Commit c6901a8b authored by Daniel van Vugt's avatar Daniel van Vugt Committed by Jeremy Bicha

Fix irregular gdk_frame_clock_get_frame_time

This fixes stuttering in animations that rely on the regularity of
gdk_frame_clock_get_frame_time.

https://bugzilla.gnome.org/show_bug.cgi?id=787665

BEFORE
gdkgears:
58 FPS and visibly stuttering
gnome-maps on a 59.95Hz monitor:
"paint" g_get_monotonic_time +17278μs, gdk_frame_clock_get_frame_time +17278μs
"paint" g_get_monotonic_time +17449μs, gdk_frame_clock_get_frame_time +17426μs
"paint" g_get_monotonic_time +17620μs, gdk_frame_clock_get_frame_time +17600μs

AFTER
gdkgears:
60 FPS and smoother
gnome-maps on a 59.95Hz monitor:
"paint" g_get_monotonic_time +18228μs, gdk_frame_clock_get_frame_time +16680μs
"paint" g_get_monotonic_time +15010μs, gdk_frame_clock_get_frame_time +16680μs
"paint" g_get_monotonic_time +17134μs, gdk_frame_clock_get_frame_time +16680μs
parent f82a6421
......@@ -123,6 +123,7 @@ gdk_frame_clock_idle_init (GdkFrameClockIdle *frame_clock_idle)
frame_clock_idle->priv = priv =
gdk_frame_clock_idle_get_instance_private (frame_clock_idle);
priv->frame_time = g_get_monotonic_time (); /* more sane than zero */
priv->freeze_count = 0;
}
......@@ -350,9 +351,37 @@ gdk_frame_clock_paint_idle (void *data)
case GDK_FRAME_CLOCK_PHASE_BEFORE_PAINT:
if (priv->freeze_count == 0)
{
priv->frame_time = compute_frame_time (clock_idle);
gint64 frame_interval = FRAME_INTERVAL;
gint64 reset_frame_time;
gint64 smoothest_frame_time;
gint64 frame_time_error;
GdkFrameTimings *prev_timings =
gdk_frame_clock_get_current_timings (clock);
if (prev_timings && prev_timings->refresh_interval)
frame_interval = prev_timings->refresh_interval;
/* We are likely not getting precisely even callbacks in real
* time, particularly if the event loop is busy.
* This is a documented limitation in the precision of
* gdk_threads_add_timeout_full and g_timeout_add_full.
*
* In order to avoid this imprecision from compounding between
* frames and affecting visual smoothness, we correct frame_time
* to more precisely match the even refresh interval of the
* physical display. This also means we proactively avoid (most)
* missed frames before they occur.
*/
smoothest_frame_time = priv->frame_time + frame_interval;
reset_frame_time = compute_frame_time (clock_idle);
frame_time_error = ABS (reset_frame_time - smoothest_frame_time);
if (frame_time_error >= frame_interval)
priv->frame_time = reset_frame_time;
else
priv->frame_time = smoothest_frame_time;
_gdk_frame_clock_begin_frame (clock);
/* Note "current" is different now so timings != prev_timings */
timings = gdk_frame_clock_get_current_timings (clock);
timings->frame_time = priv->frame_time;
......
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