Add stable sorting of storyboard elements

osu.Game/Beatmaps/Formats/LegacyStoryboardDecoder.cs

@@ -5,6 +5,7 @@ using System;
 using System.Collections.Generic;
 using System.Globalization;
 using System.IO;
+using System.Linq;
 using osuTK;
 using osuTK.Graphics;
 using osu.Framework.Graphics;
@@ -38,6 +39,10 @@ namespace osu.Game.Beatmaps.Formats
         {
             this.storyboard = storyboard;
             base.ParseStreamInto(stream, storyboard);
+
+            // OrderBy is used to guarantee that the parsing order of hitobjects with equal start times is maintained (stably-sorted)
+            foreach (StoryboardLayer layer in storyboard.Layers)
+                layer.Elements = layer.Elements.OrderBy(h => h.StartTime).ToList();
         }
 
         protected override void ParseLine(Storyboard storyboard, Section section, string line)

osu.Game/Storyboards/Drawables/DrawableStoryboardSample.cs

@@ -25,7 +25,7 @@ namespace osu.Game.Storyboards.Drawables
         public DrawableStoryboardSample(StoryboardSample sample)
         {
             this.sample = sample;
-            LifetimeStart = sample.Time;
+            LifetimeStart = sample.StartTime;
         }
 
         [BackgroundDependencyLoader]
@@ -43,27 +43,27 @@ namespace osu.Game.Storyboards.Drawables
             base.Update();
 
             // TODO: this logic will need to be consolidated with other game samples like hit sounds.
-            if (Time.Current < sample.Time)
+            if (Time.Current < sample.StartTime)
             {
                 // We've rewound before the start time of the sample
                 channel?.Stop();
 
                 // In the case that the user fast-forwards to a point far beyond the start time of the sample,
                 // we want to be able to fall into the if-conditional below (therefore we must not have a life time end)
-                LifetimeStart = sample.Time;
+                LifetimeStart = sample.StartTime;
                 LifetimeEnd = double.MaxValue;
             }
-            else if (Time.Current - Time.Elapsed < sample.Time)
+            else if (Time.Current - Time.Elapsed < sample.StartTime)
             {
                 // We've passed the start time of the sample. We only play the sample if we're within an allowable range
                 // from the sample's start, to reduce layering if we've been fast-forwarded far into the future
-                if (Time.Current - sample.Time < allowable_late_start)
+                if (Time.Current - sample.StartTime < allowable_late_start)
                     channel?.Play();
 
                 // In the case that the user rewinds to a point far behind the start time of the sample,
                 // we want to be able to fall into the if-conditional above (therefore we must not have a life time start)
                 LifetimeStart = double.MinValue;
-                LifetimeEnd = sample.Time;
+                LifetimeEnd = sample.StartTime;
             }
         }
     }

osu.Game/Storyboards/IStoryboardElement.cs

@@ -10,6 +10,8 @@ namespace osu.Game.Storyboards
         string Path { get; }
         bool IsDrawable { get; }
 
+        double StartTime { get; }
+
         Drawable CreateDrawable();
     }
 }

osu.Game/Storyboards/StoryboardLayer.cs

@@ -13,8 +13,7 @@ namespace osu.Game.Storyboards
         public bool EnabledWhenPassing = true;
         public bool EnabledWhenFailing = true;
 
-        private readonly List<IStoryboardElement> elements = new List<IStoryboardElement>();
+        public List<IStoryboardElement> Elements = new List<IStoryboardElement>();
-        public IEnumerable<IStoryboardElement> Elements => elements;
 
         public StoryboardLayer(string name, int depth)
         {
@@ -24,7 +23,7 @@ namespace osu.Game.Storyboards
 
         public void Add(IStoryboardElement element)
         {
-            elements.Add(element);
+            Elements.Add(element);
         }
 
         public DrawableStoryboardLayer CreateDrawable()

osu.Game/Storyboards/StoryboardSample.cs

@@ -11,13 +11,14 @@ namespace osu.Game.Storyboards
         public string Path { get; set; }
         public bool IsDrawable => true;
 
-        public double Time;
+        public double StartTime { get; }
+
         public float Volume;
 
         public StoryboardSample(string path, double time, float volume)
         {
             Path = path;
-            Time = time;
+            StartTime = time;
             Volume = volume;
         }