MetaInputSettings: allow edge scrolling without 2fg capable devices

We should only force edge scrolling off if two finger is enabled *and*
we actually have two finger capable devices.

https://bugzilla.gnome.org/show_bug.cgi?id=778554

src/backends/meta-input-settings-private.h

@@ -117,6 +117,9 @@ struct _MetaInputSettingsClass
                                   ClutterInputDeviceTool     *tool,
                                   GDesktopStylusButtonAction  primary,
                                   GDesktopStylusButtonAction  secondary);
+
+  gboolean (* has_two_finger_scroll) (MetaInputSettings  *settings,
+                                      ClutterInputDevice *device);
 };
 
 GType meta_input_settings_get_type (void) G_GNUC_CONST;

src/backends/meta-input-settings.c

@@ -74,6 +74,8 @@ struct _MetaInputSettingsPrivate
 #ifdef HAVE_LIBWACOM
   WacomDeviceDatabase *wacom_db;
 #endif
+
+  GHashTable *two_finger_devices;
 };
 
 typedef void (*ConfigBoolFunc)   (MetaInputSettings  *input_settings,
@@ -141,6 +143,8 @@ meta_input_settings_dispose (GObject *object)
     libwacom_database_destroy (priv->wacom_db);
 #endif
 
+  g_clear_pointer (&priv->two_finger_devices, g_hash_table_destroy);
+
   G_OBJECT_CLASS (meta_input_settings_parent_class)->dispose (object);
 }
 
@@ -477,6 +481,7 @@ update_touchpad_edge_scroll (MetaInputSettings *input_settings,
   MetaInputSettingsClass *input_settings_class;
   gboolean edge_scroll_enabled;
   gboolean two_finger_scroll_enabled;
+  gboolean two_finger_scroll_available;
   MetaInputSettingsPrivate *priv;
 
   if (device &&
@@ -487,9 +492,10 @@ update_touchpad_edge_scroll (MetaInputSettings *input_settings,
   input_settings_class = META_INPUT_SETTINGS_GET_CLASS (input_settings);
   edge_scroll_enabled = g_settings_get_boolean (priv->touchpad_settings, "edge-scrolling-enabled");
   two_finger_scroll_enabled = g_settings_get_boolean (priv->touchpad_settings, "two-finger-scrolling-enabled");
+  two_finger_scroll_available = g_hash_table_size (priv->two_finger_devices) > 0;
 
   /* If both are enabled we prefer two finger. */
-  if (edge_scroll_enabled && two_finger_scroll_enabled)
+  if (edge_scroll_enabled && two_finger_scroll_enabled && two_finger_scroll_available)
     edge_scroll_enabled = FALSE;
 
   if (device)
@@ -1268,6 +1274,23 @@ apply_stylus_settings (MetaInputSettings      *input_settings,
   update_stylus_buttonmap (input_settings, device, tool);
 }
 
+static void
+evaluate_two_finger_scrolling (MetaInputSettings  *input_settings,
+                               ClutterInputDevice *device)
+{
+  MetaInputSettingsClass *klass;
+  MetaInputSettingsPrivate *priv;
+
+  if (clutter_input_device_get_device_type (device) != CLUTTER_TOUCHPAD_DEVICE)
+    return;
+
+  klass = META_INPUT_SETTINGS_GET_CLASS (input_settings);
+  priv = meta_input_settings_get_instance_private (input_settings);
+
+  if (klass->has_two_finger_scroll (input_settings, device))
+    g_hash_table_add (priv->two_finger_devices, device);
+}
+
 static void
 meta_input_settings_device_added (ClutterDeviceManager *device_manager,
                                   ClutterInputDevice   *device,
@@ -1276,6 +1299,8 @@ meta_input_settings_device_added (ClutterDeviceManager *device_manager,
   if (clutter_input_device_get_device_mode (device) == CLUTTER_INPUT_MODE_MASTER)
     return;
 
+  evaluate_two_finger_scrolling (input_settings, device);
+
   apply_device_settings (input_settings, device);
   check_add_mappable_device (input_settings, device);
 }
@@ -1289,6 +1314,10 @@ meta_input_settings_device_removed (ClutterDeviceManager *device_manager,
 
   priv = meta_input_settings_get_instance_private (input_settings);
   g_hash_table_remove (priv->mappable_devices, device);
+
+  if (g_hash_table_remove (priv->two_finger_devices, device) &&
+      g_hash_table_size (priv->two_finger_devices) == 0)
+    apply_device_settings (input_settings, NULL);
 }
 
 static void
@@ -1327,6 +1356,13 @@ static void
 meta_input_settings_constructed (GObject *object)
 {
   MetaInputSettings *input_settings = META_INPUT_SETTINGS (object);
+  GSList *devices, *d;
+
+  devices = meta_input_settings_get_devices (input_settings, CLUTTER_TOUCHPAD_DEVICE);
+  for (d = devices; d; d = d->next)
+    evaluate_two_finger_scrolling (input_settings, d->data);
+
+  g_slist_free (devices);
 
   apply_device_settings (input_settings, NULL);
   update_keyboard_repeat (input_settings);
@@ -1390,6 +1426,8 @@ meta_input_settings_init (MetaInputSettings *settings)
                  "expect tablets to misbehave");
     }
 #endif
+
+  priv->two_finger_devices = g_hash_table_new (NULL, NULL);
 }
 
 MetaInputSettings *

src/backends/native/meta-input-settings-native.c

@@ -188,6 +188,19 @@ meta_input_settings_native_set_two_finger_scroll (MetaInputSettings            *
   device_set_scroll_method (libinput_device, current | method);
 }
 
+static gboolean
+meta_input_settings_native_has_two_finger_scroll (MetaInputSettings  *settings,
+                                                  ClutterInputDevice *device)
+{
+  struct libinput_device *libinput_device;
+
+  libinput_device = clutter_evdev_input_device_get_libinput_device (device);
+  if (!libinput_device)
+    return FALSE;
+
+  return libinput_device_config_scroll_get_methods (libinput_device) & LIBINPUT_CONFIG_SCROLL_2FG;
+}
+
 static void
 meta_input_settings_native_set_scroll_button (MetaInputSettings  *settings,
                                               ClutterInputDevice *device,
@@ -503,6 +516,8 @@ meta_input_settings_native_class_init (MetaInputSettingsNativeClass *klass)
 
   input_settings_class->set_stylus_pressure = meta_input_settings_native_set_stylus_pressure;
   input_settings_class->set_stylus_button_map = meta_input_settings_native_set_stylus_button_map;
+
+  input_settings_class->has_two_finger_scroll = meta_input_settings_native_has_two_finger_scroll;
 }
 
 static void

src/backends/x11/meta-input-settings-x11.c

@@ -284,6 +284,22 @@ meta_input_settings_x11_set_two_finger_scroll (MetaInputSettings            *set
   meta_XFree (available);
 }
 
+static gboolean
+meta_input_settings_x11_has_two_finger_scroll (MetaInputSettings  *settings,
+                                               ClutterInputDevice *device)
+{
+  guchar *available = NULL;
+  gboolean has_two_finger = TRUE;
+
+  available = get_property (device, "libinput Scroll Methods Available",
+                            XA_INTEGER, 8, SCROLL_METHOD_NUM_FIELDS);
+  if (!available || !available[SCROLL_METHOD_FIELD_2FG])
+    has_two_finger = FALSE;
+
+  meta_XFree (available);
+  return has_two_finger;
+}
+
 static void
 meta_input_settings_x11_set_scroll_button (MetaInputSettings  *settings,
                                            ClutterInputDevice *device,
@@ -743,6 +759,8 @@ meta_input_settings_x11_class_init (MetaInputSettingsX11Class *klass)
 
   input_settings_class->set_stylus_pressure = meta_input_settings_x11_set_stylus_pressure;
   input_settings_class->set_stylus_button_map = meta_input_settings_x11_set_stylus_button_map;
+
+  input_settings_class->has_two_finger_scroll = meta_input_settings_x11_has_two_finger_scroll;
 }
 
 static void