Re: Display of decomposed characters

[Eli Zaretskii <eliz@gnu.org>]

> From: Philipp <p.stephani2@gmail.com>
> Date: Thu, 18 Mar 2021 15:16:42 +0100
> Cc: help-gnu-emacs@gnu.org
> 
> >  . we check whether the current character should compose with the
> >    following and/or preceding ones
> 
> Is my understanding right that this is the step that comes too late, i.e. after font selection?

It comes after the font selection, yes.  And it cannot be any other
way, because the shaping engine must have the font to return any
meaningful results.  The results of text shaping depend heavily on the
font and its capabilities and features it supports.

> Otherwise I'd assume that the answer is always "yes" if the current character is a combining character.

Not only combining characters should be composed.  In fact, in Emacs
you can compose anything with anything else by tweaking a Lisp data
structure.

> >> What if Emacs ignored font lookup for combining characters and always picked the font of the previous base character?
> > 
> > What would that produce if the font of the previous character didn't
> > have a glyph for the accent?  The accent will disappear, or maybe will
> > be displayed as "tofu", right?  Does that sound like a good strategy?
> 
> Can't the shaping engine produce fake compositions in that case?

What do you mean by "fake compositions"? what would they entail, and
which glyphs would they use?

> >  That's bound to happen when a response comes more
> > than a month after the original exchange.
> 
> Yes, but unfortunately answering these questions takes some time, which I don't always have.  I'll try to respond more timely in the future, but I can't really promise that.

You don't have to promise, but you must understand that such long
pauses almost guarantee that misunderstandings are more frequent.