bug#18912: 24.4; mode-line corruption on graphical frames in dual-headed display

[Eli Zaretskii <eliz@gnu.org>]

> From: Stefan Monnier <monnier@iro.umontreal.ca>
> Date: Fri, 31 Oct 2014 16:30:18 -0400
> Cc: 18912@debbugs.gnu.org
> 
> > In this setup GNU Emacs corrupts the mode-line (a graphical glitch)
> > drawing over it the buffer's line that would otherwise be below it.
> 
> My guess is that it's a bug in the X11 acceleration code for your
> graphics card.

How could the graphics card "know" the details of the file that should
not be visible in the window?  The text that overwrites the mode line
is not for any of the files shown above the mode line, it's the file
that is the next one in the listing.  So the only way the acceleration
could cause that is if it returned incorrect information about the
display dimensions/pixel size.  I cannot explain to myself how this
kind of bug in the graphics card could affect Emacs, except perhaps in
a maximized frame.

Bruno, do these problems happen in a non-maximized frame, e.g. the one
you get immediately after invoking "emacs -Q"?