osu/osu.Game.Rulesets.Taiko/Objects/TaikoHitObjectDifficulty.cs

127 lines
4.9 KiB
C#

// Copyright (c) 2007-2017 ppy Pty Ltd <contact@ppy.sh>.
// Licensed under the MIT Licence - https://raw.githubusercontent.com/ppy/osu/master/LICENCE
using System;
namespace osu.Game.Rulesets.Taiko.Objects
{
internal class TaikoHitObjectDifficulty
{
/// <summary>
/// Factor by how much individual / overall strain decays per second.
/// </summary>
/// <remarks>
/// These values are results of tweaking a lot and taking into account general feedback.
/// </remarks>
internal const double DECAY_BASE = 0.30;
private const double type_change_bonus = 0.75;
private const double rhythm_change_bonus = 1.0;
private const double rhythm_change_base_threshold = 0.2;
private const double rhythm_change_base = 2.0;
internal TaikoHitObject BaseHitObject;
/// <summary>
/// Measures note density in a way
/// </summary>
internal double Strain = 1;
private double timeElapsed;
private int sameTypeSince = 1;
private bool isRim => BaseHitObject is RimHit;
public TaikoHitObjectDifficulty(TaikoHitObject baseHitObject)
{
BaseHitObject = baseHitObject;
}
internal void CalculateStrains(TaikoHitObjectDifficulty previousHitObject, double timeRate)
{
// Rather simple, but more specialized things are inherently inaccurate due to the big difference playstyles and opinions make.
// See Taiko feedback thread.
timeElapsed = (BaseHitObject.StartTime - previousHitObject.BaseHitObject.StartTime) / timeRate;
double decay = Math.Pow(DECAY_BASE, timeElapsed / 1000);
double addition = 1;
// Only if we are no slider or spinner we get an extra addition
if (previousHitObject.BaseHitObject is Hit && BaseHitObject is Hit
&& BaseHitObject.StartTime - previousHitObject.BaseHitObject.StartTime < 1000) // And we only want to check out hitobjects which aren't so far in the past
{
addition += typeChangeAddition(previousHitObject);
addition += rhythmChangeAddition(previousHitObject);
}
double additionFactor = 1.0;
// Scale AdditionFactor linearly from 0.4 to 1 for TimeElapsed from 0 to 50
if (timeElapsed < 50.0)
additionFactor = 0.4 + 0.6 * timeElapsed / 50.0;
Strain = previousHitObject.Strain * decay + addition * additionFactor;
}
private TypeSwitch lastTypeSwitchEven = TypeSwitch.None;
private double typeChangeAddition(TaikoHitObjectDifficulty previousHitObject)
{
// If we don't have the same hit type, trigger a type change!
if (previousHitObject.isRim != isRim)
{
lastTypeSwitchEven = previousHitObject.sameTypeSince % 2 == 0 ? TypeSwitch.Even : TypeSwitch.Odd;
// We only want a bonus if the parity of the type switch changes!
switch (previousHitObject.lastTypeSwitchEven)
{
case TypeSwitch.Even:
if (lastTypeSwitchEven == TypeSwitch.Odd)
return type_change_bonus;
break;
case TypeSwitch.Odd:
if (lastTypeSwitchEven == TypeSwitch.Even)
return type_change_bonus;
break;
}
}
// No type change? Increment counter and keep track of last type switch
else
{
lastTypeSwitchEven = previousHitObject.lastTypeSwitchEven;
sameTypeSince = previousHitObject.sameTypeSince + 1;
}
return 0;
}
private double rhythmChangeAddition(TaikoHitObjectDifficulty previousHitObject)
{
// We don't want a division by zero if some random mapper decides to put 2 HitObjects at the same time.
if (timeElapsed == 0 || previousHitObject.timeElapsed == 0)
return 0;
double timeElapsedRatio = Math.Max(previousHitObject.timeElapsed / timeElapsed, timeElapsed / previousHitObject.timeElapsed);
if (timeElapsedRatio >= 8)
return 0;
double difference = Math.Log(timeElapsedRatio, rhythm_change_base) % 1.0;
if (isWithinChangeThreshold(difference))
return rhythm_change_bonus;
return 0;
}
private bool isWithinChangeThreshold(double value)
{
return value > rhythm_change_base_threshold && value < 1 - rhythm_change_base_threshold;
}
private enum TypeSwitch
{
None,
Even,
Odd
}
}
}