Emit GdkDevice::changed when the slave device being used changes

When the slave device changes, the master takes the shape of the
new one, modifying its axes, this signal is more useful to catch
this situation than the n-axes property

gdk/gdkdevice.c

@@ -64,6 +64,14 @@ struct _GdkDevicePrivate
   GArray *axes;
 };
 
+enum {
+  CHANGED,
+  LAST_SIGNAL
+};
+
+static guint signals [LAST_SIGNAL] = { 0 };
+
+
 static void gdk_device_dispose      (GObject      *object);
 static void gdk_device_set_property (GObject      *object,
                                      guint         prop_id,
@@ -238,6 +246,26 @@ gdk_device_class_init (GdkDeviceClass *klass)
                                                       0, G_MAXUINT, 0,
                                                       G_PARAM_READABLE | G_PARAM_STATIC_STRINGS));
 
+  /**
+   * GdkDevice::changed:
+   * @device: the #GdkDevice that changed.
+   *
+   * The ::changed signal is emitted either when the #GdkDevice
+   * has changed the number of either axes or keys. For example
+   * In X this will normally happen when the slave device routing
+   * events through the master device changes (for example, user
+   * switches from the USB mouse to a tablet), in that case the
+   * master device will change to reflect the new slave device
+   * axes and keys.
+   */
+  signals[CHANGED] =
+    g_signal_new (g_intern_static_string ("changed"),
+                  G_TYPE_FROM_CLASS (object_class),
+                  G_SIGNAL_RUN_LAST,
+                  NULL, NULL, NULL,
+                  g_cclosure_marshal_VOID__VOID,
+                  G_TYPE_NONE, 0);
+
   g_type_class_add_private (object_class, sizeof (GdkDevicePrivate));
 }
 

gdk/x11/gdkdevicemanager-xi2.c

@@ -499,6 +499,8 @@ handle_device_changed (GdkDeviceManagerXI2  *device_manager,
 
   _gdk_device_reset_axes (device);
   translate_device_classes (display, device, ev->classes, ev->num_classes);
+
+  g_signal_emit_by_name (G_OBJECT (device), "changed");
 }
 
 static GdkCrossingMode