[gtk/gtk-3-24: 1/2] gdk: quartz: prevent titlebar events from falling to the window below

[Matthias Clasen <matthiasc src gnome org>]

commit f91b42983937c94a2875af3498fa2ea6078ec58d
Author: Jeremy Tan <jtanx outlook com>
Date:   Sat Oct 19 18:15:35 2019 +0800

    gdk: quartz: prevent titlebar events from falling to the window below

 gdk/quartz/gdkevents-quartz.c | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)
---
diff --git a/gdk/quartz/gdkevents-quartz.c b/gdk/quartz/gdkevents-quartz.c
index d525759a4f..d97cebd2bd 100644
--- a/gdk/quartz/gdkevents-quartz.c
+++ b/gdk/quartz/gdkevents-quartz.c
@@ -457,6 +457,29 @@ get_toplevel_from_ns_event (NSEvent *nsevent,
            * here, not very nice.
            */
           _gdk_quartz_events_break_all_grabs (get_time_from_ns_event (nsevent));
+
+          /* Check if the event occurred on the titlebar. If it did,
+           * explicitly return NULL to prevent going through the
+           * fallback path, which could match the window that is
+           * directly under the titlebar.
+           */
+          if (view_point.y < 0 &&
+              view_point.x >= view_frame.origin.x &&
+              view_point.x < view_frame.origin.x + view_frame.size.width)
+            {
+              NSView *superview = [view superview];
+              if (superview)
+                {
+                  NSRect superview_frame = [superview frame];
+                  int titlebar_height = superview_frame.size.height -
+                                        view_frame.size.height;
+
+                  if (titlebar_height > 0 && view_point.y >= -titlebar_height)
+                    {
+                      return NULL;
+                    }
+                }
+            }
         }
       else
         {