bug#12600: 24.2.50; linum-mode: line numbers in fringe do not refresh when resizing frame

[martin rudalics <rudalics@gmx.at>]

 >> Replace the three struct members last_modified, last_overlay_modified
 >> and window_end_valid by one struct member called last_modified_flag -
 >> actually calling it window_modified would be better.  Set
 >> window_modified to t wherever we currently reset one of the three
 >> members.  Redisplay, when fully done, would reset window_modified to nil
 >> for every window it completes instead of setting the other members.
 >
 > And when a buffer is modified or its overlays are modified, what
 > should we do to indicate to redisplay that the corresponding windows
 > might need a more thorough redisplay?

When a window shows a buffer that has been modified since the last
redisplay, that buffer must be redrawn.  More precisely, redisplay would
walk all live windows and for each window

(1) Redraw if something in the window's buffer or a setting affecting
     the display of all buffers (like the cursor type) was modified.

(2) Redraw if the window itself has been modified.

(3) Don't redraw the window otherwise.  This would cover the case where
     `point' was moved in a buffer not shown in this window or another
     window was scrolled.

This would replace checking of windows_or_buffers_changed with a
finer-grained has "this window or its buffer changed".  But after a
cursory look at redisplay_window I doubt that such a change would be
feasible.  And I have no idea to which extent (3) is already covered by
try_window_id.

martin