Re: Ligatures (was: Unify the Platforms: Cairo+FreeType+Harfbuzz Everywhere (except TTY))

[Eli Zaretskii]

> Cc: address@hidden, address@hidden, address@hidden
> From: Clément Pit-Claudel <address@hidden>
> Date: Sat, 23 May 2020 10:34:23 -0400
> 
> > Emacs doesn't need a special list for each font.  I already said that
> > several times.  Please look at some examples of composition rules we
> > already have, for example the Arabic rules at the very end of
> > misc-lang.el.  Do you see any fonts mentioned there?  These rules work
> > with any font that supports Arabic.
> 
> The only thing I'm talking about is symbol compositions in programming fonts, 
> and for these, we *will* need a custom list for each font, right?

No, we won't need custom lists.  Not if we will use the same character
composition machinery as we use now for Arabic and other scripts that
require it.

> > And finally, if a given font doesn't support some ligature, the
> > original characters will be displayed "normally", so nothing is lost,
> > and there's no need to tune the list of ligatures to each and every
> > font.  I said that as well several times already.
> 
> As long as you can produce a superset of all ligatures, yes.  My claim is 
> that this superset is ".+".

It cannot be literally ".+", if you are talking about symbols, because
(a) not every character starts a symbol, and (b) symbols cannot be of
arbitrary length.

> Otherwise, how do you handle the fact that Fira Code handles arrows
> of arbitrary lengths?

We won't handle arrows of arbitrary length, no.  Not as long as we
keep the current design of the display engine.