Couple the timeline to the audio

osu.Game.Tests/Visual/TestCaseEditorComposeTimeline.cs

@@ -14,14 +14,15 @@
 namespace osu.Game.Tests.Visual
 {
     [TestFixture]
-    public class TestCaseEditorComposeTimeline : OsuTestCase
+    public class TestCaseEditorComposeTimeline : EditorClockTestCase
     {
         public override IReadOnlyList<Type> RequiredTypes => new[] { typeof(TimelineArea), typeof(Timeline), typeof(BeatmapWaveformGraph), typeof(TimelineButton) };
 
-        private readonly TimelineArea timelineArea;
-
-        public TestCaseEditorComposeTimeline()
+        [BackgroundDependencyLoader]
+        private void load(OsuGameBase osuGame)
         {
+            TimelineArea timelineArea;
+
             Children = new Drawable[]
             {
                 new MusicController
@@ -38,11 +39,7 @@ public TestCaseEditorComposeTimeline()
                     Size = new Vector2(0.8f, 100)
                 }
             };
-        }
 
-        [BackgroundDependencyLoader]
-        private void load(OsuGameBase osuGame)
-        {
             timelineArea.Beatmap.BindTo(osuGame.Beatmap);
         }
     }

osu.Game/Screens/Edit/Screens/Compose/Timeline/Timeline.cs

@@ -1,8 +1,11 @@
 // Copyright (c) 2007-2018 ppy Pty Ltd <contact@ppy.sh>.
 // Licensed under the MIT Licence - https://raw.githubusercontent.com/ppy/osu/master/LICENCE
 
+using osu.Framework.Allocation;
 using osu.Framework.Configuration;
 using osu.Framework.Graphics;
+using osu.Framework.Input;
+using osu.Framework.Timing;
 using osu.Game.Beatmaps;
 using osu.Game.Graphics;
 
@@ -13,6 +16,8 @@ public class Timeline : ZoomableScrollContainer
         public readonly Bindable<bool> WaveformVisible = new Bindable<bool>();
         public readonly Bindable<WorkingBeatmap> Beatmap = new Bindable<WorkingBeatmap>();
 
+        private IAdjustableClock adjustableClock;
+
         public Timeline()
         {
             ZoomDuration = 200;
@@ -32,12 +37,87 @@ public Timeline()
             WaveformVisible.ValueChanged += visible => waveform.FadeTo(visible ? 1 : 0, 200, Easing.OutQuint);
         }
 
+        [BackgroundDependencyLoader]
+        private void load(IAdjustableClock adjustableClock)
+        {
+            this.adjustableClock = adjustableClock;
+        }
+
+        private bool handlingUserInput;
+        private bool trackWasPlaying;
+
         protected override void Update()
         {
             base.Update();
 
             // We want time = 0 to be at the centre of the container when scrolled to the start
             Content.Margin = new MarginPadding { Horizontal = DrawWidth / 2 };
+
+            if (!handlingUserInput)
+                ScrollTo((float)(adjustableClock.CurrentTime / Beatmap.Value.Track.Length) * Content.DrawWidth, false);
+            else
+                adjustableClock.Seek(Current / Content.DrawWidth * Beatmap.Value.Track.Length);
+        }
+
+        protected override bool OnMouseDown(InputState state, MouseDownEventArgs args)
+        {
+            if (base.OnMouseDown(state, args))
+            {
+                beginUserInput();
+                return true;
+            }
+
+            return false;
+        }
+
+        protected override bool OnMouseUp(InputState state, MouseUpEventArgs args)
+        {
+            endUserInput();
+            return base.OnMouseUp(state, args);
+        }
+
+        private void beginUserInput()
+        {
+            handlingUserInput = true;
+            trackWasPlaying = adjustableClock.IsRunning;
+            adjustableClock.Stop();
+        }
+
+        private void endUserInput()
+        {
+            handlingUserInput = false;
+            if (trackWasPlaying)
+                adjustableClock.Start();
+        }
+
+        protected override ScrollbarContainer CreateScrollbar(Direction direction) => new TimelineScrollbar(this, direction);
+
+        private class TimelineScrollbar : ScrollbarContainer
+        {
+            private readonly Timeline timeline;
+
+            public TimelineScrollbar(Timeline timeline, Direction scrollDir)
+                : base(scrollDir)
+            {
+                this.timeline = timeline;
+            }
+
+            protected override bool OnMouseDown(InputState state, MouseDownEventArgs args)
+            {
+                if (base.OnMouseDown(state, args))
+                {
+                    timeline.beginUserInput();
+                    return true;
+                }
+
+                return false;
+            }
+
+            protected override bool OnMouseUp(InputState state, MouseUpEventArgs args)
+            {
+                timeline.endUserInput();
+                return base.OnMouseUp(state, args);
+            }
         }
     }
 }