Re: Variable pitch text filling

[Eli Zaretskii <eliz@gnu.org>]

> From: Lars Ingebrigtsen <larsi@gnus.org>
> Cc: casouri@gmail.com,  tumashu@163.com,  emacs-devel@gnu.org
> Date: Sat, 04 Dec 2021 06:41:43 +0100
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> 
> >> If that's the case, perhaps we could stop doing that if we're doing a
> >> gridded display?
> >
> > That'd be much slower, I guess?  For each such separate glyph we need
> > first clear the background with the color of the face, then draw the
> > glyph itself.  Right now, we clear the background for all of the
> > glyphs in one GUI call, then write all of the glyphs in a single call
> > to the font driver.
> 
> Perhaps we could try to benchmark -- it might be acceptable (and we
> wouldn't be doing this in all buffers normally).

Actually, CJK users are likely to turn this on globally.

> But I don't know how to benchmark this.

Write some Lisp to add a (space :width (1)) display spec on every
second letter of a large buffer, and then scroll through it one line
at a time, calling redisplay after each scroll.  You'd probably need
to disable double-buffering, to avoid its skewing the results.  Some
of the slowdown will be due to processing the display properties, but
if we care about that, we could measure just that separately and
subtract.