Filling an empty slot in a font with another glyph from the same font

Question

I am trying to use an existing glyph from an OpenType font to fill an empty slot in the same font using LuaLaTeX. fontspec.pdf (v2.6g, part VI) shows a hack that can substitute already existing glyphs using fonts.handlers.otf.addfeature, but not empty slots, presumably because their name does not exist.

The font in question is the proprietary Garamond Premier Pro, but the same issue is found with EB Garamond, available in ~~outdated~~ upstream form in TeXLive as ebgaramond or ~~newer~~ as a Google Fonts fork from their repo. So while the immediate solution is to contribute to EB Garamond, the real world problem is with a font that can not be modified.

U+03F5 (ϵ) (c-shaped) is normally the glyph named epsilon1, which is the slot I want to fill with the similar enough (in Noto Sans they are linked directly) ukrainian ie U+0454 (є) which is cryptically named afii10101 (not even opentype.js.org gets it right, uni0454 will not show up in the MWE).

For text, we can use newunicodechar and it is working nicely, except the minor issue that copy-paste gives an ukrainian letter.

For math, neither 0x03F5, "uni03F5" or "epsilon1" has any effect in the Lua code. We can replace the U+03B5 if we like, but we don't. luaotfload.pdf (v2.8, chapter 5) has some info on how to combine separate fonts, but not how to (re)map glyphs from scratch within a single font.

Do we need to create a “ghost” glyph entry before we can remap it? Can we create it from scratch (and reference the outline, to get proper copy-paste)? Is there some documentation I am missing?

\documentclass{article}
\usepackage{fontspec}
\usepackage[math-style=ISO]{unicode-math}
\usepackage{newunicodechar}
\directlua{
    fonts.handlers.otf.addfeature {
        name = "cstm",
        type = "substitution",
        data = {
             [0x261E] = "afii10101",% pointing finger for example
             %[0x261E] = "uni0454",% has NO effect
             ["uni03F5"] = "afii10101",% c-shape, has NO effect
             [0x03F5] = "afii10101",% c-shape, has NO effect
             ["epsilon1"] = "afii10101",% c-shape, has NO effect
             %["uni03B5"] = "afii10101",% 3-shape, has NO effect
             %[0x03B5] = "afii10101",% 3-shape, DOES HAVE effect
             %["epsilon"] = "afii10101",% 3-shape, DOES HAVE effect
} } }
\setmainfont{EB Garamond}[RawFeature=+cstm]
\setmathfont{Latin Modern Math}
\setmathfont{EB Garamond Italic}[range=it,RawFeature=+cstm]
\newunicodechar{ϵ}{\char"0454}
\begin{document}
{\addfontfeature{RawFeature=-cstm}\itshape ☞} ← normal\par
{\addfontfeature{RawFeature=+cstm}\itshape ☞} ← substitution in action\par
\begin{tabular}{cccc}
     & 03B5           & 03F5           & 0454           \\
text & ({\itshape ε}) & ({\itshape ϵ}) & ({\itshape є}) \\
math & ($\symit{ε}$)  & ($\symit{ϵ}$)  & {\scshape n/a} \\
\end{tabular}
\end{document}

I don't think you can do this with font features. You'll have to create a virtual font. — Henri Menke, Feb 26 '18 at 22:00

score 3 · Accepted Answer · answered Feb 26 '18 at 23:28

3

You can try mapping the glyph at load time of the font. For some reason it is not italic in math mode but I don't know why.

\documentclass{article}
\usepackage{fontspec}
\usepackage[math-style=ISO]{unicode-math}
\usepackage{newunicodechar}

\usepackage{luacode}
\begin{luacode*}
local function patch(fontdata)
    if string.match(fontdata.psname or "", "^EBGaramond") then
        fontdata.characters[0x03F5] = fontdata.characters[0x0454]
    end
end
luatexbase.add_to_callback("luaotfload.patch_font", patch, "missing glyph")
\end{luacode*}

\setmainfont{EB Garamond}
\setmathfont{Latin Modern Math}
\setmathfont{EB Garamond}[range=it]
\begin{document}
\begin{tabular}{cccc}
     & 03B5           & 03F5           & 0454           \\
text & ({\itshape ε}) & ({\itshape ϵ}) & ({\itshape є}) \\
math & ($\symit{ε}$)  & ($\symit{ϵ}$)  & {\scshape n/a} \\
\end{tabular}
\end{document}

answered Feb 26 '18 at 23:28

Henri Menke

109,596

Thanks! You changed EB Garamond Italic to EB Garamond at line 18. (also, why does unicode-math only load single files?) But I think the ebgaramond fonts in TeXLive are missing proper italic anyway, at least for this range. Adding back the Italic part with these fonts I am getting good results. – gnucchi Feb 27 '18 at 00:14
@svenper For some reason EB Garamond Italic could not be found in standard TeXlive 2017. unicode-math is not only loading single files (note that I just patch every font which starts with EBGaramond). The EB Garamond shipped with TeXlive is outdated, so it is to be expected that more recent versions provide better results. – Henri Menke Feb 27 '18 at 00:32
Is there a way to change the reported unicode value of the generated slot for more semantic search and copy paste, so that $\epsilon$ becomes GREEK LUNATE EPSILON SYMBOL and not CYRILLIC SMALL LETTER UKRAINIAN IE? – gnucchi Feb 28 '18 at 09:14
@svenper Not that I know of. I think at this point it might easier to just edit the font file using, e.g., FontForge. – Henri Menke Feb 28 '18 at 19:19
\setmathfont{EBGaramond12-Italic}[range=it] works for an italic glyph in math (other size can probably be set in the optional argument). – Ulrike Fischer Mar 01 '18 at 13:28

Filling an empty slot in a font with another glyph from the same font

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