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While it is the case for the existing official Skills, Skill implementations shouldn't be required to conform to a strain based approach. There are other valid approaches to calculating skill difficulty that can be supported by abstracting the strain logic into its own StrainSkill class.
174 lines
6.4 KiB
C#
174 lines
6.4 KiB
C#
// Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
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// See the LICENCE file in the repository root for full licence text.
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using System;
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using osu.Game.Rulesets.Difficulty.Preprocessing;
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using osu.Game.Rulesets.Difficulty.Skills;
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using osu.Game.Rulesets.Difficulty.Utils;
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using osu.Game.Rulesets.Mods;
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using osu.Game.Rulesets.Taiko.Difficulty.Preprocessing;
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using osu.Game.Rulesets.Taiko.Objects;
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namespace osu.Game.Rulesets.Taiko.Difficulty.Skills
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{
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/// <summary>
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/// Calculates the rhythm coefficient of taiko difficulty.
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/// </summary>
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public class Rhythm : StrainSkill
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{
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protected override double SkillMultiplier => 10;
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protected override double StrainDecayBase => 0;
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/// <summary>
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/// The note-based decay for rhythm strain.
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/// </summary>
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/// <remarks>
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/// <see cref="StrainDecayBase"/> is not used here, as it's time- and not note-based.
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/// </remarks>
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private const double strain_decay = 0.96;
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/// <summary>
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/// Maximum number of entries in <see cref="rhythmHistory"/>.
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/// </summary>
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private const int rhythm_history_max_length = 8;
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/// <summary>
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/// Contains the last <see cref="rhythm_history_max_length"/> changes in note sequence rhythms.
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/// </summary>
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private readonly LimitedCapacityQueue<TaikoDifficultyHitObject> rhythmHistory = new LimitedCapacityQueue<TaikoDifficultyHitObject>(rhythm_history_max_length);
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/// <summary>
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/// Contains the rolling rhythm strain.
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/// Used to apply per-note decay.
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/// </summary>
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private double currentStrain;
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/// <summary>
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/// Number of notes since the last rhythm change has taken place.
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/// </summary>
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private int notesSinceRhythmChange;
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public Rhythm(Mod[] mods)
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: base(mods)
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{
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}
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protected override double StrainValueOf(DifficultyHitObject current)
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{
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// drum rolls and swells are exempt.
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if (!(current.BaseObject is Hit))
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{
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resetRhythmAndStrain();
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return 0.0;
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}
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currentStrain *= strain_decay;
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TaikoDifficultyHitObject hitObject = (TaikoDifficultyHitObject)current;
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notesSinceRhythmChange += 1;
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// rhythm difficulty zero (due to rhythm not changing) => no rhythm strain.
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if (hitObject.Rhythm.Difficulty == 0.0)
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{
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return 0.0;
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}
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double objectStrain = hitObject.Rhythm.Difficulty;
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objectStrain *= repetitionPenalties(hitObject);
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objectStrain *= patternLengthPenalty(notesSinceRhythmChange);
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objectStrain *= speedPenalty(hitObject.DeltaTime);
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// careful - needs to be done here since calls above read this value
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notesSinceRhythmChange = 0;
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currentStrain += objectStrain;
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return currentStrain;
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}
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/// <summary>
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/// Returns a penalty to apply to the current hit object caused by repeating rhythm changes.
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/// </summary>
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/// <remarks>
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/// Repetitions of more recent patterns are associated with a higher penalty.
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/// </remarks>
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/// <param name="hitObject">The current hit object being considered.</param>
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private double repetitionPenalties(TaikoDifficultyHitObject hitObject)
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{
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double penalty = 1;
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rhythmHistory.Enqueue(hitObject);
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for (int mostRecentPatternsToCompare = 2; mostRecentPatternsToCompare <= rhythm_history_max_length / 2; mostRecentPatternsToCompare++)
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{
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for (int start = rhythmHistory.Count - mostRecentPatternsToCompare - 1; start >= 0; start--)
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{
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if (!samePattern(start, mostRecentPatternsToCompare))
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continue;
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int notesSince = hitObject.ObjectIndex - rhythmHistory[start].ObjectIndex;
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penalty *= repetitionPenalty(notesSince);
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break;
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}
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}
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return penalty;
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}
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/// <summary>
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/// Determines whether the rhythm change pattern starting at <paramref name="start"/> is a repeat of any of the
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/// <paramref name="mostRecentPatternsToCompare"/>.
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/// </summary>
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private bool samePattern(int start, int mostRecentPatternsToCompare)
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{
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for (int i = 0; i < mostRecentPatternsToCompare; i++)
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{
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if (rhythmHistory[start + i].Rhythm != rhythmHistory[rhythmHistory.Count - mostRecentPatternsToCompare + i].Rhythm)
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return false;
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}
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return true;
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}
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/// <summary>
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/// Calculates a single rhythm repetition penalty.
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/// </summary>
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/// <param name="notesSince">Number of notes since the last repetition of a rhythm change.</param>
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private static double repetitionPenalty(int notesSince) => Math.Min(1.0, 0.032 * notesSince);
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/// <summary>
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/// Calculates a penalty based on the number of notes since the last rhythm change.
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/// Both rare and frequent rhythm changes are penalised.
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/// </summary>
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/// <param name="patternLength">Number of notes since the last rhythm change.</param>
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private static double patternLengthPenalty(int patternLength)
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{
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double shortPatternPenalty = Math.Min(0.15 * patternLength, 1.0);
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double longPatternPenalty = Math.Clamp(2.5 - 0.15 * patternLength, 0.0, 1.0);
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return Math.Min(shortPatternPenalty, longPatternPenalty);
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}
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/// <summary>
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/// Calculates a penalty for objects that do not require alternating hands.
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/// </summary>
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/// <param name="deltaTime">Time (in milliseconds) since the last hit object.</param>
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private double speedPenalty(double deltaTime)
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{
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if (deltaTime < 80) return 1;
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if (deltaTime < 210) return Math.Max(0, 1.4 - 0.005 * deltaTime);
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resetRhythmAndStrain();
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return 0.0;
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}
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/// <summary>
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/// Resets the rolling strain value and <see cref="notesSinceRhythmChange"/> counter.
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/// </summary>
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private void resetRhythmAndStrain()
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{
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currentStrain = 0.0;
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notesSinceRhythmChange = 0;
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}
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}
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}
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