Re: Display of decomposed characters

[Philipp Stephani]

Am Mi., 23. Dez. 2020 um 16:44 Uhr schrieb Eli Zaretskii <eliz@gnu.org>:
>
> > From: Philipp Stephani <p.stephani2@gmail.com>
> > Date: Wed, 23 Dec 2020 11:05:13 +0100
> >
> > Before filing a bug, I wanted to ask whether the following Emacs
> > behavior is intentional: Even with Cairo and Harfbuzz, Emacs displays
> > decomposed Unicode characters (e.g. "a" followed by U+0308 COMBINING
> > DIAERESIS) as separate glyphs. While that's not technically wrong, I
> > think it would be better to display them as a single glyph, in other
> > words, not distinguish between canonically equivalent Unicode strings.
>
> They are (or should be) displayed as a composed glyph if you are using
> a font that supports both a and COMBINING DIAERESIS.  Emacs cannot
> compose characters that aren't supported by the same font (because
> composition processing stops at face boundaries, and each font defines
> internally a separate face).

Interesting. Indeed the two glyphs come from different fonts. Is there
a way to force a single font for both of them? Or should the algorithm
be changed to perform composition before font selection?