Re: Emacs 28: Specific TTF font gets loaded with font-backend x instead of ftcrhb

[Eli Zaretskii]

> From: Tassilo Horn <tsdh@gnu.org>
> Cc: help-gnu-emacs@gnu.org
> Date: Tue, 04 Feb 2020 19:43:38 +0100
> 
> Is "the new way" the thing with composition-function-table?

Yes.  We should use the so-called "automatic composition", which works
via composition-function-table (as opposed to "static composition"
currently used by prettify-symbols-mode).

> Something like the Fira Code font emacs setup shown here?
> 
>   
> https://github.com/tonsky/FiraCode/wiki/Emacs-instructions#using-composition-char-table

Something like that, yes.

> I've tried that code although with the PragmataPro font in the hope it
> would work at least partly given that both fonts offer a quite large
> common subset of ligatures but couldn't see any difference, e.g., -> is
> not composed to an arrow.

That probably means PragmataPro doesn't support ligatures, at least
not the one for ->.

> Is there any documentation I could read?

This area is notoriously under-documented.  What we have (and it's
abysmally insufficient) is this:

 . the code in composite.el, including the basic composition rules for
   accented characters
 . the code which sets composition-function-table in the various files
   under lisp/language/, where language-specific composition rules are
   provided
 . the doc string of composition-get-gstring (the only place where we
   document the form of the vectors shown by "C-u C-x =" for composed
   character sequences)