bug#44180: 28.0.50; Emacs frames won't redisplay unless resized

[Eli Zaretskii <eliz@gnu.org>]

> From: Eric Abrahamsen <eric@ericabrahamsen.net>
> Cc: 44180@debbugs.gnu.org
> Date: Sun, 25 Oct 2020 09:28:09 -0700
> 
> >> Before the breakage, it's possible that the non-visible frames were not
> >> updated while they remained invisible, and I simply never knew because
> >> I couldn't see them. Now they stay un-updated until I manipulate the
> >> size of the window somehow.
> >
> > That seems to suggest that we don't trigger expose_frame calls anymore
> > for the frames that become un-fontified?
> 
> I wouldn't know, but that certainly sounds likely. I'd be happy to try
> contacting someone at i3, if that would be helpful, or to try fiddling
> with the display code.

What would help is if you put a breakpoint at expose_frame, and see
how it is called when the changes made by the offending commit are
reverted.  Please show which X event triggers that and with what
parameters.  Then do the same with the offending changes in place, and
try to figure out why the expose event doesn't get triggered.

Armed with that info, we could try finding a way of having the cake
and eating it, too.

TIA