Syntax highlighting in an HTML presentation

Question

This example shows how to produce PDF slides with syntax highlighting of source code. The example uses beamer and (presumably) pdflatex.

Another example shows syntax coloring for HTML output using htlatex. It's an unpleasant kludge

1. it precludes calling pdflatex on the same LaTeX file
2. one must experiment to find what ectt-1000 maps to
3. one defines colors for css categories, not for code syntax categories

but it works.

The following code revisits this problem and asks to do better.

\documentclass{article}
\usepackage{color}
\usepackage{listings}
\usepackage[T1]{fontenc}

\lstset{
    basicstyle=\ttfamily,
    language=C++,
    keywordstyle=\rmfamily\bfseries,
    commentstyle=\sffamily,
}

\begin{document}

\Css{div.lstlisting .ectt-1000 {font-family: monospace;color:blue}}
\Css{div.lstlisting .ecss-1000 {font-family: monospace;color:green}}
\Css{div.lstlisting .ecbx-1000 {font-family: monospace;color:red}}

\section*{Inserting source code}
\begin{lstlisting}
#include<stdio.h>
#include<iostream>
// A comment
int main(void)
{
    printf("Hello World\n");
    return 0;
}
\end{lstlisting}

\end{document}

Now commenting out the \Css lines and running pdflatex gives one output

and processing with htlatex gives another.

Can you suggest a way to make this kludge more usable by

1. correlating the two "blue" colors—even though ultimately one is defined in LaTeX's color package and the other in HTML,
2. making the \Css definitions point to colors through syntax category,
3. making it possible to process the file with pdflatex while writing/for debugging (htlatex is considerably slower)

?

Answer 1

Correct solution would be to emit html tags around each word in listings, or better, around block of same syntax style, with class attribute set according to syntax style.

Unfortunately, listings source code is complex and I can't figure out how to do that, so I will provide just a some helper to ease the color definition.

Create file textstyle4ht.sty:

\RequirePackage{xcolor}

% extract current color as hexadecimal value
\newcommand\tsf@getColor[1][.]{
    % colorname `.` holds current color
    \extractcolorspec{.}{\tsf@color}
    \expandafter\convertcolorspec\tsf@color{HTML}\tsf@color
    %\tmpcolor
}

% write css color for given css selector
\newcommand\CssColor[1]{%
    % save current color
    \tsf@getColor%
    \Css{#1{color:\#\tsf@color;}}%
}

with this package, we are able to get current color and save it to the css file.

In your example, you have \Css commands in the document. This is a bad style, correct is to provide a config file with tex4ht configurations.

hello.cfg:

\RequirePackage{textstyle4ht}
\Preamble{xhtml}
\begin{document}
\makeatletter
\newcommand\LstCss[2]{%
    \bgroup%
        \csname lst@#2\endcsname%
        \CssColor{#1}%
    \egroup%
}
\makeatother
\LstCss{div.lstlisting .ecbx-1000}{keywordstyle}
\LstCss{div.lstlisting .ecss-1000}{commentstyle}
\LstCss{div.lstlisting .ectt-1000}{basicstyle}
\EndPreamble

in this file, our textstyle4ht package is required, and new \LstCss command is provided. Difference between your version and this one is that real color defined for the style is used. You still need to find corresponding class attribute for each identifier style.

With slightly modified document:

\documentclass{article}
\usepackage{xcolor}
\usepackage{listings}
\usepackage[T1]{fontenc}

\lstset{
    basicstyle=\color{blue}\ttfamily,
    language=C++,
    keywordstyle=\color{red}\rmfamily\bfseries,
    commentstyle=\color{green}\sffamily,
}

\begin{document}

\section*{Inserting source code}
\begin{lstlisting}
#include<stdio.h>
#include<iostream>
// A comment
int main(void)
{
    printf("Hello World\n");
    return 0;
}
\end{lstlisting}

\end{document}

compile with

htlatex filename hello

the result is following: