bug#19721: 25.0.50; Mode-line not redrawn with expose events

[Eli Zaretskii <eliz@gnu.org>]

> Date: Sun, 01 Feb 2015 09:51:30 +0100
> From: martin rudalics <rudalics@gmx.at>
> CC: 19721@debbugs.gnu.org
> 
>  > If I apply both changes, mode-lines are redrawn when exposed, but some
>  > of them are not updated with C-x o.
> 
> What happens when you do something trivial like
> 
> --- a/src/window.c
> +++ b/src/window.c
> @@ -524,6 +524,8 @@ select_window (Lisp_Object window, Lisp_Object norecord, int inhibit_point_swap)
>         record_buffer (w->contents);
>       }
> 
> +  w->update_mode_line = 1;
> +
>     return window;
>   }

Thanks.

I didn't try your suggestion, but (a) it would force redrawing the
mode line even if that's not needed, just because a window got
selected, and (b) there's a tricky condition near the beginning of
redisplay_window that would bypass redisplaying a window, under some
conditions, even if its update_mode_line flag was set (my last patch
attempts at fixing that).

So I'm not sure this is the right solution.  The situation described
in this report is quite unique, in that the face used for the active
mode line causes the window glyph matrices to be resized each time a
window becomes non-selected one.  It is because of this resizing that
the mode-line row of the current matrix becomes disabled.