print crop margings for bindingoffset

Question

I would like to have a template for reformatting some arbitrary \LaTeX document in a way, that I can print and cut it, to glue it into my lab-book. To this end, the output should

• introduce a binding-offset,

• show crop margins for the binding-offset, as here the paper will be cut,

• and ideally the text width is not altered, but only moved (so the format is conserved).

While the first point is easily achievable with the bindingoffset=2cm option in the geometry package, the other two points are harder to realize:

While \geometry{showframe} prints all frames, I did not find a way to restrict it to the binding-offset margin only.

Furthermore I would like to counter the change of \textwidth when a binding-offset is introduced, regardless of the documentclass used.

\documentclass[10pt]{article}

\usepackage{geometry}
  \geometry{twoside}
  % use 20mm narrower paper than A4
  \geometry{paperheight=297mm,paperwidth=190mm}
  % still use the A4 layout
  \geometry{layout=a4paper}

\usepackage[cam,a4]{crop}
  % print crop marks on odd pages (as printout is duplex)
  \crop[cross,odd]

\usepackage[utf8]{inputenc}

\begin{document}
blablub
\end{document}

However, this leaves me with the layout on the left and white space on the right - the opposite of a binding-offset. The only option crop gives is center. So how can I align the layout on the right?

Of course I could go for the following example, but that rather feels like cheating...

\documentclass[10pt]{article}

\usepackage{geometry}
  \geometry{twoside}
  % use 40mm narrower paper than A4, cheating
  \geometry{paperheight=297mm,paperwidth=**170mm**}
  % still use the A4 layout
  \geometry{layout=a4paper}

\usepackage[cam,a4,**center**]{crop}
  % print crop marks on odd pages (as printout is duplex)
  \crop[odd]

\usepackage[utf8]{inputenc}

\begin{document}
blablub
\end{document}

Answer 1

\documentclass[a4paper]{article}
\usepackage[noaxes,pdflatex,mount2]{crop}

\makeatletter

REMOVE the following line for a real document! Here \pagecolor is just used to mark the page dimensions. crop normally paints the page background a little bit over the edges of the page, which makes sense when cropping, but I just wanted to mark the (exact) page dimensions.

\gdef\CROP@overlap{0truemm}%
\makeatother

\newlength\mybindingoffset
\setlength{\mybindingoffset}{20mm}

\RequirePackage{everyshi}
\AtBeginDocument{\EveryShipout{%

This moves the page content \mybindingoffset (here: 20mm) to the right on the first (right) page, then \mybindingoffset to the left on the next (left) page and so on.

  \hoffset\mybindingoffset\relax%
  \global\multiply\mybindingoffset by -1}%
  }

\newlength\mybindingrule
\setlength{\mybindingrule}{1mm}% probably too thick

\usepackage{pdfpages}

\AddToShipoutPictureBG{%

For positive \mybindingoffset (i.e. right side), a \rule with thickness \mybindingrule and height \paperheight is placed left (\hspace*{-\mybindingrule}) of the page (and by \rlap we pretend that it is not there anyway):

\ifdim\mybindingoffset>0pt\relax%
  \rlap{\hspace*{-\mybindingrule}{\color{black}{\rule{\mybindingrule}{\paperheight}}}}%
\else%

For left sides the \rule is placed right of the page:

  \rlap{\hspace*{\paperwidth\relax}{\color{black}{\rule{\mybindingrule}{\paperheight}}}}%
\fi%
}%

\usepackage{lipsum}
\begin{document}
\pagecolor{green}% just to better show the original page
\lipsum[1-57]
\end{document}

Note that the page layout is not changed at all, but you are losing \mybindingoffset (here: 20mm) at the right of right and at the left of left pages, because it is move outside of the page, so to speak. If that is "whitespace" anyway, it might be acceptable.