From 7daeacaff230b58a13847db3727918cf7da38d02 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bart=C5=82omiej=20Dach?= <dach.bartlomiej@gmail.com>
Date: Sun, 31 Jan 2021 17:43:16 +0100
Subject: [PATCH] Add and implement IApplicableToRate interface

---
 osu.Game/Rulesets/Mods/IApplicableToRate.cs | 20 ++++++++++++++++++++
 osu.Game/Rulesets/Mods/ModRateAdjust.cs     |  4 +++-
 osu.Game/Rulesets/Mods/ModTimeRamp.cs       | 19 ++++++++++++-------
 3 files changed, 35 insertions(+), 8 deletions(-)
 create mode 100644 osu.Game/Rulesets/Mods/IApplicableToRate.cs

diff --git a/osu.Game/Rulesets/Mods/IApplicableToRate.cs b/osu.Game/Rulesets/Mods/IApplicableToRate.cs
new file mode 100644
index 0000000000..f613867132
--- /dev/null
+++ b/osu.Game/Rulesets/Mods/IApplicableToRate.cs
@@ -0,0 +1,20 @@
+// Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
+// See the LICENCE file in the repository root for full licence text.
+
+namespace osu.Game.Rulesets.Mods
+{
+    /// <summary>
+    /// Interface that should be implemented by mods that affect the track playback speed,
+    /// and in turn, values of the track rate.
+    /// </summary>
+    public interface IApplicableToRate : IApplicableToAudio
+    {
+        /// <summary>
+        /// Returns the playback rate at <paramref name="time"/> after this mod is applied.
+        /// </summary>
+        /// <param name="time">The time instant at which the playback rate is queried.</param>
+        /// <param name="rate">The playback rate before applying this mod.</param>
+        /// <returns>The playback rate after applying this mod.</returns>
+        double ApplyToRate(double time, double rate = 1);
+    }
+}
diff --git a/osu.Game/Rulesets/Mods/ModRateAdjust.cs b/osu.Game/Rulesets/Mods/ModRateAdjust.cs
index 2150b0fb68..b016a6d43b 100644
--- a/osu.Game/Rulesets/Mods/ModRateAdjust.cs
+++ b/osu.Game/Rulesets/Mods/ModRateAdjust.cs
@@ -8,7 +8,7 @@ using osu.Framework.Graphics.Audio;
 
 namespace osu.Game.Rulesets.Mods
 {
-    public abstract class ModRateAdjust : Mod, IApplicableToAudio
+    public abstract class ModRateAdjust : Mod, IApplicableToRate
     {
         public abstract BindableNumber<double> SpeedChange { get; }
 
@@ -22,6 +22,8 @@ namespace osu.Game.Rulesets.Mods
             sample.AddAdjustment(AdjustableProperty.Frequency, SpeedChange);
         }
 
+        public double ApplyToRate(double time, double rate) => rate * SpeedChange.Value;
+
         public override string SettingDescription => SpeedChange.IsDefault ? string.Empty : $"{SpeedChange.Value:N2}x";
     }
 }
diff --git a/osu.Game/Rulesets/Mods/ModTimeRamp.cs b/osu.Game/Rulesets/Mods/ModTimeRamp.cs
index b6916c838e..7e801c3024 100644
--- a/osu.Game/Rulesets/Mods/ModTimeRamp.cs
+++ b/osu.Game/Rulesets/Mods/ModTimeRamp.cs
@@ -14,7 +14,7 @@ using osu.Game.Rulesets.UI;
 
 namespace osu.Game.Rulesets.Mods
 {
-    public abstract class ModTimeRamp : Mod, IUpdatableByPlayfield, IApplicableToBeatmap, IApplicableToAudio
+    public abstract class ModTimeRamp : Mod, IUpdatableByPlayfield, IApplicableToBeatmap, IApplicableToRate
     {
         /// <summary>
         /// The point in the beatmap at which the final ramping rate should be reached.
@@ -47,7 +47,7 @@ namespace osu.Game.Rulesets.Mods
         protected ModTimeRamp()
         {
             // for preview purpose at song select. eventually we'll want to be able to update every frame.
-            FinalRate.BindValueChanged(val => applyRateAdjustment(1), true);
+            FinalRate.BindValueChanged(val => applyRateAdjustment(double.PositiveInfinity), true);
             AdjustPitch.BindValueChanged(applyPitchAdjustment);
         }
 
@@ -75,17 +75,22 @@ namespace osu.Game.Rulesets.Mods
             finalRateTime = firstObjectStart + FINAL_RATE_PROGRESS * (lastObjectEnd - firstObjectStart);
         }
 
+        public double ApplyToRate(double time, double rate = 1)
+        {
+            double amount = (time - beginRampTime) / Math.Max(1, finalRateTime - beginRampTime);
+            double ramp = InitialRate.Value + (FinalRate.Value - InitialRate.Value) * Math.Clamp(amount, 0, 1);
+            return rate * ramp;
+        }
+
         public virtual void Update(Playfield playfield)
         {
-            applyRateAdjustment((track.CurrentTime - beginRampTime) / Math.Max(1, finalRateTime - beginRampTime));
+            applyRateAdjustment(track.CurrentTime);
         }
 
         /// <summary>
-        /// Adjust the rate along the specified ramp
+        /// Adjust the rate along the specified ramp.
         /// </summary>
-        /// <param name="amount">The amount of adjustment to apply (from 0..1).</param>
-        private void applyRateAdjustment(double amount) =>
-            SpeedChange.Value = InitialRate.Value + (FinalRate.Value - InitialRate.Value) * Math.Clamp(amount, 0, 1);
+        private void applyRateAdjustment(double time) => SpeedChange.Value = ApplyToRate(time);
 
         private void applyPitchAdjustment(ValueChangedEvent<bool> adjustPitchSetting)
         {