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

["Bruno Félix Rezende Ribeiro" <oitofelix@gnu.org>]

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Eli Zaretskii wrote:
> Again identical.  Looks like indeed it's some problem with your
> graphics card, because Emacs gets the same information in both cases:
> in both cases, only 1 pixel of the last line is visible.
> 
> I'll try to think about additional tests, but meanwhile I suggest that
> you try lowering the level of the acceleration of your card, and see
> if that helps.

Totally disabling acceleration by using the driver's option "NoAccel",
seems to fix the problem.

The conclusion we reach is that it's not an Emacs bug, despite the fact
that this weirdness only manifests in Emacs.  I never have had any
problem with my graphics card in the 5 years of usage of this machine,
working with any kind of application you can imagine, being the "Emacs
bug" the only exception.

So we came to the point where we actually find that it's not possible to
solve the bug, because it's beyond the realm of Emacs.  That doesn't
mean, however, that Emacs can't help to work around it!  As Emacs is the
only piece of software, that I know of, that triggers the bug, it's in
principle equivalent to fix the problem in its root, or to make Emacs to
work around it.  Solving the actual bug seems at first glance much
harder, as no one knows what's actually causing this mysterious bug,
that only manifests in Emacs.  On the other hand, we have a clear
understanding of what feature Emacs has to provide to *virtually* fix
the bug.

So I kindly ask you: please, provide a way to make Emacs optionally
redraw the mode-line after any scroll operation. ;-)

-- 
 ,= ,-_-. =.  Bruno Félix Rezende Ribeiro (oitofelix) [0x28D618AF]
((_/)o o(\_)) There is no system but GNU;
 `-'(. .)`-'  GNU Linux-Libre is one of its official kernels;
     \_/      All software must be free as in freedom;


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