Implement stamina consideration for Mono (single-coloured) patterns.

osu.Game.Rulesets.Taiko/Difficulty/Skills/Stamina.cs

@@ -1,33 +1,55 @@
 // Copyright (c) ppy Pty Ltd <[email protected]>. Licensed under the MIT Licence.
 // See the LICENCE file in the repository root for full licence text.
 
+using System;
 using osu.Game.Rulesets.Difficulty.Preprocessing;
 using osu.Game.Rulesets.Difficulty.Skills;
 using osu.Game.Rulesets.Mods;
 using osu.Game.Rulesets.Taiko.Difficulty.Evaluators;
+using osu.Game.Rulesets.Taiko.Difficulty.Preprocessing;
 
 namespace osu.Game.Rulesets.Taiko.Difficulty.Skills
 {
     /// <summary>
     /// Calculates the stamina coefficient of taiko difficulty.
     /// </summary>
-    public class Stamina : StrainDecaySkill
+    public class Stamina : StrainSkill
     {
-        protected override double SkillMultiplier => 1.1;
-        protected override double StrainDecayBase => 0.4;
+        private double skillMultiplier => 1.1;
+        private double strainDecayBase => 0.4;
+
+        private readonly bool singleColourStamina;
+
+        private double currentStrain;
 
         /// <summary>
         /// Creates a <see cref="Stamina"/> skill.
         /// </summary>
         /// <param name="mods">Mods for use in skill calculations.</param>
-        public Stamina(Mod[] mods)
+        /// <param name="singleColourStamina">Reads when Stamina is from a single coloured pattern.</param>
+        public Stamina(Mod[] mods, bool singleColourStamina)
             : base(mods)
         {
+            this.singleColourStamina = singleColourStamina;
         }
 
-        protected override double StrainValueOf(DifficultyHitObject current)
+        private double strainDecay(double ms) => Math.Pow(strainDecayBase, ms / 1000);
+
+        protected override double StrainValueAt(DifficultyHitObject current)
         {
-            return StaminaEvaluator.EvaluateDifficultyOf(current);
+            currentStrain *= strainDecay(current.DeltaTime);
+            currentStrain += StaminaEvaluator.EvaluateDifficultyOf(current) * skillMultiplier;
+
+            // Safely prevents previous strains from shifting as new notes are added.
+            var currentObject = current as TaikoDifficultyHitObject;
+            int index = currentObject?.Colour.MonoStreak?.HitObjects.IndexOf(currentObject) ?? 0;
+
+            if (singleColourStamina)
+                return currentStrain / (1 + Math.Exp(-(index - 10) / 2.0));
+
+            return currentStrain;
         }
+
+        protected override double CalculateInitialStrain(double time, DifficultyHitObject current) => singleColourStamina ? 0 : currentStrain * strainDecay(time - current.Previous(0).StartTime);
     }
 }

osu.Game.Rulesets.Taiko/Difficulty/TaikoDifficultyAttributes.cs

@@ -16,6 +16,12 @@ public class TaikoDifficultyAttributes : DifficultyAttributes
         [JsonProperty("stamina_difficulty")]
         public double StaminaDifficulty { get; set; }
 
+        /// <summary>
+        /// The ratio of stamina difficulty from mono-color (single colour) streams to total stamina difficulty.
+        /// </summary>
+        [JsonProperty("mono_stamina_factor")]
+        public double MonoStaminaFactor { get; set; }
+
         /// <summary>
         /// The difficulty corresponding to the rhythm skill.
         /// </summary>
@@ -60,6 +66,7 @@ public class TaikoDifficultyAttributes : DifficultyAttributes
             yield return (ATTRIB_ID_DIFFICULTY, StarRating);
             yield return (ATTRIB_ID_GREAT_HIT_WINDOW, GreatHitWindow);
             yield return (ATTRIB_ID_OK_HIT_WINDOW, OkHitWindow);
+            yield return (ATTRIB_ID_MONO_STAMINA_FACTOR, MonoStaminaFactor);
         }
 
         public override void FromDatabaseAttributes(IReadOnlyDictionary<int, double> values, IBeatmapOnlineInfo onlineInfo)
@@ -69,6 +76,7 @@ public override void FromDatabaseAttributes(IReadOnlyDictionary<int, double> val
             StarRating = values[ATTRIB_ID_DIFFICULTY];
             GreatHitWindow = values[ATTRIB_ID_GREAT_HIT_WINDOW];
             OkHitWindow = values[ATTRIB_ID_OK_HIT_WINDOW];
+            MonoStaminaFactor = values[ATTRIB_ID_MONO_STAMINA_FACTOR];
         }
     }
 }

osu.Game.Rulesets.Taiko/Difficulty/TaikoDifficultyCalculator.cs

@@ -38,7 +38,8 @@ protected override Skill[] CreateSkills(IBeatmap beatmap, Mod[] mods, double clo
             {
                 new Rhythm(mods),
                 new Colour(mods),
-                new Stamina(mods)
+                new Stamina(mods, false),
+                new Stamina(mods, true)
             };
         }
 
@@ -79,10 +80,13 @@ protected override DifficultyAttributes CreateDifficultyAttributes(IBeatmap beat
             Colour colour = (Colour)skills.First(x => x is Colour);
             Rhythm rhythm = (Rhythm)skills.First(x => x is Rhythm);
             Stamina stamina = (Stamina)skills.First(x => x is Stamina);
+            Stamina singleColourStamina = (Stamina)skills.Last(x => x is Stamina);
 
             double colourRating = colour.DifficultyValue() * colour_skill_multiplier;
             double rhythmRating = rhythm.DifficultyValue() * rhythm_skill_multiplier;
             double staminaRating = stamina.DifficultyValue() * stamina_skill_multiplier;
+            double monoStaminaRating = singleColourStamina.DifficultyValue() * stamina_skill_multiplier;
+            double monoStaminaFactor = staminaRating == 0 ? 1 : Math.Pow(monoStaminaRating / staminaRating, 5);
 
             double combinedRating = combinedDifficultyValue(rhythm, colour, stamina);
             double starRating = rescale(combinedRating * 1.4);
@@ -95,6 +99,7 @@ protected override DifficultyAttributes CreateDifficultyAttributes(IBeatmap beat
                 StarRating = starRating,
                 Mods = mods,
                 StaminaDifficulty = staminaRating,
+                MonoStaminaFactor = monoStaminaFactor,
                 RhythmDifficulty = rhythmRating,
                 ColourDifficulty = colourRating,
                 PeakDifficulty = combinedRating,

osu.Game.Rulesets.Taiko/Difficulty/TaikoPerformanceCalculator.cs

@@ -42,18 +42,18 @@ protected override PerformanceAttributes CreatePerformanceAttributes(ScoreInfo s
             if (totalSuccessfulHits > 0)
                 effectiveMissCount = Math.Max(1.0, 1000.0 / totalSuccessfulHits) * countMiss;
 
-            // TODO: The detection of rulesets is temporary until the leftover old skills have been reworked.
+            // Converts are detected and omitted from mod-specific bonuses due to the scope of current difficulty calculation.
             bool isConvert = score.BeatmapInfo!.Ruleset.OnlineID != 1;
 
             double multiplier = 1.13;
 
-            if (score.Mods.Any(m => m is ModHidden))
+            if (score.Mods.Any(m => m is ModHidden) && !isConvert)
                 multiplier *= 1.075;
 
             if (score.Mods.Any(m => m is ModEasy))
-                multiplier *= 0.975;
+                multiplier *= 0.950;
 
-            double difficultyValue = computeDifficultyValue(score, taikoAttributes, isConvert);
+            double difficultyValue = computeDifficultyValue(score, taikoAttributes);
             double accuracyValue = computeAccuracyValue(score, taikoAttributes, isConvert);
             double totalValue =
                 Math.Pow(
@@ -71,7 +71,7 @@ protected override PerformanceAttributes CreatePerformanceAttributes(ScoreInfo s
             };
         }
 
-        private double computeDifficultyValue(ScoreInfo score, TaikoDifficultyAttributes attributes, bool isConvert)
+        private double computeDifficultyValue(ScoreInfo score, TaikoDifficultyAttributes attributes)
         {
             double difficultyValue = Math.Pow(5 * Math.Max(1.0, attributes.StarRating / 0.115) - 4.0, 2.25) / 1150.0;
 
@@ -81,21 +81,25 @@ private double computeDifficultyValue(ScoreInfo score, TaikoDifficultyAttributes
             difficultyValue *= Math.Pow(0.986, effectiveMissCount);
 
             if (score.Mods.Any(m => m is ModEasy))
-                difficultyValue *= 0.985;
+                difficultyValue *= 0.90;
 
-            if (score.Mods.Any(m => m is ModHidden) && !isConvert)
+            if (score.Mods.Any(m => m is ModHidden))
                 difficultyValue *= 1.025;
 
             if (score.Mods.Any(m => m is ModHardRock))
                 difficultyValue *= 1.10;
 
             if (score.Mods.Any(m => m is ModFlashlight<TaikoHitObject>))
-                difficultyValue *= 1.050 * lengthBonus;
+                difficultyValue *= Math.Max(1, 1.050 - Math.Min(attributes.MonoStaminaFactor / 50, 1) * lengthBonus);
 
             if (estimatedUnstableRate == null)
                 return 0;
 
-            return difficultyValue * Math.Pow(SpecialFunctions.Erf(400 / (Math.Sqrt(2) * estimatedUnstableRate.Value)), 2.0);
+            // Scale accuracy more harshly on nearly-completely mono (single coloured) speed maps.
+            double accScalingExponent = 2 + attributes.MonoStaminaFactor;
+            double accScalingShift = 300 - 100 * attributes.MonoStaminaFactor;
+
+            return difficultyValue * Math.Pow(SpecialFunctions.Erf(accScalingShift / (Math.Sqrt(2) * estimatedUnstableRate.Value)), accScalingExponent);
         }
 
         private double computeAccuracyValue(ScoreInfo score, TaikoDifficultyAttributes attributes, bool isConvert)

osu.Game/Rulesets/Difficulty/DifficultyAttributes.cs

@@ -29,6 +29,7 @@ public class DifficultyAttributes
         protected const int ATTRIB_ID_SPEED_DIFFICULT_STRAIN_COUNT = 23;
         protected const int ATTRIB_ID_AIM_DIFFICULT_STRAIN_COUNT = 25;
         protected const int ATTRIB_ID_OK_HIT_WINDOW = 27;
+        protected const int ATTRIB_ID_MONO_STAMINA_FACTOR = 29;
 
         /// <summary>
         /// The mods which were applied to the beatmap.