Subject: bug#77039: 31.0.50; Flickering on macOS

From: Eli Zaretskii <[email-masked]>
Date: Sun, 23 Mar 2025 12:37:25 +0200

> Cc: [email-masked], [email-masked], [email-masked]
> Date: Sun, 23 Mar 2025 12:13:10 +0200
> From: Eli Zaretskii <[email-masked]>
> 
> So in summary, I don't see anything abnormal here.  If we want to keep
> the only-current-line-changed optimization in redisplay_internal,
> someone will have to come up with a smarter test for when line numbers
> are shown.  I think the underlying problem is that when the line
> number of the current line becomes large enough to require more
> columns for line-number display, we must redraw the entire window to
> avoid the problem with shifting or line number described in
> https://debbugs.gnu.org/cgi/bugreport.cgi?bug=54091#5 .

To clarify: this should not cause any flickering, AFAIU, because the
comparison of glyphs in subroutines of update_frame is supposed to
find that everything on the glass is already up-to-date and there's no
need to draw anything.  So flickering, which happens because portions
of the window are actually redrawn on the glass, should not happen in
this case.