c69b3bde04
The SoundTable probability field is a Bernoulli play/skip gate applied at the play site (SoundManager::PlayProbability @0x005500E0), not a selection weight — and variant selection (SoundManager::GetSound @0x00550680) is a uniform index over (n-1) that ignores probability entirely. SoundCookbook did the opposite: a cumulative-distribution walk weighted BY probability, short-circuiting single-entry lists before rolling at all. A dat census says 4,183 of 4,184 entries are single-entry and 686 of those carry probability < 1.0, so the gate was categorically absent: Speak1 idle chatter authored at 0.05 fired every trigger (~20x too often), wound/attack/ swoosh variants never dropped, and six 0.0001 entries always played. Split into retail's two steps (PickVariant + PlayProbability, composed by Select) over a new ISoundRandom modelling both retail roll ranges: the variant roll clamped below 1.0 (0x00797D48) and the gate's 1/32767 grid, which is why 0.0001 resolves to ~1.2e-4. PickVariant reproduces retail's (n-1) off-by-one verbatim per the port-faithfully rule — the last variant of a multi-entry sound is unreachable, costing exactly one wave (0x0A00051E) in the shipped dats. Also removes invented mechanism this review disproved: the dead Core SoundEntry/ISoundCache scaffold (PitchMin/PitchMax, Loop, Is3D — retail never calls SetFrequency, never sets the loop flag, and creates every gameplay buffer 2D), the engine's pitch plumbing, the int 0..7 priority cast (the dat field is a float in [0,1]; 4,100 entries collapsed to 0), and the clamp-at-the-field on volume (an unbounded gain retail clamps only after the distance divide). Tests rewritten as conformance against the disassembled values, replacing a self-referential suite that pinned the wrong model. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
71 lines
2.7 KiB
C#
71 lines
2.7 KiB
C#
using System;
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namespace AcDream.Core.Audio;
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/// <summary>
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/// The two random sources retail's sound code actually draws from. They are
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/// NOT interchangeable, and the difference is observable at small
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/// probabilities, so the seam models both rather than collapsing them.
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///
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/// <para>
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/// <b>Variant index</b> — <c>Random::RollDice(0, 1)</c> @ <c>0x0042C4C0</c>,
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/// a dual-LCG returning a float hard-clamped to <c>0.99999988</c>
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/// (<c>0x00797D48</c>), i.e. it can never return 1.0. That clamp is what
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/// makes the last variant of a multi-entry sound unreachable — see
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/// <see cref="SoundCookbook.PickVariant"/>.
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/// </para>
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///
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/// <para>
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/// <b>Probability gate</b> — C library <c>rand()</c> scaled by
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/// <c>1/32767</c> inside <c>SoundManager::PlayProbability</c> @
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/// <c>0x005500E0</c>. <c>rand()</c> returns 0..32767 INCLUSIVE, so the
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/// scaled value reaches exactly 1.0 and the grid step is ~3.05e-5. Two
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/// consequences we reproduce deliberately: a probability of 1.0 is skipped
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/// on the single roll where the value lands on 1.0 (1 chance in 32768), and
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/// the six authored 0.0001 probabilities in the shipped dats resolve to
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/// ~1.2e-4 rather than 1e-4 because only <c>rand() <= 3</c> passes.
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/// </para>
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/// </summary>
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public interface ISoundRandom
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{
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/// <summary>
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/// Retail <c>Random::RollDice(0, 1)</c>: a float in
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/// <c>[0, 0.99999988]</c>, never 1.0.
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/// </summary>
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float NextVariantRoll();
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/// <summary>
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/// Retail <c>rand() * (1/32767)</c>: a float in <c>[0, 1]</c> inclusive,
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/// quantised to the 1/32767 grid.
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/// </summary>
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float NextProbabilityRoll();
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}
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/// <summary>
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/// <see cref="ISoundRandom"/> over <see cref="Random"/>. Retail's exact LCG
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/// streams are not reproduced — nothing observable depends on the sequence,
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/// only on each roll's range and quantisation, which this preserves.
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/// </summary>
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public sealed class SoundRandom : ISoundRandom
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{
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/// <summary>
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/// Retail's clamp on <c>Random::rand</c> (<c>0x00797D48</c>). Equals
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/// <c>1 - 2^-23</c>, the largest float below 1.0.
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/// </summary>
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internal const float MaxVariantRoll = 0.99999988f;
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/// <summary>C's <c>RAND_MAX</c>; retail divides by exactly this.</summary>
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internal const int RandMax = 32767;
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private readonly Random _rng;
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public SoundRandom(Random? rng = null) => _rng = rng ?? Random.Shared;
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public float NextVariantRoll() =>
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MathF.Min(MaxVariantRoll, (float)_rng.NextDouble());
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// Next's upper bound is exclusive, so RandMax + 1 makes RAND_MAX itself
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// reachable — which is what lets the scaled roll reach exactly 1.0.
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public float NextProbabilityRoll() =>
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_rng.Next(0, RandMax + 1) * (1f / RandMax);
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}
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