Fontspec Slant Units

Question

I'm been testing the FakeSlant feature of the fontspec package. I have a question. The package documentation is not clear what the units are for the FakeSlant=# key=value parameter. My guess on the units based off testing is 1/100th of a degree, but I'm not confident about this honestly.

\setmainfont{Source Serif 4}[%Available for free on Google Fonts.
    Kerning=On%
    ,SlantedFont={Source Serif 4}
        ,SlantedFeatures={%
            Kerning=On%
            ,FakeSlant=0.18
            }
]

EDIT: Did some more testing. It looks like the FakeSlant parameter accepts values from -1 to 1 but I'm still unsure what those values mean exactly.

score 2 · Accepted Answer · answered Nov 23 '22 at 13:57

2

Maybe I am wrong, but the slant value seems to be the tangens of the slanting angle. That is, if the font axis is slanted by x degrees (0 degrees meaning upright), the slant value would be tan(x). Thus, a slant value of 1 represents a slanting angle of 45 degrees (and a value of -1 an angle of -45 degrees).

Compare:

\documentclass[tikz]{standalone}
\usepackage{fontspec}
\setmainfont{Noto Serif}
\begin{document}
\begin{tikzpicture}
\draw[red] (45:-0.5) -- (45:1);
\node at (45:0.5) 
    % tan(45deg) = 1
    {\addfontfeature{FakeSlant=1}I};

% subtraction from 90 degrees in order to make 0 degrees match upright
\draw[yellow] ({90-20}:-0.5) -- ({90-20}:1);
\node at ({90-20}:0.5) 
    % tan(20deg) = 0.36397
    {\addfontfeature{FakeSlant=0.36397}I};

\draw[blue] ({90-5}:-0.5) -- ({90-5}:1);
\node at ({90-5}:0) 
    % tan(5deg) = 0.08749
    {\addfontfeature{FakeSlant=0.08749}I};


\end{tikzpicture}
\end{document}

answered Nov 23 '22 at 13:57

Jasper Habicht

48,848

1

This would probably also explain, why values larger than 1 or smaller than -1 are not possible ... – Jasper Habicht Nov 23 '22 at 14:15
2

Yes, skew is tan: PDF reference, p118 – Cicada Nov 23 '22 at 15:18
1

@Cicada but your previous comment regarding the sin/cos matrix might be valid anyways, since tan can be derived vom sin and cos. – Jasper Habicht Nov 23 '22 at 15:23
1

@User23456234 No, it is skewing, you can easily see this if you look at a wide letter, such as capital M for instance: if you rotate it, the two stems won“t sit on the (same) baseline anymore. – Jasper Habicht Nov 23 '22 at 15:34
1

cos and sin is for rotation – Cicada Nov 23 '22 at 15:37

Cicada · Answer 2 · 2022-11-24T06:15:49.550

Using the cm pdfliteral:

MWE

pdftex
\protected\def\rbox#1{%
  \setbox0\hbox{{#1}}%
  \setbox2\hbox{%
  \special{pdf:literal q}%
  \special{pdf:literal -1 0 0 1 0 0 cm}\rlap{\copy0}
\special{pdf:literal Q}}%
    \hbox to --1\wd0{\kern--1\wd0\box2\hss}%
}
\rbox{abc $\mapsto $ xyz}
Text text text, $abc\mathbin{\rbox{ $\mapsto$}}xyz$, text text text.
% note the space: >>\rbox{ $<<
\protected\def\rbox#1{%
  \setbox0\hbox{{#1}}%
  \setbox2\hbox{%
  \special{pdf:literal q}%
  \special{pdf:literal -1 0 -0.2 1 0 0 cm}\rlap{\copy0}
\special{pdf:literal Q}}%
    \hbox to --1\wd0{\kern--1\wd0\box2\hss}%
}
\rbox{abc $\mapsto $ xyz}
\protected\def\rbox#1{%
  \setbox0\hbox{{#1}}%
  \setbox2\hbox{%
  \special{pdf:literal q}%
  \special{pdf:literal -1 1 -0.2 4 0 -50 cm}\rlap{\copy0}
\special{pdf:literal Q}}%
    \hbox to --1\wd0{\kern--1\wd0\box2\hss}%
}
\rbox{abc $\mapsto $ xyz}
\bye

Substantive code adapted from Scale text (\scalebox) in Plain TeX/XeTeX to make it narrower via Left \mapsto arrow

Some sort of reference example could be useful:

MWE

pdftex
\vskip2ex%
\protected\def\rbox#1{%
  #1: %
  \setbox0\hbox{{abc}}%
  \setbox2\hbox{%
  \special{pdf:literal q}%
  \special{pdf:literal #1 cm}\rlap{\copy0}%
  \special{pdf:literal Q}%
}%
\hbox to --1\wd0{\kern1\wd0\box2\hss}%
\vrule
   \vskip1ex%
   }
no change: \rbox{1 0 0 1 0 0 }
translate: \rbox{1 0 0 1 50 35 }
scaling: \rbox{2 0 0 0.5 0 0 }
scaling: \rbox{0.5 0 0 2 0 0 }
reflection: \rbox{1 0 0 -1 0 0 }
reflection: \rbox{-1 0 0 -1 0 0 }
reflection: \rbox{-1 0 0 1 0 0 }
skew: \rbox{1 0.5 0 1 0 0 }
skew: \rbox{1 0 0.5 1 0 0 }
skew: \rbox{1 0 -0.5 1 0 0 }
skew: \rbox{1 -0.5 -0.5 1 0 0 } % 1 tan-x tan-y 1 0 0
\vskip1ex
rotation: \rbox{1 1 -1 1 0 0 }
rotation: \rbox{-1 -1 1 -1 0 0 }
\vskip1ex
rotation: \rbox{0.86 0.5 -0.5 0.86 0 0 }%cos30 sin30 -sin30 cos30
\vskip1ex
rotation: \rbox{0.98 0.21 -0.21 0.98 0 0 } % -12 degrees
\protected\def\rboxc{%
  \setbox0\hbox{{abc}}%
  \setbox2\hbox{%
  \special{pdf:literal q}%
  \special{pdf:literal 2 0 0 2 0 0 cm}%scale
  \special{pdf:literal 1 0 -0.5 1 0 0 cm}%skew
  \special{pdf:literal 0.86 0.5 -0.5 0.86 0 0  cm}%rotate
  \special{pdf:literal -1 0 0 1 0 0 cm}{\copy0}%reflect
  \special{pdf:literal Q}%
  }%
\hbox to --1\wd0{\kern1\wd0\box2\hss}%
\vrule
   \vskip1ex%
   }
combined:
\rboxc
\bye

Fontspec Slant Units

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