Add a hook run upon monitor configuration changes

* doc/lispref/frames.texi (Multiple Terminals): Document new
hook `display-monitors-changed-functions'.
* etc/NEWS: Announce new abnormal hook.

* src/keyboard.c (kbd_buffer_get_event): Handle
MONITORS_CHANGED_EVENT.
(syms_of_keyboard): New hook and defsyms.
* src/termhooks.h (enum event_kind): Add new event
`MONITORS_CHANGED_EVENT'.

* src/xterm.c (handle_one_xevent): Handle RRNotify and
RRScreenChangeNotify events.
(x_term_init): Select for RRScreenChange, RRCrtcChange and
RROutputChange.
* src/xterm.h (struct x_display_info): Improve RandR version
detection.

1 files changed, 10 insertions, 0 deletions

diff --git a/doc/lispref/frames.texi b/doc/lispref/frames.texi
index 5ea060871f4..7d600b5a0c5 100644
--- a/doc/lispref/frames.texi
+++ b/doc/lispref/frames.texi
@@ -458,6 +458,16 @@ monitor, the same string as returned by the function
 @var{display} should be the name of an X display (a string).
 @end deffn
 
+@cindex monitor change functions
+@defvar display-monitors-changed-functions
+This variable is an abnormal hook run when the monitor configuration
+changes, which can happen if a monitor is rotated, moved, added or
+removed from a multiple-monitor setup, if the primary monitor changes,
+or if the resolution of a monitor changes.  It is called with a single
+argument consisting of the terminal on which the monitor configuration
+changed.
+@end defvar
+
 @node Frame Geometry
 @section Frame Geometry
 @cindex frame geometry