Re: Fallback fonts in LuaTeX via 'luaotfload.add_fallback' (was "Fontsets")

[Max Nikulin]

On 12/07/2022 22:26, Juan Manuel Macías wrote:
> Today I discovered that luaotfload included in v. 3.12 a new
> experimental function, luaotfload.add_fallback, to be able to add a list
> of fallback fonts to a LuaTeX document, at a low level.
...
>    \documentclass{article}
>    \usepackage{fontspec}
>    \directlua{
>    luaotfload.add_fallback ("fallbacktest",{
>    "oldstandard:mode=harf;script=grek;color=0000FF;",
>    "oldstandard:mode=harf;script=cyrl;color=0000FF;",
>    "freeserif:mode=harf;script=arab;color=0000FF;",
>    "freeserif:mode=harf;script=dev2;color=0000FF;",
>    })}
>    \setmainfont{latinmodernroman}[RawFeature={fallback=fallbacktest}]
...
> The main drawback I've found to this (at least I don't know how to solve
> it at the moment) is that the fallback feature cannot be added via
> \defaultfontfeatures. That would avoid having to (re)define all the
> main/sans/mono/math families.

I agree that defining fallbacks for each font family is inconvenient. 
Defining font per script resembles specifying fonts per language in 
babel configuration, however fallback should work without explicit 
switching of language. I have seen that babel may determine language 
from character code points, but I have not tried if it works reliable 
and if it affects performance (as it does for fallback fonts).

Maybe I did not read the manual with enough attention, maybe I tried it 
with too old version of LuaTeX, but I had a problem with Emoji. 
Depending on font such symbols either broke compilation or did not 
appear in PDF (accordingly to pdffonts font was embedded, text may be 
copied, but PDF viewers displayed blank space).

https://list.orgmode.org/orgmode/scuirf$m7o$1@ciao.gmane.io/
Maxim Nikulin. Re: org-mode export to (latex) PDF. Sat, 17 Jul 2021 
19:35:57 +0700