[gtk+] wayland: avoid jitter in keyboard repeat

[Christian Hergert <chergert src gnome org>]

commit 724d3be794bc6faa79b9a17681fe77c67d280a99
Author: Christian Hergert <chergert redhat com>
Date:   Mon Apr 25 18:10:09 2016 -0700

    wayland: avoid jitter in keyboard repeat
    
    When synthesizing keyboard repeat, we can potentially drift further from
    the mark depending on the timing of the frame callback and how long it
    took to deliver the event.
    
    This patch attempts to reduce this by tracking from a stable epoch the
    time of our next keyboard repeat.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=765567

 gdk/wayland/gdkdevice-wayland.c |   18 ++++++++++++++++--
 1 files changed, 16 insertions(+), 2 deletions(-)
---
diff --git a/gdk/wayland/gdkdevice-wayland.c b/gdk/wayland/gdkdevice-wayland.c
index 856437d..c6823c1 100644
--- a/gdk/wayland/gdkdevice-wayland.c
+++ b/gdk/wayland/gdkdevice-wayland.c
@@ -177,6 +177,7 @@ struct _GdkWaylandSeat
   guint32 repeat_timer;
   guint32 repeat_key;
   guint32 repeat_count;
+  gint64 repeat_deadline;
   GSettings *keyboard_settings;
   uint32_t keyboard_time;
 
@@ -1815,6 +1816,9 @@ deliver_key_event (GdkWaylandSeat *seat,
   GdkKeymap *keymap;
   xkb_keysym_t sym;
   guint delay, interval, timeout;
+  gint64 begin_time, now;
+
+  begin_time = g_get_monotonic_time ();
 
   stop_key_repeat (seat);
 
@@ -1862,10 +1866,20 @@ deliver_key_event (GdkWaylandSeat *seat,
   seat->repeat_count++;
   seat->repeat_key = key;
 
+  interval *= 1000L;
+  delay *= 1000L;
+
+  now = g_get_monotonic_time ();
+
   if (seat->repeat_count == 1)
-    timeout = delay;
+    seat->repeat_deadline = begin_time + delay;
+  else if (seat->repeat_deadline + interval > now)
+    seat->repeat_deadline += interval;
   else
-    timeout = interval;
+    /* frame delay caused us to miss repeat deadline */
+    seat->repeat_deadline = now;
+
+  timeout = (seat->repeat_deadline - now) / 1000L;
 
   seat->repeat_timer =
     gdk_threads_add_timeout (timeout, keyboard_repeat, seat);