Merge 544ba25743 into f09d8f097a

osu.Game.Rulesets.Taiko/Difficulty/Evaluators/ReadingEvaluator.cs

@@ -0,0 +1,45 @@
+// 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.
+
+using osu.Game.Rulesets.Difficulty.Utils;
+using osu.Game.Rulesets.Taiko.Difficulty.Preprocessing;
+
+namespace osu.Game.Rulesets.Taiko.Difficulty.Evaluators
+{
+    public static class ReadingEvaluator
+    {
+        private const double high_sv_multiplier = 1.0;
+
+        /// <summary>
+        /// Calculates the influence of higher slider velocities on hitobject difficulty.
+        /// The bonus is determined based on the EffectiveBPM, shifting within a defined range
+        /// between the upper and lower boundaries to reflect how increased slider velocity impacts difficulty.
+        /// </summary>
+        /// <param name="noteObject">The hit object to evaluate.</param>
+        /// <returns>The reading difficulty value for the given hit object.</returns>
+        public static double EvaluateDifficultyOf(TaikoDifficultyHitObject noteObject)
+        {
+            double effectiveBPM = noteObject.EffectiveBPM;
+
+            const double velocity_max = 640;
+            const double velocity_min = 480;
+
+            const double center = (velocity_max + velocity_min) / 2;
+            const double range = velocity_max - velocity_min;
+
+            return high_sv_multiplier * DifficultyCalculationUtils.Logistic(effectiveBPM, center, 1.0 / (range / 10));
+        }
+
+        /// <summary>
+        /// Calculates the object density based on the DeltaTime, EffectiveBPM, and CurrentSliderVelocity.
+        /// </summary>
+        /// <param name="noteObject">The current noteObject to evaluate.</param>
+        /// <returns>The calculated object density.</returns>
+        public static double CalculateObjectDensity(TaikoDifficultyHitObject noteObject)
+        {
+            double objectDensity = 50 * DifficultyCalculationUtils.Logistic(noteObject.DeltaTime, 200, 1.0 / 300);
+
+            return 1 - DifficultyCalculationUtils.Logistic(noteObject.EffectiveBPM, objectDensity, 1.0 / 240);
+        }
+    }
+}

osu.Game.Rulesets.Taiko/Difficulty/Evaluators/RhythmEvaluator.cs

@@ -0,0 +1,137 @@
+// 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.
+
+using System;
+using System.Collections.Generic;
+using osu.Game.Rulesets.Difficulty.Preprocessing;
+using osu.Game.Rulesets.Difficulty.Utils;
+using osu.Game.Rulesets.Taiko.Difficulty.Preprocessing;
+using osu.Game.Rulesets.Taiko.Difficulty.Preprocessing.Rhythm;
+using osu.Game.Rulesets.Taiko.Difficulty.Preprocessing.Rhythm.Data;
+
+namespace osu.Game.Rulesets.Taiko.Difficulty.Evaluators
+{
+    public class RhythmEvaluator
+    {
+        /// <summary>
+        /// Multiplier for a given denominator term.
+        /// </summary>
+        private static double termPenalty(double ratio, int denominator, double power, double multiplier)
+        {
+            return -multiplier * Math.Pow(Math.Cos(denominator * Math.PI * ratio), power);
+        }
+
+        /// <summary>
+        /// Calculates the difficulty of a given ratio using a combination of periodic penalties and bonuses.
+        /// </summary>
+        private static double ratioDifficulty(double ratio, int terms = 8)
+        {
+            // Sum of n = 8 terms of periodic penalty.
+            double difficulty = 0;
+
+            for (int i = 1; i <= terms; ++i)
+            {
+                difficulty += termPenalty(ratio, i, 2, 1);
+            }
+
+            difficulty += terms;
+
+            // Give bonus to near-1 ratios
+            difficulty += DifficultyCalculationUtils.BellCurve(ratio, 1, 0.5);
+
+            // Penalize ratios that are VERY near 1
+            difficulty -= DifficultyCalculationUtils.BellCurve(ratio, 1, 0.3);
+
+            return difficulty / Math.Sqrt(8);
+        }
+
+        /// <summary>
+        /// Determines if the pattern of hit object intervals is consistent based on a given threshold.
+        /// </summary>
+        private static bool isConsistentPattern(EvenHitObjects evenHitObjects, double threshold = 0.1)
+        {
+            // Collect the last 4 intervals (current and the last 3 previous).
+            List<double?> intervals = new List<double?>();
+            var currentObject = evenHitObjects;
+            const int interval_count = 4;
+
+            for (int i = 0; i < interval_count && currentObject != null; i++)
+            {
+                intervals.Add(currentObject.HitObjectInterval);
+                currentObject = currentObject.Previous;
+            }
+
+            intervals.RemoveAll(interval => interval == null);
+
+            // If there are fewer than 4 valid intervals, skip the consistency check.
+            if (intervals.Count < interval_count)
+                return false;
+
+            for (int i = 0; i < intervals.Count; i++)
+            {
+                for (int j = i + 1; j < intervals.Count; j++)
+                {
+                    double ratio = intervals[i]!.Value / intervals[j]!.Value;
+                    if (Math.Abs(1 - ratio) <= threshold) // If any two intervals are similar, return true.
+                        return true;
+                }
+            }
+
+            // No similar intervals were found.
+            return false;
+        }
+
+        private static double evaluateDifficultyOf(EvenHitObjects evenHitObjects, double hitWindow)
+        {
+            double intervalDifficulty = ratioDifficulty(evenHitObjects.HitObjectIntervalRatio);
+            double? previousInterval = evenHitObjects.Previous?.HitObjectInterval;
+
+            // If a previous interval exists and there are multiple hit objects in the sequence:
+            if (previousInterval != null && evenHitObjects.Children.Count > 1)
+            {
+                double expectedDurationFromPrevious = (double)previousInterval * evenHitObjects.Children.Count;
+                double durationDifference = Math.Abs(evenHitObjects.Duration - expectedDurationFromPrevious);
+
+                intervalDifficulty *= DifficultyCalculationUtils.Logistic(
+                    durationDifference / hitWindow,
+                    midpointOffset: 0.5,
+                    multiplier: 1.5,
+                    maxValue: 1);
+            }
+
+            // Penalise regular intervals within the last four intervals.
+            if (isConsistentPattern(evenHitObjects))
+            {
+                intervalDifficulty *= 0.4;
+            }
+
+            // Penalise patterns that can be hit within a single hit window.
+            intervalDifficulty *= DifficultyCalculationUtils.Logistic(
+                evenHitObjects.Duration / hitWindow,
+                midpointOffset: 0.5,
+                multiplier: 1,
+                maxValue: 1);
+
+            return intervalDifficulty;
+        }
+
+        private static double evaluateDifficultyOf(EvenPatterns evenPatterns)
+        {
+            return ratioDifficulty(evenPatterns.IntervalRatio);
+        }
+
+        public static double EvaluateDifficultyOf(DifficultyHitObject hitObject, double hitWindow)
+        {
+            TaikoDifficultyHitObjectRhythm rhythm = ((TaikoDifficultyHitObject)hitObject).Rhythm;
+            double difficulty = 0.0d;
+
+            if (rhythm.EvenHitObjects?.FirstHitObject == hitObject) // Difficulty for EvenHitObjects
+                difficulty += evaluateDifficultyOf(rhythm.EvenHitObjects, hitWindow);
+
+            if (rhythm.EvenPatterns?.FirstHitObject == hitObject) // Difficulty for EvenPatterns
+                difficulty += evaluateDifficultyOf(rhythm.EvenPatterns) * rhythm.Difficulty;
+
+            return difficulty;
+        }
+    }
+}

osu.Game.Rulesets.Taiko/Difficulty/Preprocessing/Colour/Data/MonoStreak.cs

@@ -1,9 +1,9 @@
 // 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.
 
+using System.Collections.Generic;
 using osu.Game.Rulesets.Difficulty.Preprocessing;
 using osu.Game.Rulesets.Taiko.Objects;
-using System.Collections.Generic;
 
 namespace osu.Game.Rulesets.Taiko.Difficulty.Preprocessing.Colour.Data
 {

osu.Game.Rulesets.Taiko/Difficulty/Preprocessing/Reading/EffectiveBPMPreprocessor.cs

@@ -0,0 +1,50 @@
+// 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.
+
+using System.Collections.Generic;
+using osu.Game.Beatmaps;
+using osu.Game.Beatmaps.ControlPoints;
+
+namespace osu.Game.Rulesets.Taiko.Difficulty.Preprocessing.Reading
+{
+    public class EffectiveBPMPreprocessor
+    {
+        private readonly IList<TaikoDifficultyHitObject> noteObjects;
+        private readonly double globalSliderVelocity;
+
+        public EffectiveBPMPreprocessor(IBeatmap beatmap, List<TaikoDifficultyHitObject> noteObjects)
+        {
+            this.noteObjects = noteObjects;
+            globalSliderVelocity = beatmap.Difficulty.SliderMultiplier;
+        }
+
+        /// <summary>
+        /// Calculates and sets the effective BPM and slider velocity for each note object, considering clock rate and scroll speed.
+        /// </summary>
+        public void ProcessEffectiveBPM(ControlPointInfo controlPointInfo, double clockRate)
+        {
+            foreach (var currentNoteObject in noteObjects)
+            {
+                double startTime = currentNoteObject.StartTime * clockRate;
+
+                // Retrieve the timing point at the note's start time
+                TimingControlPoint currentControlPoint = controlPointInfo.TimingPointAt(startTime);
+
+                // Calculate the slider velocity at the note's start time.
+                double currentSliderVelocity = calculateSliderVelocity(controlPointInfo, startTime, clockRate);
+                currentNoteObject.CurrentSliderVelocity = currentSliderVelocity;
+
+                currentNoteObject.EffectiveBPM = currentControlPoint.BPM * currentSliderVelocity;
+            }
+        }
+
+        /// <summary>
+        /// Calculates the slider velocity based on control point info and clock rate.
+        /// </summary>
+        private double calculateSliderVelocity(ControlPointInfo controlPointInfo, double startTime, double clockRate)
+        {
+            var activeEffectControlPoint = controlPointInfo.EffectPointAt(startTime);
+            return globalSliderVelocity * (activeEffectControlPoint.ScrollSpeed) * clockRate;
+        }
+    }
+}

osu.Game.Rulesets.Taiko/Difficulty/Preprocessing/Rhythm/Data/EvenHitObjects.cs

@@ -0,0 +1,94 @@
+// 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.
+
+using System.Collections.Generic;
+using osu.Game.Rulesets.Difficulty.Preprocessing;
+
+namespace osu.Game.Rulesets.Taiko.Difficulty.Preprocessing.Rhythm.Data
+{
+    /// <summary>
+    /// Represents a group of <see cref="TaikoDifficultyHitObject"/>s with no rhythm variation.
+    /// </summary>
+    public class EvenHitObjects : EvenRhythm<TaikoDifficultyHitObject>, IHasInterval
+    {
+        public TaikoDifficultyHitObject FirstHitObject => Children[0];
+
+        public EvenHitObjects? Previous;
+
+        /// <summary>
+        /// <see cref="DifficultyHitObject.StartTime"/> of the first hit object.
+        /// </summary>
+        public double StartTime => Children[0].StartTime;
+
+        /// <summary>
+        /// The interval between the first and final hit object within this group.
+        /// </summary>
+        public double Duration => Children[^1].StartTime - Children[0].StartTime;
+
+        /// <summary>
+        /// The interval in ms of each hit object in this <see cref="EvenHitObjects"/>. This is only defined if there is
+        /// more than two hit objects in this <see cref="EvenHitObjects"/>.
+        /// </summary>
+        public double? HitObjectInterval;
+
+        /// <summary>
+        /// The ratio of <see cref="HitObjectInterval"/> between this and the previous <see cref="EvenHitObjects"/>. In the
+        /// case where one or both of the <see cref="HitObjectInterval"/> is undefined, this will have a value of 1.
+        /// </summary>
+        public double HitObjectIntervalRatio = 1;
+
+        /// <summary>
+        /// The interval between the <see cref="StartTime"/> of this and the previous <see cref="EvenHitObjects"/>.
+        /// </summary>
+        public double Interval { get; private set; } = double.PositiveInfinity;
+
+        public EvenHitObjects(EvenHitObjects? previous, List<TaikoDifficultyHitObject> data, ref int i)
+            : base(data, ref i, 5)
+        {
+            Previous = previous;
+
+            foreach (var hitObject in Children)
+            {
+                hitObject.Rhythm.EvenHitObjects = this;
+
+                // Pass the HitObjectInterval to each child.
+                hitObject.HitObjectInterval = HitObjectInterval;
+            }
+
+            calculateIntervals();
+        }
+
+        public static List<EvenHitObjects> GroupHitObjects(List<TaikoDifficultyHitObject> data)
+        {
+            List<EvenHitObjects> flatPatterns = new List<EvenHitObjects>();
+
+            // Index does not need to be incremented, as it is handled within EvenRhythm's constructor.
+            for (int i = 0; i < data.Count;)
+            {
+                EvenHitObjects? previous = flatPatterns.Count > 0 ? flatPatterns[^1] : null;
+                flatPatterns.Add(new EvenHitObjects(previous, data, ref i));
+            }
+
+            return flatPatterns;
+        }
+
+        private void calculateIntervals()
+        {
+            // Calculate the average interval between hitobjects, or null if there are fewer than two.
+            HitObjectInterval = Children.Count < 2 ? null : (Children[^1].StartTime - Children[0].StartTime) / (Children.Count - 1);
+
+            // If both the current and previous intervals are available, calculate the ratio.
+            if (Previous?.HitObjectInterval != null && HitObjectInterval != null)
+            {
+                HitObjectIntervalRatio = HitObjectInterval.Value / Previous.HitObjectInterval.Value;
+            }
+
+            if (Previous == null)
+            {
+                return;
+            }
+
+            Interval = StartTime - Previous.StartTime;
+        }
+    }
+}

osu.Game.Rulesets.Taiko/Difficulty/Preprocessing/Rhythm/Data/EvenPatterns.cs

@@ -0,0 +1,55 @@
+// 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.
+
+using System.Collections.Generic;
+using System.Linq;
+
+namespace osu.Game.Rulesets.Taiko.Difficulty.Preprocessing.Rhythm.Data
+{
+    /// <summary>
+    /// Represents <see cref="EvenHitObjects"/> grouped by their <see cref="EvenHitObjects.StartTime"/>'s interval.
+    /// </summary>
+    public class EvenPatterns : EvenRhythm<EvenHitObjects>
+    {
+        public EvenPatterns? Previous { get; private set; }
+
+        /// <summary>
+        /// The <see cref="EvenHitObjects.Interval"/> between children <see cref="EvenHitObjects"/> within this group.
+        /// If there is only one child, this will have the value of the first child's <see cref="EvenHitObjects.Interval"/>.
+        /// </summary>
+        public double ChildrenInterval => Children.Count > 1 ? Children[1].Interval : Children[0].Interval;
+
+        /// <summary>
+        /// The ratio of <see cref="ChildrenInterval"/> between this and the previous <see cref="EvenPatterns"/>. In the
+        /// case where there is no previous <see cref="EvenPatterns"/>, this will have a value of 1.
+        /// </summary>
+        public double IntervalRatio => ChildrenInterval / Previous?.ChildrenInterval ?? 1.0d;
+
+        public TaikoDifficultyHitObject FirstHitObject => Children[0].FirstHitObject;
+
+        public IEnumerable<TaikoDifficultyHitObject> AllHitObjects => Children.SelectMany(child => child.Children);
+
+        private EvenPatterns(EvenPatterns? previous, List<EvenHitObjects> data, ref int i)
+            : base(data, ref i, 5)
+        {
+            Previous = previous;
+
+            foreach (TaikoDifficultyHitObject hitObject in AllHitObjects)
+            {
+                hitObject.Rhythm.EvenPatterns = this;
+            }
+        }
+
+        public static void GroupPatterns(List<EvenHitObjects> data)
+        {
+            List<EvenPatterns> evenPatterns = new List<EvenPatterns>();
+
+            // Index does not need to be incremented, as it is handled within the EvenRhythm constructor.
+            for (int i = 0; i < data.Count;)
+            {
+                EvenPatterns? previous = evenPatterns.Count > 0 ? evenPatterns[^1] : null;
+                evenPatterns.Add(new EvenPatterns(previous, data, ref i));
+            }
+        }
+    }
+}

osu.Game.Rulesets.Taiko/Difficulty/Preprocessing/Rhythm/Data/EvenRhythm.cs

@@ -0,0 +1,73 @@
+// 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.
+
+using System;
+using System.Collections.Generic;
+
+namespace osu.Game.Rulesets.Taiko.Difficulty.Preprocessing.Rhythm.Data
+{
+    /// <summary>
+    /// A base class for grouping <see cref="IHasInterval"/>s by their interval. In edges where an interval change
+    /// occurs, the <see cref="IHasInterval"/> is added to the group with the smaller interval.
+    /// </summary>
+    public abstract class EvenRhythm<ChildType>
+        where ChildType : IHasInterval
+    {
+        public IReadOnlyList<ChildType> Children { get; private set; }
+
+        /// <summary>
+        /// Determines if the intervals between two child objects are within a specified margin of error,
+        /// indicating that the intervals are effectively "flat" or consistent.
+        /// </summary>
+        private bool isFlat(ChildType current, ChildType previous, double marginOfError)
+        {
+            return Math.Abs(current.Interval - previous.Interval) <= marginOfError;
+        }
+
+        /// <summary>
+        /// Create a new <see cref="EvenRhythm{ChildType}"/> from a list of <see cref="IHasInterval"/>s, and add
+        /// them to the <see cref="Children"/> list until the end of the group.
+        /// </summary>
+        /// <param name="data">The list of <see cref="IHasInterval"/>s.</param>
+        /// <param name="i">
+        /// Index in <paramref name="data"/> to start adding children. This will be modified and should be passed into
+        /// the next <see cref="EvenRhythm{ChildType}"/>'s constructor.
+        /// </param>
+        /// <param name="marginOfError">
+        /// The margin of error for the interval, within of which no interval change is considered to have occured.
+        /// </param>
+        protected EvenRhythm(List<ChildType> data, ref int i, double marginOfError)
+        {
+            List<ChildType> children = new List<ChildType>();
+            Children = children;
+            children.Add(data[i]);
+            i++;
+
+            for (; i < data.Count - 1; i++)
+            {
+                // An interval change occured, add the current data if the next interval is larger.
+                if (!isFlat(data[i], data[i + 1], marginOfError))
+                {
+                    if (data[i + 1].Interval > data[i].Interval + marginOfError)
+                    {
+                        children.Add(data[i]);
+                        i++;
+                    }
+
+                    return;
+                }
+
+                // No interval change occured
+                children.Add(data[i]);
+            }
+
+            // Check if the last two objects in the data form a "flat" rhythm pattern within the specified margin of error.
+            // If true, add the current object to the group and increment the index to process the next object.
+            if (data.Count > 2 && isFlat(data[^1], data[^2], marginOfError))
+            {
+                children.Add(data[i]);
+                i++;
+            }
+        }
+    }
+}

osu.Game.Rulesets.Taiko/Difficulty/Preprocessing/Rhythm/IHasInterval.cs

@@ -0,0 +1,13 @@
+// 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.Taiko.Difficulty.Preprocessing.Rhythm
+{
+    /// <summary>
+    /// The interface for hitobjects that provide an interval value,
+    /// </summary>
+    public interface IHasInterval
+    {
+        double Interval { get; }
+    }
+}

osu.Game.Rulesets.Taiko/Difficulty/Preprocessing/Rhythm/TaikoDifficultyHitObjectRhythm.cs

@@ -1,24 +1,82 @@
 // 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.
 
+using System;
+using System.Linq;
+using osu.Game.Rulesets.Taiko.Difficulty.Preprocessing.Rhythm.Data;
+
 namespace osu.Game.Rulesets.Taiko.Difficulty.Preprocessing.Rhythm
 {
     /// <summary>
-    /// Represents a rhythm change in a taiko map.
+    /// Stores rhythm data for a <see cref="TaikoDifficultyHitObject"/>.
     /// </summary>
     public class TaikoDifficultyHitObjectRhythm
     {
+        /// <summary>
+        /// The group of hit objects with consistent rhythm that this object belongs to.
+        /// </summary>
+        public EvenHitObjects? EvenHitObjects;
+
+        /// <summary>
+        /// The larger pattern of rhythm groups that this object is part of.
+        /// </summary>
+        public EvenPatterns? EvenPatterns;
+
+        /// <summary>
+        /// The ratio of current <see cref="Rulesets.Difficulty.Preprocessing.DifficultyHitObject.DeltaTime"/>
+        /// to previous <see cref="Rulesets.Difficulty.Preprocessing.DifficultyHitObject.DeltaTime"/> for the rhythm change.
+        /// A <see cref="Ratio"/> above 1 indicates a slow-down; a <see cref="Ratio"/> below 1 indicates a speed-up.
+        /// </summary>
+        public readonly double Ratio;
+
         /// <summary>
         /// The difficulty multiplier associated with this rhythm change.
         /// </summary>
         public readonly double Difficulty;
 
         /// <summary>
-        /// The ratio of current <see cref="osu.Game.Rulesets.Difficulty.Preprocessing.DifficultyHitObject.DeltaTime"/>
-        /// to previous <see cref="osu.Game.Rulesets.Difficulty.Preprocessing.DifficultyHitObject.DeltaTime"/> for the rhythm change.
-        /// A <see cref="Ratio"/> above 1 indicates a slow-down; a <see cref="Ratio"/> below 1 indicates a speed-up.
+        /// List of most common rhythm changes in taiko maps. This is used as a display value.
         /// </summary>
-        public readonly double Ratio;
+        /// <remarks>
+        /// The general guidelines for the values are:
+        /// <list type="bullet">
+        /// <item>rhythm changes with ratio closer to 1 (that are <i>not</i> 1) are harder to play,</item>
+        /// <item>speeding up is <i>generally</i> harder than slowing down (with exceptions of rhythm changes requiring a hand switch).</item>
+        /// </list>
+        /// </remarks>
+        private static readonly TaikoDifficultyHitObjectRhythm[] common_rhythms =
+        {
+            new TaikoDifficultyHitObjectRhythm(1, 1, 0.0),
+            new TaikoDifficultyHitObjectRhythm(2, 1, 0.3),
+            new TaikoDifficultyHitObjectRhythm(1, 2, 0.5),
+            new TaikoDifficultyHitObjectRhythm(3, 1, 0.3),
+            new TaikoDifficultyHitObjectRhythm(1, 3, 0.35),
+            new TaikoDifficultyHitObjectRhythm(3, 2, 0.6),
+            new TaikoDifficultyHitObjectRhythm(2, 3, 0.4),
+            new TaikoDifficultyHitObjectRhythm(5, 4, 0.5),
+            new TaikoDifficultyHitObjectRhythm(4, 5, 0.7)
+        };
+
+        /// <summary>
+        /// Initialises a new instance of <see cref="TaikoDifficultyHitObjectRhythm"/>s,
+        /// calculating the closest rhythm change and its associated difficulty for the current hit object.
+        /// </summary>
+        /// <param name="current">The current <see cref="TaikoDifficultyHitObject"/> being processed.</param>
+        public TaikoDifficultyHitObjectRhythm(TaikoDifficultyHitObject current)
+        {
+            var previous = current.Previous(0);
+
+            if (previous == null)
+            {
+                Ratio = 1;
+                Difficulty = 0.0;
+                return;
+            }
+
+            TaikoDifficultyHitObjectRhythm closestRhythm = getClosestRhythm(current.DeltaTime, previous.DeltaTime);
+            Ratio = closestRhythm.Ratio;
+            Difficulty = closestRhythm.Difficulty;
+        }
 
         /// <summary>
         /// Creates an object representing a rhythm change.
@@ -26,10 +84,24 @@ namespace osu.Game.Rulesets.Taiko.Difficulty.Preprocessing.Rhythm
         /// <param name="numerator">The numerator for <see cref="Ratio"/>.</param>
         /// <param name="denominator">The denominator for <see cref="Ratio"/></param>
         /// <param name="difficulty">The difficulty multiplier associated with this rhythm change.</param>
-        public TaikoDifficultyHitObjectRhythm(int numerator, int denominator, double difficulty)
+        private TaikoDifficultyHitObjectRhythm(int numerator, int denominator, double difficulty)
         {
             Ratio = numerator / (double)denominator;
             Difficulty = difficulty;
         }
+
+        /// <summary>
+        /// Determines the closest rhythm change from <see cref="common_rhythms"/> that matches the timing ratio
+        /// between the current and previous intervals.
+        /// </summary>
+        /// <param name="currentDeltaTime">The time difference between the current hit object and the previous one.</param>
+        /// <param name="previousDeltaTime">The time difference between the previous hit object and the one before it.</param>
+        /// <returns>The closest matching rhythm from <see cref="common_rhythms"/>.</returns>
+        private TaikoDifficultyHitObjectRhythm getClosestRhythm(double currentDeltaTime, double previousDeltaTime)
+        {
+            double ratio = currentDeltaTime / previousDeltaTime;
+            return common_rhythms.OrderBy(x => Math.Abs(x.Ratio - ratio)).First();
         }
     }
+}
+

osu.Game.Rulesets.Taiko/Difficulty/Preprocessing/TaikoDifficultyHitObject.cs

@@ -1,27 +1,36 @@
 // 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.
 
-using System;
 using System.Collections.Generic;
 using System.Linq;
 using osu.Game.Rulesets.Difficulty.Preprocessing;
 using osu.Game.Rulesets.Objects;
-using osu.Game.Rulesets.Taiko.Objects;
 using osu.Game.Rulesets.Taiko.Difficulty.Preprocessing.Colour;
 using osu.Game.Rulesets.Taiko.Difficulty.Preprocessing.Rhythm;
+using osu.Game.Rulesets.Taiko.Objects;
 
 namespace osu.Game.Rulesets.Taiko.Difficulty.Preprocessing
 {
     /// <summary>
     /// Represents a single hit object in taiko difficulty calculation.
     /// </summary>
-    public class TaikoDifficultyHitObject : DifficultyHitObject
+    public class TaikoDifficultyHitObject : DifficultyHitObject, IHasInterval
     {
         /// <summary>
         /// The list of all <see cref="TaikoDifficultyHitObject"/> of the same colour as this <see cref="TaikoDifficultyHitObject"/> in the beatmap.
         /// </summary>
         private readonly IReadOnlyList<TaikoDifficultyHitObject>? monoDifficultyHitObjects;
 
+        /// <summary>
+        /// The adjusted BPM of this hit object, based on its slider velocity and scroll speed.
+        /// </summary>
+        public double EffectiveBPM;
+
+        /// <summary>
+        /// The current slider velocity of this hit object.
+        /// </summary>
+        public double CurrentSliderVelocity;
+
         /// <summary>
         /// The index of this <see cref="TaikoDifficultyHitObject"/> in <see cref="monoDifficultyHitObjects"/>.
         /// </summary>
@@ -42,12 +51,19 @@ namespace osu.Game.Rulesets.Taiko.Difficulty.Preprocessing
         /// </summary>
         public readonly TaikoDifficultyHitObjectRhythm Rhythm;
 
+        /// <summary>
+        /// The interval between this hit object and the surrounding hit objects in its rhythm group.
+        /// </summary>
+        public double? HitObjectInterval { get; set; }
+
         /// <summary>
         /// Colour data for this hit object. This is used by colour evaluator to calculate colour difficulty, but can be used
         /// by other skills in the future.
         /// </summary>
         public readonly TaikoDifficultyHitObjectColour Colour;
 
+        public double Interval => DeltaTime;
+
         /// <summary>
         /// Creates a new difficulty hit object.
         /// </summary>
@@ -71,7 +87,7 @@ namespace osu.Game.Rulesets.Taiko.Difficulty.Preprocessing
 
             // Create the Colour object, its properties should be filled in by TaikoDifficultyPreprocessor
             Colour = new TaikoDifficultyHitObjectColour();
-            Rhythm = getClosestRhythm(lastObject, lastLastObject, clockRate);
+            Rhythm = new TaikoDifficultyHitObjectRhythm(this);
 
             switch ((hitObject as Hit)?.Type)
             {
@@ -95,43 +111,6 @@ namespace osu.Game.Rulesets.Taiko.Difficulty.Preprocessing
             }
         }
 
-        /// <summary>
-        /// List of most common rhythm changes in taiko maps.
-        /// </summary>
-        /// <remarks>
-        /// The general guidelines for the values are:
-        /// <list type="bullet">
-        /// <item>rhythm changes with ratio closer to 1 (that are <i>not</i> 1) are harder to play,</item>
-        /// <item>speeding up is <i>generally</i> harder than slowing down (with exceptions of rhythm changes requiring a hand switch).</item>
-        /// </list>
-        /// </remarks>
-        private static readonly TaikoDifficultyHitObjectRhythm[] common_rhythms =
-        {
-            new TaikoDifficultyHitObjectRhythm(1, 1, 0.0),
-            new TaikoDifficultyHitObjectRhythm(2, 1, 0.3),
-            new TaikoDifficultyHitObjectRhythm(1, 2, 0.5),
-            new TaikoDifficultyHitObjectRhythm(3, 1, 0.3),
-            new TaikoDifficultyHitObjectRhythm(1, 3, 0.35),
-            new TaikoDifficultyHitObjectRhythm(3, 2, 0.6), // purposefully higher (requires hand switch in full alternating gameplay style)
-            new TaikoDifficultyHitObjectRhythm(2, 3, 0.4),
-            new TaikoDifficultyHitObjectRhythm(5, 4, 0.5),
-            new TaikoDifficultyHitObjectRhythm(4, 5, 0.7)
-        };
-
-        /// <summary>
-        /// Returns the closest rhythm change from <see cref="common_rhythms"/> required to hit this object.
-        /// </summary>
-        /// <param name="lastObject">The gameplay <see cref="HitObject"/> preceding this one.</param>
-        /// <param name="lastLastObject">The gameplay <see cref="HitObject"/> preceding <paramref name="lastObject"/>.</param>
-        /// <param name="clockRate">The rate of the gameplay clock.</param>
-        private TaikoDifficultyHitObjectRhythm getClosestRhythm(HitObject lastObject, HitObject lastLastObject, double clockRate)
-        {
-            double prevLength = (lastObject.StartTime - lastLastObject.StartTime) / clockRate;
-            double ratio = DeltaTime / prevLength;
-
-            return common_rhythms.OrderBy(x => Math.Abs(x.Ratio - ratio)).First();
-        }
-
         public TaikoDifficultyHitObject? PreviousMono(int backwardsIndex) => monoDifficultyHitObjects?.ElementAtOrDefault(MonoIndex - (backwardsIndex + 1));
 
         public TaikoDifficultyHitObject? NextMono(int forwardsIndex) => monoDifficultyHitObjects?.ElementAtOrDefault(MonoIndex + (forwardsIndex + 1));

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

@@ -0,0 +1,49 @@
+// 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.
+
+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;
+using osu.Game.Rulesets.Taiko.Objects;
+
+namespace osu.Game.Rulesets.Taiko.Difficulty.Skills
+{
+    /// <summary>
+    /// Calculates the reading coefficient of taiko difficulty.
+    /// </summary>
+    public class Reading : StrainDecaySkill
+    {
+        protected override double SkillMultiplier => 1.0;
+        protected override double StrainDecayBase => 0.4;
+
+        private double currentStrain;
+
+        public double ObjectDensity { get; private set; }
+
+        public Reading(Mod[] mods)
+            : base(mods)
+        {
+        }
+
+        protected override double StrainValueOf(DifficultyHitObject current)
+        {
+            if (current is not TaikoDifficultyHitObject taikoObject)
+                return 0.0;
+
+            // Drum Rolls and Swells are exempt.
+            if (current.BaseObject is not Hit)
+            {
+                return 0.0;
+            }
+
+            ObjectDensity = ReadingEvaluator.CalculateObjectDensity(taikoObject) * 10;
+
+            currentStrain *= StrainDecayBase;
+            currentStrain += ReadingEvaluator.EvaluateDifficultyOf(taikoObject) * SkillMultiplier;
+
+            return currentStrain;
+        }
+    }
+}

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

@@ -1,13 +1,10 @@
 // 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.
 
-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.Preprocessing;
-using osu.Game.Rulesets.Taiko.Objects;
-using osu.Game.Utils;
+using osu.Game.Rulesets.Taiko.Difficulty.Evaluators;
 
 namespace osu.Game.Rulesets.Taiko.Difficulty.Skills
 {
@@ -16,158 +13,26 @@ namespace osu.Game.Rulesets.Taiko.Difficulty.Skills
     /// </summary>
     public class Rhythm : StrainDecaySkill
     {
-        protected override double SkillMultiplier => 10;
-        protected override double StrainDecayBase => 0;
+        protected override double SkillMultiplier => 1.6;
+        protected override double StrainDecayBase => 0.4;
 
-        /// <summary>
-        /// The note-based decay for rhythm strain.
-        /// </summary>
-        /// <remarks>
-        /// <see cref="StrainDecayBase"/> is not used here, as it's time- and not note-based.
-        /// </remarks>
-        private const double strain_decay = 0.96;
+        private readonly double greatHitWindow;
 
-        /// <summary>
-        /// Maximum number of entries in <see cref="rhythmHistory"/>.
-        /// </summary>
-        private const int rhythm_history_max_length = 8;
-
-        /// <summary>
-        /// Contains the last <see cref="rhythm_history_max_length"/> changes in note sequence rhythms.
-        /// </summary>
-        private readonly LimitedCapacityQueue<TaikoDifficultyHitObject> rhythmHistory = new LimitedCapacityQueue<TaikoDifficultyHitObject>(rhythm_history_max_length);
-
-        /// <summary>
-        /// Contains the rolling rhythm strain.
-        /// Used to apply per-note decay.
-        /// </summary>
-        private double currentStrain;
-
-        /// <summary>
-        /// Number of notes since the last rhythm change has taken place.
-        /// </summary>
-        private int notesSinceRhythmChange;
-
-        public Rhythm(Mod[] mods)
+        public Rhythm(Mod[] mods, double greatHitWindow)
             : base(mods)
         {
+            this.greatHitWindow = greatHitWindow;
         }
 
         protected override double StrainValueOf(DifficultyHitObject current)
         {
-            // drum rolls and swells are exempt.
-            if (!(current.BaseObject is Hit))
-            {
-                resetRhythmAndStrain();
-                return 0.0;
-            }
+            double difficulty = RhythmEvaluator.EvaluateDifficultyOf(current, greatHitWindow);
 
-            currentStrain *= strain_decay;
+            // To prevent abuse of exceedingly long intervals between awkward rhythms, we penalise its difficulty.
+            if (current.DeltaTime > 400)
+                difficulty *= 0.5;
 
-            TaikoDifficultyHitObject hitObject = (TaikoDifficultyHitObject)current;
-            notesSinceRhythmChange += 1;
-
-            // rhythm difficulty zero (due to rhythm not changing) => no rhythm strain.
-            if (hitObject.Rhythm.Difficulty == 0.0)
-            {
-                return 0.0;
-            }
-
-            double objectStrain = hitObject.Rhythm.Difficulty;
-
-            objectStrain *= repetitionPenalties(hitObject);
-            objectStrain *= patternLengthPenalty(notesSinceRhythmChange);
-            objectStrain *= speedPenalty(hitObject.DeltaTime);
-
-            // careful - needs to be done here since calls above read this value
-            notesSinceRhythmChange = 0;
-
-            currentStrain += objectStrain;
-            return currentStrain;
-        }
-
-        /// <summary>
-        /// Returns a penalty to apply to the current hit object caused by repeating rhythm changes.
-        /// </summary>
-        /// <remarks>
-        /// Repetitions of more recent patterns are associated with a higher penalty.
-        /// </remarks>
-        /// <param name="hitObject">The current hit object being considered.</param>
-        private double repetitionPenalties(TaikoDifficultyHitObject hitObject)
-        {
-            double penalty = 1;
-
-            rhythmHistory.Enqueue(hitObject);
-
-            for (int mostRecentPatternsToCompare = 2; mostRecentPatternsToCompare <= rhythm_history_max_length / 2; mostRecentPatternsToCompare++)
-            {
-                for (int start = rhythmHistory.Count - mostRecentPatternsToCompare - 1; start >= 0; start--)
-                {
-                    if (!samePattern(start, mostRecentPatternsToCompare))
-                        continue;
-
-                    int notesSince = hitObject.Index - rhythmHistory[start].Index;
-                    penalty *= repetitionPenalty(notesSince);
-                    break;
-                }
-            }
-
-            return penalty;
-        }
-
-        /// <summary>
-        /// Determines whether the rhythm change pattern starting at <paramref name="start"/> is a repeat of any of the
-        /// <paramref name="mostRecentPatternsToCompare"/>.
-        /// </summary>
-        private bool samePattern(int start, int mostRecentPatternsToCompare)
-        {
-            for (int i = 0; i < mostRecentPatternsToCompare; i++)
-            {
-                if (rhythmHistory[start + i].Rhythm != rhythmHistory[rhythmHistory.Count - mostRecentPatternsToCompare + i].Rhythm)
-                    return false;
-            }
-
-            return true;
-        }
-
-        /// <summary>
-        /// Calculates a single rhythm repetition penalty.
-        /// </summary>
-        /// <param name="notesSince">Number of notes since the last repetition of a rhythm change.</param>
-        private static double repetitionPenalty(int notesSince) => Math.Min(1.0, 0.032 * notesSince);
-
-        /// <summary>
-        /// Calculates a penalty based on the number of notes since the last rhythm change.
-        /// Both rare and frequent rhythm changes are penalised.
-        /// </summary>
-        /// <param name="patternLength">Number of notes since the last rhythm change.</param>
-        private static double patternLengthPenalty(int patternLength)
-        {
-            double shortPatternPenalty = Math.Min(0.15 * patternLength, 1.0);
-            double longPatternPenalty = Math.Clamp(2.5 - 0.15 * patternLength, 0.0, 1.0);
-            return Math.Min(shortPatternPenalty, longPatternPenalty);
-        }
-
-        /// <summary>
-        /// Calculates a penalty for objects that do not require alternating hands.
-        /// </summary>
-        /// <param name="deltaTime">Time (in milliseconds) since the last hit object.</param>
-        private double speedPenalty(double deltaTime)
-        {
-            if (deltaTime < 80) return 1;
-            if (deltaTime < 210) return Math.Max(0, 1.4 - 0.005 * deltaTime);
-
-            resetRhythmAndStrain();
-            return 0.0;
-        }
-
-        /// <summary>
-        /// Resets the rolling strain value and <see cref="notesSinceRhythmChange"/> counter.
-        /// </summary>
-        private void resetRhythmAndStrain()
-        {
-            currentStrain = 0.0;
-            notesSinceRhythmChange = 0;
+            return difficulty;
         }
     }
 }

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

@@ -28,6 +28,18 @@ namespace osu.Game.Rulesets.Taiko.Difficulty
         [JsonProperty("rhythm_difficulty")]
         public double RhythmDifficulty { get; set; }
 
+        /// <summary>
+        /// The difficulty corresponding to the reading skill.
+        /// </summary>
+        [JsonProperty("reading_difficulty")]
+        public double ReadingDifficulty { get; set; }
+
+        /// <summary>
+        /// Determines the object density of a beatmap, based on DeltaTime.
+        /// </summary>
+        [JsonProperty("object_density")]
+        public double ObjectDensity { get; set; }
+
         /// <summary>
         /// The difficulty corresponding to the colour skill.
         /// </summary>
@@ -35,10 +47,25 @@ namespace osu.Game.Rulesets.Taiko.Difficulty
         public double ColourDifficulty { get; set; }
 
         /// <summary>
-        /// The difficulty corresponding to the hardest parts of the map.
+        /// The penalty factor corresponding to patterns based on their correlation between skills.
         /// </summary>
-        [JsonProperty("peak_difficulty")]
-        public double PeakDifficulty { get; set; }
+        [JsonProperty("simple_pattern_factor")]
+        public double SimplePattern { get; set; }
+
+        /// <summary>
+        /// Determines the amount of difficult strain peaks present within each skill.
+        /// </summary>
+        [JsonProperty("stamina_difficult_strains")]
+        public double StaminaTopStrains { get; set; }
+
+        [JsonProperty("rhythm_difficult_strains")]
+        public double RhythmTopStrains { get; set; }
+
+        [JsonProperty("reading_difficult_strains")]
+        public double ReadingTopStrains { get; set; }
+
+        [JsonProperty("colour_difficult_strains")]
+        public double ColourTopStrains { get; set; }
 
         /// <summary>
         /// The perceived hit window for a GREAT hit inclusive of rate-adjusting mods (DT/HT/etc).

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

@@ -8,10 +8,13 @@ using osu.Game.Beatmaps;
 using osu.Game.Rulesets.Difficulty;
 using osu.Game.Rulesets.Difficulty.Preprocessing;
 using osu.Game.Rulesets.Difficulty.Skills;
+using osu.Game.Rulesets.Difficulty.Utils;
 using osu.Game.Rulesets.Mods;
 using osu.Game.Rulesets.Scoring;
 using osu.Game.Rulesets.Taiko.Difficulty.Preprocessing;
 using osu.Game.Rulesets.Taiko.Difficulty.Preprocessing.Colour;
+using osu.Game.Rulesets.Taiko.Difficulty.Preprocessing.Reading;
+using osu.Game.Rulesets.Taiko.Difficulty.Preprocessing.Rhythm.Data;
 using osu.Game.Rulesets.Taiko.Difficulty.Skills;
 using osu.Game.Rulesets.Taiko.Mods;
 using osu.Game.Rulesets.Taiko.Scoring;
@@ -21,11 +24,20 @@ namespace osu.Game.Rulesets.Taiko.Difficulty
     public class TaikoDifficultyCalculator : DifficultyCalculator
     {
         private const double difficulty_multiplier = 0.084375;
-        private const double rhythm_skill_multiplier = 0.2 * difficulty_multiplier;
-        private const double colour_skill_multiplier = 0.375 * difficulty_multiplier;
+        private const double rhythm_skill_multiplier = 0.070 * difficulty_multiplier;
+        private const double reading_skill_multiplier = 0.100 * difficulty_multiplier;
+        private const double colour_skill_multiplier = 0.425 * difficulty_multiplier;
         private const double stamina_skill_multiplier = 0.375 * difficulty_multiplier;
 
-        public override int Version => 20241007;
+        private double simpleRhythmPenalty = 1;
+        private double simpleColourPenalty = 1;
+
+        private double colourDifficultStrains;
+        private double rhythmDifficultStrains;
+        private double readingDifficultStrains;
+        private double staminaDifficultStrains;
+
+        public override int Version => 20241115;
 
         public TaikoDifficultyCalculator(IRulesetInfo ruleset, IWorkingBeatmap beatmap)
             : base(ruleset, beatmap)
@@ -34,9 +46,13 @@ namespace osu.Game.Rulesets.Taiko.Difficulty
 
         protected override Skill[] CreateSkills(IBeatmap beatmap, Mod[] mods, double clockRate)
         {
+            HitWindows hitWindows = new HitWindows();
+            hitWindows.SetDifficulty(beatmap.Difficulty.OverallDifficulty);
+
             return new Skill[]
             {
-                new Rhythm(mods),
+                new Rhythm(mods, hitWindows.WindowFor(HitResult.Great) / clockRate),
+                new Reading(mods),
                 new Colour(mods),
                 new Stamina(mods, false),
                 new Stamina(mods, true)
@@ -53,25 +69,67 @@ namespace osu.Game.Rulesets.Taiko.Difficulty
 
         protected override IEnumerable<DifficultyHitObject> CreateDifficultyHitObjects(IBeatmap beatmap, double clockRate)
         {
-            List<DifficultyHitObject> difficultyHitObjects = new List<DifficultyHitObject>();
-            List<TaikoDifficultyHitObject> centreObjects = new List<TaikoDifficultyHitObject>();
-            List<TaikoDifficultyHitObject> rimObjects = new List<TaikoDifficultyHitObject>();
-            List<TaikoDifficultyHitObject> noteObjects = new List<TaikoDifficultyHitObject>();
+            var hitWindows = new HitWindows();
+            hitWindows.SetDifficulty(beatmap.Difficulty.OverallDifficulty);
 
+            var difficultyHitObjects = new List<DifficultyHitObject>();
+            var centreObjects = new List<TaikoDifficultyHitObject>();
+            var rimObjects = new List<TaikoDifficultyHitObject>();
+            var noteObjects = new List<TaikoDifficultyHitObject>();
+            EffectiveBPMPreprocessor bpmLoader = new EffectiveBPMPreprocessor(beatmap, noteObjects);
+
+            // Generate TaikoDifficultyHitObjects from the beatmap's hit objects.
             for (int i = 2; i < beatmap.HitObjects.Count; i++)
             {
-                difficultyHitObjects.Add(
-                    new TaikoDifficultyHitObject(
-                        beatmap.HitObjects[i], beatmap.HitObjects[i - 1], beatmap.HitObjects[i - 2], clockRate, difficultyHitObjects,
-                        centreObjects, rimObjects, noteObjects, difficultyHitObjects.Count)
-                );
+                difficultyHitObjects.Add(new TaikoDifficultyHitObject(
+                    beatmap.HitObjects[i],
+                    beatmap.HitObjects[i - 1],
+                    beatmap.HitObjects[i - 2],
+                    clockRate,
+                    difficultyHitObjects,
+                    centreObjects,
+                    rimObjects,
+                    noteObjects,
+                    difficultyHitObjects.Count
+                ));
             }
 
+            var groupedHitObjects = EvenHitObjects.GroupHitObjects(noteObjects);
+
             TaikoColourDifficultyPreprocessor.ProcessAndAssign(difficultyHitObjects);
+            EvenPatterns.GroupPatterns(groupedHitObjects);
+            bpmLoader.ProcessEffectiveBPM(beatmap.ControlPointInfo, clockRate);
 
             return difficultyHitObjects;
         }
 
+        /// <summary>
+        /// Calculates the combined penalty based on the relationship between skills.
+        /// Lower skill values are penalised more heavily relative to predefined thresholds and their
+        /// interaction with the opposing skill rating.
+        /// </summary>
+        private double simplePatternPenalty(double rhythmRating, double colourRating, double clockRate)
+        {
+            double colourThreshold = 1.25 * clockRate; // Threshold changes based on rate
+            const double stamina_threshold = 1250.0;
+
+            // We count difficult stamina strains to ensure that even if there's no rhythm, very heavy stamina maps still give their respective difficulty.
+            double staminaTransition = Math.Clamp((staminaDifficultStrains - stamina_threshold) / (1350 - stamina_threshold), 0, 1);
+            double staminaFactor = (1 - staminaTransition) * 1.0 + staminaTransition * 0.85;
+            staminaFactor *= Math.Min(1, stamina_threshold / Math.Min(2000, staminaDifficultStrains));
+
+            simpleRhythmPenalty = patternRating(rhythmRating, 2.5, 5, colourRating);
+            simpleRhythmPenalty *= staminaFactor;
+            simpleRhythmPenalty = Math.Max(0, simpleRhythmPenalty);
+
+            // For awkwardly snapped maps with low rhythm strain count, we add a penalty.
+            double rhythmTransition = 1 - Math.Max(0, (50 - rhythmDifficultStrains) / 50.0);
+            double colourFactor = Math.Max(1, 0.50 * ((colourThreshold - colourRating) / colourThreshold));
+            simpleColourPenalty = Math.Max(0, rhythmTransition * colourFactor);
+
+            return simpleRhythmPenalty;
+        }
+
         protected override DifficultyAttributes CreateDifficultyAttributes(IBeatmap beatmap, Mod[] mods, Skill[] skills, double clockRate)
         {
             if (beatmap.HitObjects.Count == 0)
@@ -79,24 +137,31 @@ namespace osu.Game.Rulesets.Taiko.Difficulty
 
             Colour colour = (Colour)skills.First(x => x is Colour);
             Rhythm rhythm = (Rhythm)skills.First(x => x is Rhythm);
+            Reading reading = (Reading)skills.First(x => x is Reading);
             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 readingRating = reading.DifficultyValue() * reading_skill_multiplier;
+            double objectDensity = reading.ObjectDensity;
             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);
+            colourDifficultStrains = colour.CountTopWeightedStrains();
+            rhythmDifficultStrains = rhythm.CountTopWeightedStrains();
+            readingDifficultStrains = reading.CountTopWeightedStrains();
+            staminaDifficultStrains = stamina.CountTopWeightedStrains() * Math.Min(clockRate, 1.25); // Bonus is capped past 1.25x rate
 
-            // TODO: This is temporary measure as we don't detect abuse of multiple-input playstyles of converts within the current system.
+            double patternPenalty = simplePatternPenalty(rhythmRating, colourRating, clockRate);
+
+            double combinedRating = combinedDifficultyValue(rhythm, reading, colour, stamina);
+            double starRating = rescale(combinedRating * 1.8);
+
+            // Converts are penalised outside of the scope of difficulty calculation, as our assumptions surrounding playstyle becomes out-of-scope.
             if (beatmap.BeatmapInfo.Ruleset.OnlineID == 0)
             {
-                starRating *= 0.925;
-                // For maps with low colour variance and high stamina requirement, multiple inputs are more likely to be abused.
-                if (colourRating < 2 && staminaRating > 8)
                 starRating *= 0.80;
             }
 
@@ -109,9 +174,15 @@ namespace osu.Game.Rulesets.Taiko.Difficulty
                 Mods = mods,
                 StaminaDifficulty = staminaRating,
                 MonoStaminaFactor = monoStaminaFactor,
-                RhythmDifficulty = rhythmRating,
+                SimplePattern = patternPenalty,
+                RhythmDifficulty = rhythmRating * 8,
+                ReadingDifficulty = readingRating * 1.5,
+                ObjectDensity = objectDensity,
                 ColourDifficulty = colourRating,
-                PeakDifficulty = combinedRating,
+                StaminaTopStrains = staminaDifficultStrains,
+                RhythmTopStrains = rhythmDifficultStrains,
+                ReadingTopStrains = readingDifficultStrains,
+                ColourTopStrains = colourDifficultStrains,
                 GreatHitWindow = hitWindows.WindowFor(HitResult.Great) / clockRate,
                 OkHitWindow = hitWindows.WindowFor(HitResult.Ok) / clockRate,
                 MaxCombo = beatmap.GetMaxCombo(),
@@ -120,17 +191,6 @@ namespace osu.Game.Rulesets.Taiko.Difficulty
             return attributes;
         }
 
-        /// <summary>
-        /// Applies a final re-scaling of the star rating.
-        /// </summary>
-        /// <param name="sr">The raw star rating value before re-scaling.</param>
-        private double rescale(double sr)
-        {
-            if (sr < 0) return sr;
-
-            return 10.43 * Math.Log(sr / 8 + 1);
-        }
-
         /// <summary>
         /// Returns the combined star rating of the beatmap, calculated using peak strains from all sections of the map.
         /// </summary>
@@ -138,22 +198,26 @@ namespace osu.Game.Rulesets.Taiko.Difficulty
         /// For each section, the peak strains of all separate skills are combined into a single peak strain for the section.
         /// The resulting partial rating of the beatmap is a weighted sum of the combined peaks (higher peaks are weighted more).
         /// </remarks>
-        private double combinedDifficultyValue(Rhythm rhythm, Colour colour, Stamina stamina)
+        private double combinedDifficultyValue(Rhythm rhythm, Reading reading, Colour colour, Stamina stamina)
         {
             List<double> peaks = new List<double>();
 
             var colourPeaks = colour.GetCurrentStrainPeaks().ToList();
             var rhythmPeaks = rhythm.GetCurrentStrainPeaks().ToList();
+            var readingPeaks = reading.GetCurrentStrainPeaks().ToList();
             var staminaPeaks = stamina.GetCurrentStrainPeaks().ToList();
 
             for (int i = 0; i < colourPeaks.Count; i++)
             {
-                double colourPeak = colourPeaks[i] * colour_skill_multiplier;
-                double rhythmPeak = rhythmPeaks[i] * rhythm_skill_multiplier;
-                double staminaPeak = staminaPeaks[i] * stamina_skill_multiplier;
+                // Peaks uses separate constants due to strain pertaining differently to display values.
+                double baseColourPeak = colourPeaks[i] * 0.0359;
+                double colourPeak = baseColourPeak * Math.Exp(-simpleRhythmPenalty / 14);
+                double rhythmPeak = rhythmPeaks[i] * 0.0379 * simpleColourPenalty;
+                double staminaPeak = staminaPeaks[i] * 0.0317;
+                double readingPeak = readingPeaks[i] * reading_skill_multiplier;
 
-                double peak = norm(1.5, colourPeak, staminaPeak);
-                peak = norm(2, peak, rhythmPeak);
+                double peak = DifficultyCalculationUtils.Norm(1.5, colourPeak, staminaPeak);
+                peak = DifficultyCalculationUtils.Norm(2, peak, rhythmPeak, readingPeak);
 
                 // Sections with 0 strain are excluded to avoid worst-case time complexity of the following sort (e.g. /b/2351871).
                 // These sections will not contribute to the difficulty.
@@ -174,10 +238,31 @@ namespace osu.Game.Rulesets.Taiko.Difficulty
         }
 
         /// <summary>
-        /// Returns the <i>p</i>-norm of an <i>n</i>-dimensional vector.
+        /// Calculates the penalty for skills based on their relationship making up a pattern.
+        /// Penalising ratings where patterns have a major difference in value.
         /// </summary>
-        /// <param name="p">The value of <i>p</i> to calculate the norm for.</param>
-        /// <param name="values">The coefficients of the vector.</param>
-        private double norm(double p, params double[] values) => Math.Pow(values.Sum(x => Math.Pow(x, p)), 1 / p);
+        private double patternRating(double rating, double threshold, double upperBound, double otherRating)
+        {
+            if (rating > threshold)
+                return 0;
+
+            // To prevent against breaking values we define 0.01 as minimum difficulty.
+            rating = Math.Max(0.01, rating);
+            otherRating = Math.Max(0.01, otherRating);
+
+            // Penalise based on logarithmic difference from the skill-based threshold, scaled by the influence of the other rating
+            return Math.Log(threshold / rating) * Math.Min(upperBound, Math.Log(Math.Max(1, otherRating - upperBound)) + upperBound);
+        }
+
+        /// <summary>
+        /// Applies a final re-scaling of the star rating.
+        /// </summary>
+        /// <param name="sr">The raw star rating value before re-scaling.</param>
+        private double rescale(double sr)
+        {
+            if (sr < 0) return sr;
+
+            return 10.43 * Math.Log(sr / 8 + 1);
+        }
     }
 }

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

@@ -86,9 +86,6 @@ namespace osu.Game.Rulesets.Taiko.Difficulty
             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 *= Math.Max(1, 1.050 - Math.Min(attributes.MonoStaminaFactor / 50, 1) * lengthBonus);
 
@@ -97,7 +94,7 @@ namespace osu.Game.Rulesets.Taiko.Difficulty
 
             // Scale accuracy more harshly on nearly-completely mono (single coloured) speed maps.
             double accScalingExponent = 2 + attributes.MonoStaminaFactor;
-            double accScalingShift = 300 - 100 * attributes.MonoStaminaFactor;
+            double accScalingShift = 400 - 100 * attributes.MonoStaminaFactor;
 
             return difficultyValue * Math.Pow(SpecialFunctions.Erf(accScalingShift / (Math.Sqrt(2) * estimatedUnstableRate.Value)), accScalingExponent);
         }
@@ -159,7 +156,7 @@ namespace osu.Game.Rulesets.Taiko.Difficulty
                 double n = totalHits;
 
                 // Proportion of greats + goods hit.
-                double p = totalSuccessfulHits / n;
+                double p = Math.Max(0, totalSuccessfulHits - 0.0005 * countOk) / n;
 
                 // We can be 99% confident that p is at least this value.
                 double pLowerBound = (n * p + z * z / 2) / (n + z * z) - z / (n + z * z) * Math.Sqrt(n * p * (1 - p) + z * z / 4);

osu.Game/Rulesets/Difficulty/Utils/DifficultyCalculationUtils.cs

@@ -2,6 +2,7 @@
 // See the LICENCE file in the repository root for full licence text.
 
 using System;
+using System.Linq;
 
 namespace osu.Game.Rulesets.Difficulty.Utils
 {
@@ -46,5 +47,23 @@ namespace osu.Game.Rulesets.Difficulty.Utils
         /// <param name="exponent">Exponent</param>
         /// <returns>The output of logistic function</returns>
         public static double Logistic(double exponent, double maxValue = 1) => maxValue / (1 + Math.Exp(exponent));
+
+        /// <summary>
+        /// Calculates a Gaussian-based bell curve function (https://en.wikipedia.org/wiki/Gaussian_function)
+        /// </summary>
+        /// <param name="x">Value to calculate the function for</param>
+        /// <param name="mean">The mean (center) of the bell curve</param>
+        /// <param name="width">The width (spread) of the curve</param>
+        /// <param name="multiplier">Multiplier to adjust the curve's height</param>
+        /// <returns>The output of the bell curve function of <paramref name="x"/></returns>
+        public static double BellCurve(double x, double mean, double width, double multiplier = 1.0) => multiplier * Math.Exp(Math.E * -(Math.Pow(x - mean, 2) / Math.Pow(width, 2)));
+
+        /// <summary>
+        /// Returns the <i>p</i>-norm of an <i>n</i>-dimensional vector (https://en.wikipedia.org/wiki/Norm_(mathematics))
+        /// </summary>
+        /// <param name="p">The value of <i>p</i> to calculate the norm for.</param>
+        /// <param name="values">The coefficients of the vector.</param>
+        /// <returns>The <i>p</i>-norm of the vector.</returns>
+        public static double Norm(double p, params double[] values) => Math.Pow(values.Sum(x => Math.Pow(x, p)), 1 / p);
     }
 }