87 lines
2.2 KiB
C
87 lines
2.2 KiB
C
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/*
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* Paula.h
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* -------
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* Purpose: Emulating the Amiga's sound chip, Paula, by implementing resampling using band-limited steps (BLEPs)
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* Notes : (currently none)
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* Authors: OpenMPT Devs
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* Antti S. Lankila
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* The OpenMPT source code is released under the BSD license. Read LICENSE for more details.
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*/
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#pragma once
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#include "BuildSettings.h"
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#include "Snd_defs.h"
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#include "Mixer.h"
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OPENMPT_NAMESPACE_BEGIN
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namespace Paula
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{
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inline constexpr int PAULA_HZ = 3546895;
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inline constexpr int MINIMUM_INTERVAL = 4; // Tradeoff between quality and speed (lower = less aliasing)
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inline constexpr int BLEP_SCALE = 17; // TODO: Should be 1 for float mixer
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inline constexpr int BLEP_SIZE = 2048;
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using BlepArray = std::array<mixsample_t, BLEP_SIZE>;
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class BlepTables
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{
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enum AmigaFilter
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{
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A500Off = 0,
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A500On,
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A1200Off,
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A1200On,
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Unfiltered,
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NumFilterTypes
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};
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std::array<Paula::BlepArray, AmigaFilter::NumFilterTypes> WinSincIntegral;
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public:
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void InitTables();
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const Paula::BlepArray &GetAmigaTable(Resampling::AmigaFilter amigaType, bool enableFilter) const;
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};
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class State
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{
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// MAX_BLEPS configures how many BLEPs (volume steps) are being kept track of per channel,
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// and thus directly influences how much memory this feature wastes per virtual channel.
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// Paula::BLEP_SIZE / Paula::MINIMUM_INTERVAL would be a safe maximum,
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// but even a sample (alternating at +1/-1, thus causing a step on every frame) played at 200 kHz,
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// which is way out of spec for the Amiga, will only get close to 128 active BLEPs with Paula::MINIMUM_INTERVAL == 4.
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// Hence 128 is chosen as a tradeoff between quality and memory consumption.
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static constexpr uint16 MAX_BLEPS = 128;
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struct Blep
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{
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int16 level;
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uint16 age;
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};
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public:
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SamplePosition remainder, stepRemainder;
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int numSteps; // Number of full-length steps
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private:
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uint16 activeBleps = 0, firstBlep = 0; // Count of simultaneous bleps to keep track of
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int16 globalOutputLevel = 0; // The instantenous value of Paula output
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Blep blepState[MAX_BLEPS];
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public:
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State(uint32 sampleRate = 48000);
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void Reset();
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void InputSample(int16 sample);
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int OutputSample(const BlepArray &WinSincIntegral);
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void Clock(int cycles);
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};
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}
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OPENMPT_NAMESPACE_END
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