[HarfBuzz] Ligatures

[Eli Zaretskii]

> Date: Sat, 23 May 2020 16:33:12 +0100
> From: Richard Wordingham <richard.wordingham at ntlworld.com>
> 
> On Sat, 23 May 2020 11:25:38 +0300
> Eli Zaretskii <eliz at gnu.org> wrote:
> 
> > > From: Khaled Hosny <dr.khaled.hosny at gmail.com>
> > > Date: Sat, 23 May 2020 09:51:21 +0200
> > > Cc: harfbuzz at lists.freedesktop.org
> > > What are you going to do about kerning, or mark positioning?
> > > Partially kerning arbitrary glyphs (because the sub string match
> > > some regular expression) is worse than not kerning at all.  
> > 
> > I don't think I understand the question.  How is kerning related to
> > the issue at hand?  I'm not an expert on typesetting text (so maybe I
> > don't even understand what exactly is meant by "kerning" in this
> > context), so please tell more details about this.
> 
> The simplest way of laying out proportionally spaced text is to have a
> fixed glyph-dependent distance ('advance width') from the 'origin' of a
> glyph to the origin of the next glyph and simply lay them out in a
> sequence, like movable type. However, if one chooses widths suitable
> for the sequences 'AM' and 'MV', then there may be an unsightly gap in
> the middle of 'AV'. Kerning is basically the process of adjusting those
> gaps.  Kerning is done by the shaper.  To do it, it needs the
> whole sequence of characters.

Ah, okay, thanks.  Then yes, Emacs just uses the advance width that we
get from the metrics of each glyph.