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Re: Ligature support

From: Eli Zaretskii
Subject: Re: Ligature support
Date: Sat, 06 Nov 2021 20:34:58 +0200

> From: Lars Ingebrigtsen <larsi@gnus.org>
> Cc: emacs-devel@gnu.org
> Date: Sat, 06 Nov 2021 19:08:30 +0100
> Eli Zaretskii <eliz@gnu.org> writes:
> > 30% slowdown is already a bad sign.
> Oh yeah, it means that we can't just do that.  If we want to send
> everything through hb_shape, we'd have to change our display to optimise
> for that case.  (Which I'm guessing would be a lot of work.)

We basically need to rethink the entire design of the display engine.
It starts with the basic premise in the design that buffer text is
examined one character at a time, and all the layout decisions for
that character are made before we proceed to the next character.  This
already required quite esoteric jumps through hoops to add character
composition (which needs to examine sequences of characters, and when
composable characters are detected, skip them all after processing
them).  If we want to pass most or all of the text through the shaping
engine all that needs to go away, and we need something very

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