bug#38199: 27.0.50; [Cairo] Display artifacts (small vertical colored bars)

[Bastian Beischer <bastian.beischer@gmail.com>]

On Thu, Nov 14, 2019 at 2:30 PM Eli Zaretskii <eliz@gnu.org> wrote:
>
> > From: Bastian Beischer <bastian.beischer@gmail.com>
> > Date: Wed, 13 Nov 2019 20:32:24 +0100
> >
> > When emacs is built with cairo I see small display artifacts from time
> > to time, in particular there are small thin vertical bars, for example,
> > with the default theme (starting from emacs -Q) I get those bars in the
> > mode-line and they are always in a cyan color, but it is possible that
> > other occurences can be observed even with emacs -Q.
> >
> > In real world usage I have seen these bars in regular buffers, too,
> > usually they are red and/or blue but that might depend on my theme.
> >
> > A recipe to produce them (on my machine) is:
> >
> > 1) emacs -Q
> > 2) M-<
> > 3) C-space
> > 4) M->
> > 5) M-w
> > 6) C-y (repeat ten or twenty times)
> >
> > Then move around in the resulting buffer and after a bit of cursor
> > movement the vertical lines appear. They are not permanent and often
> > disappear when the buffer is refreshed.
>
> Did you try to disable "advanced" or "optimization" features of your
> display driver software?  Or upgrade it to a newer version?  The
> artifacts your screenshot shows don't look like something Emacs could
> produce.

You are right: It could well be a cairo library or driver issue. I am
using the default optimized builds from the Arch Linux x86_64
repository, which means:

cairo: 1.17.2+17+g52a7c79fd-2
Xorg: 1.20.5-4
mesa: 19.2.3-2
linux: 5.3.11.1-1

My GPU is NVIDIA Geforce GTX 285 (nouveau kernel driver, combined with
modesetting / glamor). Should I report a bug against cairo?

>
> Can someone else reproduce this in a Cairo build?
>
> Thanks.