osu/osu.Game.Rulesets.Taiko/Difficulty/TaikoDifficultyCalculator.cs

145 lines
6.0 KiB
C#

// 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(),
};
}
}