[HarfBuzz] Ligatures

[Eli Zaretskii]

> Date: Sat, 23 May 2020 20:06:32 +0100
> From: Richard Wordingham <richard.wordingham at ntlworld.com>
> 
> There are three different tools for producing what looks like an "ffi"
> ligature:
> 
> 1) Make a ligature
> 2) Contextual substitution
> 3) A mix of contextual substitution and kerning.
> 
> A font that uses the first will produce a ligature for Emacs.
> 
> A font that uses contextual substitution will not work - you will just
> see the 3 unligated characters with their default glyphs.
> 
> A font that uses a mix of contextual substitution and kerning will
> likewise fail.  However, if is possible that you might get the "ff"
> ligature and a normal 'i', or a normal 'f' and an "fi" ligature.
> 
> From the point of view of someone who expects full shaping, what result
> you get will be arbitrary, depending on how the font designer has
> marshalled his tools.

I understand.  Still, the result looks reasonably good in most cases,
especially in an editor whose main purpose is to edit programs, and
which doesn't pretend to produce typographical accuracy.