From 4faeb12731b81ce617042973155cc4b5737e1133 Mon Sep 17 00:00:00 2001
From: Daniel van Vugt <daniel.van.vugt@canonical.com>
Date: Mon, 29 Oct 2018 19:05:46 +0800
Subject: [PATCH] clutter/stage-cogl: Reschedule update on present

If an update (new frame) had been scheduled already before
`_clutter_stage_cogl_presented` was called then that means it was
scheduled for the wrong time. Because the `last_presentation_time` has
changed since then. And using an `update_time` based on an outdated
presentation time results in scheduling frames too early, filling the
buffer queue (triple buffering or worse) and high visual latency.

So if we do receive a presentation event when an update is already
scheduled, remember to reschedule the update based on the newer
`last_presentation_time`. This way we avoid overfilling the buffer queue
and limit ourselves to double buffering for less visible lag.

Closes: https://gitlab.gnome.org/GNOME/mutter/issues/334

Prerequisite: https://gitlab.gnome.org/GNOME/mutter/merge_requests/520

https://gitlab.gnome.org/GNOME/mutter/merge_requests/281
---
 clutter/clutter/cogl/clutter-stage-cogl.c | 16 ++++++++++++++++
 clutter/clutter/cogl/clutter-stage-cogl.h |  2 ++
 2 files changed, 18 insertions(+)

diff --git a/clutter/clutter/cogl/clutter-stage-cogl.c b/clutter/clutter/cogl/clutter-stage-cogl.c
index 80ed474a9..973272f9c 100644
--- a/clutter/clutter/cogl/clutter-stage-cogl.c
+++ b/clutter/clutter/cogl/clutter-stage-cogl.c
@@ -77,6 +77,10 @@ enum
   PROP_LAST
 };
 
+static void
+clutter_stage_cogl_schedule_update (ClutterStageWindow *stage_window,
+                                    gint                sync_delay);
+
 static void
 clutter_stage_cogl_unrealize (ClutterStageWindow *stage_window)
 {
@@ -122,6 +126,16 @@ _clutter_stage_cogl_presented (ClutterStageCogl *stage_cogl,
     }
 
   _clutter_stage_presented (stage_cogl->wrapper, frame_event, frame_info);
+
+  if (frame_event == COGL_FRAME_EVENT_COMPLETE &&
+      stage_cogl->update_time != -1)
+    {
+      ClutterStageWindow *stage_window = CLUTTER_STAGE_WINDOW (stage_cogl);
+
+      stage_cogl->update_time = -1;
+      clutter_stage_cogl_schedule_update (stage_window,
+                                          stage_cogl->last_sync_delay);
+    }
 }
 
 static gboolean
@@ -159,6 +173,8 @@ clutter_stage_cogl_schedule_update (ClutterStageWindow *stage_window,
   if (stage_cogl->update_time != -1)
     return;
 
+  stage_cogl->last_sync_delay = sync_delay;
+
   now = g_get_monotonic_time ();
 
   if (sync_delay < 0)
diff --git a/clutter/clutter/cogl/clutter-stage-cogl.h b/clutter/clutter/cogl/clutter-stage-cogl.h
index 17958cd24..aead9785e 100644
--- a/clutter/clutter/cogl/clutter-stage-cogl.h
+++ b/clutter/clutter/cogl/clutter-stage-cogl.h
@@ -59,6 +59,8 @@ struct _ClutterStageCogl
    * junk frames to start with. */
   unsigned int frame_count;
 
+  gint last_sync_delay;
+
   cairo_rectangle_int_t bounding_redraw_clip;
 
   guint initialized_redraw_clip : 1;