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

[martin rudalics <rudalics@gmx.at>]

 > Emacs uses standard Xlib calls to draw its windows and communicate to
 > X the dimensions to be used to clip partially visible lines.  Any
 > program that does the same will bump into the same issues.

Today hardly any program restricts window sizes in the way Emacs does
via size hints.

 > It's not possible to solve it in Emacs, but not in general.

There must be one "not" too many here ;-)

 > Your card
 > probably has firmware, which could be updated, and a device driver,
 > which could be upgraded.  I'd suggest to do that, if at all possible
 > and practical.  Or even replace the card with another one.
 >
 >> So I kindly ask you: please, provide a way to make Emacs optionally
 >> redraw the mode-line after any scroll operation. ;-)
 >
 > I'm not yet convinced that Emacs can do _anything_ to provide a
 > workaround for this problem.  See my other messages as to why.

We should make sure that the bug happens with every pixelwise resize
operation, for example, when dragging the mode line between windows.  If
it doesn't happen in such cases, the problem might be due in some sort
of interference of the window manager which simply doesn't like Emacs to
make a frame fullscreen when at the same time fullscreen doesn't match
Emacs' size hints.

martin