mirror of https://github.com/ppy/osu
71 lines
2.7 KiB
C#
71 lines
2.7 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 System.Collections.Generic;
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using System.Diagnostics;
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using System.Linq;
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namespace osu.Game.Rulesets.Scoring
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{
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public static class HitEventExtensions
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{
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/// <summary>
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/// Calculates the "unstable rate" for a sequence of <see cref="HitEvent"/>s.
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/// </summary>
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/// <remarks>
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/// Uses <a href="https://en.wikipedia.org/wiki/Algorithms_for_calculating_variance#Welford's_online_algorithm">Welford's online algorithm</a>.
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/// </remarks>
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/// <returns>
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/// A non-null <see langword="double"/> value if unstable rate could be calculated,
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/// and <see langword="null"/> if unstable rate cannot be calculated due to <paramref name="hitEvents"/> being empty.
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/// </returns>
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public static double? CalculateUnstableRate(this IEnumerable<HitEvent> hitEvents)
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{
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Debug.Assert(hitEvents.All(ev => ev.GameplayRate != null));
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int count = 0;
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double mean = 0;
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double sumOfSquares = 0;
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foreach (var e in hitEvents)
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{
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if (!AffectsUnstableRate(e))
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continue;
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count++;
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// Division by gameplay rate is to account for TimeOffset scaling with gameplay rate.
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double currentValue = e.TimeOffset / e.GameplayRate!.Value;
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double nextMean = mean + (currentValue - mean) / count;
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sumOfSquares += (currentValue - mean) * (currentValue - nextMean);
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mean = nextMean;
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}
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if (count == 0)
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return null;
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return 10.0 * Math.Sqrt(sumOfSquares / count);
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}
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/// <summary>
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/// Calculates the average hit offset/error for a sequence of <see cref="HitEvent"/>s, where negative numbers mean the user hit too early on average.
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/// </summary>
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/// <returns>
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/// A non-null <see langword="double"/> value if unstable rate could be calculated,
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/// and <see langword="null"/> if unstable rate cannot be calculated due to <paramref name="hitEvents"/> being empty.
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/// </returns>
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public static double? CalculateAverageHitError(this IEnumerable<HitEvent> hitEvents)
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{
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double[] timeOffsets = hitEvents.Where(AffectsUnstableRate).Select(ev => ev.TimeOffset).ToArray();
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if (timeOffsets.Length == 0)
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return null;
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return timeOffsets.Average();
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}
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public static bool AffectsUnstableRate(HitEvent e) => !(e.HitObject.HitWindows is HitWindows.EmptyHitWindows) && e.Result.IsHit();
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}
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}
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