Fontspec: separately scale uppercase and lowercase so `tt` has same cap-to-x-height ratio as main font

Question

TL/DR

I understand this is a perverse question, but—is it possible, in fontspec/XeLaTeX|LuaLaTeX, to separately scale uppercase and lowercase letters of a monospace typewriter font to achieve the effect of having

• lowercase letters scaled to "MatchLowercase", and
• uppercase letters to "MatchUppercase",

so that the cap-to-x-height ratio matches the main font.

I understand that this would destroy kerning calculations in a normal font, but for monospace, it seems reasonably straightforward to horizontally stack non-overlapping boxes. (Though I suspect this may create eye-soreness for initial-case words where simple stacking will create extra space between the uppercase first letter and the lowercase tail: W·ord.)

Bonus for suggesting a monospace typewriter font that harmonises with EB Garamond.

Longform

I'm using XeLaTeX at the moment, but I have a lot of branches so the document compiles with LuaLaTeX as well. I'm using fontspec.

I'm writing a document with lots of code and I'm using EB Garamond for the body (and Garamond-Math.otf for math). I've had a heck of a time finding a monospace/typewriter font that looks good with garamond.

I've settled on IBM Plex Mono:

\setmonofont{IBMPlexMono}%
  [
  , Path = {…}
  , UprightFont = *-Regular.otf
  , ItalicFont = *-Italic.otf
  , BoldFont = *-Bold.otf
  , BoldItalicFont = *-BoldItalic.otf
  , Scale=MatchLowercase
  ]

though I welcome recommendations, especially those that have fairly broad unicode support for UTF in comments.

Given the fixed choice of IBM Plex Mono, my problem is that the cap-to-x-height ratio between EB Garamond and Plex are so different that it looks a little strange with inline code when I scale by MatchLowercase.

Answer 1

It's indeed a perverse question, I'm afraid.

The font designer decided about the proportion between capital and lowercase letter and you're trying to ruin their artwork.

Anyway, it's possible to do it with kernel commands.

\documentclass{article}
\usepackage{fontspec}

\setmainfont{TeX Gyre Pagella}

\setmonofont{IBMPlexMono}[
  Extension=.otf,
  UprightFont = *-Regular,
  ItalicFont = *-Italic,
  BoldFont = *-Bold,
  BoldItalicFont = *-BoldItalic,
  Scale=MatchLowercase,
]
\newfontfamily{\UCMONO}{IBMPlexMono}[
  Extension=.otf,
  UprightFont = *-Regular,
  ItalicFont = *-Italic,
  BoldFont = *-Bold,
  BoldItalicFont = *-BoldItalic,
  Scale=MatchUppercase,
]

\ExplSyntaxOn
\NewDocumentCommand{\atexttt}{m}
 {
  \texttt { \text_map_function:nN { #1 } \__timtro_uclc:n }
 }

\cs_new_protected:Nn \__timtro_uclc:n
 {
  \str_if_eq:eeTF { #1 } { \text_lowercase:n { #1 } }
   { #1 } { {\UCMONO#1} }
 }
\ExplSyntaxOff

\begin{document}

Sm \atexttt{Sm} \texttt{Sm}

\end{document}

Comment: the picture clearly show how bad your idea is. 😊 Look at the uppercase “S” and you'll see that the stroke thickness is visibly different from the “m”. You also lose the “monospacedness”, because capital letters will be wider than lowercase.

For long verbatim-like parts don't use this. And don't use it at all. 🙃

Answer 2

I wrote some code similar to this back in 2018, which scales uppercase and lowercase separately to fake small caps.

For this purpose, you could simplify it considerably. You don’t want to capitalize the scaled lowercase letters, and you might or might not want to scale them horizontally as I did. The code to automatically determine the x-height would change to instead use the x-height of the main font.

However, you should first look for a sans-serif monospace font with a more similar x-height.

Answer 3

Perhaps something like this might be of some limited use?

Adapting from my answer at Fake small caps with XeTeX/fontspec?, I control the vertical scale of upper and lower-case letters in \fauxtt with \Cscale and \Vscale. The horizontal scale of the tt letters is adjusted, if desired, via \Hscale.

In the MWE, the first line of output is unadjusted tt. In the 2nd line of output is \fauxtt.

\documentclass{article}
\usepackage{fontspec,graphicx,xcolor}
\usepackage{graphicx}
\makeatletter
\makeatother
\newcommand\fauxtt[1]{\fauxtthelper#1 \relax\relax}
\def\fauxtthelper#1 #2\relax{%
  \fauxtthelphelp#1\relax\relax%
  \if\relax#2\relax\else\ \fauxtthelper#2\relax\fi%
}
\def\fauxtthelphelp#1#2\relax{%
  \ifnum`#1=\lccode`#1\relax\scalebox{\Hscale}[\Vscale]{\ttfamily#1}\else%
    \scalebox{\Hscale}[\Cscale]{\ttfamily#1}\fi%
  \ifx\relax#2\relax\else\fauxtthelphelp#2\relax\fi}
\begin{document}
\fontspec{Palatino Linotype}
\def\Hscale{1.00}\def\Vscale{1.05}\def\Cscale{1.13}%

\noindent\rlap{\color{red}\rule[4.5pt]{2in}{.1pt}}%
\rlap{\color{red}\rule{2in}{.1pt}}%
\rlap{\color{red}\rule[7pt]{2in}{.1pt}}%
Sm
\texttt{Sm}

\noindent\rlap{\color{red}\rule[4.5pt]{2in}{.1pt}}%
\rlap{\color{red}\rule{2in}{.1pt}}%
\rlap{\color{red}\rule[7pt]{2in}{.1pt}}%
Sm
\fauxtt{Sm}
\end{document}