osu/osu.Game.Rulesets.Osu/Difficulty/Skills/Skill.cs

101 lines
4.4 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 osu.Game.Rulesets.Osu.Difficulty.Preprocessing;
using osu.Game.Rulesets.Osu.Difficulty.Utils;
using osu.Game.Rulesets.Osu.Objects;
namespace osu.Game.Rulesets.Osu.Difficulty.Skills
{
/// <summary>
/// Used to processes strain values of <see cref="OsuDifficultyHitObject"/>s, keep track of strain levels caused by the processed objects
/// and to calculate a final difficulty value representing the difficulty of hitting all the processed objects.
/// </summary>
public abstract class Skill
{
/// <summary>
/// Strain values are multiplied by this number for the given skill. Used to balance the value of different skills between each other.
/// </summary>
protected abstract double SkillMultiplier { get; }
/// <summary>
/// Determines how quickly strain decays for the given skill.
/// For example a value of 0.15 indicates that strain decays to 15% of its original value in one second.
/// </summary>
protected abstract double StrainDecayBase { get; }
/// <summary>
/// <see cref="OsuDifficultyHitObject"/>s that were processed previously. They can affect the strain values of the following objects.
/// </summary>
protected readonly History<OsuDifficultyHitObject> Previous = new History<OsuDifficultyHitObject>(2); // Contained objects not used yet
private double currentStrain = 1; // We keep track of the strain level at all times throughout the beatmap.
private double currentSectionPeak = 1; // We also keep track of the peak strain level in the current section.
private readonly List<double> strainPeaks = new List<double>();
/// <summary>
/// Process an <see cref="OsuDifficultyHitObject"/> and update current strain values accordingly.
/// </summary>
public void Process(OsuDifficultyHitObject current)
{
currentStrain *= strainDecay(current.DeltaTime);
if (!(current.BaseObject is Spinner))
currentStrain += StrainValueOf(current) * SkillMultiplier;
currentSectionPeak = Math.Max(currentStrain, currentSectionPeak);
Previous.Push(current);
}
/// <summary>
/// Saves the current peak strain level to the list of strain peaks, which will be used to calculate an overall difficulty.
/// </summary>
public void SaveCurrentPeak()
{
if (Previous.Count > 0)
strainPeaks.Add(currentSectionPeak);
}
/// <summary>
/// Sets the initial strain level for a new section.
/// </summary>
/// <param name="offset">The beginning of the new section in milliseconds</param>
public void StartNewSectionFrom(double offset)
{
// The maximum strain of the new section is not zero by default, strain decays as usual regardless of section boundaries.
// This means we need to capture the strain level at the beginning of the new section, and use that as the initial peak level.
if (Previous.Count > 0)
currentSectionPeak = currentStrain * strainDecay(offset - Previous[0].BaseObject.StartTime);
}
/// <summary>
/// Returns the calculated difficulty value representing all processed <see cref="OsuDifficultyHitObject"/>s.
/// </summary>
public double DifficultyValue()
{
strainPeaks.Sort((a, b) => b.CompareTo(a)); // Sort from highest to lowest strain.
double difficulty = 0;
double weight = 1;
// Difficulty is the weighted sum of the highest strains from every section.
foreach (double strain in strainPeaks)
{
difficulty += strain * weight;
weight *= 0.9;
}
return difficulty;
}
/// <summary>
/// Calculates the strain value of an <see cref="OsuDifficultyHitObject"/>. This value is affected by previously processed objects.
/// </summary>
protected abstract double StrainValueOf(OsuDifficultyHitObject current);
private double strainDecay(double ms) => Math.Pow(StrainDecayBase, ms / 1000);
}
}