[Tex/LaTex] Custom chapter title protruding in left margin

chapterssectioningtitlesec

Based on this answer, I tried my hand at defining my own chapter title formatting. The idea is to align the chapter title to the right (a chapter always opening on an odd page) and underline it with a rule that protrudes into the right margin. When the chapter title is short, it works nicely. When it stretches far to the left however, the chapter number sometimes gets shoved into the left margin, where the binding is supposed to be, so that's a big no-no. I'm not very good at this, so maybe it's a very silly mistake. Thanks in advance for any advice!

My MWE:

\documentclass{book}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage{xcolor}
\usepackage{changepage}
\usepackage[calcwidth]{titlesec}
\usepackage{lipsum}

% Redefine chapter command
\newlength\mylen
\setlength\mylen{1cm}
\titleformat{\chapter}[hang]{\Huge\bfseries}{\textcolor{gray}{\thechapter}}{2pc}{\raggedleft}[\vspace{-20pt}%
   {%
      \begin{adjustwidth}{}{-\mylen}%
        \makebox[\linewidth][r]{\rule{\dimexpr\titlewidth+\mylen\relax}{1pt}}%
      \end{adjustwidth}%
   }%
  ]
\titlespacing{\chapter}{0pt}{0pt}{2cm}

\begin{document}

\chapter{A tremendously-long chapter title illustrating the bug I'm experiencing}

\lipsum[1]

\end{document}

enter image description here

Best Answer

Here's one possible solution; the basic idea is to capture the title (#1 in the explicit option for titlesec), to box it inside a varwidth environment and decide the length of the rule to be used (\ftitlewd+2pc) , by using a conditional test comparing the actual width of the title (\titlewd) and the width that was initially reserved to typeset it (\titleboxwd=\textwidth-\mylen=\textwidth-3pc):

\documentclass{book}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage{xcolor}
\usepackage{varwidth}
\usepackage[calcwidth,explicit]{titlesec}
\usepackage{lipsum}

\newlength\mylen
\newsavebox\mybox
\newlength\titlewd
\newlength\ftitlewd
\newlength\titleboxwd
\setlength\mylen{3pc}
\setlength\titleboxwd{\dimexpr\textwidth-\mylen\relax}
\setlength\ftitlewd{\titleboxwd}

\newcommand\chapfont{\Huge\bfseries\raggedleft}

\titleformat{\chapter}[hang]
  {\chapfont\filleft}
  {}{0pc}
  {\parbox[t]{\mylen}{\textcolor{gray}{\thechapter}\hfill}%
    \begin{lrbox}{\mybox}%
    \begin{varwidth}[t]{\titleboxwd}%
      \chapfont#1%
    \end{varwidth}%
    \end{lrbox}%
    \settowidth\titlewd{\usebox\mybox}%
    \ifdim\titlewd<\titleboxwd%
          \global\setlength\ftitlewd{\titlewd}%
    \fi%
    \parbox[t]{\ftitlewd}{\usebox\mybox}%
  }
  [\vskip-1.4ex{\makebox[0pt][l]{%
    \hspace*{-\ftitlewd}\rule{\dimexpr\ftitlewd+2pc\relax}{1.5pt}}}%
  ]
\titleformat{name=\chapter,numberless}[hang]
  {\chapfont\filleft}
  {}{0pc}
  {%
    \begin{lrbox}{\mybox}%
    \begin{varwidth}[t]{\titleboxwd}%
      \chapfont#1%
    \end{varwidth}%
    \end{lrbox}%
    \settowidth\titlewd{\usebox\mybox}%
    \ifdim\titlewd<\titleboxwd%
          \global\setlength\ftitlewd{\titlewd}%
    \fi%
    \parbox[t]{\ftitlewd}{\usebox\mybox}%
  }
  [\vskip-1.4ex{\makebox[0pt][l]{%
    \hspace*{-\ftitlewd}\rule{\dimexpr\ftitlewd+2pc\relax}{1.5pt}}}%
  ]
\titlespacing*{\chapter}
  {1\mylen}{50pt}{40pt}

\begin{document}

\chapter*{An Unnumbered Chapter}
\lipsum[4]
\chapter{A tremendously Long Chapter Title Showing a Solution}
\lipsum[4]
\chapter{Short Chapter Title}
\lipsum[4]

\end{document}

Some images of the resulting chapter headings: first, an unnumbered chapter (this will be the formatting fot the ToC, LoF, LoT and bibliography):

enter image description here

A numbered chapter with a long title:

enter image description here

and a numbered chapter with a short title:

enter image description here

Feel free to change the lengths to suit your needs.

As a personal note (of course, not more than a suggestion), with the requested layout, the position of the chapter number will vary from chapter to chapter and I am not sure that this is a good choice. Perhaps you could reconsider this.

The following variation places the chapter number outside the right margin, at the same distance that the rule protusion:

\documentclass{book}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage{xcolor}
\usepackage{varwidth}
\usepackage[calcwidth,explicit]{titlesec}
\usepackage{lipsum}

\newsavebox\mybox

\newlength\mylen
\newlength\titlewd
\newlength\ftitlewd
\newlength\titleboxwd
\setlength\mylen{3pc}
\setlength\titleboxwd{\dimexpr\textwidth-\mylen\relax}
\setlength\ftitlewd{\titleboxwd}

\newcommand\chapfont{\Huge\bfseries\raggedleft}

\titleformat{\chapter}[hang]
  {\chapfont\filleft}
  {}{0pc}
  {%
    \begin{lrbox}{\mybox}%
    \begin{varwidth}[t]{\titleboxwd}%
      \chapfont#1%
    \end{varwidth}%
    \end{lrbox}%
    \settowidth\titlewd{\usebox\mybox}%
    \ifdim\titlewd<\titleboxwd%
          \global\setlength\ftitlewd{\titlewd}%
    \fi%
    \parbox[t]{\ftitlewd}{\usebox\mybox}%
    \makebox[0pt][l]{\parbox[t]{4pc}{\hfill\textcolor{gray}{\thechapter}}}%
  }
  [\vskip-1.4ex{\makebox[0pt][l]{%
    \hspace*{-\ftitlewd}\rule{\dimexpr\ftitlewd+4pc\relax}{1.5pt}}}%
  ]
\titleformat{name=\chapter,numberless}[hang]
  {\chapfont\filleft}
  {}{0pc}
  {%
    \begin{lrbox}{\mybox}%
    \begin{varwidth}[t]{\titleboxwd}%
      \chapfont#1%
    \end{varwidth}%
    \end{lrbox}%
    \settowidth\titlewd{\usebox\mybox}%
    \ifdim\titlewd<\titleboxwd%
          \global\setlength\ftitlewd{\titlewd}%
    \fi%
    \parbox[t]{\ftitlewd}{\usebox\mybox}%
  }
  [\vskip-1.4ex{\makebox[0pt][l]{%
    \hspace*{-\ftitlewd}\rule{\dimexpr\ftitlewd+4pc\relax}{1.5pt}}}%
  ]
\titlespacing*{\chapter}
  {1\mylen}{50pt}{40pt}

\begin{document}

\chapter*{An Unnumbered Chapter}
\lipsum[4]
\chapter{A tremendously Long Chapter Title Showing a Solution}
\lipsum[4]
\chapter{Short Chapter Title}
\lipsum[4]

\end{document}

The corresponding images:

enter image description here

enter image description here

enter image description here

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