Add gdk_frame_timings_get_predicted_presentation_time()

For an operation like synchronizing audio to video playback, we need to
be able to predict the time that a frame will be presented. The details
of this depend on the windowing system, so make the backend predict
a presentation time for ::begin-frame and set it on the GdkFrameTimings.

The timing algorithm of GdkFrameClockIdle is adjusted to give predictable
presentation times for frames that are not throttled by the windowing
system.

Helper functions:

 gdk_frame_clock_get_current_frame_timings()
 gdk_frame_clock_get_refresh_info()

are added for operations that would otherwise be needed multiple times
in different locations.

https://bugzilla.gnome.org/show_bug.cgi?id=685460

1 files changed, 73 insertions, 0 deletions

diff --git a/gdk/gdkframeclock.c b/gdk/gdkframeclock.c
index ecb84bd8aa..fd41d94533 100644
--- a/gdk/gdkframeclock.c
+++ b/gdk/gdkframeclock.c
@@ -378,3 +378,76 @@ gdk_frame_clock_frame_requested (GdkFrameClock *clock)
   g_signal_emit (G_OBJECT (clock),
                  signals[FRAME_REQUESTED], 0);
 }
+
+GdkFrameTimings *
+gdk_frame_clock_get_current_frame_timings (GdkFrameClock *clock)
+{
+  GdkFrameHistory *history;
+  gint64 frame_counter;
+
+  g_return_val_if_fail (GDK_IS_FRAME_CLOCK (clock), 0);
+
+  history = gdk_frame_clock_get_history (clock);
+  frame_counter = gdk_frame_history_get_frame_counter (history);
+  return gdk_frame_history_get_timings (history, frame_counter);
+}
+
+
+#define DEFAULT_REFRESH_INTERVAL 16667 /* 16.7ms (1/60th second) */
+#define MAX_HISTORY_AGE 150000         /* 150ms */
+
+void
+gdk_frame_clock_get_refresh_info (GdkFrameClock *clock,
+                                  gint64         base_time,
+                                  gint64        *refresh_interval_return,
+                                  gint64        *presentation_time_return)
+{
+  GdkFrameHistory *history;
+  gint64 frame_counter;
+
+  g_return_if_fail (GDK_IS_FRAME_CLOCK (clock));
+
+  history = gdk_frame_clock_get_history (clock);
+  frame_counter = gdk_frame_history_get_frame_counter (history);
+
+  if (presentation_time_return)
+    *presentation_time_return = 0;
+  if (refresh_interval_return)
+    *refresh_interval_return = DEFAULT_REFRESH_INTERVAL;
+
+  while (TRUE)
+    {
+      GdkFrameTimings *timings = gdk_frame_history_get_timings (history, frame_counter);
+      gint64 presentation_time;
+      gint64 refresh_interval;
+
+      if (timings == NULL)
+        return;
+
+      refresh_interval = gdk_frame_timings_get_refresh_interval (timings);
+      presentation_time = gdk_frame_timings_get_presentation_time (timings);
+
+      if (presentation_time != 0)
+        {
+          if (presentation_time > base_time - MAX_HISTORY_AGE &&
+              presentation_time_return)
+            {
+              if (refresh_interval == 0)
+                refresh_interval = DEFAULT_REFRESH_INTERVAL;
+
+              if (refresh_interval_return)
+                *refresh_interval_return = refresh_interval;
+
+              while (presentation_time < base_time)
+                presentation_time += refresh_interval;
+
+              if (presentation_time_return)
+                *presentation_time_return = presentation_time;
+            }
+
+          return;
+        }
+
+      frame_counter--;
+    }
+}