// 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 System.Linq; using osu.Game.Beatmaps; using osu.Game.Rulesets.Difficulty; using osu.Game.Rulesets.Mods; using osu.Game.Rulesets.Taiko.Mods; using osu.Game.Rulesets.Taiko.Objects; namespace osu.Game.Rulesets.Taiko.Difficulty { internal class TaikoDifficultyCalculator : DifficultyCalculator { private const double star_scaling_factor = 0.04125; /// <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> private const double strain_step = 400; /// <summary> /// The weighting of each strain value decays to this number * it's previous value /// </summary> private const double decay_weight = 0.9; public TaikoDifficultyCalculator(Ruleset ruleset, WorkingBeatmap beatmap) : base(ruleset, beatmap) { } protected override DifficultyAttributes Calculate(IBeatmap beatmap, Mod[] mods, double timeRate) { if (!beatmap.HitObjects.Any()) return new TaikoDifficultyAttributes(mods, 0); var difficultyHitObjects = new List<TaikoHitObjectDifficulty>(); foreach (var hitObject in beatmap.HitObjects) difficultyHitObjects.Add(new TaikoHitObjectDifficulty((TaikoHitObject)hitObject)); // Sort DifficultyHitObjects by StartTime of the HitObjects - just to make sure. difficultyHitObjects.Sort((a, b) => a.BaseHitObject.StartTime.CompareTo(b.BaseHitObject.StartTime)); if (!calculateStrainValues(difficultyHitObjects, timeRate)) return new DifficultyAttributes(mods, 0); double starRating = calculateDifficulty(difficultyHitObjects, timeRate) * star_scaling_factor; return new TaikoDifficultyAttributes(mods, starRating) { // Todo: This int cast is temporary to achieve 1:1 results with osu!stable, and should be remoevd in the future GreatHitWindow = (int)(beatmap.HitObjects.First().HitWindows.Great / 2) / timeRate, MaxCombo = beatmap.HitObjects.Count(h => h is Hit) }; } private bool calculateStrainValues(List<TaikoHitObjectDifficulty> objects, double timeRate) { // Traverse hitObjects in pairs to calculate the strain value of NextHitObject from the strain value of CurrentHitObject and environment. using (var hitObjectsEnumerator = objects.GetEnumerator()) { if (!hitObjectsEnumerator.MoveNext()) return false; TaikoHitObjectDifficulty current = hitObjectsEnumerator.Current; // 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()) { var next = hitObjectsEnumerator.Current; next?.CalculateStrains(current, timeRate); current = next; } return true; } } private double calculateDifficulty(List<TaikoHitObjectDifficulty> objects, double timeRate) { 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 TaikoHitObjectDifficulty previousHitObject = null; foreach (var hitObject in objects) { // 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(TaikoHitObjectDifficulty.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; } protected override Mod[] DifficultyAdjustmentMods => new Mod[] { new TaikoModDoubleTime(), new TaikoModHalfTime(), new TaikoModEasy(), new TaikoModHardRock(), }; } }