CLK/Components/OPx/Implementation/WaveformGenerator.hpp

//
//  WaveformGenerator.hpp
//  Clock Signal
//
//  Created by Thomas Harte on 03/05/2020.
//  Copyright © 2020 Thomas Harte. All rights reserved.
//

#pragma once

#include "Tables.hpp"
#include "LowFrequencyOscillator.hpp"

namespace Yamaha::OPL {

enum class Waveform {
	Sine, HalfSine, AbsSine, PulseSine
};

template <int phase_precision> class WaveformGenerator {
public:
	/*!
		@returns The output of waveform @c form at [integral] phase @c phase.
	*/
	static constexpr LogSign wave(Waveform form, int phase) {
		constexpr int waveforms[4][4] = {
			{1023, 1023, 1023, 1023},	// Sine: don't mask in any quadrant.
			{511, 511, 0, 0},			// Half sine: keep the first half intact, lock to 0 in the second half.
			{511, 511, 511, 511},		// AbsSine: endlessly repeat the first half of the sine wave.
			{255, 0, 255, 0},			// PulseSine: act as if the first quadrant is in the first and third; lock the other two to 0.
		};
		return negative_log_sin(phase & waveforms[int(form)][(phase >> 8) & 3]);
	}

	/*!
		@returns The output of waveform @c form at [scaled] phase @c scaled_phase given the modulation input @c modulation.
	*/
	static constexpr LogSign wave(const Waveform form, const int scaled_phase, const LogSign modulation) {
		const int scaled_phase_offset = modulation.level(phase_precision);
		const int phase = (scaled_phase + scaled_phase_offset) >> phase_precision;
		return wave(form, phase);
	}

	/*!
		@returns Snare output, calculated from the current LFSR state as captured in @c oscillator and an operator's phase.
	*/
	static constexpr LogSign snare(const LowFrequencyOscillator &oscillator, const int phase) {
		// If noise is 0, output is positive.
		// If noise is 1, output is negative.
		// If (noise ^ sign) is 0, output is 0. Otherwise it is max.
		const int sign = phase & 0x200;
		const int level = ((phase >> 9) & 1) ^ oscillator.lfsr;
		return negative_log_sin(sign + (level << 8));
	}

	/*!
		@returns Cymbal output, calculated from an operator's phase and a modulator's phase.
	*/
	static constexpr LogSign cymbal(const int carrier_phase, const int modulator_phase) {
		return negative_log_sin(256 + (phase_combination(carrier_phase, modulator_phase) << 9));
	}

	/*!
		@returns High-hat output, calculated from the current LFSR state as captured in @c oscillator, an operator's phase and a modulator's phase.
	*/
	static constexpr LogSign high_hat(
		const LowFrequencyOscillator &oscillator,
		const int carrier_phase,
		const int modulator_phase
	) {
		constexpr int angles[] = {0x234, 0xd0, 0x2d0, 0x34};
		return negative_log_sin(angles[
			phase_combination(carrier_phase, modulator_phase) |
			(oscillator.lfsr << 1)
		]);
	}

private:
	/*!
		@returns The phase bit used for cymbal and high-hat generation, which is a function of two operators' phases.
	*/
	static constexpr int phase_combination(const int carrier_phase, const int modulator_phase) {
		return (
			((carrier_phase >> 5) ^ (carrier_phase >> 3)) &
			((modulator_phase >> 7) ^ (modulator_phase >> 2)) &
			((carrier_phase >> 5) ^ (modulator_phase >> 3))
		) & 1;
	}
};

}