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

[Eli Zaretskii <eliz@gnu.org>]

> Date: Tue, 04 Feb 2014 08:17:38 +0200
> From: Dmitry Gutov <dgutov@yandex.ru>
> CC: 16621@debbugs.gnu.org, monnier@IRO.UMontreal.CA
> 
> > You mean, outside Emacs?  Yes, probably, but then this isn't an Emacs
> > issue, and I know absolutely nothing about it.
> 
> Would a windowing system know which Emacs display states are 
> "consistent", and which aren't?

If hints are needed, we could do that.

> AFAIU, flickering happens when the screen refreshes while Emacs display 
> is in an inconsistent state. Like, you've cleared a rectangle to paint a 
> character in it, but haven't yet painted it
> 
> If you copied the rendered state into a buffer, then cleared and painted 
> the character there, then rendered the buffer into the window as a 
> whole, the windowing system won't get a chance to see and display the 
> intermediate state.

Avoiding the cursor redraws sounds much easier, but again, I'm not an
expert on this.  Perhaps Jan could comment.