Re: Ligature support

[Eli Zaretskii]

> From: Lars Ingebrigtsen <larsi@gnus.org>
> Cc: gregory@heytings.org,  mattiase@acm.org,  emacs-devel@gnu.org,
>   schwab@linux-m68k.org,  stefankangas@gmail.com,  raman@google.com
> Date: Fri, 05 Nov 2021 16:20:19 +0100
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> 
> > Why do we need to depend on the font?  As I said, if the font doesn't
> > have a ligature, font-shape-gstring will return nil, and we will then
> > display the characters as individual glyphs.  Isn't that what is
> > expected?
> 
> Different fonts have different ligatures (or "ligatures").  Since we
> don't want to send all strings through font-shape-gstring (because
> that'll be slow), we'll have to be selective as usual, I think?

How many ligatures are there in the best of all fonts?  If the number
of the ligatures is not too large, then passing them to the shaper may
not be such a terrible idea.

So I think we should first consider which ligatures we'd like to
support, and whether the answer differs depending on the major mode.
For example, ligatures like ==> etc. are relevant to prog-mode modes,
but probably not to text modes.  By contrast, "ff" and "fi" are
relevant only to text mode, I think.