htlatex and subfigures

Question

Is it possible to have htlatex generate side-by-side subfigures? The mwe tex file

\documentclass{article}

\ifdefined\HCode
\usepackage[compatibility=false]{caption}
\def\pgfsysdriver{pgfsys-tex4ht.def}
\else
\usepackage[]{caption}
\fi
\usepackage{subcaption}
\usepackage[]{graphicx}

\begin{document}

\begin{figure}[htpb]
  \centering
  \begin{subfigure}{0.45\textwidth}
    \centering
    \includegraphics[width=\textwidth]{image1.png}
    \caption{Image 1}
  \end{subfigure}
  \begin{subfigure}{0.45\textwidth}
    \centering
    \includegraphics[width=\textwidth]{image2.png}
    \caption{Image 2}
  \end{subfigure}
  \caption{Main Caption}
\end{figure}

\end{document}

together with the config file

\Preamble{html}

\Configure{@HEAD}{\HCode{<link href="basic.css" rel="stylesheet" type="text/css" />\Hnewline}} 

\ConfigureEnv{figure}
   {\HCode{<div class="figure"\Hnewline>}%
    \bgroup \Configure{float}{\ShowPar}{}{}%
   }
   {\egroup
    \HCode{</div>}\ShowPar
\par}
{}{}

\Css{div.caption {text-align:left;font-size:83\%;text-indent:0em; margin-left:2em; margin-right:2em; }}
\Css{div.caption span.id{font-variant: small-caps; white-space: nowrap; }}
\Css{.figure div.caption{text-align: center;}}
\Css{div.figure{text-align:center;clear:both;overflow:auto;width:100\%;margin-bottom:1em;}}

\begin{document}

\makeatletter
% Various helper functions
% default font size
\newcommand\emwidth{16}
\let\emwidth\f@size
% convert pt to rem
\newcommand\CalcRem[1]{\strip@pt\dimexpr(#1)/\emwidth}

\Configure{graphics*}
{png}
{% we must add the image to the list of output files
  \special{t4ht+@File: \csname Gin@base\endcsname.png}
  \Picture[pict]{\csname Gin@base\endcsname\PictExt
  \space style="width:\CalcRem{\Gin@req@width}em;"
  }%  
}
\makeatother

\EndPreamble

generates

I have read this threads:

• Htlatex and subcaption - can htlatex be extended?

• configuring minipage in htlatex

But, I cannot piece together how I might achieve the desired result. I have included the graphics configuration in the .cfg file because it is important that I be able to scale the images.

Answer 1

Try this config file:

\Preamble{xhtml}

\Configure{@HEAD}{\HCode{<link href="basic.css" rel="stylesheet" type="text/css" />\Hnewline}} 
\DeclareGraphicsRule{.png}{bmp}{.xbb}{}

\ConfigureEnv{figure}
   {\ifvmode\IgnorePar\fi\EndP\HCode{<div class="figure"\Hnewline>}%
    \bgroup \Configure{float}{\ShowPar}{}{}%
   }
   {\egroup
    \ifvmode\IgnorePar\fi\EndP\HCode{</div>}\ShowPar
\par}
{}{}

\ConfigureEnv{subfigure}{\ifvmode\IgnorePar\fi\EndP\HCode{<div class="subfigure">}}{\ifvmode\IgnorePar\fi\EndP\HCode{</div>}}{}{}
\Css{.subfigure{display: inline-block;}}
\Css{.subfigure img{display:block;}}

\Css{div.caption {text-align:left;font-size:83\%;text-indent:0em; margin-left:2em; margin-right:2em; }}
\Css{div.caption span.id{font-variant: small-caps; white-space: nowrap; }}
\Css{.figure div.caption{text-align: center;}}
\Css{div.figure{text-align:center;clear:both;overflow:auto;width:100\%;margin-bottom:1em;}}

\begin{document}

\makeatletter
% Various helper functions
% default font size
\newcommand\emwidth{16}
\let\emwidth\f@size
% convert pt to rem
\newcommand\CalcRem[1]{\strip@pt\dimexpr(#1)/\emwidth}

\Configure{graphics*}
{png}
{% we must add the image to the list of output files
  \special{t4ht+@File: \csname Gin@base\endcsname.png}
  \Picture[pict]{\csname Gin@base\endcsname\PictExt
  \space style="width:\CalcRem{\Gin@req@width}em;"
  }%  
}
\makeatother

\EndPreamble

The important changes are:

\DeclareGraphicsRule{.png}{bmp}{.xbb}{}

this will enable to use correct bounding box for the images. See this answer for details.

\ConfigureEnv{figure}
   {\ifvmode\IgnorePar\fi\EndP\HCode{<div class="figure"\Hnewline>}%
    \bgroup \Configure{float}{\ShowPar}{}{}%
   }
   {\egroup
    \ifvmode\IgnorePar\fi\EndP\HCode{</div>}\ShowPar
\par}
{}{}

I've added \ifvmode\IgnorePar\fi\EndP for correct handling of paragraphs. See Control the <p> tags inserted by tex4ht for details.

Now the actual code for subfigure:

\ConfigureEnv{subfigure}{\ifvmode\IgnorePar\fi\EndP\HCode{<div class="subfigure">}}{\ifvmode\IgnorePar\fi\EndP\HCode{</div>}}{}{}
\Css{.subfigure{display: inline-block;}}
\Css{.subfigure img{display:block;}}

This add <div class="subfigure"> element and needed CSS configurations. The first one will make subfigures float next themselves, the second will put caption bellow the image.

The result: