[mutter] clutter/stage-cogl: Stop `schedule_update` repeatedly returning `now`

[Georges Basile Stavracas Neto <gbsneto src gnome org>]

commit 35aa278194ea26aef10928877a0792a371bbdd42
Author: Daniel van Vugt <daniel van vugt canonical com>
Date:   Thu Dec 20 17:24:09 2018 +0800

    clutter/stage-cogl: Stop `schedule_update` repeatedly returning `now`
    
    That could happen if the backend did not provide presentation timestamps,
    or if the screen was not changing other than the hardware cursor:
    
      if (stage_cogl->last_presentation_time == 0||
          stage_cogl->last_presentation_time < now - 150000)
        {
          stage_cogl->update_time = now;
          return;
        }
    
    By setting `update_time` to `now`, master_clock_get_swap_wait_time()
    returns 0:
    
      gint64 now = g_source_get_time (master_clock->source);
      if (min_update_time < now)
        {
          return 0;
        }
      else
        {
          gint64 delay_us = min_update_time - now;
          return (delay_us + 999) / 1000;
        }
    
    However, zero is a value unsupported by the default master clock
    due to:
    
      if (swap_delay != 0)
        return swap_delay;
    
    All cases are now handled by extrapolating when the next presentation
    time would be and calculating an appropriate update time to meet that.
    
    We also need to add a check for `update_time == last_update_time`, which
    is a situation that just became possible since we support old (or zero)
    values of `last_presentation_time`. This avoids getting more than one
    stage update per frame interval when input events arrive without
    triggering a stage redraw (e.g. moving the hardware cursor).
    
    https://gitlab.gnome.org/GNOME/mutter/merge_requests/363

 clutter/clutter/cogl/clutter-stage-cogl.c | 16 ++++------------
 clutter/clutter/cogl/clutter-stage-cogl.h |  1 +
 2 files changed, 5 insertions(+), 12 deletions(-)
---
diff --git a/clutter/clutter/cogl/clutter-stage-cogl.c b/clutter/clutter/cogl/clutter-stage-cogl.c
index 1f69b3092..229015b90 100644
--- a/clutter/clutter/cogl/clutter-stage-cogl.c
+++ b/clutter/clutter/cogl/clutter-stage-cogl.c
@@ -185,18 +185,6 @@ clutter_stage_cogl_schedule_update (ClutterStageWindow *stage_window,
       return;
     }
 
-  /* We only extrapolate presentation times for 150ms  - this is somewhat
-   * arbitrary. The reasons it might not be accurate for larger times are
-   * that the refresh interval might be wrong or the vertical refresh
-   * might be downclocked if nothing is going on onscreen.
-   */
-  if (stage_cogl->last_presentation_time == 0||
-      stage_cogl->last_presentation_time < now - 150000)
-    {
-      stage_cogl->update_time = now;
-      return;
-    }
-
   refresh_rate = stage_cogl->refresh_rate;
   if (refresh_rate <= 0.0)
     refresh_rate = clutter_get_default_frame_rate ();
@@ -220,6 +208,9 @@ clutter_stage_cogl_schedule_update (ClutterStageWindow *stage_window,
     next_presentation_time += refresh_interval;
 
   stage_cogl->update_time = next_presentation_time - max_render_time_allowed;
+
+  if (stage_cogl->update_time == stage_cogl->last_update_time)
+    stage_cogl->update_time = stage_cogl->last_update_time + refresh_interval;
 }
 
 static gint64
@@ -238,6 +229,7 @@ clutter_stage_cogl_clear_update_time (ClutterStageWindow *stage_window)
 {
   ClutterStageCogl *stage_cogl = CLUTTER_STAGE_COGL (stage_window);
 
+  stage_cogl->last_update_time = stage_cogl->update_time;
   stage_cogl->update_time = -1;
 }
 
diff --git a/clutter/clutter/cogl/clutter-stage-cogl.h b/clutter/clutter/cogl/clutter-stage-cogl.h
index aead9785e..a69c424eb 100644
--- a/clutter/clutter/cogl/clutter-stage-cogl.h
+++ b/clutter/clutter/cogl/clutter-stage-cogl.h
@@ -53,6 +53,7 @@ struct _ClutterStageCogl
 
   gint64 last_presentation_time;
   gint64 update_time;
+  int64_t last_update_time;
 
   /* We only enable clipped redraws after 2 frames, since we've seen
    * a lot of drivers can struggle to get going and may output some