From 50f8ab3dfb07c9cc12b0fb5598ecadfdecf3b43d Mon Sep 17 00:00:00 2001
From: Dean Herbert <pe@ppy.sh>
Date: Wed, 3 Apr 2019 16:58:20 +0900
Subject: [PATCH 1/2] Fix gameplay offset handling on seeks

---
 .../Screens/Play/GameplayClockContainer.cs    | 37 ++++++++++++-------
 1 file changed, 23 insertions(+), 14 deletions(-)

diff --git a/osu.Game/Screens/Play/GameplayClockContainer.cs b/osu.Game/Screens/Play/GameplayClockContainer.cs
index c13222c6de..fc7a9ddd20 100644
--- a/osu.Game/Screens/Play/GameplayClockContainer.cs
+++ b/osu.Game/Screens/Play/GameplayClockContainer.cs
@@ -36,6 +36,8 @@ namespace osu.Game.Screens.Play
         /// </summary>
         private readonly DecoupleableInterpolatingFramedClock adjustableClock;
 
+        private readonly double gameplayStartTime;
+
         public readonly Bindable<double> UserPlaybackRate = new BindableDouble(1)
         {
             Default = 1,
@@ -52,11 +54,14 @@ namespace osu.Game.Screens.Play
 
         private Bindable<double> userAudioOffset;
 
-        private readonly FramedOffsetClock offsetClock;
+        private readonly FramedOffsetClock userOffsetClock;
+
+        private readonly FramedOffsetClock platformOffsetClock;
 
         public GameplayClockContainer(WorkingBeatmap beatmap, double gameplayStartTime)
         {
             this.beatmap = beatmap;
+            this.gameplayStartTime = gameplayStartTime;
 
             RelativeSizeAxes = Axes.Both;
 
@@ -64,30 +69,31 @@ namespace osu.Game.Screens.Play
 
             adjustableClock = new DecoupleableInterpolatingFramedClock { IsCoupled = false };
 
-            adjustableClock.Seek(Math.Min(0, gameplayStartTime - beatmap.BeatmapInfo.AudioLeadIn));
-
-            adjustableClock.ProcessFrame();
-
             // Lazer's audio timings in general doesn't match stable. This is the result of user testing, albeit limited.
             // This only seems to be required on windows. We need to eventually figure out why, with a bit of luck.
-            var platformOffsetClock = new FramedOffsetClock(adjustableClock) { Offset = RuntimeInfo.OS == RuntimeInfo.Platform.Windows ? 22 : 0 };
+            platformOffsetClock = new FramedOffsetClock(adjustableClock) { Offset = RuntimeInfo.OS == RuntimeInfo.Platform.Windows ? 22 : 0 };
 
             // the final usable gameplay clock with user-set offsets applied.
-            offsetClock = new FramedOffsetClock(platformOffsetClock);
+            userOffsetClock = new FramedOffsetClock(platformOffsetClock);
 
             // the clock to be exposed via DI to children.
-            GameplayClock = new GameplayClock(offsetClock);
+            GameplayClock = new GameplayClock(userOffsetClock);
 
             GameplayClock.IsPaused.BindTo(IsPaused);
         }
 
+        private double totalOffset => userOffsetClock.Offset + platformOffsetClock.Offset;
+
         [BackgroundDependencyLoader]
         private void load(OsuConfigManager config)
         {
             userAudioOffset = config.GetBindable<double>(OsuSetting.AudioOffset);
-            userAudioOffset.BindValueChanged(offset => offsetClock.Offset = offset.NewValue, true);
+            userAudioOffset.BindValueChanged(offset => userOffsetClock.Offset = offset.NewValue, true);
 
             UserPlaybackRate.ValueChanged += _ => updateRate();
+
+            Seek(Math.Min(0, gameplayStartTime - beatmap.BeatmapInfo.AudioLeadIn));
+            adjustableClock.ProcessFrame();
         }
 
         public void Restart()
@@ -104,9 +110,7 @@ namespace osu.Game.Screens.Play
                     this.Delay(750).Schedule(() =>
                     {
                         if (!IsPaused.Value)
-                        {
-                            adjustableClock.Start();
-                        }
+                            Start();
                     });
                 });
             });
@@ -121,7 +125,12 @@ namespace osu.Game.Screens.Play
             IsPaused.Value = false;
         }
 
-        public void Seek(double time) => adjustableClock.Seek(time);
+        public void Seek(double time)
+        {
+            // remove the offset component here because most of the time we want the seek to be aligned to gameplay, not the audio track.
+            // we may want to consider reversing the application of offsets in the future as it may feel more correct.
+            adjustableClock.Seek(time - totalOffset);
+        }
 
         public void Stop()
         {
@@ -138,7 +147,7 @@ namespace osu.Game.Screens.Play
         protected override void Update()
         {
             if (!IsPaused.Value)
-                offsetClock.ProcessFrame();
+                userOffsetClock.ProcessFrame();
 
             base.Update();
         }

From efd7bea7712463013746f1a9295402303d819120 Mon Sep 17 00:00:00 2001
From: Dean Herbert <pe@ppy.sh>
Date: Wed, 3 Apr 2019 17:01:11 +0900
Subject: [PATCH 2/2] Add further xmldoc

---
 osu.Game/Screens/Play/GameplayClockContainer.cs | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/osu.Game/Screens/Play/GameplayClockContainer.cs b/osu.Game/Screens/Play/GameplayClockContainer.cs
index fc7a9ddd20..5ded375259 100644
--- a/osu.Game/Screens/Play/GameplayClockContainer.cs
+++ b/osu.Game/Screens/Play/GameplayClockContainer.cs
@@ -125,6 +125,13 @@ namespace osu.Game.Screens.Play
             IsPaused.Value = false;
         }
 
+        /// <summary>
+        /// Seek to a specific time in gameplay.
+        /// <remarks>
+        /// Adjusts for any offsets which have been applied (so the seek may not be the expected point in time on the underlying audio track).
+        /// </remarks>
+        /// </summary>
+        /// <param name="time">The destination time to seek to.</param>
         public void Seek(double time)
         {
             // remove the offset component here because most of the time we want the seek to be aligned to gameplay, not the audio track.