[gtk: 12/60] a11y: Do not notify of empty state changes

[Matthias Clasen <matthiasc src gnome org>]

commit 8a2b3f0692f34d4d0a5f3e112a44c9d03c3182df
Author: Emmanuele Bassi <ebassi gnome org>
Date:   Wed Aug 5 18:05:46 2020 +0100

    a11y: Do not notify of empty state changes
    
    If the ATContext state hasn't changed—for instance, if the accessible
    attributes have been set to their default value, or have been set to the
    same value—do not emit an accessible state change. State changes can be
    arbitrarily expensive, so we want to ensure that they are meaningful.

 gtk/gtkatcontext.c        | 37 +++++++++++++++++++++++++++++++------
 gtk/gtkatcontextprivate.h |  4 ++++
 2 files changed, 35 insertions(+), 6 deletions(-)
---
diff --git a/gtk/gtkatcontext.c b/gtk/gtkatcontext.c
index 9cdbd0e9f3..e1e2edd599 100644
--- a/gtk/gtkatcontext.c
+++ b/gtk/gtkatcontext.c
@@ -425,6 +425,12 @@ gtk_at_context_update (GtkATContext *self)
 {
   g_return_if_fail (GTK_IS_AT_CONTEXT (self));
 
+  /* There's no point in notifying of state changes if there weren't any */
+  if (self->updated_properties == 0 &&
+      self->updated_relations == 0 &&
+      self->updated_states == 0)
+    return;
+
   GtkAccessibleStateChange changed_states =
     gtk_accessible_attribute_set_get_changed (self->states);
   GtkAccessiblePropertyChange changed_properties =
@@ -435,6 +441,10 @@ gtk_at_context_update (GtkATContext *self)
   g_signal_emit (self, obj_signals[STATE_CHANGE], 0,
                  changed_states, changed_properties, changed_relations,
                  self->states, self->properties, self->relations);
+
+  self->updated_properties = 0;
+  self->updated_relations = 0;
+  self->updated_states = 0;
 }
 
 /*< private >
@@ -457,10 +467,15 @@ gtk_at_context_set_accessible_state (GtkATContext       *self,
 {
   g_return_if_fail (GTK_IS_AT_CONTEXT (self));
 
+  gboolean res = FALSE;
+
   if (value != NULL)
-    gtk_accessible_attribute_set_add (self->states, state, value);
+    res = gtk_accessible_attribute_set_add (self->states, state, value);
   else
-    gtk_accessible_attribute_set_remove (self->states, state);
+    res = gtk_accessible_attribute_set_remove (self->states, state);
+
+  if (res)
+    self->updated_states |= (1 << state);
 }
 
 /*< private >
@@ -519,10 +534,15 @@ gtk_at_context_set_accessible_property (GtkATContext          *self,
 {
   g_return_if_fail (GTK_IS_AT_CONTEXT (self));
 
+  gboolean res = FALSE;
+
   if (value != NULL)
-    gtk_accessible_attribute_set_add (self->properties, property, value);
+    res = gtk_accessible_attribute_set_add (self->properties, property, value);
   else
-    gtk_accessible_attribute_set_remove (self->properties, property);
+    res = gtk_accessible_attribute_set_remove (self->properties, property);
+
+  if (res)
+    self->updated_properties |= (1 << property);
 }
 
 /*< private >
@@ -581,10 +601,15 @@ gtk_at_context_set_accessible_relation (GtkATContext          *self,
 {
   g_return_if_fail (GTK_IS_AT_CONTEXT (self));
 
+  gboolean res = FALSE;
+
   if (value != NULL)
-    gtk_accessible_attribute_set_add (self->relations, relation, value);
+    res = gtk_accessible_attribute_set_add (self->relations, relation, value);
   else
-    gtk_accessible_attribute_set_remove (self->relations, relation);
+    res = gtk_accessible_attribute_set_remove (self->relations, relation);
+
+  if (res)
+    self->updated_relations |= (1 << relation);
 }
 
 /*< private >
diff --git a/gtk/gtkatcontextprivate.h b/gtk/gtkatcontextprivate.h
index 2ac85bde2d..2b916187fd 100644
--- a/gtk/gtkatcontextprivate.h
+++ b/gtk/gtkatcontextprivate.h
@@ -90,6 +90,10 @@ struct _GtkATContext
   GtkAccessibleAttributeSet *states;
   GtkAccessibleAttributeSet *properties;
   GtkAccessibleAttributeSet *relations;
+
+  GtkAccessibleStateChange updated_states;
+  GtkAccessiblePropertyChange updated_properties;
+  GtkAccessibleRelationChange updated_relations;
 };
 
 struct _GtkATContextClass