// 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.Skills; using osu.Game.Rulesets.Mods; using System.Linq; using osu.Framework.Utils; namespace osu.Game.Rulesets.Osu.Difficulty.Skills { public abstract class OsuStrainSkill : StrainSkill { /// <summary> /// The number of sections with the highest strains, which the peak strain reductions will apply to. /// This is done in order to decrease their impact on the overall difficulty of the map for this skill. /// </summary> protected virtual int ReducedSectionCount => 10; /// <summary> /// The baseline multiplier applied to the section with the biggest strain. /// </summary> protected virtual double ReducedStrainBaseline => 0.75; protected List<double> ObjectStrains = new List<double>(); protected double Difficulty; protected OsuStrainSkill(Mod[] mods) : base(mods) { } public override double DifficultyValue() { Difficulty = 0; double weight = 1; // 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. var peaks = GetCurrentStrainPeaks().Where(p => p > 0); List<double> strains = peaks.OrderDescending().ToList(); // We are reducing the highest strains first to account for extreme difficulty spikes for (int i = 0; i < Math.Min(strains.Count, ReducedSectionCount); i++) { double scale = Math.Log10(Interpolation.Lerp(1, 10, Math.Clamp((float)i / ReducedSectionCount, 0, 1))); strains[i] *= Interpolation.Lerp(ReducedStrainBaseline, 1.0, scale); } // Difficulty is the weighted sum of the highest strains from every section. // We're sorting from highest to lowest strain. foreach (double strain in strains.OrderDescending()) { Difficulty += strain * weight; weight *= DecayWeight; } return Difficulty; } /// <summary> /// Returns the number of strains weighted against the top strain. /// The result is scaled by clock rate as it affects the total number of strains. /// </summary> public double CountDifficultStrains() { if (Difficulty == 0) return 0.0; double consistentTopStrain = Difficulty / 10; // What would the top strain be if all strain values were identical // Use a weighted sum of all strains. Constants are arbitrary and give nice values return ObjectStrains.Sum(s => 1.1 / (1 + Math.Exp(-10 * (s / consistentTopStrain - 0.88)))); } public static double DifficultyToPerformance(double difficulty) => Math.Pow(5.0 * Math.Max(1.0, difficulty / 0.0675) - 4.0, 3.0) / 100000.0; } }