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

[Eli Zaretskii]

> From: "Jan D." <jan.h.d@swipnet.se>
> Date: Tue, 4 Feb 2014 23:08:13 +0100
> Cc: Dmitry Gutov <dgutov@yandex.ru>,
>  "16621@debbugs.gnu.org" <16621@debbugs.gnu.org>,
>  "monnier@IRO.UMontreal.CA" <monnier@IRO.UMontreal.CA>
> 
> So, if there is a way to avoid cursor redraws, go for it.

Can you tell when does the cursor need to be redrawn on X?

> Double buffering is a port specific solution, unless the display engine does 
> double buffering by having two sets of glyphs and compares them to see what 
> has really changed. Sounds like a big project.

We do have 2 sets of glyphs, but they are not guaranteed to be
complete: we only care about the portions of display that changed, so
the parts that we know didn't change we don't bother updating.