Draw italic box as a placeholder (around a single letter) in a word

Question

I am comparing a lot of different cases that are all following a predefined naming scheme. I would now like to replace one of the character in the name with a box to indicate that this parameter is changed for the compared cases.

This is the solution I have found so far but I am not quite happy with it.

\documentclass[a4paper, 12pt]{article} 
\usepackage{xcolor}


\begin{document}
    1818{\color{red}\framebox{X}}cBb-1day    

    \textit{1818{\color{red}\framebox{X}}cBb-1day }

    \emph{1818{\color{red}\framebox{X}}cBb-1day }

\end{document}

The first line is quite ok but I would like the box to be just as wide as the X (I am going to make that white in the final document).

For the next to lines I have the additional problem that I would like the box to be adjusted to the text stile (e.g. italic or whatever I might later use).

Answer 1

This makes use of two really nice answers. Joseph Wright at Detect which text "mode" (normal, italic, bold, etc.) is currently in use? tells how to determine the current font shape, which I use to determine if I am in italic or not.

Bruno at Shear transform a "box" shows how to slant a box.

Together, I use Bruno's \slantbox to slant the box while retaining the italic shape of the letter, when it is determined by Joseph's method if I am in italic shape.

What I had to do was determine the slant appropriate for this font, which I ascertained as 0.24. I also set the \fboxsep to -\fboxrule, so that the boxed letter would take up exactly the same amount of horizontal space as the underlying letter.

EDITED to slant box while retaining italic component inside box, as witnessed by example with f in the box.

At the end of the MWE, I show the result of the new macro \itbox{}.

\documentclass[a4paper, 12pt]{article} 
\usepackage{xcolor}
% FROM BRUNO's ANSWER AT 
% https://tex.stackexchange.com/questions/63179/shear-transform-a-box/63188#63188
\newsavebox{\foobox}
\newcommand{\slantbox}[2][.5]{\mbox{%
        \sbox{\foobox}{#2}%
        \hskip\wd\foobox
        \pdfsave
        \pdfsetmatrix{1 0 #1 1}%
        \llap{\usebox{\foobox}}%
        \pdfrestore
}}
% FROM JOSEPH'S ANSWER AT
% https://tex.stackexchange.com/questions/31649/detect-which-text-mode-normal-italic-bold-etc-is-currently-in-use
\makeatletter
\newcommand*{\IfItalicTF}{%
  \ifx\f@shape\my@test@it
    \expandafter\@firstoftwo
  \else
    \expandafter\@secondoftwo
  \fi
}
\newcommand*{\my@test@it}{it}
\makeatother
%
\def\myfbox#1{\edef\tmp{\the\fboxsep}\fboxsep=-\fboxrule\relax%
  \textcolor{red}{\IfItalicTF{\itbox{#1}}{\fbox{#1}}}%
  \fboxsep=\tmp\relax%
}
\def\itslant{.24}
\def\itbox#1{\slantbox[\itslant]{\fbox{\slantbox[-\itslant]{\itshape#1}}}}
\parindent 0pt
\begin{document}
1818\myfbox{X}cBb-1day \par
\textit{1818\myfbox{X}cBb-1day }\par
\emph{1818\myfbox{X}cBb-1day }\par
\emph{1818f\myfbox{f}cBb-1day }\par
\itbox{this box should be italic} 
\end{document}

A simplified definition that automatically computes the slant factor of the current font (it is stored in \fontdimen1\font); using groups we ensure that color doesn't spill out and also that \fboxsep needn't be restored:

\makeatletter
\newcommand{\myfbox}[1]{%
  \leavevmode % for \color
  \begingroup
  \fboxsep=-\fboxrule
  \color{red}
  \edef\computed@slant{\strip@pt\fontdimen1\font}%
  \ifdim\computed@slant pt=\z@
    % no slant, just do a simple \fbox
    \fbox{#1}%
  \else
    \slantbox[\computed@slant]{\fbox{\slantbox[-\computed@slant]{#1}}}%
  \fi
  \endgroup
}
\makeatother

A full example, showing also that the width is correct (in the ff example the ligature needs to be broken, of course).

\documentclass[a4paper,12pt]{article}
\usepackage{xcolor}
% FROM BRUNO's ANSWER AT 
% https://tex.stackexchange.com/questions/63179/shear-transform-a-box/63188#63188
\newsavebox{\foobox}
\newcommand{\slantbox}[2][.5]{\mbox{%
        \sbox{\foobox}{#2}%
        \hskip\wd\foobox
        \pdfsave
        \pdfsetmatrix{1 0 #1 1}%
        \llap{\usebox{\foobox}}%
        \pdfrestore
}}

\makeatletter
\newcommand{\myfbox}[1]{%
  \leavevmode % for \color
  \begingroup
  \fboxsep=-\fboxrule
  \color{red}
  \edef\computed@slant{\strip@pt\fontdimen1\font}%
  \ifdim\computed@slant pt=\z@
    % no slant, just do a simple \fbox
    \fbox{#1}%
  \else
    \slantbox[\computed@slant]{\fbox{\slantbox[-\computed@slant]{#1}}}%
  \fi
  \endgroup
}
\makeatother

\newcommand{\test}[1]{%
  \sbox0{#1}#1 -- \the\wd0
}

\begin{document}

\test{1818XcBb-1day}\par
\test{1818\myfbox{X}cBb-1day}

\test{\textit{1818XcBb-1day}}\par
\test{\textit{1818\myfbox{X}cBb-1day}}

\test{\emph{1818XcBb-1day}}\par
\test{\emph{1818\myfbox{X}cBb-1day}}

\test{\emph{1818f{}fcBb-1day}}\par
\test{\emph{1818f\myfbox{f}cBb-1day}}

\end{document}

Answer 2

A small solution, but it doesn't look very nice ;-)

\documentclass[a4paper, 12pt]{article} 
\usepackage{xcolor}

\setlength{\fboxsep}{0pt}

\begin{document}
1818{\color{red}\framebox{X}}cBb-1day    

\textit{1818{\color{red}\framebox{X}}cBb-1day }

\emph{1818{\color{red}\framebox{X}}cBb-1day }

\end{document}

Some improved version for slanted boxes (and text, but not italic as requested)

\documentclass[a4paper, 12pt]{article} 
\usepackage{xcolor}
\usepackage{xparse}
\usepackage{tikz}

\NewDocumentCommand{\namingscheme}{D<>{}O{white}mO{X}}{%
  \begingroup
  \setlength{\fboxsep}{0pt}
  \tikz\node[#1] {1818\textcolor{#2}{\fbox{#4}}#3};
  \endgroup
}


\begin{document}
1818{\color{red}\framebox{X}}cBb-1day    

\textit{1818{\color{red}\framebox{X}}cBb-1day }

\emph{1818{\color{red}\framebox{X}}cBb-1day }

\textit{\namingscheme<xslant=0.15>[red]{cBb-1day}}

\end{document}

Disclaimer: I stole the code for the slanted text from an answer by Gonzalo Medina to one of my questions: Text from different viewports

Answer 3

Here is a simple solution for only the non-italic text. I think it also looks fine with italic text, but maybe you disagree.

\documentclass{article}
\usepackage{amssymb}
\begin{document}
sample$\Box{}$text

\textit{sample$\Box{}$text}
\end{document}