bug#16621: 24.3.50; Periodic timer + overlays = flickering near point

[Eli Zaretskii]

> From: Stefan Monnier <monnier@iro.umontreal.ca>
> Cc: jan.h.d@swipnet.se,  dgutov@yandex.ru,  16621@debbugs.gnu.org
> Date: Thu, 06 Feb 2014 08:08:08 -0500
> 
> > window that might need it.  The second phase, which is entered from
> > update_frame or update_window, compares the "desired" matrices with
> > the "current" ones, and actually redraws the changed portions of the
> > display, if any.  This second phase knows nothing about the flags you
> > mention, and doesn't need to, because it already refrains from
> > displaying the screen portions which didn't change.
> 
> IIUC it does know a bit about it, in that only frames which had
> a redisplay bit set somewhere are passed to update_frame (at least that
> was the intention).

Maybe I'm blind, but I don't see that.  In any case, the selected
frame seems to be updated regardless, if only we come to the 'update'
label in redisplay_internal.  We can avoid that label, but not when
echo-area display is active.