b},{\a+sqrt(3)/2*\b})                  --
      cycle;
    \end{scope}
  }	
\end{tikzpicture}


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