Keep display mm width and height up to date after changes

* src/xfns.c (Fx_display_mm_width, Fx_display_mm_height): Use
new fields if they are set.
* src/xterm.c (handle_one_xevent): Set new fields on RRNotify if
the screen is correct.
* src/xterm.h (struct x_display_info): New fields
`screen_mm_width', `screen_mm_height'.

3 files changed, 20 insertions, 2 deletions

diff --git a/src/xfns.c b/src/xfns.c
index 401ad816955..8237e8870cd 100644
--- a/src/xfns.c
+++ b/src/xfns.c
@@ -5434,6 +5434,9 @@ for each physical monitor, use `display-monitor-attributes-list'.  */)
 {
   struct x_display_info *dpyinfo = check_x_display_info (terminal);
 
+  if (dpyinfo->screen_mm_height)
+    return make_fixnum (dpyinfo->screen_mm_height);
+
   return make_fixnum (HeightMMOfScreen (dpyinfo->screen));
 }
 
@@ -5451,6 +5454,9 @@ for each physical monitor, use `display-monitor-attributes-list'.  */)
 {
   struct x_display_info *dpyinfo = check_x_display_info (terminal);
 
+  if (dpyinfo->screen_mm_width)
+    return make_fixnum (dpyinfo->screen_mm_width);
+
   return make_fixnum (WidthMMOfScreen (dpyinfo->screen));
 }
 
diff --git a/src/xterm.c b/src/xterm.c
index 65d3eaf83f2..908185c3d10 100644
--- a/src/xterm.c
+++ b/src/xterm.c
@@ -20417,8 +20417,15 @@ handle_one_xevent (struct x_display_info *dpyinfo,
               notify = ((XRRScreenChangeNotifyEvent *) event);
               timestamp = notify->timestamp;
 
-              dpyinfo->screen_width = notify->width;
-              dpyinfo->screen_height = notify->height;
+              /* Don't set screen dimensions if the notification is
+                 for a different screen.  */
+              if (notify->root == dpyinfo->root_window)
+                {
+                  dpyinfo->screen_width = notify->width;
+                  dpyinfo->screen_height = notify->height;
+                  dpyinfo->screen_mm_width = notify->mwidth;
+                  dpyinfo->screen_mm_height = notify->mheight;
+                }
             }
           else
             timestamp = 0;
diff --git a/src/xterm.h b/src/xterm.h
index bc2e138aa99..c8e86d5d094 100644
--- a/src/xterm.h
+++ b/src/xterm.h
@@ -708,6 +708,11 @@ struct x_display_info
      that didn't happen.  */
   int screen_width;
   int screen_height;
+
+  /* The mm width and height of the screen.  Updated on
+     RRScreenChangeNotify.  */
+  int screen_mm_width;
+  int screen_mm_height;
 };
 
 #ifdef HAVE_X_I18N