Add the Fade-In effect to DrawableSwell

osu.Game.Rulesets.Taiko/Objects/Drawables/DrawableHit.cs

@@ -6,13 +6,17 @@
 using System;
 using System.Diagnostics;
 using System.Linq;
+using System.Runtime.InteropServices;
 using JetBrains.Annotations;
+using Microsoft.Extensions.Logging;
 using osu.Framework.Bindables;
 using osu.Framework.Graphics;
 using osu.Framework.Input.Events;
+using osu.Game.Beatmaps.ControlPoints;
 using osu.Game.Rulesets.Objects.Drawables;
 using osu.Game.Rulesets.Scoring;
 using osu.Game.Rulesets.Taiko.Skinning.Default;
+using osu.Game.Rulesets.Taiko.UI;
 using osu.Game.Skinning;
 using osuTK;
 
@@ -38,6 +42,21 @@ public TaikoAction? HitAction
 
         private double? lastPressHandleTime;
 
+        /// <summary>
+        /// Duration of the Fade-In time of the hit.
+        /// </summary>
+        private const double fade_in_duration = 5000;
+
+        /// <summary>
+        /// Opacity difference of fade-in effect between scroll speeds.
+        /// </summary>
+        private const double fade_in_curve_factor = 200;
+
+        /// <summary>
+        /// Minimum time between HitObject.StartTime and LifetimeStart.
+        /// </summary>
+        private const double min_start_time_delta = 90;
+
         private readonly Bindable<HitType> type = new Bindable<HitType>();
 
         public DrawableHit()
@@ -142,6 +161,19 @@ public override void OnReleased(KeyBindingReleaseEvent<TaikoAction> e)
             base.OnReleased(e);
         }
 
+        protected override void UpdateInitialTransforms()
+        {
+            double start_time_delta = HitObject.StartTime - LifetimeStart;
+            // scale Alpha value to adjust to stable's fade-in object opacity when LifetimeStart begins, being the first accessible time point in which changing Alpha is possible
+            Alpha = (float)(1d - Math.Exp(-(start_time_delta - min_start_time_delta) / fade_in_curve_factor));
+
+            using (BeginAbsoluteSequence(LifetimeStart))
+            {
+                // makes the fade-in effect negligible on low enough scroll speeds
+                this.FadeIn(fade_in_duration * (1 - Alpha));
+            }
+        }
+
         protected override void UpdateHitStateTransforms(ArmedState state)
         {
             Debug.Assert(HitObject.HitWindows != null);

osu.Game.Rulesets.Taiko/Objects/Drawables/DrawableSwell.cs

@@ -35,6 +35,15 @@ public partial class DrawableSwell : DrawableTaikoHitObject<Swell>
         /// </summary>
         private const double ring_appear_offset = 100;
 
+        /// <summary>
+        /// Offset away from the start time of the swell at which the Fade-In effect starts.
+        /// </summary>
+        private const double fade_in_offset = 1833;
+        /// <summary>
+        /// Duration of the Fade-In time of the swell.
+        /// </summary>
+        private const double fade_in_duration = 666;
+
         private Vector2 baseSize;
 
         private readonly Container<DrawableSwellTick> ticks;
@@ -248,10 +257,20 @@ protected override void CheckForResult(bool userTriggered, double timeOffset)
             }
         }
 
+        protected override void UpdateInitialTransforms()
+        {
+            // allow for the fade-in effect
+            Alpha = 0;
+        }
+
         protected override void UpdateStartTimeStateTransforms()
         {
             base.UpdateStartTimeStateTransforms();
 
+            // swell fade-in effect from stable
+            using (BeginDelayedSequence(-fade_in_offset))
+                this.FadeIn(fade_in_duration, Easing.In);
+
             using (BeginDelayedSequence(-ring_appear_offset))
                 targetRing.ScaleTo(target_ring_scale, 400, Easing.OutQuint);
         }