core: enable XInput2 by default

This is nothing but the beginning, things work with a single
pointer/keyboard pair, but will be largely broken with multiple
devices interacting simultaneously, so we first need a policy
to establish a sensible behavior for extra pointer/keyboard
pairs.

the MUTTER_USE_CORE_DEVICES envvar has been added to force use
of Xlib core events for devices in order to check for regressions.

src/core/display.c

@@ -553,7 +553,8 @@ meta_display_open (void)
   the_display->static_gravity_works = g_getenv ("MUTTER_USE_STATIC_GRAVITY") != NULL;
   
   meta_bell_init (the_display);
-  the_display->device_map = meta_device_map_new (the_display, TRUE);
+  the_display->device_map = meta_device_map_new (the_display,
+                                                 meta_get_use_core_devices ());
 
   meta_display_init_keys (the_display);
 

src/core/main.c

@@ -301,6 +301,9 @@ static GSourceFuncs event_funcs = {
 static void
 meta_clutter_init (void)
 {
+  if (!meta_get_use_core_devices ())
+    clutter_x11_enable_xinput ();
+
   clutter_x11_set_display (GDK_DISPLAY_XDISPLAY (gdk_display_get_default ()));
   clutter_x11_disable_event_retrieval ();
 
@@ -414,6 +417,8 @@ meta_init (void)
     meta_set_verbose (TRUE);
   if (g_getenv ("MUTTER_DEBUG"))
     meta_set_debugging (TRUE);
+  if (g_getenv ("MUTTER_USE_CORE_DEVICES"))
+    meta_set_use_core_devices (TRUE);
 
   if (g_get_home_dir ())
     if (chdir (g_get_home_dir ()) < 0)

src/core/util.c

@@ -50,6 +50,7 @@ meta_topic_real_valist (MetaDebugTopic topic,
 static gint verbose_topics = 0;
 static gboolean is_debugging = FALSE;
 static gboolean replace_current = FALSE;
+static gboolean use_core_devices = FALSE;
 static int no_prefix = 0;
 
 #ifdef WITH_VERBOSE_MODE
@@ -178,6 +179,18 @@ meta_set_debugging (gboolean setting)
   is_debugging = setting;
 }
 
+gboolean
+meta_get_use_core_devices (void)
+{
+  return use_core_devices;
+}
+
+void
+meta_set_use_core_devices (gboolean setting)
+{
+  use_core_devices = setting;
+}
+
 gboolean
 meta_get_replace_current_wm (void)
 {

src/meta/util.h

@@ -38,6 +38,9 @@ gboolean meta_is_syncing (void);
 void     meta_set_syncing (gboolean setting);
 void     meta_set_replace_current_wm (gboolean setting);
 
+gboolean meta_get_use_core_devices (void);
+void     meta_set_use_core_devices (gboolean setting);
+
 void meta_debug_spew_real (const char *format,
                            ...) G_GNUC_PRINTF (1, 2);
 void meta_verbose_real    (const char *format,

src/ui/ui.c

@@ -61,15 +61,8 @@ struct _MetaUI
 void
 meta_ui_init (void)
 {
-  /* As of 2.91.7, Gdk uses XI2 by default, which conflicts with the
+  if (meta_get_use_core_devices ())
-   * direct X calls we use - in particular, events caused by calls to
-   * XGrabPointer/XGrabKeyboard are no longer understood by GDK, while
-   * GDK will no longer generate the core XEvents we process.
-   * So at least for now, enforce the previous behavior.
-   */
-#if GTK_CHECK_VERSION(2, 91, 7)
     gdk_disable_multidevice ();
-#endif
 
   if (!gtk_init_check (NULL, NULL))
     meta_fatal ("Unable to open X display %s\n", XDisplayName (NULL));