Realization on Catch Star Rating

osu.Game.Rulesets.Catch/Difficulty/CatchDifficultyCalculator.cs

@@ -1,18 +1,174 @@
 // Copyright (c) 2007-2018 ppy Pty Ltd <contact@ppy.sh>.
 // Licensed under the MIT Licence - https://raw.githubusercontent.com/ppy/osu/master/LICENCE
 
+using System;
 using System.Collections.Generic;
 using osu.Game.Beatmaps;
 using osu.Game.Rulesets.Difficulty;
+using osu.Game.Rulesets.Mods;
+using osu.Game.Rulesets.Catch.Objects;
+using osu.Game.Rulesets.Catch.UI;
+using osu.Game.Rulesets.Objects;
 
 namespace osu.Game.Rulesets.Catch.Difficulty
 {
     public class CatchDifficultyCalculator : DifficultyCalculator
     {
-        public CatchDifficultyCalculator(IBeatmap beatmap) : base(beatmap)
+        private const double STAR_SCALING_FACTOR = 0.145;
+        private const float PLAYFIELD_WIDTH = CatchPlayfield.BASE_WIDTH;
+
+        private readonly List<CatchDifficultyHitObject> difficultyHitObjects = new List<CatchDifficultyHitObject>();
+
+        public CatchDifficultyCalculator(IBeatmap beatmap)
+            : base(beatmap)
         {
         }
 
-        public override double Calculate(Dictionary<string, double> categoryDifficulty = null) => 0;
+        public CatchDifficultyCalculator(IBeatmap beatmap, Mod[] mods)
+            : base(beatmap, mods)
+        {
+        }
+
+        public override double Calculate(Dictionary<string, double> categoryDifficulty = null)
+        {
+
+            difficultyHitObjects.Clear();
+
+            float circleSize = Beatmap.BeatmapInfo.BaseDifficulty.CircleSize;
+            float catcherWidth = (1.0f - 0.7f * (circleSize - 5) / 5) * 0.62064f * 172;
+            //float catcherWidth = (float)(305.0f / 1.6f * ((102.4f * (1.0f - 0.7 * (circleSize - 5.0f)) / 5.0f) / 128.0f * 0.7f));
+            float catcherWidthHalf = catcherWidth / 2;
+            catcherWidthHalf *= 0.8f;
+
+            foreach (var hitObject in Beatmap.HitObjects)
+            {
+                // We want to only consider fruits that contribute to the combo. Droplets are addressed as accuracy and spinners are not relevant for "skill" calculations.
+                if (hitObject is Fruit)
+                {
+                    difficultyHitObjects.Add(new CatchDifficultyHitObject((CatchHitObject)hitObject, catcherWidthHalf));
+                }
+                if (hitObject is JuiceStream)
+                {
+                    IEnumerator<HitObject> nestedHitObjectsEnumerator = hitObject.NestedHitObjects.GetEnumerator();
+                    while (nestedHitObjectsEnumerator.MoveNext())
+                    {
+                        CatchHitObject objectInJuiceStream = (CatchHitObject)nestedHitObjectsEnumerator.Current;
+                        if (!(objectInJuiceStream is TinyDroplet))
+                            difficultyHitObjects.Add(new CatchDifficultyHitObject(objectInJuiceStream, catcherWidthHalf));
+                    }
+                }
+            }
+
+            difficultyHitObjects.Sort((a, b) => a.BaseHitObject.StartTime.CompareTo(b.BaseHitObject.StartTime));
+
+            if (!CalculateStrainValues()) return 0;
+
+            double starRating = Math.Sqrt(CalculateDifficulty()) * STAR_SCALING_FACTOR;
+
+            if (categoryDifficulty != null)
+            {
+                categoryDifficulty["Aim"] = starRating;
+
+                double ar = Beatmap.BeatmapInfo.BaseDifficulty.ApproachRate;
+                double preEmpt = BeatmapDifficulty.DifficultyRange(ar, 1800, 1200, 450) / TimeRate;
+
+                categoryDifficulty["AR"] = preEmpt > 1200.0 ? -(preEmpt - 1800.0) / 120.0 : -(preEmpt - 1200.0) / 150.0 + 5.0;
+
+                //categoryDifficulty.Add("AR", (preEmpt > 1200.0 ? -(preEmpt - 1800.0) / 120.0 : -(preEmpt - 1200.0) / 150.0 + 5.0).ToString("0.00", GameBase.nfi));
+                //categoryDifficulty.Add("Max combo", DifficultyHitObjects.Count.ToString(GameBase.nfi));
+            }
+
+            return starRating;
+        }
+
+        protected bool CalculateStrainValues()
+        {
+            // Traverse hitObjects in pairs to calculate the strain value of NextHitObject from the strain value of CurrentHitObject and environment.
+            using (List<CatchDifficultyHitObject>.Enumerator hitObjectsEnumerator = difficultyHitObjects.GetEnumerator())
+            {
+
+                if (!hitObjectsEnumerator.MoveNext()) return false;
+
+                CatchDifficultyHitObject currentHitObject = hitObjectsEnumerator.Current;
+                CatchDifficultyHitObject nextHitObject;
+
+                // First hitObject starts at strain 1. 1 is the default for strain values, so we don't need to set it here. See DifficultyHitObject.
+                while (hitObjectsEnumerator.MoveNext())
+                {
+                    nextHitObject = hitObjectsEnumerator.Current;
+                    nextHitObject.CalculateStrains(currentHitObject, TimeRate);
+                    currentHitObject = nextHitObject;
+                }
+
+                return true;
+            }
+        }
+        
+        /// <summary>
+        /// In milliseconds. For difficulty calculation we will only look at the highest strain value in each time interval of size STRAIN_STEP.
+        /// This is to eliminate higher influence of stream over aim by simply having more HitObjects with high strain.
+        /// The higher this value, the less strains there will be, indirectly giving long beatmaps an advantage.
+        /// </summary>
+        protected const double STRAIN_STEP = 750;
+
+        /// <summary>
+        /// The weighting of each strain value decays to this number * it's previous value
+        /// </summary>
+        protected const double DECAY_WEIGHT = 0.94;
+
+        protected double CalculateDifficulty()
+        {
+            // The strain step needs to be adjusted for the algorithm to be considered equal with speed changing mods
+            double actualStrainStep = STRAIN_STEP * TimeRate;
+
+            // Find the highest strain value within each strain step
+            List<double> highestStrains = new List<double>();
+            double intervalEndTime = actualStrainStep;
+            double maximumStrain = 0; // We need to keep track of the maximum strain in the current interval
+
+            CatchDifficultyHitObject previousHitObject = null;
+            foreach (CatchDifficultyHitObject hitObject in difficultyHitObjects)
+            {
+                // While we are beyond the current interval push the currently available maximum to our strain list
+                while (hitObject.BaseHitObject.StartTime > intervalEndTime)
+                {
+                    highestStrains.Add(maximumStrain);
+
+                    // The maximum strain of the next interval is not zero by default! We need to take the last hitObject we encountered, take its strain and apply the decay
+                    // until the beginning of the next interval.
+                    if (previousHitObject == null)
+                    {
+                        maximumStrain = 0;
+                    }
+                    else
+                    {
+                        double decay = Math.Pow(CatchDifficultyHitObject.DECAY_BASE, (intervalEndTime - previousHitObject.BaseHitObject.StartTime) / 1000);
+                        maximumStrain = previousHitObject.Strain * decay;
+                    }
+
+                    // Go to the next time interval
+                    intervalEndTime += actualStrainStep;
+                }
+
+                // Obtain maximum strain
+                maximumStrain = Math.Max(hitObject.Strain, maximumStrain);
+
+                previousHitObject = hitObject;
+            }
+
+
+            // Build the weighted sum over the highest strains for each interval
+            double difficulty = 0;
+            double weight = 1;
+            highestStrains.Sort((a, b) => b.CompareTo(a)); // Sort from highest to lowest strain.
+
+            foreach (double strain in highestStrains)
+            {
+                difficulty += weight * strain;
+                weight *= DECAY_WEIGHT;
+            }
+
+            return difficulty;
+        }
     }
 }

osu.Game.Rulesets.Catch/Difficulty/CatchDifficultyHitObject.cs

@@ -0,0 +1,127 @@
+using System;
+using osu.Game.Rulesets.Catch.Objects;
+using osu.Game.Rulesets.Catch.UI;
+using OpenTK;
+
+namespace osu.Game.Rulesets.Catch.Difficulty
+{
+    class CatchDifficultyHitObject
+    {
+        internal static readonly double DECAY_BASE = 0.20;
+        private const float NORMALIZED_HITOBJECT_RADIUS = 41.0f;
+        private const float ABSOLUTE_PLAYER_POSITIONING_ERROR = 16f;
+        private float playerPositioningError;
+
+        internal CatchHitObject BaseHitObject;
+
+        /// <summary>
+        /// Measures jump difficulty. CtB doesn't have something like button pressing speed or accuracy
+        /// </summary>
+        internal double Strain = 1;
+
+        /// <summary>
+        /// This is required to keep track of lazy player movement (always moving only as far as necessary)
+        /// Without this quick repeat sliders / weirdly shaped streams might become ridiculously overrated
+        /// </summary>
+        internal float PlayerPositionOffset;
+        internal float LastMovement;
+
+        internal float NormalizedPosition;
+        internal float ActualNormalizedPosition => NormalizedPosition + PlayerPositionOffset;
+
+        internal CatchDifficultyHitObject(CatchHitObject baseHitObject, float catcherWidthHalf)
+        {
+            BaseHitObject = baseHitObject;
+
+            // We will scale everything by this factor, so we can assume a uniform CircleSize among beatmaps.
+            float scalingFactor = NORMALIZED_HITOBJECT_RADIUS / catcherWidthHalf;
+
+            playerPositioningError = ABSOLUTE_PLAYER_POSITIONING_ERROR;// * scalingFactor;
+            NormalizedPosition = baseHitObject.X * CatchPlayfield.BASE_WIDTH * scalingFactor;
+        }
+
+        private const double DIRECTION_CHANGE_BONUS = 12.5;
+        internal void CalculateStrains(CatchDifficultyHitObject previousHitObject, double timeRate)
+        {
+            // Rather simple, but more specialized things are inherently inaccurate due to the big difference playstyles and opinions make.
+            // See Taiko feedback thread.
+            double timeElapsed = (BaseHitObject.StartTime - previousHitObject.BaseHitObject.StartTime) / timeRate;
+            double decay = Math.Pow(DECAY_BASE, timeElapsed / 1000);
+
+            // Update new position with lazy movement.
+            PlayerPositionOffset =
+                MathHelper.Clamp(
+                    previousHitObject.ActualNormalizedPosition,
+                    NormalizedPosition - (NORMALIZED_HITOBJECT_RADIUS - playerPositioningError),
+                    NormalizedPosition + (NORMALIZED_HITOBJECT_RADIUS - playerPositioningError)) // Obtain new lazy position, but be stricter by allowing for an error of a certain degree of the player.
+                - NormalizedPosition; // Subtract HitObject position to obtain offset
+
+            LastMovement = DistanceTo(previousHitObject);
+            double addition = spacingWeight(LastMovement);
+
+            if (NormalizedPosition < previousHitObject.NormalizedPosition)
+            {
+                LastMovement = -LastMovement;
+            }
+
+            CatchHitObject previousHitCircle = previousHitObject.BaseHitObject;
+
+            double additionBonus = 0;
+            double sqrtTime = Math.Sqrt(Math.Max(timeElapsed, 25));
+
+            // Direction changes give an extra point!
+            if (Math.Abs(LastMovement) > 0.1)
+            {
+                if (Math.Abs(previousHitObject.LastMovement) > 0.1 && Math.Sign(LastMovement) != Math.Sign(previousHitObject.LastMovement))
+                {
+                    double bonus = DIRECTION_CHANGE_BONUS / sqrtTime;
+
+                    // Weight bonus by how 
+                    double bonusFactor = Math.Min(playerPositioningError, Math.Abs(LastMovement)) / playerPositioningError;
+
+                    // We want time to play a role twice here!
+                    addition += bonus * bonusFactor;
+
+                    // Bonus for tougher direction switches and "almost" hyperdashes at this point
+                    if (previousHitCircle != null && previousHitCircle.DistanceToHyperDash <= 10.0f / CatchPlayfield.BASE_WIDTH)
+                    {
+                        additionBonus += 0.3 * bonusFactor;
+                    }
+                }
+
+                // Base bonus for every movement, giving some weight to streams.
+                addition += 7.5 * Math.Min(Math.Abs(LastMovement), NORMALIZED_HITOBJECT_RADIUS * 2) / (NORMALIZED_HITOBJECT_RADIUS * 6) / sqrtTime;
+            }
+
+            // Bonus for "almost" hyperdashes at corner points
+            if (previousHitCircle != null && previousHitCircle.DistanceToHyperDash <= 10.0f / CatchPlayfield.BASE_WIDTH)
+            {
+                if (!previousHitCircle.HyperDash)
+                {
+                    additionBonus += 1.0;
+                }
+                else
+                {
+                    // After a hyperdash we ARE in the correct position. Always!
+                    PlayerPositionOffset = 0;
+                }
+
+                addition *= 1.0 + additionBonus * ((10 - previousHitCircle.DistanceToHyperDash * CatchPlayfield.BASE_WIDTH) / 10);
+            }
+
+            addition *= 850.0 / Math.Max(timeElapsed, 25);
+
+            Strain = previousHitObject.Strain * decay + addition;
+        }
+
+        private static double spacingWeight(float distance)
+        {
+            return Math.Pow(distance, 1.3) / 500;
+        }
+
+        internal float DistanceTo(CatchDifficultyHitObject other)
+        {
+            return Math.Abs(ActualNormalizedPosition - other.ActualNormalizedPosition);
+        }
+    }
+}