Compatibility issue with \renewenvironment{figure} and [H] placement

Question

This is related to Shift all floats on page horizontally. While trying to redefine the standard figure environment I've run into compatibility issues with the [H] placement specifier from the float package.

Consider the simple example below which just adds some text to be displayed at the beginning and the end of the environment.

\documentclass{article}

\usepackage{mwe}

\makeatletter
\renewenvironment{figure}[1][\fps@figure]
  {\@float{figure}[#1]before}
  {after\end@float}
\makeatother

\usepackage{float}

\begin{document}

\begin{figure}[h]
   \includegraphics[width=.8\linewidth]{example-image}
\end{figure}

\end{document}

This works as expected with the standard latex figure placement specifiers by displaying the graphics between the "before" and "after" words, as illustrated by the image below. However, when I try to use [H] instead of [h] the text supposed to appear after the graphics is gone. Any suggestions how the example above could be fixed to work with the [H] placement specifier?

Answer 1

The problem lives in the code of the float package: If the placement [H] is used, \endfigure will be redefined locally with no respect on the original definition of \endfigure:

\def\@float@HH#1[H]{%
% Locally redefine the end of the environment.
  \expandafter\let\csname end#1\endcsname\float@endH
  ...

As consequence the following code compiles fine, although \jhzsweiurziuewzriuewzritewt is (obviously) not defined at all and therefore should give an error when used:

\documentclass{article}
\usepackage{mwe}

\makeatletter
\renewenvironment{figure}[1][\fps@figure]
  {\@float{figure}[#1]before}
  {\jhzsweiurziuewzriuewzritewt} % not defined but compiles fine anyway ;-)
\makeatother

\usepackage{float}

\begin{document}

\begin{figure}[H]
   \includegraphics[width=.8\linewidth]{example-image}
\end{figure}

\end{document}

What can we do about it? Patching \float@endH as well. We do this inside the redefinition of figure (and not globally) so the patch does not affect the other floating environments:

\documentclass{article}
\usepackage{mwe}

\makeatletter
\renewenvironment{figure}[1][\fps@figure]
  {% Next two code lines: Adaption to "HERE" feature of the float package
   \let\float@endH@ORI\float@endH
   \def\float@endH{after\float@endH@ORI}%
   % ...or \pretocmd{\float@endH}{after}{}{} when using `etoolbox`
   \@float{figure}[#1]before}
  {after\end@float}
\makeatother

\usepackage{float}

\begin{document}

\begin{figure}[H]
   \includegraphics[width=.8\linewidth]{example-image}
\end{figure}

\end{document}

Answer 2

The macro \fps@figure doesn't have an H option. To implement the H option from the figure package, you would need something like this:

\documentclass{article}
\usepackage{caption}
\usepackage{mwe}
\usepackage{showframe}

\newenvironment{Hfigure}{\setcaptiontype{figure}%
  \vskip\textfloatsep\begin{minipage}{\columnwidth}}%
  {\end{minipage}\vskip\textfloatsep\noindent}

\begin{document}
before
\begin{Hfigure}
\centering
\includegraphics{example-image}
\caption{test}
\end{Hfigure}
after
\end{document}