Tightly integrate tree updates with surface rendering, so there's always at least one tree update before each surface commit, as required by Newton, without the AccessKit context having to do extra surface commits itself. This should also prevent multiple tree updates per frame across platforms.

gdk/wayland/gdksurface-wayland.c

@@ -449,6 +449,14 @@ gdk_wayland_surface_commit (GdkSurface *surface)
   wl_surface_commit (impl->display_server.wl_surface);
 }
 
+void
+gdk_wayland_surface_force_next_commit (GdkSurface *surface)
+{
+  GdkWaylandSurface *impl = GDK_WAYLAND_SURFACE (surface);
+
+  impl->has_pending_subsurface_commits = TRUE;
+}
+
 void
 gdk_wayland_surface_notify_committed (GdkSurface *surface)
 {

gdk/wayland/gdkwaylandsurface.h

@@ -43,5 +43,8 @@ GType                    gdk_wayland_surface_get_type             (void);
 GDK_AVAILABLE_IN_ALL
 struct wl_surface       *gdk_wayland_surface_get_wl_surface       (GdkSurface *surface);
 
+GDK_AVAILABLE_IN_ALL
+void                     gdk_wayland_surface_force_next_commit    (GdkSurface *surface);
+
 G_END_DECLS
 

gtk/a11y/gtkaccesskitcontext.c

@@ -1853,3 +1853,12 @@ gtk_accesskit_context_add_to_update (GtkAccessKitContext   *self,
   accesskit_tree_update_push_node (update, self->id,
                                    accesskit_node_builder_build (builder));
 }
+
+void
+gtk_accesskit_context_update_tree (GtkAccessKitContext *self)
+{
+  if (!gtk_at_context_is_realized (GTK_AT_CONTEXT (self)))
+    return;
+
+  gtk_accesskit_root_update_tree (self->root);
+}

gtk/a11y/gtkaccesskitcontextprivate.h

@@ -42,4 +42,7 @@ void
 gtk_accesskit_context_add_to_update (GtkAccessKitContext   *self,
                                      accesskit_tree_update *update);
 
+void
+gtk_accesskit_context_update_tree (GtkAccessKitContext *self);
+
 G_END_DECLS

gtk/a11y/gtkaccesskitroot.c

@@ -44,7 +44,7 @@ struct _GtkAccessKitRoot
   GHashTable *contexts;
   GArray *update_queue;
   gboolean did_initial_update;
-  gint update_id;
+  gboolean requested_initial_tree;
 
 #if defined(GDK_WINDOWING_WIN32)
   accesskit_windows_subclassing_adapter *adapter;
@@ -72,7 +72,6 @@ gtk_accesskit_root_finalize (GObject *gobject)
 
   g_clear_pointer (&self->contexts, g_hash_table_destroy);
   g_clear_pointer (&self->update_queue, g_array_unref);
-  g_clear_handle_id (&self->update_id, g_source_remove);
 
 #if defined(GDK_WINDOWING_WIN32)
   g_clear_pointer (&self->adapter, accesskit_windows_subclassing_adapter_free);
@@ -223,6 +222,7 @@ request_initial_tree_main_thread (void *data)
 {
   GtkAccessKitRoot *self = data;
   accesskit_tree_update *update = build_full_update (self);
+  self->requested_initial_tree = TRUE;
   self->did_initial_update = TRUE;
   return update;
 }
@@ -237,35 +237,21 @@ update_if_active (GtkAccessKitRoot *self, accesskit_tree_update_factory factory)
   if (events)
     accesskit_windows_queued_events_raise (events);
 #elif defined(GDK_WINDOWING_WAYLAND)
-  /* TBD: Newton treats accessibility tree updates as double-buffered state,
-     meaning the surface has to be committed after the update is sent.
-     Can we more tightly integrate accessibility updates with rendering,
-     so everything happens atomically as intended, rather than queuing
-     an idle callback for the accessibility update, then committing
-     the surface? */
   GdkSurface *surface = gtk_native_get_surface (GTK_NATIVE (self->root_widget));
-  struct wl_surface *wl_surface = gdk_wayland_surface_get_wl_surface (surface);
-
+  gdk_wayland_surface_force_next_commit (surface);
   accesskit_newton_adapter_update_if_active (self->adapter, factory, self);
-  wl_surface_commit (wl_surface);
 /* TODO: other platforms */
 #endif
 }
 
-static gboolean
-initial_update (gpointer data)
+static void
+queue_tree_update (GtkAccessKitRoot *self)
 {
-  GtkAccessKitRoot *self = data;
+  if (!gtk_widget_get_mapped (GTK_WIDGET (self->root_widget)))
+    return;
 
-  self->update_id = 0;
-
-  if (gtk_widget_get_mapped (GTK_WIDGET (self->root_widget)))
-    {
-      update_if_active (self, build_full_update);
-      self->did_initial_update = TRUE;
-    }
-
-  return G_SOURCE_REMOVE;
+  GdkSurface *surface = gtk_native_get_surface (GTK_NATIVE (self->root_widget));
+  gdk_surface_queue_render (surface);
 }
 
 static accesskit_tree_update *
@@ -273,8 +259,8 @@ request_initial_tree_other_thread (void *data)
 {
   GtkAccessKitRoot *self = data;
 
-  if (!self->update_id)
-    self->update_id = g_idle_add (initial_update, self);
+  queue_tree_update (self);
+  self->requested_initial_tree = TRUE;
 
   return NULL;
 }
@@ -292,8 +278,8 @@ deactivate_accessibility (void *data)
 
   /* TODO: Unrealize AT contexts. Which ones? */
   g_clear_pointer (&self->update_queue, g_array_unref);
-  g_clear_handle_id (&self->update_id, g_source_remove);
   self->did_initial_update = FALSE;
+  self->requested_initial_tree = FALSE;
 }
 
 static void
@@ -485,19 +471,6 @@ build_incremental_update (void *data)
   return update;
 }
 
-static gboolean
-incremental_update (gpointer data)
-{
-  GtkAccessKitRoot *self = data;
-
-  self->update_id = 0;
-
-  if (gtk_widget_get_mapped (GTK_WIDGET (self->root_widget)))
-    update_if_active (self, build_incremental_update);
-
-  return G_SOURCE_REMOVE;
-}
-
 void
 gtk_accesskit_root_queue_update (GtkAccessKitRoot *self,
                                  guint32           id,
@@ -508,6 +481,17 @@ gtk_accesskit_root_queue_update (GtkAccessKitRoot *self,
 
   add_to_update_queue (self, id, force_to_end);
 
-  if (!self->update_id)
-    self->update_id = g_idle_add (incremental_update, self);
+  queue_tree_update (self);
+}
+
+void
+gtk_accesskit_root_update_tree (GtkAccessKitRoot *self)
+{
+  if (self->did_initial_update && self->update_queue)
+    update_if_active (self, build_incremental_update);
+  else if (self->requested_initial_tree)
+    {
+      update_if_active (self, build_full_update);
+      self->did_initial_update = TRUE;
+    }
 }

gtk/a11y/gtkaccesskitrootprivate.h

@@ -49,4 +49,7 @@ gtk_accesskit_root_queue_update (GtkAccessKitRoot *self,
                                  guint32           id,
                                  gboolean          force_to_end);
 
+void
+gtk_accesskit_root_update_tree (GtkAccessKitRoot *self);
+
 G_END_DECLS

gtk/gtkwidget.c

@@ -71,6 +71,7 @@
 #include "gtktestatcontextprivate.h"
 
 #include "inspector/window.h"
+#include "a11y/gtkaccesskitcontextprivate.h"
 
 #include "gdk/gdkeventsprivate.h"
 #include "gdk/gdkprofilerprivate.h"
@@ -12077,6 +12078,7 @@ gtk_widget_render (GtkWidget            *widget,
                    const cairo_region_t *region)
 {
   GtkWidgetPrivate *priv = gtk_widget_get_instance_private (widget);
+  GtkATContext *at_ctx;
   GtkSnapshot *snapshot;
   GskRenderer *renderer;
   GskRenderNode *root;
@@ -12090,6 +12092,11 @@ gtk_widget_render (GtkWidget            *widget,
   if (!GTK_IS_NATIVE (widget))
     return;
 
+  at_ctx = gtk_accessible_get_at_context (GTK_ACCESSIBLE (widget));
+  if (GTK_IS_ACCESSKIT_CONTEXT (at_ctx))
+    gtk_accesskit_context_update_tree (GTK_ACCESSKIT_CONTEXT (at_ctx));
+  g_object_unref (at_ctx);
+
   renderer = gtk_native_get_renderer (GTK_NATIVE (widget));
   if (renderer == NULL)
     return;