[gtk+/gtk-3-4] xi2: ignore extraneous events for smooth scroll

[Matthias Clasen <matthiasc src gnome org>]

commit 37e3722d3a80be13bd8f7a4d3ac8edc923fc2750
Author: Cosimo Cecchi <cosimoc gnome org>
Date:   Fri Apr 20 17:34:08 2012 -0400

    xi2: ignore extraneous events for smooth scroll
    
    Since the event will be ignored anyway after it's translated (slave
    devices are disabled), don't let it run in the smooth scroll code path,
    as it will burn our caches for the actual event we're interested in.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=673644

 gdk/x11/gdkdevicemanager-xi2.c |   23 +++++++++++++++--------
 1 files changed, 15 insertions(+), 8 deletions(-)
---
diff --git a/gdk/x11/gdkdevicemanager-xi2.c b/gdk/x11/gdkdevicemanager-xi2.c
index a34bd09..15f095b 100644
--- a/gdk/x11/gdkdevicemanager-xi2.c
+++ b/gdk/x11/gdkdevicemanager-xi2.c
@@ -1305,13 +1305,24 @@ gdk_x11_device_manager_xi2_translate_event (GdkEventTranslator *translator,
     case XI_Motion:
       {
         XIDeviceEvent *xev = (XIDeviceEvent *) ev;
-        GdkDevice *source_device;
+        GdkDevice *source_device, *device;
         gdouble delta_x, delta_y;
 
         source_device = g_hash_table_lookup (device_manager->id_table,
                                              GUINT_TO_POINTER (xev->sourceid));
+        device = g_hash_table_lookup (device_manager->id_table,
+                                      GUINT_TO_POINTER (xev->deviceid));
 
-        if (scroll_valuators_changed (GDK_X11_DEVICE_XI2 (source_device),
+        /* When scrolling, X might send events twice here; once with both the
+         * device and the source device set to the physical device, and once
+         * with the device set to the master device.
+         * Since we are only interested in the latter, and
+         * scroll_valuators_changed() updates the valuator cache for the
+         * source device, we need to explicitly ignore the first event in
+         * order to get the correct delta for the second.
+         */
+        if (gdk_device_get_device_type (device) != GDK_DEVICE_TYPE_SLAVE &&
+            scroll_valuators_changed (GDK_X11_DEVICE_XI2 (source_device),
                                       &xev->valuators, &delta_x, &delta_y))
           {
             event->scroll.type = GDK_SCROLL;
@@ -1333,9 +1344,7 @@ gdk_x11_device_manager_xi2_translate_event (GdkEventTranslator *translator,
             event->scroll.delta_x = delta_x;
             event->scroll.delta_y = delta_y;
 
-            event->scroll.device = g_hash_table_lookup (device_manager->id_table,
-                                                        GUINT_TO_POINTER (xev->deviceid));
-
+            event->scroll.device = device;
             gdk_event_set_source_device (event, source_device);
 
             event->scroll.state = _gdk_x11_device_xi2_translate_state (&xev->mods, &xev->buttons, &xev->group);
@@ -1350,9 +1359,7 @@ gdk_x11_device_manager_xi2_translate_event (GdkEventTranslator *translator,
         event->motion.x_root = (gdouble) xev->root_x;
         event->motion.y_root = (gdouble) xev->root_y;
 
-        event->motion.device = g_hash_table_lookup (device_manager->id_table,
-                                                    GINT_TO_POINTER (xev->deviceid));
-
+        event->motion.device = device;
         gdk_event_set_source_device (event, source_device);
 
         event->motion.state = _gdk_x11_device_xi2_translate_state (&xev->mods, &xev->buttons, &xev->group);