wayland/surface-role: Keep track of the surface main monitor

Toplevels get the main monitor from their MetaWindow and have no main
monitor when the toplevel is not mapped.

Subsurfaces get the main monitor from their parent surface.

DnD and cursors get the main monitor from the current cursor position no
matter if the cursor is actually being shown or not.

Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/3941>

src/core/window.c

@@ -223,6 +223,7 @@ enum
   PROP_EFFECT,
   PROP_SUSPEND_STATE,
   PROP_MAPPED,
+  PROP_MAIN_MONITOR,
 
   PROP_LAST,
 };
@@ -444,6 +445,9 @@ meta_window_get_property(GObject         *object,
     case PROP_MAPPED:
       g_value_set_boolean (value, win->mapped);
       break;
+    case PROP_MAIN_MONITOR:
+      g_value_set_object (value, win->monitor);
+      break;
     default:
       G_OBJECT_WARN_INVALID_PROPERTY_ID (object, prop_id, pspec);
       break;
@@ -614,6 +618,11 @@ meta_window_class_init (MetaWindowClass *klass)
                           FALSE,
                           G_PARAM_READABLE | G_PARAM_STATIC_STRINGS);
 
+  obj_props[PROP_MAIN_MONITOR] =
+    g_param_spec_object ("main-monitor", NULL, NULL,
+                         META_TYPE_LOGICAL_MONITOR,
+                         G_PARAM_READABLE | G_PARAM_STATIC_STRINGS);
+
   g_object_class_install_properties (object_class, PROP_LAST, obj_props);
 
   window_signals[WORKSPACE_CHANGED] =
@@ -965,6 +974,8 @@ meta_window_main_monitor_changed (MetaWindow               *window,
   if (window->monitor)
     g_signal_emit_by_name (window->display, "window-entered-monitor",
                            window->monitor->number, window);
+
+  g_object_notify_by_pspec (G_OBJECT (window), obj_props[PROP_MAIN_MONITOR]);
 }
 
 MetaLogicalMonitor *

src/wayland/meta-wayland-cursor-surface.c

@@ -92,9 +92,6 @@ cursor_sprite_prepare_at (MetaCursorSprite         *cursor_sprite,
 {
   MetaWaylandSurfaceRole *role = META_WAYLAND_SURFACE_ROLE (cursor_surface);
   MetaWaylandSurface *surface = meta_wayland_surface_role_get_surface (role);
-
-  if (!meta_wayland_surface_is_xwayland (surface))
-    {
   MetaContext *context =
     meta_wayland_compositor_get_context (surface->compositor);
   MetaBackend *backend = meta_context_get_backend (context);
@@ -104,6 +101,9 @@ cursor_sprite_prepare_at (MetaCursorSprite         *cursor_sprite,
 
   logical_monitor =
     meta_monitor_manager_get_logical_monitor_at (monitor_manager, x, y);
+
+  if (!meta_wayland_surface_is_xwayland (surface))
+    {
       if (logical_monitor)
         {
           int surface_scale = surface->applied_state.scale;
@@ -121,6 +121,7 @@ cursor_sprite_prepare_at (MetaCursorSprite         *cursor_sprite,
         }
     }
 
+  meta_wayland_surface_set_main_monitor (surface, logical_monitor);
   meta_wayland_surface_update_outputs (surface);
 }
 

src/wayland/meta-wayland-data-device.c

@@ -483,13 +483,24 @@ static void
 data_device_update_position (MetaWaylandDragGrab *drag_grab,
                              graphene_point_t    *point)
 {
+  MetaWaylandCompositor *compositor =
+    meta_wayland_seat_get_compositor (drag_grab->seat);
+  MetaContext *context = meta_wayland_compositor_get_context (compositor);
+  MetaBackend *backend = meta_context_get_backend (context);
+  MetaMonitorManager *monitor_manager =
+    meta_backend_get_monitor_manager (backend);
   MetaFeedbackActor *feedback_actor =
     META_FEEDBACK_ACTOR (drag_grab->feedback_actor);
+  MetaLogicalMonitor *monitor;
 
   if (!drag_grab->drag_surface)
     return;
 
   meta_feedback_actor_set_position (feedback_actor, point->x, point->y);
+
+  monitor = meta_monitor_manager_get_logical_monitor_at (monitor_manager,
+                                                         point->x, point->y);
+  meta_wayland_surface_set_main_monitor (drag_grab->drag_surface, monitor);
 }
 
 static gboolean

src/wayland/meta-wayland-shell-surface.c

@@ -36,6 +36,7 @@ typedef struct _MetaWaylandShellSurfacePrivate
 
   gulong unmanaging_handler_id;
   gulong highest_scale_monitor_handler_id;
+  GBinding *main_monitor_binding;
 } MetaWaylandShellSurfacePrivate;
 
 G_DEFINE_ABSTRACT_TYPE_WITH_PRIVATE (MetaWaylandShellSurface,
@@ -114,6 +115,9 @@ clear_window (MetaWaylandShellSurface *shell_surface)
     clutter_actor_set_reactive (CLUTTER_ACTOR (surface_actor), FALSE);
 
   meta_wayland_surface_notify_unmapped (surface);
+
+  meta_wayland_surface_set_main_monitor (surface, NULL);
+  g_clear_object (&priv->main_monitor_binding);
 }
 
 static void
@@ -151,6 +155,11 @@ meta_wayland_shell_surface_set_window (MetaWaylandShellSurface *shell_surface,
 
   meta_window_update_monitor (window, META_WINDOW_UPDATE_MONITOR_FLAGS_NONE);
 
+  priv->main_monitor_binding =
+    g_object_bind_property (G_OBJECT (window), "main-monitor",
+                            G_OBJECT (surface), "main-monitor",
+                            G_BINDING_DEFAULT | G_BINDING_SYNC_CREATE);
+
   priv->highest_scale_monitor_handler_id =
     g_signal_connect_swapped (window, "highest-scale-monitor-changed",
                               G_CALLBACK (meta_wayland_surface_notify_highest_scale_monitor),

src/wayland/meta-wayland-surface.c

@@ -707,6 +707,7 @@ meta_wayland_surface_apply_placement_ops (MetaWaylandSurface      *parent,
       if (!op->sibling)
         {
           surface->applied_state.parent = NULL;
+          meta_wayland_surface_set_main_monitor (surface, NULL);
           continue;
         }
 
@@ -732,6 +733,8 @@ meta_wayland_surface_apply_placement_ops (MetaWaylandSurface      *parent,
                                 surface->applied_state.subsurface_branch_node);
           break;
         }
+
+      meta_wayland_surface_set_main_monitor (surface, parent->main_monitor);
     }
 }
 
@@ -2559,6 +2562,8 @@ meta_wayland_surface_set_main_monitor_internal (MetaWaylandSurface *surface,
                                                 MetaLogicalMonitor *logical_monitor,
                                                 gconstpointer       not_this_monitor)
 {
+  MetaWaylandSurface *subsurface_surface;
+
   if (surface->main_monitor == logical_monitor)
     return;
 
@@ -2579,6 +2584,10 @@ meta_wayland_surface_set_main_monitor_internal (MetaWaylandSurface *surface,
   surface->main_monitor = logical_monitor;
 
   g_object_notify_by_pspec (G_OBJECT (surface), obj_props[PROP_MAIN_MONITOR]);
+
+  META_WAYLAND_SURFACE_FOREACH_SUBSURFACE (&surface->committed_state,
+                                           subsurface_surface)
+    meta_wayland_surface_set_main_monitor (subsurface_surface, logical_monitor);
 }
 
 static void