From 737197591d812d0abdbf733d05bd4e411b050a9a Mon Sep 17 00:00:00 2001
From: apollo-dw <83023433+apollo-dw@users.noreply.github.com>
Date: Mon, 13 Jun 2022 17:49:56 +0100
Subject: [PATCH] Change doubletap algorithm

---
 .../Difficulty/Evaluators/SpeedEvaluator.cs    | 18 ++++++++++++------
 .../Difficulty/Skills/Speed.cs                 |  3 ++-
 2 files changed, 14 insertions(+), 7 deletions(-)

diff --git a/osu.Game.Rulesets.Osu/Difficulty/Evaluators/SpeedEvaluator.cs b/osu.Game.Rulesets.Osu/Difficulty/Evaluators/SpeedEvaluator.cs
index 85203dd157..e68e7a8653 100644
--- a/osu.Game.Rulesets.Osu/Difficulty/Evaluators/SpeedEvaluator.cs
+++ b/osu.Game.Rulesets.Osu/Difficulty/Evaluators/SpeedEvaluator.cs
@@ -2,7 +2,6 @@
 // See the LICENCE file in the repository root for full licence text.
 
 using System;
-using osu.Framework.Utils;
 using osu.Game.Rulesets.Difficulty.Preprocessing;
 using osu.Game.Rulesets.Osu.Difficulty.Preprocessing;
 using osu.Game.Rulesets.Osu.Objects;
@@ -31,14 +30,21 @@ public static double EvaluateDifficultyOf(DifficultyHitObject current, double gr
             // derive strainTime for calculation
             var osuCurrObj = (OsuDifficultyHitObject)current;
             var osuPrevObj = current.Index > 0 ? (OsuDifficultyHitObject)current.Previous(0) : null;
+            var osuNextObj = (OsuDifficultyHitObject)current.Next(0);
 
             double strainTime = osuCurrObj.StrainTime;
             double greatWindowFull = greatWindow * 2;
-            double speedWindowRatio = strainTime / greatWindowFull;
+            double doubletapness = 1;
 
-            // Aim to nerf cheesy rhythms (Very fast consecutive doubles with large deltatimes between)
-            if (osuPrevObj != null && strainTime < greatWindowFull && osuPrevObj.StrainTime > strainTime)
-                strainTime = Interpolation.Lerp(osuPrevObj.StrainTime, strainTime, speedWindowRatio);
+            // Nerf doubletappable doubles.
+            if (osuNextObj != null)
+            {
+                double currDeltaTime = Math.Max(1, osuCurrObj.DeltaTime);
+                double nextDeltaTime = Math.Max(1, osuNextObj.DeltaTime);
+                double speedRatio = Math.Min(1, currDeltaTime / nextDeltaTime);
+                double windowRatio = Math.Min(1, currDeltaTime / greatWindowFull);
+                doubletapness = Math.Pow(speedRatio, 1 - windowRatio);
+            }
 
             // Cap deltatime to the OD 300 hitwindow.
             // 0.93 is derived from making sure 260bpm OD8 streams aren't nerfed harshly, whilst 0.92 limits the effect of the cap.
@@ -53,7 +59,7 @@ public static double EvaluateDifficultyOf(DifficultyHitObject current, double gr
             double travelDistance = osuPrevObj?.TravelDistance ?? 0;
             double distance = Math.Min(single_spacing_threshold, travelDistance + osuCurrObj.MinimumJumpDistance);
 
-            return (speedBonus + speedBonus * Math.Pow(distance / single_spacing_threshold, 3.5)) / strainTime;
+            return (speedBonus + speedBonus * Math.Pow(distance / single_spacing_threshold, 3.5)) * doubletapness / strainTime;
         }
     }
 }
diff --git a/osu.Game.Rulesets.Osu/Difficulty/Skills/Speed.cs b/osu.Game.Rulesets.Osu/Difficulty/Skills/Speed.cs
index 055e1cb66e..3e4e55262c 100644
--- a/osu.Game.Rulesets.Osu/Difficulty/Skills/Speed.cs
+++ b/osu.Game.Rulesets.Osu/Difficulty/Skills/Speed.cs
@@ -5,6 +5,7 @@
 using osu.Game.Rulesets.Difficulty.Preprocessing;
 using osu.Game.Rulesets.Mods;
 using osu.Game.Rulesets.Osu.Difficulty.Evaluators;
+using osu.Game.Rulesets.Osu.Difficulty.Preprocessing;
 
 namespace osu.Game.Rulesets.Osu.Difficulty.Skills
 {
@@ -35,7 +36,7 @@ public Speed(Mod[] mods, double hitWindowGreat)
 
         protected override double StrainValueAt(DifficultyHitObject current)
         {
-            currentStrain *= strainDecay(current.DeltaTime);
+            currentStrain *= strainDecay(((OsuDifficultyHitObject)current).StrainTime);
             currentStrain += SpeedEvaluator.EvaluateDifficultyOf(current, greatWindow) * skillMultiplier;
 
             currentRhythm = RhythmEvaluator.EvaluateDifficultyOf(current, greatWindow);