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145 lines
6.0 KiB
C#
145 lines
6.0 KiB
C#
// Copyright (c) 2007-2018 ppy Pty Ltd <contact@ppy.sh>.
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// Licensed under the MIT Licence - https://raw.githubusercontent.com/ppy/osu/master/LICENCE
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using System;
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using System.Collections.Generic;
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using System.Linq;
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using osu.Game.Beatmaps;
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using osu.Game.Rulesets.Difficulty;
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using osu.Game.Rulesets.Mods;
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using osu.Game.Rulesets.Taiko.Mods;
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using osu.Game.Rulesets.Taiko.Objects;
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namespace osu.Game.Rulesets.Taiko.Difficulty
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{
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internal class TaikoDifficultyCalculator : DifficultyCalculator
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{
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private const double star_scaling_factor = 0.04125;
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/// <summary>
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/// In milliseconds. For difficulty calculation we will only look at the highest strain value in each time interval of size STRAIN_STEP.
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/// This is to eliminate higher influence of stream over aim by simply having more HitObjects with high strain.
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/// The higher this value, the less strains there will be, indirectly giving long beatmaps an advantage.
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/// </summary>
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private const double strain_step = 400;
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/// <summary>
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/// The weighting of each strain value decays to this number * it's previous value
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/// </summary>
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private const double decay_weight = 0.9;
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public TaikoDifficultyCalculator(Ruleset ruleset, WorkingBeatmap beatmap)
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: base(ruleset, beatmap)
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{
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}
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protected override DifficultyAttributes Calculate(IBeatmap beatmap, Mod[] mods, double timeRate)
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{
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if (!beatmap.HitObjects.Any())
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return new TaikoDifficultyAttributes(mods, 0);
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var difficultyHitObjects = new List<TaikoHitObjectDifficulty>();
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foreach (var hitObject in beatmap.HitObjects)
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difficultyHitObjects.Add(new TaikoHitObjectDifficulty((TaikoHitObject)hitObject));
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// Sort DifficultyHitObjects by StartTime of the HitObjects - just to make sure.
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difficultyHitObjects.Sort((a, b) => a.BaseHitObject.StartTime.CompareTo(b.BaseHitObject.StartTime));
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if (!calculateStrainValues(difficultyHitObjects, timeRate))
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return new DifficultyAttributes(mods, 0);
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double starRating = calculateDifficulty(difficultyHitObjects, timeRate) * star_scaling_factor;
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return new TaikoDifficultyAttributes(mods, starRating)
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{
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// Todo: This int cast is temporary to achieve 1:1 results with osu!stable, and should be remoevd in the future
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GreatHitWindow = (int)(beatmap.HitObjects.First().HitWindows.Great / 2) / timeRate,
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MaxCombo = beatmap.HitObjects.Count(h => h is Hit)
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};
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}
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private bool calculateStrainValues(List<TaikoHitObjectDifficulty> objects, double timeRate)
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{
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// Traverse hitObjects in pairs to calculate the strain value of NextHitObject from the strain value of CurrentHitObject and environment.
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using (var hitObjectsEnumerator = objects.GetEnumerator())
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{
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if (!hitObjectsEnumerator.MoveNext()) return false;
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TaikoHitObjectDifficulty current = hitObjectsEnumerator.Current;
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// First hitObject starts at strain 1. 1 is the default for strain values, so we don't need to set it here. See DifficultyHitObject.
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while (hitObjectsEnumerator.MoveNext())
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{
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var next = hitObjectsEnumerator.Current;
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next?.CalculateStrains(current, timeRate);
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current = next;
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}
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return true;
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}
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}
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private double calculateDifficulty(List<TaikoHitObjectDifficulty> objects, double timeRate)
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{
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double actualStrainStep = strain_step * timeRate;
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// Find the highest strain value within each strain step
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List<double> highestStrains = new List<double>();
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double intervalEndTime = actualStrainStep;
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double maximumStrain = 0; // We need to keep track of the maximum strain in the current interval
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TaikoHitObjectDifficulty previousHitObject = null;
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foreach (var hitObject in objects)
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{
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// While we are beyond the current interval push the currently available maximum to our strain list
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while (hitObject.BaseHitObject.StartTime > intervalEndTime)
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{
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highestStrains.Add(maximumStrain);
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// 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
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// until the beginning of the next interval.
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if (previousHitObject == null)
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{
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maximumStrain = 0;
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}
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else
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{
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double decay = Math.Pow(TaikoHitObjectDifficulty.DECAY_BASE, (intervalEndTime - previousHitObject.BaseHitObject.StartTime) / 1000);
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maximumStrain = previousHitObject.Strain * decay;
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}
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// Go to the next time interval
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intervalEndTime += actualStrainStep;
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}
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// Obtain maximum strain
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maximumStrain = Math.Max(hitObject.Strain, maximumStrain);
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previousHitObject = hitObject;
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}
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// Build the weighted sum over the highest strains for each interval
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double difficulty = 0;
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double weight = 1;
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highestStrains.Sort((a, b) => b.CompareTo(a)); // Sort from highest to lowest strain.
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foreach (double strain in highestStrains)
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{
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difficulty += weight * strain;
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weight *= decay_weight;
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}
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return difficulty;
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}
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protected override Mod[] DifficultyAdjustmentMods => new Mod[]
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{
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new TaikoModDoubleTime(),
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new TaikoModHalfTime(),
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new TaikoModEasy(),
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new TaikoModHardRock(),
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};
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}
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}
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