Long division looks broken in LuaTeX and XeTeX

[matteocoder]

Description

The line over the numbers or formula in a long division does not connect well to the u+027cc symbol.

Add info or delete as appropriate:

• Relevant for XeTeX
• Relevant for LuaTeX
• Issue tracker has been searched for similar issues? Yes.

Minimal example demonstrating the issue

\documentclass{article}
\usepackage{unicode-math}
\setmathfont{XITSMath-Regular.otf}% Try STIX2Math.otf or cambria.ttc as well.
\begin{document}
\[
  \longdivision{a = b}
\]
\end{document}

Further details

Setup: TeX Live 2019 for Windows, LuaTeX 1.10, XeTeX 3.14159265-2.6-0.999991, unicode-math 0.80.

Edit: here are the screenshots for the fonts mentioned previously:

• XITS Math
• STIX Two Math
• Cambria Math

[stone-zeng]

Cambria Math is actually correct, you need to scale it to enough size:

For small size your os may not render it smoothly.

But for XITS and STIX2, the problem is from the design of these fonts:

The value radicalRuleThickness in XITS Math/STIXTwoMath is 66/68, while the actual thickness of the horizontal line in uni27CC is 54/55, so you may expect the breaking point. For Cambria Math, however, this value is 133 (ignore the device table) and the line is 133 as well, so it goes fit.

Reference: https://docs.microsoft.com/typography/opentype/spec/math

[matteocoder]

Thanks for your thorough reply @stone-zeng . In this case, should I open an issue on the XITS and STIX repos?