shell/monitor-group: Avoid doing extra work

A lot of our calculations only change based on (unlikely) external
events, simply cache those parts and only update when the underlying
properties actually change.

Notable is base_direction, which was previously being calculated
repeatedly per workspace per monitor on every interpolate — now it's
simply a private int.

This seriously cuts down the number of calls, vs just maths, we need to
do at each step including eliminating a repeated `g_object_get` in favour
of a gboolean flag.

src/shell-monitor-group.c

@@ -31,10 +31,18 @@
 typedef struct _ShellMonitorGroupPrivate ShellMonitorGroupPrivate;
 struct _ShellMonitorGroupPrivate
 {
+  ShellGlobal *global;
+  MetaWorkspaceManager *workspace_manager;
+  StThemeContext *theme_context;
+
   ClutterActor *container;
   GPtrArray *workspace_groups;
-  
+
   int index, width, height;
+  float base_distance;
+
+  gboolean is_vertical;
+  gboolean is_rtl;
 };
 
 enum
@@ -60,6 +68,16 @@ shell_monitor_group_dispose (GObject *object)
   ShellMonitorGroupPrivate *priv =
     shell_monitor_group_get_instance_private (SHELL_MONITOR_GROUP (object));
 
+  g_clear_weak_pointer (&priv->global);
+
+  if (priv->workspace_manager)
+    g_signal_handlers_disconnect_by_data (priv->workspace_manager, object);
+  g_clear_weak_pointer (&priv->workspace_manager);
+
+  if (priv->theme_context)
+    g_signal_handlers_disconnect_by_data (priv->theme_context, object);
+  g_clear_weak_pointer (&priv->theme_context);
+
   g_clear_weak_pointer (&priv->container);
   g_clear_pointer (&priv->workspace_groups, g_ptr_array_unref);
 
@@ -82,11 +100,9 @@ shell_monitor_group_set_property (GObject      *object,
       break;
     case PROP_MONITOR_WIDTH:
       priv->width = g_value_get_int (value);
-      clutter_actor_set_size (CLUTTER_ACTOR (object), g_value_get_int (value), priv->height);
       break;
     case PROP_MONITOR_HEIGHT:
       priv->height = g_value_get_int (value);
-      clutter_actor_set_size (CLUTTER_ACTOR (object), priv->width, g_value_get_int (value));
       break;
     case PROP_PROGRESS:
       shell_monitor_group_set_progress (SHELL_MONITOR_GROUP (object),
@@ -131,6 +147,35 @@ shell_monitor_group_get_property (GObject      *object,
     }
 }
 
+static void
+update_base_distance (ShellMonitorGroup *self)
+{
+  ShellMonitorGroupPrivate *priv =
+    shell_monitor_group_get_instance_private (self);
+  int spacing =
+    WORKSPACE_SPACING * st_theme_context_get_scale_factor (priv->theme_context);
+
+  if (priv->is_vertical)
+    priv->base_distance = priv->height + spacing;
+  else
+    priv->base_distance = priv->width + spacing;
+
+  g_object_notify_by_pspec (G_OBJECT (self), obj_props[PROP_BASE_DISTANCE]);
+}
+
+static void
+shell_monitor_group_constructed (GObject *object)
+{
+  ShellMonitorGroup *self = SHELL_MONITOR_GROUP (object);
+  ShellMonitorGroupPrivate *priv =
+    shell_monitor_group_get_instance_private (self);
+
+  G_OBJECT_CLASS (shell_monitor_group_parent_class)->constructed (object);
+
+  clutter_actor_set_size (CLUTTER_ACTOR (object), priv->width, priv->height);
+  update_base_distance (self);
+}
+
 static void
 shell_monitor_group_class_init (ShellMonitorGroupClass *klass)
 {
@@ -139,6 +184,7 @@ shell_monitor_group_class_init (ShellMonitorGroupClass *klass)
   object_class->dispose = shell_monitor_group_dispose;
   object_class->set_property = shell_monitor_group_set_property;
   object_class->get_property = shell_monitor_group_get_property;
+  object_class->constructed = shell_monitor_group_constructed;
 
   obj_props[PROP_INDEX] =
     g_param_spec_int ("index", NULL, NULL,
@@ -164,71 +210,122 @@ shell_monitor_group_class_init (ShellMonitorGroupClass *klass)
   g_object_class_install_properties (object_class, PROP_LAST, obj_props);
 }
 
+static void
+layout_rows_changed (ShellMonitorGroup *self)
+{
+  ShellMonitorGroupPrivate *priv =
+    shell_monitor_group_get_instance_private (self);
+  int rows;
+
+  /*
+   * TODO: https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/3351
+   * priv->is_vertical =
+   *   meta_workspace_manager_get_layout_rows (priv->workspace_manager) == -1;
+   */
+  g_object_get (priv->workspace_manager, "layout-rows", &rows, NULL);
+
+  priv->is_vertical = rows == -1;
+  update_base_distance (self);
+
+  g_object_notify_by_pspec (G_OBJECT (self), obj_props[PROP_PROGRESS]);
+}
+
+static void
+scale_factor_changed (ShellMonitorGroup *self)
+{
+  update_base_distance (self);
+
+  g_object_notify_by_pspec (G_OBJECT (self), obj_props[PROP_PROGRESS]);
+}
+
+static void
+text_direction_changed (ShellMonitorGroup *self)
+{
+  ShellMonitorGroupPrivate *priv =
+    shell_monitor_group_get_instance_private (self);
+
+  priv->is_rtl =
+    clutter_actor_get_text_direction (CLUTTER_ACTOR (self)) == CLUTTER_TEXT_DIRECTION_RTL;
+
+  g_object_notify_by_pspec (G_OBJECT (self), obj_props[PROP_PROGRESS]);
+}
+
 static void
 shell_monitor_group_init (ShellMonitorGroup *self)
 {
   ShellMonitorGroupPrivate *priv =
     shell_monitor_group_get_instance_private (self);
+  ShellGlobal *global = shell_global_get ();
+  MetaWorkspaceManager *workspace_manager =
+    shell_global_get_workspace_manager (global);
+  StThemeContext *theme_context =
+    st_theme_context_get_for_stage (shell_global_get_stage (global));
   ClutterActor *container = clutter_actor_new ();
 
+  g_set_weak_pointer (&priv->global, global);
+  g_set_weak_pointer (&priv->workspace_manager, workspace_manager);
+  g_set_weak_pointer (&priv->theme_context, theme_context);
+
   g_set_weak_pointer (&priv->container, container);
   clutter_actor_add_child (CLUTTER_ACTOR (self), container);
 
   priv->workspace_groups = g_ptr_array_new_with_free_func (g_object_unref);
+
+  g_object_freeze_notify (G_OBJECT (self));
+  g_signal_connect_swapped (priv->workspace_manager,
+                            "notify::layout-rows", G_CALLBACK (layout_rows_changed),
+                            self);
+  layout_rows_changed (self);
+
+  g_signal_connect_swapped (priv->theme_context,
+                            "notify::scale-factor", G_CALLBACK (scale_factor_changed),
+                            self);
+  scale_factor_changed (self);
+
+  g_signal_connect_swapped (self,
+                            "notify::text-direction", G_CALLBACK (text_direction_changed),
+                            self);
+  text_direction_changed (self);
+  g_object_thaw_notify (G_OBJECT (self));
 }
 
 float
 shell_monitor_group_get_base_distance (ShellMonitorGroup *self)
 {
   ShellMonitorGroupPrivate *priv;
-  ShellGlobal *global = shell_global_get ();
-  StThemeContext *context;
-  int scale, spacing, rows;
 
   g_return_val_if_fail (SHELL_IS_MONITOR_GROUP (self), 0.0);
 
   priv = shell_monitor_group_get_instance_private (self);
-
-  context = st_theme_context_get_for_stage (shell_global_get_stage (global));
-  scale = st_theme_context_get_scale_factor (context);
-  /* TODO: Add mutter API? */
-  g_object_get (shell_global_get_workspace_manager (global),
-                "layout-rows", &rows,
-                NULL);
-
-  spacing = WORKSPACE_SPACING * scale;
-
-  if (rows == -1)
-    return priv->height + spacing;
   
-  return priv->width + spacing;
+  return priv->base_distance;
+}
+
+static float
+get_progress_from_actor (ShellMonitorGroup *self,
+                         ClutterActor      *actor)
+{
+  ShellMonitorGroupPrivate *priv =
+    shell_monitor_group_get_instance_private (self);
+
+  if (priv->is_vertical)
+    return clutter_actor_get_y (actor) / priv->base_distance;
+  else if (priv->is_rtl)
+    return -clutter_actor_get_x (actor) / priv->base_distance;
+  else
+    return clutter_actor_get_x (actor) / priv->base_distance;
 }
 
 float
 shell_monitor_group_get_progress (ShellMonitorGroup *self)
 {
   ShellMonitorGroupPrivate *priv;
-  ShellGlobal *global = shell_global_get ();
-  int rows;
-  float base_distance;
 
   g_return_val_if_fail (SHELL_IS_MONITOR_GROUP (self), 0.0);
 
   priv = shell_monitor_group_get_instance_private (self);
 
-  /* TODO: Add mutter API? */
+  return -get_progress_from_actor (self, priv->container);
-  g_object_get (shell_global_get_workspace_manager (global),
-                "layout-rows", &rows,
-                NULL);
-
-  base_distance = shell_monitor_group_get_base_distance (self);
-
-  if (rows == -1)
-    return -clutter_actor_get_y (priv->container) / base_distance;
-  else if (clutter_actor_get_text_direction (CLUTTER_ACTOR (self)) == CLUTTER_TEXT_DIRECTION_RTL)
-    return clutter_actor_get_x (priv->container) / base_distance;
-  else
-    return -clutter_actor_get_x (priv->container) / base_distance;
 }
 
 void
@@ -236,54 +333,21 @@ shell_monitor_group_set_progress (ShellMonitorGroup *self,
                                   float              progress)
 {
   ShellMonitorGroupPrivate *priv;
-  ShellGlobal *global = shell_global_get ();
-  int rows;
-  float base_distance;
 
   g_return_if_fail (SHELL_IS_MONITOR_GROUP (self));
 
   priv = shell_monitor_group_get_instance_private (self);
 
-  /* TODO: Add mutter API? */
+  if (priv->is_vertical)
-  g_object_get (shell_global_get_workspace_manager (global),
+    clutter_actor_set_y (priv->container, -roundf (progress * priv->base_distance));
-                "layout-rows", &rows,
+  else if (priv->is_rtl)
-                NULL);
+    clutter_actor_set_x (priv->container, roundf (progress * priv->base_distance));
-
-  base_distance = shell_monitor_group_get_base_distance (self);
-
-  if (rows == -1)
-    clutter_actor_set_y (priv->container, -roundf (progress * base_distance));
-  else if (clutter_actor_get_text_direction (CLUTTER_ACTOR (self)) == CLUTTER_TEXT_DIRECTION_RTL)
-    clutter_actor_set_x (priv->container, roundf (progress * base_distance));
   else
-    clutter_actor_set_x (priv->container, -roundf (progress * base_distance));
+    clutter_actor_set_x (priv->container, -roundf (progress * priv->base_distance));
 
   g_object_notify_by_pspec (G_OBJECT (self), obj_props[PROP_PROGRESS]);
 }
 
-static float
-get_workspace_group_progress (ShellMonitorGroup   *self,
-                              ShellWorkspaceGroup *group)
-{
-  ShellGlobal *global = shell_global_get ();
-  int rows;
-  float base_distance;
-
-  /* TODO: Add mutter API? */
-  g_object_get (shell_global_get_workspace_manager (global),
-                "layout-rows", &rows,
-                NULL);
-
-  base_distance = shell_monitor_group_get_base_distance (self);
-
-  if (rows == -1)
-    return clutter_actor_get_y (CLUTTER_ACTOR (group)) / base_distance;
-  else if (clutter_actor_get_text_direction (CLUTTER_ACTOR (self)) == CLUTTER_TEXT_DIRECTION_RTL)
-    return -clutter_actor_get_x (CLUTTER_ACTOR (group)) / base_distance;
-  else
-    return clutter_actor_get_x (CLUTTER_ACTOR (group)) / base_distance;
-}
-
 float
 shell_monitor_group_get_workspace_progress (ShellMonitorGroup *self,
                                             MetaWorkspace     *workspace)
@@ -304,7 +368,8 @@ shell_monitor_group_get_workspace_progress (ShellMonitorGroup *self,
       workspace_group = g_ptr_array_index (priv->workspace_groups, i);
 
       if (meta_workspace_index (shell_workspace_group_get_workspace (workspace_group)) == target_index)
-        return get_workspace_group_progress (self, workspace_group);
+        return get_progress_from_actor (self,
+                                        CLUTTER_ACTOR (workspace_group));
     }
 
   g_return_val_if_reached (0.0);
@@ -334,7 +399,8 @@ shell_monitor_group_get_snap_points (ShellMonitorGroup *self,
   data = g_new0 (float, priv->workspace_groups->len + 1);
 
   for (size_t i = 0; i < priv->workspace_groups->len; i++)
-    data[i] = get_workspace_group_progress (self, g_ptr_array_index (priv->workspace_groups, i));
+    data[i] = get_progress_from_actor (self,
+                                       g_ptr_array_index (priv->workspace_groups, i));
 
   *points = data;
 }
@@ -433,7 +499,7 @@ shell_monitor_group_find_closest_workspace (ShellMonitorGroup *self,
   for (size_t i = 0; i < priv->workspace_groups->len; i++)
     {
       group = g_ptr_array_index (priv->workspace_groups, i);
-      distance = get_workspace_group_progress (self, group);
+      distance = get_progress_from_actor (self, CLUTTER_ACTOR (group));
       value = fabsf (distance - progress);
 
       if (G_UNLIKELY (min_distance < 0))