CLK/Components/OPL2/Implementation/Channel.cpp

//
//  Channel.cpp
//  Clock Signal
//
//  Created by Thomas Harte on 15/04/2020.
//  Copyright © 2020 Thomas Harte. All rights reserved.
//

#include "Channel.hpp"

using namespace Yamaha::OPL;

void Channel::set_frequency_low(uint8_t value) {
	period_ = (period_ &~0xff) | value;
}

void Channel::set_10bit_frequency_octave_key_on(uint8_t value) {
	period_ = (period_ & 0xff) | ((value & 3) << 8);
	octave_ = (value >> 2) & 0x7;
	key_on_ = value & 0x20;
	frequency_shift_ = 0;
}

void Channel::set_9bit_frequency_octave_key_on(uint8_t value) {
	period_ = (period_ & 0xff) | ((value & 1) << 8);
	octave_ = (value >> 1) & 0x7;
	key_on_ = value & 0x10;;
	frequency_shift_ = 1;
}

void Channel::set_feedback_mode(uint8_t value) {
	feedback_strength_ = (value >> 1) & 0x7;
	use_fm_synthesis_ = value & 1;
}

int Channel::update(Operator *modulator, Operator *carrier, OperatorOverrides *modulator_overrides, OperatorOverrides *carrier_overrides) {
	modulator->update(modulator_state_, key_on_, period_ << frequency_shift_, octave_, modulator_overrides);
	carrier->update(carrier_state_, key_on_, period_ << frequency_shift_, octave_, carrier_overrides);

	// TODO: almost everything. This is a quick test.
	// Specifically: use lookup tables.
	const auto modulator_level = level(modulator_state_, 0.0f);	// TODO: what's the proper scaling on this?
	return int(level(carrier_state_, modulator_level) * 20'000.0f);
}

bool Channel::is_audible(Operator *carrier, OperatorOverrides *carrier_overrides) {
	return carrier->is_audible(carrier_state_, carrier_overrides);
}

float Channel::level(OperatorState &state, float modulator_level) {
	const float phase = modulator_level + float(state.phase) / 1024.0f;
	const float phase_attenuation = logf(1.0f + sinf(float(M_PI) * 2.0f * phase));
	const float total_attenuation = phase_attenuation + float(state.attenuation) / 1023.0f;
	const float result = expf(total_attenuation / 2.0f);

	return result;
}