Clever Underlining

Question

I'm using ulem package to perform clean underlining as advised here https://alexwlchan.net/2017/10/latex-underlines/

It works like a charm, but the line stays at the same thickness whatever the font size.

As a first try, I want the parameters to change accordingly when the font is settled to HUGE (max size with the moresize package).

However when trying to use it, I get an error message "Undefined Control Sequence".

% !TEX TS-program = lualatex
\documentclass[fontsize=12pt,DIV=calc,oneside]{scrarticle}
\usepackage{contour}
\usepackage[normalem]{ulem}
\usepackage{moresize}
% Underline
\makeatletter    
\newcommand{\cleverul}[1]
{%
    \ifthenelse{\equal{\f@size}{\pointsize{\normalsize}}}%
    {%
        \setlength{\ULdepth}{1.8pt}%
        \renewcommand{\ULthickness}{0.8pt}%
        \uline{\phantom{#1}}%
        \llap{\contour{white}{#1}}%
    }%
    \ifthenelse{\equal{\f@size}{\pointsize{\HUGE}}}%
    {%
    \setlength{\ULdepth}{3pt}%
    \renewcommand{\ULthickness}{1.5pt}%
    \uline{\phantom{#1}}%
    \llap{\contour{white}{#1}}
    }%
}%
\makeatother


\begin{document}
\cleverul{try}


\end{document}

Answer 1

You can use a simple calculation instead of detection:

\documentclass[fontsize=12pt,DIV=calc,oneside]{scrarticle}
\usepackage{contour}
\usepackage[normalem]{ulem}
\usepackage{moresize}
\usepackage{fp}
% Underline
\contourlength{0.8pt} % Specifies the distance between the underline and the character parts it does not want to touch.
\makeatletter
\newcommand{\cleverul}[1]
{%
    \FPmul\cleverul@temp{\f@size}{0.15}% This is \f@size * 0.15
    \setlength{\ULdepth}{\cleverul@temp pt}%
    \FPdiv\cleverul@temp{\f@size}{15}% This is \f@size / 15
    \renewcommand{\ULthickness}{\cleverul@temp pt}%
    \uline{\phantom{#1}}%
    \llap{\contour{white}{#1}}%
}%
\makeatother
\begin{document}
\noindent\cleverul{try}
\HUGE
\noindent\cleverul{try}
\end{document}

Works like a charm with URLs in Biblatex, just add the following line :

\DeclareFieldFormat{url}{\cleverul{\url{#1}}} % Without the word URL.

or

\DeclareFieldFormat{url}{\mkbibacro{URL}\addcolon\space\cleverul{\url{#1}}} % With the word URL.

Answer 2

You can simply set \ULthickness to a font-dependent length:

\documentclass[fontsize=12pt,DIV=calc,oneside]{scrarticle}
\usepackage{fix-cm}  
\usepackage{contour}
\usepackage[normalem]{ulem}
\usepackage{moresize}
\renewcommand\ULthickness{.04em}
\begin{document}
\raggedright
{\tiny  \uline{try \the\dimexpr\ULthickness}}
\uline{try \the\dimexpr\ULthickness}
{\huge \uline{try \the\dimexpr\ULthickness}}
{\HUGE \uline{try \the\dimexpr\ULthickness}}
\end{document}

Answer 3

Isn't that beautiful.

  \documentclass[fontsize=12pt,DIV=calc,oneside]{scrarticle}
\usepackage{moresize}
\usepackage{contour}
\usepackage[normalem]{ulem}
\usepackage{fp}


% Clever Underline

    \makeatletter
    \newcommand{\cleverul}[1]
    {%
        \FPmul\cleverul@temp{\f@size}{0.15}% This is \f@size * 0.15
        \setlength{\ULdepth}{\cleverul@temp pt}%
        \FPdiv\cleverul@temp{\f@size}{15}% This is \f@size / 15
        \renewcommand{\ULthickness}{\cleverul@temp pt}%
                \uline{\phantom{#1}}%
        \llap{\contour{white}{#1}}%
    }%
    \makeatother

\begin{document}

\noindent\tiny I want to give a \cleverul{try}\\
\scriptsize I want to give a {\cleverul{try}}\\
\footnotesize I want to give a \cleverul{try}\\
\small I want to give a \cleverul{try}\\
\normalsize I want to give a \normalsize\cleverul{try}\\
\large I want to give a \cleverul{try}\\
\Large I want to give a \cleverul{try}\\
\LARGE I want to give \cleverul{try}\\
\Huge I want to give a \cleverul{try}\\
\HUGE I want to give a \cleverul{try}\\

\end{document}