x11: Add another mechanism to ignore crossing events

This is similar, but reserved for the crossing events induced by the
input shape changes on our overlay window. The mechanism in the previous
commit does again protect against this, so this mechanism may go away.

Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/3267>

src/x11/events.c

@@ -920,35 +920,6 @@ handle_window_focus_event (MetaX11Display *x11_display,
     }
 }
 
-static gboolean
-crossing_serial_is_ignored (MetaX11Display *x11_display,
-                            unsigned long   serial)
-{
-  int i;
-
-  i = 0;
-  while (i < N_IGNORED_CROSSING_SERIALS)
-    {
-      if (x11_display->ignored_crossing_serials[i] == serial)
-        return TRUE;
-      ++i;
-    }
-  return FALSE;
-}
-
-static void
-reset_ignored_crossing_serials (MetaX11Display *x11_display)
-{
-  int i;
-
-  i = 0;
-  while (i < N_IGNORED_CROSSING_SERIALS)
-    {
-      x11_display->ignored_crossing_serials[i] = 0;
-      ++i;
-    }
-}
-
 static gboolean
 handle_input_xevent (MetaX11Display *x11_display,
                      XIEvent        *input_event,
@@ -991,7 +962,7 @@ handle_input_xevent (MetaX11Display *x11_display,
       /* Check if we've entered a window; do this even if window->has_focus to
        * avoid races.
        */
-      if (window && !crossing_serial_is_ignored (x11_display, serial) &&
+      if (window &&
           enter_event->mode != XINotifyGrab &&
           enter_event->mode != XINotifyUngrab &&
           enter_event->detail != XINotifyInferior &&
@@ -1002,12 +973,6 @@ handle_input_xevent (MetaX11Display *x11_display,
                                     enter_event->time,
                                     enter_event->root_x,
                                     enter_event->root_y);
-
-          if (window->type != META_WINDOW_DOCK)
-            {
-              /* stop ignoring stuff */
-              reset_ignored_crossing_serials (x11_display);
-            }
         }
       break;
     case XI_Leave:

src/x11/meta-x11-display-private.h

@@ -37,15 +37,6 @@
 #include "meta-x11-stack-private.h"
 #include "x11/meta-sync-counter.h"
 
-/* This is basically a bogus number, just has to be large enough
- * to handle the expected case of the alt+tab operation, where
- * we want to ignore serials from UnmapNotify on the tab popup,
- * and the LeaveNotify/EnterNotify from the pointer ungrab. It
- * also has to be big enough to hold ignored serials from the point
- * where we reshape the stage to the point where we get events back.
- */
-#define N_IGNORED_CROSSING_SERIALS  10
-
 typedef struct _MetaGroupPropHooks  MetaGroupPropHooks;
 typedef struct _MetaWindowPropHooks MetaWindowPropHooks;
 
@@ -165,12 +156,6 @@ struct _MetaX11Display
 
   guint closing : 1;
 
-  /* serials of leave/unmap events that may
-   * correspond to an enter event we should
-   * ignore
-   */
-  unsigned long ignored_crossing_serials[N_IGNORED_CROSSING_SERIALS];
-
   int composite_event_base;
   int composite_error_base;
   int composite_major_version;

src/x11/meta-x11-display.c

@@ -1294,13 +1294,6 @@ meta_x11_display_new (MetaDisplay  *display,
   x11_display->server_focus_window = None;
   x11_display->server_focus_serial = 0;
 
-  i = 0;
-  while (i < N_IGNORED_CROSSING_SERIALS)
-    {
-      x11_display->ignored_crossing_serials[i] = 0;
-      ++i;
-    }
-
   x11_display->prop_hooks = NULL;
   meta_x11_display_init_window_prop_hooks (x11_display);
   x11_display->group_prop_hooks = NULL;
@@ -2333,29 +2326,6 @@ prefs_changed_callback (MetaPreference pref,
     }
 }
 
-static void
-meta_x11_display_add_ignored_crossing_serial (MetaX11Display *x11_display,
-                                              unsigned long   serial)
-{
-  int i;
-
-  /* don't add the same serial more than once */
-  if (serial ==
-      x11_display->ignored_crossing_serials[N_IGNORED_CROSSING_SERIALS - 1])
-    return;
-
-  /* shift serials to the left */
-  i = 0;
-  while (i < (N_IGNORED_CROSSING_SERIALS - 1))
-    {
-      x11_display->ignored_crossing_serials[i] =
-        x11_display->ignored_crossing_serials[i + 1];
-      ++i;
-    }
-  /* put new one on the end */
-  x11_display->ignored_crossing_serials[i] = serial;
-}
-
 void
 meta_x11_display_set_stage_input_region (MetaX11Display *x11_display,
                                          XserverRegion   region)
@@ -2370,15 +2340,6 @@ meta_x11_display_set_stage_input_region (MetaX11Display *x11_display,
   stage_xwindow = meta_x11_get_stage_window (stage);
   XFixesSetWindowShapeRegion (xdisplay, stage_xwindow,
                               ShapeInput, 0, 0, region);
-
-  /*
-   * It's generally a good heuristic that when a crossing event is generated
-   * because we reshape the overlay, we don't want it to affect
-   * focus-follows-mouse focus - it's not the user doing something, it's the
-   * environment changing under the user.
-   */
-  meta_x11_display_add_ignored_crossing_serial (x11_display,
-                                                XNextRequest (xdisplay));
   XFixesSetWindowShapeRegion (xdisplay,
                               x11_display->composite_overlay_window,
                               ShapeInput, 0, 0, region);