Variable #467

zauguin · 2022-05-23T21:45:51Z

Status

READY/FOR DISCUSSION

Description

Add an interface for loading variable fonts under LuaLaTeX.

While fontspec already had undocumented Width and Weight font features (probably for Multiple Master fonts), these didn't set the current values to work for Variable fonts with luaotfload. Also there was no interface to set arbitrary axes. This was particularly problematic since luaotfload expects all axis values to be passed in a single axis feature, so using RawFeature to set one axis overwrites the values for all previously set axes.

Therefore this PR, besides making Weight and Width compatible with luaotfload and Variable fonts, adds a companion to RawFeature called RawAxis which allows to set arbitrary axis values.

Todos

Tests added to cover new/fixed functionality
Documentation if necessary
Code follows expl3 style guidelines

Minimal example demonstrating the new/fixed functionality

\documentclass{article}
\usepackage{unicode-math}
\setmainfont{NotoSerif}[
  Extension = .ttf,
  UprightFont = *-VF,
  ItalicFont  = *-Italic-VF,
  Weight = 200,
  Width = 75,
  RawAxis = {CTGR=100},
]
\begin{document}
This is the Extra Light Condensed Display style.
\end{document}

zauguin · 2022-05-23T21:47:54Z

fontspec-doc-featset.tex

@@ -608,6 +608,66 @@ \subsection{Letter spacing}
 In particular, small amounts of letter spacing can be very useful, when setting small caps or all caps titles.
 Also see the OpenType \opt{Uppercase} option of the \feat{Letters} feature (\vref{sec:letters}).

+
+\section{Variable fonts} \label{sec:variable}


Not sure if this is the best place for this, but since it's not really OpenType specific due to the MM stuff I thought that a generic place is best.

It's okay for now. The situation would anything non-OpenType fontspec is rather weird and uncertain

fontspec-doc-featset.tex

zauguin · 2022-05-23T21:50:54Z

fontspec-doc-featset.tex

+\subsection{Weight} \label{sec:variable-weight}
+For fonts with a variable weight axis, the weight can be specified through the
+\feat{Weight} feature. The value should be between 0 and 1000, where typically
+400 corresponds to regular wight and 700 is a bold font.
+\begin{Verbatim}
+  \fontspec{Source Serif Variable}[Weight=700]
+  Bold                                     \\
+  \fontspec{Source Serif Variable}[Weight=200]
+  Extra Light                              \\
+\end{Verbatim}
+
+
+\subsection{Width} \label{sec:variable-width}
+Similarly, the \feat{Width} feature allows specifying the value of the width axis,
+where the value is a percentage of normal width.
+\begin{Verbatim}
+  \fontspec{Noto Serif}[Width=100]
+  Normal Width                             \\
+  \fontspec{Noto Serif}[Width=75]
+  Condensed                                \\
+\end{Verbatim}


Not tested with Multiple Master fonts, but since the code was already there I assume that it works for them.

Let's see if anyone actually tries :) From memory MacOS has deprecated a number of APIs that XeTeX used to use to make this work in the older xdv2pdf backend. I can't recall what xdvipdfmx does

xdvipdfmx never supported Apple GX, and when xdv2pdf was finally retired I foolishly removed GX support from XeTeX as being dead technology (I thought no the primitives are still there by they do nothing).

zauguin · 2022-05-23T21:52:29Z

testfiles/fontload-variable.lvt

+\ifluahbtex
+  \defaultfontfeatures{Renderer=HarfBuzz}
+\fi


The feature generally also works for the Node renderer, but the HarfBuzz supports is a bit more consistent IMO. (I'm probably biased though)

zauguin · 2022-05-23T21:55:05Z

fontspec-code-internal.dtx

+% \begin{macro}{\@@_get_variations:}
+% \cmd{\@@_get_variations:} builds the feature string representing the
+% current variation instance and/or axis settings.
+%    \begin{macrocode}
+\cs_new:Nn \@@_format_axis:nn
+  {
+    #1 = #2 ,
+  }
+\cs_new:Nn \@@_get_variations:
+  {
+    \tl_if_empty:NF \g_@@_instance_tl
+      {
+        instance = { \g_@@_instance_tl };
+      }
+      \prop_if_empty:NF \g_@@_rawvariations_prop
+      {
+        axis = {
+          \prop_map_function:NN \g_@@_rawvariations_prop \@@_format_axis:nn
+        };
+      }
+  }
+%    \end{macrocode}
+% \end{macro}
+%


These are not made LuaTeX specific since I could imagine a similar interface applying to XeTeX too if they ever get Variable font support.

zauguin · 2022-05-23T21:56:49Z

This would require adding NotoSerif-VF.ttf from https://github.com/googlefonts/noto-fonts/raw/main/unhinted/variable-ttf/NotoSerif-VF.ttf to @wspr's fontspec-test-fonts repo

wspr

Amazing, thank you so much! I had one question about naming -- wdyt?

I am sorry I have never had the time to explore this properly, I have always been very excited for MM technology. Sigh, if only there were more hours in the day. Next someone needs to integrate microtype expansion using variable axes fonts :)

wspr · 2022-05-24T13:24:06Z

fontspec-doc-featset.tex

@@ -608,6 +608,66 @@ \subsection{Letter spacing}
 In particular, small amounts of letter spacing can be very useful, when setting small caps or all caps titles.
 Also see the OpenType \opt{Uppercase} option of the \feat{Letters} feature (\vref{sec:letters}).

+
+\section{Variable fonts} \label{sec:variable}


It's okay for now. The situation would anything non-OpenType fontspec is rather weird and uncertain

wspr · 2022-05-24T13:24:31Z

fontspec-code-keyval.dtx

+% \subsubsection{Variation instances}
+%
+%    \begin{macrocode}
+\@@_keys_define_code:nnn {fontspec-opentype} {Instance}


Is "Instance" specific enough or would "VariationInstance" be better? (Not sure, just thinking out loud). WDYT?

I don't really have a qualified opinion on that. Personally I prefer Instance, but that's purely subjective.

wspr · 2022-05-24T13:27:14Z

fontspec-doc-featset.tex

+\subsection{Weight} \label{sec:variable-weight}
+For fonts with a variable weight axis, the weight can be specified through the
+\feat{Weight} feature. The value should be between 0 and 1000, where typically
+400 corresponds to regular wight and 700 is a bold font.
+\begin{Verbatim}
+  \fontspec{Source Serif Variable}[Weight=700]
+  Bold                                     \\
+  \fontspec{Source Serif Variable}[Weight=200]
+  Extra Light                              \\
+\end{Verbatim}
+
+
+\subsection{Width} \label{sec:variable-width}
+Similarly, the \feat{Width} feature allows specifying the value of the width axis,
+where the value is a percentage of normal width.
+\begin{Verbatim}
+  \fontspec{Noto Serif}[Width=100]
+  Normal Width                             \\
+  \fontspec{Noto Serif}[Width=75]
+  Condensed                                \\
+\end{Verbatim}


Let's see if anyone actually tries :) From memory MacOS has deprecated a number of APIs that XeTeX used to use to make this work in the older xdv2pdf backend. I can't recall what xdvipdfmx does

zauguin added 6 commits May 23, 2022 23:32

Add infrastructure for variable fonts

b66a05f

Add variation axis interface

ae04fc4

Add font instance interface

43a7894

Document Variable font interface

38d8370

Add testfile for variable fonts

f10f947

Document spotty engine support

d54dbb7

zauguin commented May 23, 2022

View reviewed changes

fontspec-doc-featset.tex Show resolved Hide resolved

zauguin commented May 23, 2022

View reviewed changes

zauguin requested review from u-fischer and wspr May 23, 2022 21:58

wspr approved these changes May 24, 2022

View reviewed changes

Add Slant axis

913d5a2

zauguin mentioned this pull request May 29, 2022

Add NotoSerif-VF.ttf wspr/fontspec-test-fonts#1

Merged

zauguin added 2 commits May 30, 2022 22:10

More precise syntax

e6ec5d2

Document Instance key

cf390ff

zauguin merged commit 8e3494e into main Jun 24, 2022

zauguin deleted the variable branch June 30, 2022 13:17

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zauguin May 24, 2022 •

edited

wspr May 24, 2022

Variable #467

Variable #467

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zauguin commented May 23, 2022

Status

Description

Todos

Minimal example demonstrating the new/fixed functionality

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zauguin commented May 23, 2022

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zauguin May 24, 2022 • edited

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zauguin May 24, 2022 •

edited