LaTeX: to create xbb files (for use with dvipdfmx) only using pdfLaTeX

bxxbb.sty

% bxxbb.sty
%
% package declaration
\NeedsTeXFormat{LaTeX2e}
\ProvidesPackage{bxxbb}[2014/06/15 v0.1]

% preparationd
\def\bxxb@pkgname{bxxbb}

% environment check
\ifx\pdfoutput\@undefined\else \ifnum\pdfoutput>\z@
  \ifx\pdfximagebbox\@undefined\else
    \let\bxxb@work=t
  \fi
\fi\fi

%% options
\DeclareOption{autostop}{%
  \let\bxxb@autostop=t%
}
\DeclareOption{noautostop}{%
  \let\bxxb@autostop=f%
}
\ProcessOptions*

%--------------------------------------- public interface

%%<*>\extractbb[<page>]{<image_file>}
\newcommand*{\extractbb}{%
  \kernel@ifnextchar[%]
   {\bxxb@extractbb@a}{\bxxb@extractbb@a[]}%
}
% (now defined as no-op)
\def\bxxb@extractbb@a[#1]#2{}

%%<*> \xbbquit
% Quit the TeX process now.
% (now defined as no-op)
\newcommand*{\xbbquit}{}

% If not running on pdfTeX, stop loading the package.
\ifx t\bxxb@work\else
\expandafter\endinput\fi\relax

%--------------------------------------- main
% (e-TeX is assumed afterwards)

%% variables
\newwrite\bxxb@xbb

%% \bxxb@pp : the string '%%'
\begingroup \escapechar\m@ne
\xdef\bxxb@pp{\string\%\string\%}
\endgroup

%% redefinition
\def\bxxb@extractbb@a[#1]#2{%
  \bxxb@write@xbb{#1}{#2}%
  \bxxb@maybe@quit
}
\def\xbbquit{%
  \PackageWarning\bxxb@pkgname{Quit now}%
  \@@end
}

%% \bxxb@maybe@quit
\ifx f\bxxb@autostop
  \let\bxxb@maybe@quit\relax
\else
  \def\bxxb@maybe@quit{%
    \kernel@ifnextchar\extractbb
     {\relax}{\xbbquit}%
  }
\fi

%% \bxxb@write@xbb{<page>}{<image_file>}
\def\bxxb@write@xbb#1#2{%
  % obtain bbox value
  \edef\bxxb@x{#1}%
  \edef\bxxb@x{\ifx\bxxb@x\@empty\else page \bxxb@x\fi}%
  \pdfximage\bxxb@x{#2}%
  \edef\bxxb@bbox{%
    \pdfximagebbox\pdflastximage 1 \space
    \pdfximagebbox\pdflastximage 2 \space
    \pdfximagebbox\pdflastximage 3 \space
    \pdfximagebbox\pdflastximage 4}%
  \edef\bxxb@x{%
   \the\z@\space\the\z@\space\the\z@\space\the\z@}%
  \ifx\bxxb@bbox\bxxb@x
    \setbox\z@\hbox{\pdfrefximage\pdflastximage}%
    \edef\bxxb@bbox{\the\z@\space\the\z@\space
     \the\wd\z@\space\the\ht\z@}%
  \fi
  % create xbb file
  \filename@parse{#2}%
  \immediate\openout\bxxb@xbb=%
   \filename@area\filename@base.xbb\relax
  \immediate\write\bxxb@xbb{%
    \bxxb@pp Title: #2^^J%
    \bxxb@pp BoundingBox: \bxxb@bbox^^J%
    \bxxb@pp HiResBoundingBox: \bxxb@bbox^^J%
  }%
  \immediate\closeout\bxxb@xbb
  \typeout{>> bbox of image '#2' = [\bxxb@bbox]}%
}

%--------------------------------------- done
\endinput
%% EOF

sample-bxxbb.tex

% Write instructions for creating xbb files before \documentclass
% command. When this source file is compiled with pdfLaTeX, only
% this "pre-preamble" part will be executed.
\RequirePackage{bxxbb}
\extractbb{tiger.pdf}
\extractbb{tigra.png}
% When the source file is compiled with a non-pdfLaTeX engine,
% the "pre-preamble" part will be ignored and the normal source
% lines thereafter will be processed.
\documentclass[a4paper,dvipdfmx]{jsarticle}
\usepackage{graphicx}
\begin{document}
\begin{center}
\includegraphics[width=100pt]{tiger.pdf}
\end{center}
\end{document}