Re: Tick Reduction

[Eli Zaretskii]

> From: Stefan Monnier <monnier@iro.umontreal.ca>
> Cc: larsi@gnus.org,  emacs-devel@gnu.org
> Date: Sat, 20 Nov 2021 09:06:45 -0500
> 
> Eli Zaretskii [2021-11-20 15:32:04] wrote:
> >> From: Stefan Monnier <monnier@iro.umontreal.ca>
> >> Cc: larsi@gnus.org,  emacs-devel@gnu.org
> >> Date: Sat, 20 Nov 2021 08:11:06 -0500
> >> >> Yes, we may have to declare that for functions that "emulate" the
> >> >> redisplay internally, the resulting horizontal position info might not
> >> >> always be quite right (might not reflect what you'll see on the glass)
> >> >> for text tat uses the new alignment functionality :-(
> >> > That will break quite a few features, I'm afraid.
> >> This will completely depend on the specifics of when/how the answer
> >> isn't quite right, of course.
> > AFAIU, it will never be right, as long as this kind of alignment is
> > used on display.
> 
> That completely depends on what the "redisplay emulation" code does.
> It could opt to use the old (unreliable) glyph matrix to compute its
> (documented as unreliable 🙍) info, in which case it could end up
> breaking less often (but more spectacularly when it does)?

As I explained earlier, that code cannot use the glyph matrix, because
it is required to work with text that is not displayed at all.