Add preempt adjustment and fade in first end circle with slider to match stable

osu.Game.Rulesets.Osu/Objects/Slider.cs

@@ -174,10 +174,9 @@ namespace osu.Game.Rulesets.Osu.Objects
                         // we need to use the LegacyLastTick here for compatibility reasons (difficulty).
                         // it is *okay* to use this because the TailCircle is not used for any meaningful purpose in gameplay.
                         // if this is to change, we should revisit this.
-                        AddNested(TailCircle = new SliderTailCircle
+                        AddNested(TailCircle = new SliderTailCircle(this)
                         {
                             RepeatIndex = e.SpanIndex,
-                            SpanDuration = SpanDuration,
                             StartTime = e.Time,
                             Position = EndPosition,
                             StackHeight = StackHeight
@@ -185,10 +184,9 @@ namespace osu.Game.Rulesets.Osu.Objects
                         break;
 
                     case SliderEventType.Repeat:
-                        AddNested(new SliderRepeat
+                        AddNested(new SliderRepeat(this)
                         {
                             RepeatIndex = e.SpanIndex,
-                            SpanDuration = SpanDuration,
                             StartTime = StartTime + (e.SpanIndex + 1) * SpanDuration,
                             Position = Position + Path.PositionAt(e.PathProgress),
                             StackHeight = StackHeight,

osu.Game.Rulesets.Osu/Objects/SliderEndCircle.cs

@@ -8,12 +8,20 @@ using osu.Game.Rulesets.Scoring;
 namespace osu.Game.Rulesets.Osu.Objects
 {
     /// <summary>
-    /// A hitcircle which is at the end of a slider path (either repeat or final tail).
+    /// A hit circle which is at the end of a slider path (either repeat or final tail).
     /// </summary>
     public abstract class SliderEndCircle : HitCircle
     {
+        private readonly Slider slider;
+
+        protected SliderEndCircle(Slider slider)
+        {
+            this.slider = slider;
+        }
+
         public int RepeatIndex { get; set; }
-        public double SpanDuration { get; set; }
+
+        public double SpanDuration => slider.SpanDuration;
 
         protected override void ApplyDefaultsToSelf(ControlPointInfo controlPointInfo, BeatmapDifficulty difficulty)
         {
@@ -27,6 +35,14 @@ namespace osu.Game.Rulesets.Osu.Objects
                 // The next end circle should appear exactly after the previous circle (on the same end) is hit.
                 TimePreempt = SpanDuration * 2;
             }
+            else
+            {
+                // taken from osu-stable
+                const float first_end_circle_preempt_adjust = 2 / 3f;
+
+                // The first end circle should fade in with the slider.
+                TimePreempt = (StartTime - slider.StartTime) + slider.TimePreempt * first_end_circle_preempt_adjust;
+            }
         }
 
         protected override HitWindows CreateHitWindows() => HitWindows.Empty;

osu.Game.Rulesets.Osu/Objects/SliderRepeat.cs

@@ -9,6 +9,11 @@ namespace osu.Game.Rulesets.Osu.Objects
 {
     public class SliderRepeat : SliderEndCircle
     {
+        public SliderRepeat(Slider slider)
+            : base(slider)
+        {
+        }
+
         public override Judgement CreateJudgement() => new SliderRepeatJudgement();
 
         public class SliderRepeatJudgement : OsuJudgement

osu.Game.Rulesets.Osu/Objects/SliderTailCircle.cs

@@ -14,6 +14,11 @@ namespace osu.Game.Rulesets.Osu.Objects
     /// </summary>
     public class SliderTailCircle : SliderEndCircle
     {
+        public SliderTailCircle(Slider slider)
+            : base(slider)
+        {
+        }
+
         public override Judgement CreateJudgement() => new SliderTailJudgement();
 
         public class SliderTailJudgement : OsuJudgement