# Faking optical size feature using XeLaTeX, fontspec

Is it possible to approximate fake "optical sizes" with fontspec using a font which doesn't have this feature (in my case, Cambria)?

The use case here is that I'm writing a scientific text with lots of in-text \textsuperscript and \textsubscript which would really benefit from being slightly bolder.

• The short answer is: "no" :) – Will Robertson May 8 '18 at 7:48
• The slightly longer answer is that MAYBE with adjusting weight and width just a little you could create something that wasn't terribly ugly on first glance. – Will Robertson May 8 '18 at 7:49
• Thanks, that's what I suspected, but for some reason I can't get a minimal working example for FakeBold with Cambria. Is this expected? – Mathieu May 8 '18 at 8:15
• See my comment to Henri Menke's answer below: the current default macOS PDF engine fails to render FakeBold. Oh well... – Mathieu May 8 '18 at 11:56
• Update: the PDFkit bug appears to have been fixed in the latest macOS update (10.13.4, 17E199). – Mathieu May 12 '18 at 13:07

If it is only about the super and subscript, you could redefine those macros to add boldening using PDF literals.

\documentclass{article}
\usepackage{letltxmacro}
\usepackage{fontspec}

\LetLtxMacro\oldtextsuperscript\textsuperscript
\LetLtxMacro\oldtextsubscript\textsubscript

\newcommand\embolden[1]{%
\special{pdf:literal 2 Tr 1.0 w}% adjust the 1.0
#1%
\special{pdf:literal 0 Tr 0 w}%
}
\DeclareRobustCommand\textsuperscript[1]{%
\oldtextsuperscript{\embolden{#1}}%
}
\DeclareRobustCommand\textsubscript[1]{%
\oldtextsubscript{\embolden{#1}}%
}

\begin{document}

Hello\textsuperscript{Hello}
World\textsubscript{World}

\end{document}


• Wow, thanks, that solves quite nicely my original issue. On the flip side, I've discovered that macOS High Sierra's Preview.app completely fails to render your emboldened sub/superscripts as intended. The fault lies with Preview, though, not with XeLaTeX, because Adobe Reader renders everything correctly. – Mathieu May 8 '18 at 11:55
• @Mathieu — oh, that's a real shame. I'd heard the new PDF rendering engine in macOS was a step backwards... – Will Robertson May 8 '18 at 13:38
• Amazingly, this bug appears to have been fixed in the latest macOS update (10.13.4, 17E199). Thanks again. – Mathieu May 12 '18 at 13:06