Reduce pollution in DrawableHitObject in favor of a loosely-coupled IScrollingHitObject.

osu.Desktop.VisualTests/Tests/TestCaseScrollingHitObjects.cs

@@ -152,11 +152,13 @@ namespace osu.Desktop.VisualTests.Tests
             }
         }
 
-        private class TestDrawableHitObject : DrawableHitObject
+        private class TestDrawableHitObject : DrawableHitObject, IScrollingHitObject
         {
             private readonly Box background;
             private const float height = 14;
 
+            public BindableDouble LifetimeOffset { get; } = new BindableDouble();
+
             public TestDrawableHitObject(HitObject hitObject)
                 : base(hitObject)
             {

osu.Game.Rulesets.Mania/Objects/Drawables/DrawableManiaHitObject.cs

@@ -10,7 +10,7 @@ using osu.Game.Rulesets.Objects.Drawables;
 
 namespace osu.Game.Rulesets.Mania.Objects.Drawables
 {
-    public abstract class DrawableManiaHitObject<TObject> : DrawableHitObject<ManiaHitObject, ManiaJudgement>
+    public abstract class DrawableManiaHitObject<TObject> : DrawableScrollingHitObject<ManiaHitObject, ManiaJudgement>
         where TObject : ManiaHitObject
     {
         /// <summary>

osu.Game/Rulesets/Objects/Drawables/DrawableHitObject.cs

@@ -18,22 +18,6 @@ namespace osu.Game.Rulesets.Objects.Drawables
 {
     public abstract class DrawableHitObject : Container
     {
-        private readonly BindableDouble lifetimeOffset = new BindableDouble();
-        /// <summary>
-        /// Time offset before the hit object start time at which this <see cref="DrawableHitObject"/> becomes visible and the time offset
-        /// after the hit object's end time after which it expires.
-        ///
-        /// <para>
-        /// This provides only a default life time range, however classes inheriting from <see cref="DrawableHitObject"/> should expire their state through
-        /// <see cref="DrawableHitObject{TObject, TJudgement}.UpdateState(ArmedState)"/> if more tight control over the life time is desired.
-        /// </para>
-        /// </summary>
-        public BindableDouble LifetimeOffset
-        {
-            get { return lifetimeOffset; }
-            set { lifetimeOffset.BindTo(value); }
-        }
-
         public readonly HitObject HitObject;
 
         /// <summary>
@@ -45,22 +29,6 @@ namespace osu.Game.Rulesets.Objects.Drawables
         {
             HitObject = hitObject;
         }
-
-        public override double LifetimeStart
-        {
-            get { return Math.Min(HitObject.StartTime - lifetimeOffset, base.LifetimeStart); }
-            set { base.LifetimeStart = value; }
-        }
-
-        public override double LifetimeEnd
-        {
-            get
-            {
-                var endTime = (HitObject as IHasEndTime)?.EndTime ?? HitObject.StartTime;
-                return Math.Max(endTime + LifetimeOffset, base.LifetimeEnd);
-            }
-            set { base.LifetimeEnd = value; }
-        }
     }
 
     public abstract class DrawableHitObject<TObject> : DrawableHitObject
@@ -217,13 +185,12 @@ namespace osu.Game.Rulesets.Objects.Drawables
         private List<DrawableHitObject<TObject, TJudgement>> nestedHitObjects;
         protected IEnumerable<DrawableHitObject<TObject, TJudgement>> NestedHitObjects => nestedHitObjects;
 
-        protected void AddNested(DrawableHitObject<TObject, TJudgement> h)
+        protected virtual void AddNested(DrawableHitObject<TObject, TJudgement> h)
         {
             if (nestedHitObjects == null)
                 nestedHitObjects = new List<DrawableHitObject<TObject, TJudgement>>();
 
             h.OnJudgement += d => OnJudgement?.Invoke(d);
-            h.LifetimeOffset = LifetimeOffset;
             nestedHitObjects.Add(h);
         }
 

osu.Game/Rulesets/Objects/Drawables/DrawableScrollingHitObject.cs

@@ -0,0 +1,49 @@
+// Copyright (c) 2007-2017 ppy Pty Ltd <contact@ppy.sh>.
+// Licensed under the MIT Licence - https://raw.githubusercontent.com/ppy/osu/master/LICENCE
+
+using System;
+using osu.Framework.Configuration;
+using osu.Game.Rulesets.Judgements;
+using osu.Game.Rulesets.Objects.Types;
+
+namespace osu.Game.Rulesets.Objects.Drawables
+{
+    /// <summary>
+    /// A basic class that overrides <see cref="DrawableHitObject{TObject, TJudgement}"/> and implements <see cref="IScrollingHitObject"/>.
+    /// </summary>
+    public abstract class DrawableScrollingHitObject<TObject, TJudgement> : DrawableHitObject<TObject, TJudgement>, IScrollingHitObject
+        where TObject : HitObject
+        where TJudgement : Judgement
+    {
+        public BindableDouble LifetimeOffset { get; } = new BindableDouble();
+
+        public DrawableScrollingHitObject(TObject hitObject)
+            : base(hitObject)
+        {
+        }
+
+        public override double LifetimeStart
+        {
+            get { return Math.Min(HitObject.StartTime - LifetimeOffset, base.LifetimeStart); }
+            set { base.LifetimeStart = value; }
+        }
+
+        public override double LifetimeEnd
+        {
+            get
+            {
+                var endTime = (HitObject as IHasEndTime)?.EndTime ?? HitObject.StartTime;
+                return Math.Max(endTime + LifetimeOffset, base.LifetimeEnd);
+            }
+            set { base.LifetimeEnd = value; }
+        }
+
+        protected override void AddNested(DrawableHitObject<TObject, TJudgement> h)
+        {
+            var scrollingHitObject = h as IScrollingHitObject;
+            scrollingHitObject?.LifetimeOffset.BindTo(LifetimeOffset);
+
+            base.AddNested(h);
+        }
+    }
+}

osu.Game/Rulesets/Objects/Drawables/IScrollingHitObject.cs

@@ -0,0 +1,25 @@
+// Copyright (c) 2007-2017 ppy Pty Ltd <contact@ppy.sh>.
+// Licensed under the MIT Licence - https://raw.githubusercontent.com/ppy/osu/master/LICENCE
+
+using osu.Framework.Configuration;
+using osu.Framework.Graphics;
+
+namespace osu.Game.Rulesets.Objects.Drawables
+{
+    /// <summary>
+    /// An interface that exposes properties required for scrolling hit objects to be properly displayed.
+    /// </summary>
+    public interface IScrollingHitObject : IDrawable
+    {
+        /// <summary>
+        /// Time offset before the hit object start time at which this <see cref="IScrollingHitObject"/> becomes visible and the time offset
+        /// after the hit object's end time after which it expires.
+        ///
+        /// <para>
+        /// This provides only a default life time range, however classes inheriting from <see cref="IScrollingHitObject"/> should override
+        /// their life times if more tight control is desired.
+        /// </para>
+        /// </summary>
+        BindableDouble LifetimeOffset { get; }
+    }
+}

osu.Game/Rulesets/Timing/SpeedAdjustmentCollection.cs

@@ -51,6 +51,13 @@ namespace osu.Game.Rulesets.Timing
             this.scrollingAxes = scrollingAxes;
         }
 
+        public override void Add(SpeedAdjustmentContainer speedAdjustment)
+        {
+            speedAdjustment.VisibleTimeRange.BindTo(VisibleTimeRange);
+            speedAdjustment.ScrollingAxes = scrollingAxes;
+            base.Add(speedAdjustment);
+        }
+
         /// <summary>
         /// Adds a hit object to this <see cref="SpeedAdjustmentCollection"/>. The hit objects will be kept in a queue
         /// and will be processed when new <see cref="SpeedAdjustmentContainer"/>s are added to this <see cref="SpeedAdjustmentCollection"/>.
@@ -58,14 +65,10 @@ namespace osu.Game.Rulesets.Timing
         /// <param name="hitObject">The hit object to add.</param>
         public void Add(DrawableHitObject hitObject)
         {
-            queuedHitObjects.Enqueue(hitObject);
+            if (!(hitObject is IScrollingHitObject))
-        }
+                throw new InvalidOperationException($"Hit objects added to a {nameof(SpeedAdjustmentCollection)} must implement {nameof(IScrollingHitObject)}.");
 
-        public override void Add(SpeedAdjustmentContainer speedAdjustment)
+            queuedHitObjects.Enqueue(hitObject);
-        {
-            speedAdjustment.VisibleTimeRange.BindTo(VisibleTimeRange);
-            speedAdjustment.ScrollingAxes = scrollingAxes;
-            base.Add(speedAdjustment);
         }
 
         protected override void Update()

osu.Game/Rulesets/Timing/SpeedAdjustmentContainer.cs

@@ -82,7 +82,9 @@ namespace osu.Game.Rulesets.Timing
 
         public override void Add(DrawableHitObject drawable)
         {
-            drawable.LifetimeOffset.BindTo(VisibleTimeRange);
+            var scrollingHitObject = drawable as IScrollingHitObject;
+            scrollingHitObject?.LifetimeOffset.BindTo(VisibleTimeRange);
+
             base.Add(drawable);
         }
 

osu.Game/osu.Game.csproj

@@ -185,6 +185,7 @@
     <Compile Include="Rulesets\Objects\SliderCurve.cs" />
     <Compile Include="Rulesets\Objects\Types\CurveType.cs" />
     <Compile Include="Rulesets\Objects\Drawables\IDrawableHitObjectWithProxiedApproach.cs" />
+    <Compile Include="Rulesets\Objects\Drawables\IScrollingHitObject.cs" />
     <Compile Include="Rulesets\Judgements\Judgement.cs" />
     <Compile Include="Rulesets\Objects\HitObjectParser.cs" />
     <Compile Include="Rulesets\Objects\HitObjectStartTimeComparer.cs" />
@@ -223,6 +224,7 @@
     <Compile Include="Beatmaps\Drawables\DifficultyColouredContainer.cs" />
     <Compile Include="Beatmaps\Drawables\Panel.cs" />
     <Compile Include="Rulesets\Objects\Drawables\DrawableHitObject.cs" />
+    <Compile Include="Rulesets\Objects\Drawables\DrawableScrollingHitObject.cs" />
     <Compile Include="Rulesets\Objects\HitObject.cs" />
     <Compile Include="Configuration\OsuConfigManager.cs" />
     <Compile Include="Overlays\Notifications\IHasCompletionTarget.cs" />