Xi: force dtime to 0 on the first BarrierHit

dtime to the previous event is 0 on the first BarrierHit event.
Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
Reviewed-by: Jasper St. Pierre <jstpierre@mecheye.net>
Signed-off-by: Keith Packard <keithp@keithp.com>

Xi/xibarriers.c

@@ -435,6 +435,7 @@ input_constrain_cursor(DeviceIntPtr dev, ScreenPtr screen,
     dir = barrier_get_direction(current_x, current_y, x, y);
 
     while (dir != 0) {
+        int new_sequence;
         struct PointerBarrierDevice *pbd;
 
         c = barrier_find_nearest(cs, master, dir, current_x, current_y, x, y);
@@ -444,6 +445,8 @@ input_constrain_cursor(DeviceIntPtr dev, ScreenPtr screen,
         nearest = &c->barrier;
 
         pbd = GetBarrierDevice(c, master->id);
+        new_sequence = !pbd->hit;
+
         pbd->seen = TRUE;
         pbd->hit = TRUE;
 
@@ -466,7 +469,7 @@ input_constrain_cursor(DeviceIntPtr dev, ScreenPtr screen,
         ev.event_id = pbd->barrier_event_id;
         ev.barrierid = c->id;
 
-        ev.dt = ms - pbd->last_timestamp;
+        ev.dt = new_sequence ? 0 : ms - pbd->last_timestamp;
         ev.window = c->window;
         pbd->last_timestamp = ms;