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Remove delegate allocation in jitter calculation in FramedClock #6122

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merged 3 commits into from
Jan 11, 2024
Merged

Remove delegate allocation in jitter calculation in FramedClock #6122

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237af89
Remove delegate allocation in jitter calculation in `FramedClock`
peppy Jan 10, 2024
c4efa5a
Also remove enumerator overhead from `Average()`
peppy Jan 10, 2024
3e30306
Merge branch 'master' into frame-calc-delegate-overhead
bdach Jan 11, 2024
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18 changes: 13 additions & 5 deletions osu.Framework/Timing/FramedClock.cs
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Original file line number Diff line number Diff line change
@@ -1,10 +1,9 @@
// Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
// See the LICENCE file in the repository root for full licence text.

using osu.Framework.Extensions.TypeExtensions;
using System;
using System.Diagnostics;
using System.Linq;
using osu.Framework.Extensions.TypeExtensions;

namespace osu.Framework.Timing
{
Expand Down Expand Up @@ -85,9 +84,18 @@ public virtual void ProcessFrame()
FramesPerSecond = (int)Math.Ceiling(framesSinceLastCalculation * 1000f / timeSinceLastCalculation);

// simple stddev
double avg = betweenFrameTimes.Average();
double stddev = Math.Sqrt(betweenFrameTimes.Average(v => Math.Pow(v - avg, 2)));
Jitter = stddev;
double sum = 0;
double sumOfSquares = 0;

foreach (double v in betweenFrameTimes)
{
sum += v;
sumOfSquares += v * v;
}

double avg = sum / betweenFrameTimes.Length;
double variance = (sumOfSquares / betweenFrameTimes.Length) - (avg * avg);
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I am shook that this can be done and be actually correct.

Proof:

$$ \begin{align} \sigma_x &= \frac{\sum_i (x_i - \bar{x})^2}{|x|} = \\ &= \frac{\sum_i (x_i^2 - 2x_i \bar{x} + \bar{x}^2)}{|x|} = \\ &= \frac{\sum_i x_i^2}{|x|} - 2 \bar{x} \frac{\sum_i x_i}{|x|} + \bar{x}^2 \cdot \frac{\sum_i 1}{|x|} = \\ &= \frac{\sum_i x_i^2}{|x|} - 2 \bar{x} \cdot \bar{x} + \bar{x}^2 \cdot \frac{|x|}{|x|} = \\ &= \frac{\sum_i x_i^2}{|x|} - \bar{x}^2 \end{align} $$

wherein $x_i$ are elements of a set, $\bar{x}$ is the mean of the set, and $|x|$ is the cardinality of the set.

I thought there was no way this was gonna work but kept failing to find counterexamples...

Jitter = Math.Sqrt(variance);
}

timeSinceLastCalculation = framesSinceLastCalculation = 0;
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