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From: Eli Zaretskii <eliz@gnu.org>
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Subject: Re: Ligatures
Date: Sat, 23 May 2020 16:10:31 +0300
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Cc: cpitclaudel@gmail.com, alan@idiocy.org, pipcet@gmail.com,
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To: Stefan Monnier <monnier@iro.umontreal.ca>
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In-Reply-To: <jwvlflilt61.fsf-monnier+emacs@gnu.org> (message from Stefan
 Monnier on Sat, 23 May 2020 08:47:57 -0400)
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> From: Stefan Monnier <monnier@iro.umontreal.ca>
> Cc: Pip Cet <pipcet@gmail.com>,  cpitclaudel@gmail.com,  alan@idiocy.org,
>   emacs-devel@gnu.org
> Date: Sat, 23 May 2020 08:47:57 -0400
> 
> I wonder how it is supposed to work and it works in other applications:

I have no idea.  If someone does, it would be good to hear the
details.

> Do current applications use a heuristic like "ligatures won't reduce the
> size by more than a factor 2, so estimate the lower bound on the final
> size to be at most half of what the font metrics say", so they will send
> up to twice as much text to be shaped as needed, and then they throw
> away the left overs?

As I wrote elsewhere, HarfBuzz developers actually prefer to see the
entire paragraph, not just screen line, because some shaping decisions
depend on that.  Not sure what the other applications do about that.