Display colored strings in small font size

Question

I want to display random strings made up of 's' and 'f' such that every s is white on a blue background and every f is white on a red background. I can make it work fine in normal text, but when I want to display it in \scriptsize it seems to not get small enough.

The code I'm using is:

\newcommand{\ss}[0]{\colorbox{blue}{\textcolor{white}{{\texttt{\scriptsize{s\strut}}}}}}
\newcommand{\ff}[0]{\colorbox{red}{\textcolor{white}{{\texttt{\scriptsize{f\strut}}}}}}

and then when I want to show a string I write something like:

\ss\ff\ss\ff\ff\ff\ss\ss

Answer 1

I think it's better to use a simpler macro, as far as usage is concerned.

\documentclass{article}
\usepackage{xparse,xcolor}

\ExplSyntaxOn

\NewDocumentCommand{\fs}{m}
 {
  \tl_map_function:nN { #1 } \firth_fs:n
 }

\cs_new_protected:Nn \firth_fs:n
 {
  \str_case:nn { #1 }
   {
    {f}{\__firth_fs_box:nn { red } { f }}
    {s}{\__firth_fs_box:nn { blue } { s }}
    % add more cases if needed
   }
 }
\cs_new_protected:Nn \__firth_fs_box:nn
 {
  \colorbox{#1}
   {
    \color{white}
    \use:c { check@mathfonts }
    \fontsize { \use:c{ sf@size } } { 0 } \selectfont
    #2 \vphantom{f} % possibly 'fy' if letters with descenders are used
   }
 }

\ExplSyntaxOff

\begin{document}

X \fs{sfsfffs} X

\medskip

\Large X \fs{sfsfffs} X

\medskip

\footnotesize X \fs{sfsfffs} X

\end{document}

You can even enter

\fs{s f s fff s}

as spaces are ignored.

Answer 2

Welcome here!

As said in the comments, \ss is already defined, so you need either to redefine it or define another command for printing the s.

However, \strut is a \vrule of 8.5pt height, 3.5pt depth and a width of 0pt.

That doesn't fit automagically to scriptsize. But you can adapt \strut:

\documentclass{article}

\usepackage{xcolor}

\renewcommand{\strut}{\vrule height5pt depth0pt width0pt}
\renewcommand{\ss}[0]{\colorbox{blue}{\textcolor{white}{{\texttt{\scriptsize{s\strut}}}}}}
\newcommand{\ff}[0]{\colorbox{red}{\scriptsize\textcolor{white}{{\texttt{{f\strut}}}}}}



\begin{document}
\ss\ff\ss\ff\ff\ff\ss\ss
\end{document}

See:

However, changing \strut or redefining \ss may have unwanted side effects. Maybe instead of redefining strut, give it another name \turts, e.g. Same for \ss.