[mutter] tests/clutter/frame-clock-timeline: Loosen duration testing

[Marge Bot <marge-bot src gnome org>]

commit f5498950d34557693c092e7d362da54c67b5c581
Author: Daniel van Vugt <daniel van vugt canonical com>
Date:   Wed Dec 15 15:51:12 2021 +0800

    tests/clutter/frame-clock-timeline: Loosen duration testing
    
    The final tick of a timeline is >= its duration, but when using ticks that
    are slightly in the future ("next presentation time") this means the final
    tick will execute and complete the timeline up to one frame interval before
    the timestamp of that final tick.
    
    For the single clock test we now just check if the overall duration is
    within one frame of the expected timeline duration.
    
    The dual clock (switching) test needs a threshold of two frames because
    starting each new clock creates a phase shift (error) of up to one frame.
    
    Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/2161>

 src/tests/clutter/conform/frame-clock-timeline.c | 22 ++++++++++++++++------
 1 file changed, 16 insertions(+), 6 deletions(-)
---
diff --git a/src/tests/clutter/conform/frame-clock-timeline.c 
b/src/tests/clutter/conform/frame-clock-timeline.c
index 0f9f04d794..ff90b60b1e 100644
--- a/src/tests/clutter/conform/frame-clock-timeline.c
+++ b/src/tests/clutter/conform/frame-clock-timeline.c
@@ -2,6 +2,7 @@
 #include "tests/clutter-test-utils.h"
 
 static const float refresh_rate = 60.0;
+static const int64_t refresh_interval_us = G_USEC_PER_SEC / refresh_rate;
 
 static ClutterFrameResult
 timeline_frame_clock_frame (ClutterFrameClock *frame_clock,
@@ -61,6 +62,8 @@ frame_clock_timeline_basic (void)
   int frame_counter;
   int64_t before_us;
   int64_t after_us;
+  int64_t duration_us;
+  int64_t lateness_us;
 
   main_loop = g_main_loop_new (NULL, FALSE);
   frame_clock = clutter_frame_clock_new (refresh_rate,
@@ -97,10 +100,10 @@ frame_clock_timeline_basic (void)
   g_main_loop_run (main_loop);
 
   after_us = g_get_monotonic_time ();
+  duration_us = after_us - before_us;
+  lateness_us = duration_us - ms2us (clutter_timeline_get_duration (timeline));
 
-  g_assert_cmpint (after_us - before_us,
-                   >=,
-                   ms2us (clutter_timeline_get_duration (timeline)));
+  g_assert_cmpint (lateness_us, >, -refresh_interval_us);
 
   g_assert_true (marker1_reached);
 
@@ -140,6 +143,8 @@ frame_clock_timeline_switch (void)
   int frame_counter;
   int64_t before_us;
   int64_t after_us;
+  int64_t duration_us;
+  int64_t lateness_us;
 
   main_loop = g_main_loop_new (NULL, FALSE);
 
@@ -181,10 +186,15 @@ frame_clock_timeline_switch (void)
   g_main_loop_run (main_loop);
 
   after_us = g_get_monotonic_time ();
+  duration_us = after_us - before_us;
+  lateness_us = duration_us - ms2us (clutter_timeline_get_duration (timeline));
 
-  g_assert_cmpint (after_us - before_us,
-                   >=,
-                   ms2us (clutter_timeline_get_duration (timeline)));
+  /* Our threshold is two frames. This is because switching a timeline to a
+   * new clock of the same frequency shifts the phase up to one frame. And
+   * this timeline has seen two different clocks so its overall duration may
+   * be out by almost two frames. But more than two frames is a bug.
+   */
+  g_assert_cmpint (lateness_us, >, -2 * refresh_interval_us);
 
   g_assert (clutter_timeline_get_frame_clock (timeline) == frame_clock2);