Show current chapter number on each page margin

Question

I'm making a reference manual using scrbook. I'd like to include a "tab" that shows the current chapter number in a 1.5cm gray rectangle on the outside edge of every page. Within the rectangle would be the current chapter number. This would allow readers to quickly locate the beginning of a particular chapter by looking at the edge of the printed book.

As an added challenge, the chapter tab needs to move down the page as the chapter number increases. For example, in chapter 1, the chapter tab would be located 1cm from the top of the page; for chapter 2, it would be located 2.5cm from the top of the page (1cm white space, plus 1.5cm for the height of the previous chapter tab), and so on.

Is this possible? If so, how can do implement it?

Answer 1

Here's a possibility using the background package (change the settings according to your needs). Using \AddLabels the tabs are activated; \RemoveLabels deactivates the tabs:

\documentclass[openany]{scrbook}
\usepackage[contents={},opacity=1,scale=1,color=black]{background}
\usepackage[a6paper]{geometry}% just for the example
\usepackage{tikzpagenodes}
\usepackage{totcount}
\usepackage{lipsum}% just to generate text for the example
\usetikzlibrary{calc}

\newif\ifMaterial

\newlength\LabelSize
\setlength\LabelSize{2.5cm}

\AtBeginDocument{%
\regtotcounter{chapter}
\setlength\LabelSize{\dimexpr\textheight/\totvalue{chapter}\relax}
\ifdim\LabelSize>2.5cm\relax
  \global\setlength\LabelSize{2.5cm}
\fi
}

\newcommand\AddLabels{%
\Materialtrue%
\AddEverypageHook{%
\ifMaterial%
\ifodd\value{page} %
 \backgroundsetup{
  angle=90,
  position={current page.east|-current page text area.north  east},
  vshift=15pt,
  hshift=-\thechapter*\LabelSize,
  contents={%
  \tikz\node[fill=gray!30,anchor=west,text width=\LabelSize,
    align=center,text height=15pt,text depth=10pt,font=\large\sffamily] {\thechapter};
  }%
 }
 \else
 \backgroundsetup{
  angle=90,
  position={current page.west|-current page text area.north west},
  vshift=-15pt,
  hshift=-\thechapter*\LabelSize,
  contents={%
  \tikz\node[fill=gray!30,anchor=west,text width=\LabelSize,
    align=center,text height=15pt,text depth=10pt,font=\large\sffamily] {\thechapter};
  }%
 }
 \fi
 \BgMaterial%
\else\relax\fi}%
}

\newcommand\RemoveLabels{\Materialfalse}

\begin{document}

\chapter{Test Chapter One}
\AddLabels
\lipsum[1-2]
\chapter{Test Chapter Two}
\lipsum[1-2]
\chapter{Test Chapter Three}
\lipsum[1-2]
\chapter{Test Chapter Four}
\lipsum[1-2]
\chapter{Test Chapter Five}
\RemoveLabels
\lipsum[1-2]

\end{document}

Answer 2

In April 2002, the web site of the Koma project, Markus Kohm himself presents both commented code for chapter-thumbs, complemented by a pdf as output.

According to him, it should work with every class with \chapter{}-environment and is based on scrpage2. While xcolor allows coloured backgrounds, graphicx provides rotation of the entries to be printed. In difference to the previously presented solution by Gonzalo Medina, the one by Markus Kohm displays the mark only on the odd side (the right one).

Answer 3

The following suggestion bases on an example in the appendix of the KOMA-Script book (German):

\documentclass[10pt,twoside,parskip=half]{scrbook} % Document class for PhD manuscript
\linespread{1.1}
\usepackage[
   paperwidth=170mm,
   paperheight=240mm,
   top=2.5cm, bottom=3cm,
   inner=30mm, outer=25mm,
   heightrounded=true
]{geometry}

\usepackage{graphicx}
\usepackage{xcolor}
\usepackage{scrlayer-scrpage}

% the following bases on an example in the KOMA-Script book:
\newcommand*{\firstchapterthumbskip}{.1\paperheight}
\newcommand*{\lastchapterthumbskip}{\firstchapterthumbskip}
\newcommand*{\chapterthumbheight}{2em}
\newcommand*{\chapterthumbwidth}{.1\paperheight}
\newcommand*{\chapterthumbskip}{.1\paperheight}
\newcommand*{\chapterthumbboxcolor}{gray!30}
\newcommand*{\chapterthumbcolor}{black}
\newcommand*{\chapterthumbformat}{\thechapter}
\newkomafont{chapterthumb}{\normalfont\Large\sffamily\color{\chapterthumbcolor}}

\makeatletter
\newcommand*\chapterthumb@box{%
  \parbox[c][\chapterthumbheight][c]{\chapterthumbwidth}{%
      \centering\usekomafont{chapterthumb}{\chapterthumbformat}%
  }%
}
\newcommand*{\chapterthumbbox}{%
  \if@mainmatter
    \ifnum\value{chapter}>\z@
      \ifnum \value{chapterthumb}<\z@
      \else
        \begingroup
          \protected@edef\reserved@a{\chapterthumbformat}%
          \ifx\reserved@a\lastchapterthumbformat\else
            \stepcounter{chapterthumb}%
            \global\let\lastchapterthumbformat\reserved@a
          \fi
          \@tempcnta=\numexpr 
            \dimexpr 
              \paperheight
              -\firstchapterthumbskip
              -\chapterthumbwidth
              -\lastchapterthumbskip
            \relax / \dimexpr 
                       \chapterthumbskip 
                     \relax
            +1
          \relax
          \ifnum \value{chapterthumb}<\@tempcnta
          \else
            \setcounter{chapterthumb}{0}%
          \fi
          \vspace*{%
            \dimexpr 
              \firstchapterthumbskip
              + ( \chapterthumbskip )
                * \value{chapterthumb}%
              - \baselineskip
            \relax
          }\par
          \setlength{\fboxsep}{0pt}%
          \ifodd\value{page}
            \hfill
            \makebox[0pt][r]{%
              \rotatebox[origin=tr]{90}{%
                \colorbox{\chapterthumbboxcolor}{%
                  \parbox[t][\chapterthumbheight]{\chapterthumbwidth}{%
                    \chapterthumb@box
                    \vskip3mm
                  }}}}%
          \else
            \hspace*{-3mm}%
            \makebox[0pt][l]{%
              \rotatebox[origin=tr]{90}{%
                \colorbox{\chapterthumbboxcolor}{%
                  \parbox{\chapterthumbwidth}{%
                    \vskip3mm
                    \chapterthumb@box
                  }}}}%
          \fi
        \endgroup
      \fi
    \fi
  \fi
}
\makeatother

\newcounter{chapterthumb}
\setcounter{chapterthumb}{10000}
\newcommand*{\lastchapterthumbformat}{\relax}

\DeclareNewLayer[%
  background,%
  outermargin,%
  contents=\chapterthumbbox
]{chapterthumb}

\newcommand*\EnableChapterthumb{%
  \IfLayerAtPageStyle{scrheadings}{chapterthumb}{}
    {\AddLayersToPageStyle{@everystyle@}{chapterthumb}}%
}
\newcommand*\DisableChapterthumb{%
  \RemoveLayersFromPageStyle{@everystyle@}{chapterthumb}%
}

\EnableChapterthumb

\usepackage{blindtext}% only for dummy text
\begin{document}
\tableofcontents
\blinddocument\blinddocument\blinddocument
\blinddocument\blinddocument\blinddocument
\blinddocument\blinddocument\blinddocument
\blinddocument\blinddocument\blinddocument
\end{document}

Result: