Rewrite of the colour skill & refactoring of difficulty calculation within osu!taiko

osu.Game.Rulesets.Taiko.Tests/TaikoDifficultyCalculatorTest.cs

@@ -16,13 +16,13 @@ public class TaikoDifficultyCalculatorTest : DifficultyCalculatorTest
     {
         protected override string ResourceAssembly => "osu.Game.Rulesets.Taiko";
 
-        [TestCase(1.9971301024093662d, 200, "diffcalc-test")]
-        [TestCase(1.9971301024093662d, 200, "diffcalc-test-strong")]
+        [TestCase(3.1098944660126882d, 200, "diffcalc-test")]
+        [TestCase(3.1098944660126882d, 200, "diffcalc-test-strong")]
         public void Test(double expectedStarRating, int expectedMaxCombo, string name)
             => base.Test(expectedStarRating, expectedMaxCombo, name);
 
-        [TestCase(3.1645810961313674d, 200, "diffcalc-test")]
-        [TestCase(3.1645810961313674d, 200, "diffcalc-test-strong")]
+        [TestCase(4.0974106752474251d, 200, "diffcalc-test")]
+        [TestCase(4.0974106752474251d, 200, "diffcalc-test-strong")]
         public void TestClockRateAdjusted(double expectedStarRating, int expectedMaxCombo, string name)
             => Test(expectedStarRating, expectedMaxCombo, name, new TaikoModDoubleTime());
 

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

@@ -0,0 +1,67 @@
+// 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.Taiko.Difficulty.Preprocessing;
+using osu.Game.Rulesets.Taiko.Difficulty.Preprocessing.Colour;
+using osu.Game.Rulesets.Taiko.Difficulty.Preprocessing.Colour.Data;
+
+namespace osu.Game.Rulesets.Taiko.Difficulty.Evaluators
+{
+    public class ColourEvaluator
+    {
+        /// <summary>
+        /// A sigmoid function. It gives a value between (middle - height/2) and (middle + height/2).
+        /// </summary>
+        /// <param name="val">The input value.</param>
+        /// <param name="center">The center of the sigmoid, where the largest gradient occurs and value is equal to middle.</param>
+        /// <param name="width">The radius of the sigmoid, outside of which values are near the minimum/maximum.</param>
+        /// <param name="middle">The middle of the sigmoid output.</param>
+        /// <param name="height">The height of the sigmoid output. This will be equal to max value - min value.</param>
+        private static double sigmoid(double val, double center, double width, double middle, double height)
+        {
+            double sigmoid = Math.Tanh(Math.E * -(val - center) / width);
+            return sigmoid * (height / 2) + middle;
+        }
+
+        /// <summary>
+        /// Evaluate the difficulty of the first note of a <see cref="MonoEncoding"/>.
+        /// </summary>
+        public static double EvaluateDifficultyOf(MonoEncoding encoding)
+        {
+            return sigmoid(encoding.Index, 2, 2, 0.5, 1) * EvaluateDifficultyOf(encoding.Parent!) * 0.5;
+        }
+
+        /// <summary>
+        /// Evaluate the difficulty of the first note of a <see cref="ColourEncoding"/>.
+        /// </summary>
+        public static double EvaluateDifficultyOf(ColourEncoding encoding)
+        {
+            return sigmoid(encoding.Index, 2, 2, 0.5, 1) * EvaluateDifficultyOf(encoding.Parent!);
+        }
+
+        /// <summary>
+        /// Evaluate the difficulty of the first note of a <see cref="CoupledColourEncoding"/>.
+        /// </summary>
+        public static double EvaluateDifficultyOf(CoupledColourEncoding encoding)
+        {
+            return 2 * (1 - sigmoid(encoding.RepetitionInterval, 2, 2, 0.5, 1));
+        }
+
+        public static double EvaluateDifficultyOf(DifficultyHitObject hitObject)
+        {
+            TaikoDifficultyHitObjectColour colour = ((TaikoDifficultyHitObject)hitObject).Colour;
+            double difficulty = 0.0d;
+
+            if (colour.MonoEncoding != null) // Difficulty for MonoEncoding
+                difficulty += EvaluateDifficultyOf(colour.MonoEncoding);
+            if (colour.ColourEncoding != null) // Difficulty for ColourEncoding
+                difficulty += EvaluateDifficultyOf(colour.ColourEncoding);
+            if (colour.CoupledColourEncoding != null) // Difficulty for CoupledColourEncoding
+                difficulty += EvaluateDifficultyOf(colour.CoupledColourEncoding);
+
+            return difficulty;
+        }
+    }
+}

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

@@ -0,0 +1,53 @@
+// 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.Taiko.Difficulty.Preprocessing;
+using osu.Game.Rulesets.Taiko.Objects;
+
+namespace osu.Game.Rulesets.Taiko.Difficulty.Evaluators
+{
+    public class StaminaEvaluator
+    {
+        /// <summary>
+        /// Applies a speed bonus dependent on the time since the last hit performed using this key.
+        /// </summary>
+        /// <param name="interval">The interval between the current and previous note hit using the same key.</param>
+        private static double speedBonus(double interval)
+        {
+            // Cap to 600bpm 1/4, 25ms note interval, 50ms key interval
+            // Interval will be capped at a very small value to avoid infinite/negative speed bonuses.
+            // TODO - This is a temporary measure as we need to implement methods of detecting playstyle-abuse of SpeedBonus.
+            interval = Math.Max(interval, 50);
+
+            return 30 / interval;
+        }
+
+        /// <summary>
+        /// Evaluates the minimum mechanical stamina required to play the current object. This is calculated using the
+        /// maximum possible interval between two hits using the same key, by alternating 2 keys for each colour.
+        /// </summary>
+        public static double EvaluateDifficultyOf(DifficultyHitObject current)
+        {
+            if (current.BaseObject is not Hit)
+            {
+                return 0.0;
+            }
+
+            // Find the previous hit object hit by the current key, which is two notes of the same colour prior.
+            TaikoDifficultyHitObject taikoCurrent = (TaikoDifficultyHitObject)current;
+            TaikoDifficultyHitObject? keyPrevious = taikoCurrent.PreviousMono(1);
+
+            if (keyPrevious == null)
+            {
+                // There is no previous hit object hit by the current key
+                return 0.0;
+            }
+
+            double objectStrain = 0.5; // Add a base strain to all objects
+            objectStrain += speedBonus(taikoCurrent.StartTime - keyPrevious.StartTime);
+            return objectStrain;
+        }
+    }
+}

osu.Game.Rulesets.Taiko/Difficulty/Preprocessing/Colour/Data/ColourEncoding.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.Rulesets.Taiko.Objects;
+
+namespace osu.Game.Rulesets.Taiko.Difficulty.Preprocessing.Colour.Data
+{
+    /// <summary>
+    /// Encodes a list of <see cref="MonoEncoding"/>s.
+    /// <see cref="MonoEncoding"/>s with the same <see cref="MonoEncoding.RunLength"/> are grouped together.
+    /// </summary>
+    public class ColourEncoding
+    {
+        /// <summary>
+        /// <see cref="MonoEncoding"/>s that are grouped together within this <see cref="ColourEncoding"/>.
+        /// </summary>
+        public readonly List<MonoEncoding> Payload = new List<MonoEncoding>();
+
+        /// <summary>
+        /// The parent <see cref="CoupledColourEncoding"/> that contains this <see cref="ColourEncoding"/>
+        /// </summary>
+        public CoupledColourEncoding? Parent;
+
+        /// <summary>
+        /// Index of this encoding within it's parent encoding
+        /// </summary>
+        public int Index;
+
+        /// <summary>
+        /// Determine if this <see cref="ColourEncoding"/> is a repetition of another <see cref="ColourEncoding"/>. This
+        /// is a strict comparison and is true if and only if the colour sequence is exactly the same.
+        /// </summary>
+        public bool IsRepetitionOf(ColourEncoding other)
+        {
+            return HasIdenticalMonoLength(other) &&
+                   other.Payload.Count == Payload.Count &&
+                   (other.Payload[0].EncodedData[0].BaseObject as Hit)?.Type ==
+                   (Payload[0].EncodedData[0].BaseObject as Hit)?.Type;
+        }
+
+        /// <summary>
+        /// Determine if this <see cref="ColourEncoding"/> has the same mono length of another <see cref="ColourEncoding"/>.
+        /// </summary>
+        public bool HasIdenticalMonoLength(ColourEncoding other)
+        {
+            return other.Payload[0].RunLength == Payload[0].RunLength;
+        }
+    }
+}

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

@@ -0,0 +1,89 @@
+// 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.Colour.Data
+{
+    /// <summary>
+    /// Encodes a list of <see cref="ColourEncoding"/>s, grouped together by back and forth repetition of the same
+    /// <see cref="ColourEncoding"/>. Also stores the repetition interval between this and the previous <see cref="CoupledColourEncoding"/>.
+    /// </summary>
+    public class CoupledColourEncoding
+    {
+        /// <summary>
+        /// Maximum amount of <see cref="CoupledColourEncoding"/>s to look back to find a repetition.
+        /// </summary>
+        private const int max_repetition_interval = 16;
+
+        /// <summary>
+        /// The <see cref="ColourEncoding"/>s that are grouped together within this <see cref="CoupledColourEncoding"/>.
+        /// </summary>
+        public readonly List<ColourEncoding> Payload = new List<ColourEncoding>();
+
+        /// <summary>
+        /// The previous <see cref="CoupledColourEncoding"/>. This is used to determine the repetition interval.
+        /// </summary>
+        public readonly CoupledColourEncoding? Previous;
+
+        /// <summary>
+        /// How many <see cref="CoupledColourEncoding"/> between the current and previous identical <see cref="CoupledColourEncoding"/>.
+        /// If no repetition is found this will have a value of <see cref="max_repetition_interval"/> + 1.
+        /// </summary>
+        public int RepetitionInterval { get; private set; } = max_repetition_interval + 1;
+
+        public CoupledColourEncoding(CoupledColourEncoding? previous)
+        {
+            Previous = previous;
+        }
+
+        /// <summary>
+        /// Returns true if other is considered a repetition of this encoding. This is true if other's first two payloads
+        /// have identical mono lengths.
+        /// </summary>
+        private bool isRepetitionOf(CoupledColourEncoding other)
+        {
+            if (Payload.Count != other.Payload.Count) return false;
+
+            for (int i = 0; i < Math.Min(Payload.Count, 2); i++)
+            {
+                if (!Payload[i].HasIdenticalMonoLength(other.Payload[i])) return false;
+            }
+
+            return true;
+        }
+
+        /// <summary>
+        /// Finds the closest previous <see cref="CoupledColourEncoding"/> that has the identical <see cref="Payload"/>.
+        /// Interval is defined as the amount of <see cref="CoupledColourEncoding"/> chunks between the current and repeated encoding.
+        /// </summary>
+        public void FindRepetitionInterval()
+        {
+            if (Previous?.Previous == null)
+            {
+                RepetitionInterval = max_repetition_interval + 1;
+                return;
+            }
+
+            CoupledColourEncoding? other = Previous.Previous;
+            int interval = 2;
+
+            while (interval < max_repetition_interval)
+            {
+                if (isRepetitionOf(other))
+                {
+                    RepetitionInterval = Math.Min(interval, max_repetition_interval);
+                    return;
+                }
+
+                other = other.Previous;
+                if (other == null) break;
+
+                ++interval;
+            }
+
+            RepetitionInterval = max_repetition_interval + 1;
+        }
+    }
+}

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

@@ -0,0 +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 osu.Game.Rulesets.Difficulty.Preprocessing;
+using osu.Game.Rulesets.Taiko.Objects;
+using System.Collections.Generic;
+
+namespace osu.Game.Rulesets.Taiko.Difficulty.Preprocessing.Colour.Data
+{
+    /// <summary>
+    /// Encode colour information for a sequence of <see cref="TaikoDifficultyHitObject"/>s. Consecutive <see cref="TaikoDifficultyHitObject"/>s
+    /// of the same <see cref="HitType"/> are encoded within the same <see cref="MonoEncoding"/>.
+    /// </summary>
+    public class MonoEncoding
+    {
+        /// <summary>
+        /// List of <see cref="DifficultyHitObject"/>s that are encoded within this <see cref="MonoEncoding"/>.
+        /// </summary>
+        public List<TaikoDifficultyHitObject> EncodedData { get; private set; } = new List<TaikoDifficultyHitObject>();
+
+        /// <summary>
+        /// The parent <see cref="ColourEncoding"/> that contains this <see cref="MonoEncoding"/>
+        /// </summary>
+        public ColourEncoding? Parent;
+
+        /// <summary>
+        /// Index of this encoding within it's parent encoding
+        /// </summary>
+        public int Index;
+
+        /// <summary>
+        /// How long the mono pattern encoded within is
+        /// </summary>
+        public int RunLength => EncodedData.Count;
+    }
+}