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Re: Variable pitch text filling

From: Feng Shu
Subject: Re: Variable pitch text filling
Date: Fri, 03 Dec 2021 16:17:56 +0800
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/29.0.50 (gnu/linux)

Eli Zaretskii <eliz@gnu.org> writes:

>> Date: Thu, 02 Dec 2021 22:18:51 +0200
>> From: Eli Zaretskii <eliz@gnu.org>
>> Cc: tumashu@163.com, larsi@gnus.org, emacs-devel@gnu.org
>> > Emacs adds spaces after the character under point, but the space obstructs 
>> > the character after. If I hold on C-f and go over every character, their 
>> > alignment are fixed:
>> Yes, I see it as well.  Strange.  I guess I'm missing something here.
>> Hmm...
> I'm very sorry.  This cannot work.  The problem is that we can easily
> change the pixel-width of the character glyphs Emacs uses for its
> layout calculations (which is what the change did), but when we
> actually draw the glyphs on the glass, we ask the font backend to draw
> a series of glyphs in one go, and the font backend uses the original
> glyph metrics as reported by the font.  So, unless we draw each glyph
> separately (which is what moving the cursor through text causes us to
> do), something that will slow down redisplay, we cannot add spacing to
> characters that way.
> This is one of the "TIL" situations each one of us has with Emacs from
> time to time.  It means my thinking about adding character spacing was
> based on wrong assumptions, and the only way to do that is to add
> stretch glyphs (which can be done only between words).
> I reverted the changeset installed yesterday.

this is really a bad news :-(


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