Initial community commit

Src/external_dependencies/openmpt-trunk/soundlib/Paula.h

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