osu/osu.Game.Rulesets.Mania/Difficulty/ManiaDifficultyCalculator.cs

175 lines
7.3 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.Mania.Beatmaps;
using osu.Game.Rulesets.Mania.Mods;
using osu.Game.Rulesets.Mania.Objects;
using osu.Game.Rulesets.Mods;
namespace osu.Game.Rulesets.Mania.Difficulty
{
internal class ManiaDifficultyCalculator : DifficultyCalculator
{
private const double star_scaling_factor = 0.018;
/// <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;
private readonly bool isForCurrentRuleset;
public ManiaDifficultyCalculator(Ruleset ruleset, WorkingBeatmap beatmap)
: base(ruleset, beatmap)
{
isForCurrentRuleset = beatmap.BeatmapInfo.Ruleset.Equals(ruleset.RulesetInfo);
}
protected override DifficultyAttributes Calculate(IBeatmap beatmap, Mod[] mods, double timeRate)
{
if (!beatmap.HitObjects.Any())
return new ManiaDifficultyAttributes(mods, 0);
var difficultyHitObjects = new List<ManiaHitObjectDifficulty>();
int columnCount = ((ManiaBeatmap)beatmap).TotalColumns;
// Sort DifficultyHitObjects by StartTime of the HitObjects - just to make sure.
// Note: Stable sort is done so that the ordering of hitobjects with equal start times doesn't change
difficultyHitObjects.AddRange(beatmap.HitObjects.Select(h => new ManiaHitObjectDifficulty((ManiaHitObject)h, columnCount)).OrderBy(h => h.BaseHitObject.StartTime));
if (!calculateStrainValues(difficultyHitObjects, timeRate))
return new DifficultyAttributes(mods, 0);
double starRating = calculateDifficulty(difficultyHitObjects, timeRate) * star_scaling_factor;
return new ManiaDifficultyAttributes(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
};
}
private bool calculateStrainValues(List<ManiaHitObjectDifficulty> 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;
ManiaHitObjectDifficulty 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<ManiaHitObjectDifficulty> 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
ManiaHitObjectDifficulty 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 individualDecay = Math.Pow(ManiaHitObjectDifficulty.INDIVIDUAL_DECAY_BASE, (intervalEndTime - previousHitObject.BaseHitObject.StartTime) / 1000);
double overallDecay = Math.Pow(ManiaHitObjectDifficulty.OVERALL_DECAY_BASE, (intervalEndTime - previousHitObject.BaseHitObject.StartTime) / 1000);
maximumStrain = previousHitObject.IndividualStrain * individualDecay + previousHitObject.OverallStrain * overallDecay;
}
// Go to the next time interval
intervalEndTime += actualStrainStep;
}
// Obtain maximum strain
double strain = hitObject.IndividualStrain + hitObject.OverallStrain;
maximumStrain = Math.Max(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
{
get
{
var mods = new Mod[]
{
new ManiaModDoubleTime(),
new ManiaModHalfTime(),
new ManiaModEasy(),
new ManiaModHardRock(),
};
if (isForCurrentRuleset)
return mods;
// if we are a convert, we can be played in any key mod.
return mods.Concat(new Mod[]
{
new ManiaModKey1(),
new ManiaModKey2(),
new ManiaModKey3(),
new ManiaModKey4(),
new ManiaModKey5(),
new ManiaModKey6(),
new ManiaModKey7(),
new ManiaModKey8(),
new ManiaModKey9(),
}).ToArray();
}
}
}
}