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114 lines
3.1 KiB
C++
114 lines
3.1 KiB
C++
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//
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// EnvelopeGenerator.hpp
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// Clock Signal
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//
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// Created by Thomas Harte on 01/05/2020.
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// Copyright © 2020 Thomas Harte. All rights reserved.
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//
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#ifndef EnvelopeGenerator_h
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#define EnvelopeGenerator_h
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#include <optional>
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#include <functional>
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namespace Yamaha {
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namespace OPL {
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/*!
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Models an OPL-style envelope generator.
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Damping is optional; if damping is enabled then if there is a transition to key-on while
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attenuation is less than maximum then attenuation will be quickly transitioned to maximum
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before the attack phase can begin.
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in real hardware damping is used by the envelope generators associated with
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carriers, with phases being reset upon the transition from damping to attack.
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This code considers application of tremolo to be a function of the envelope generator;
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this is largely for logical conformity with the phase generator that necessarily has to
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apply vibrato.
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*/
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template <int precision> class EnvelopeGenerator {
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public:
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/*!
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Advances the envelope generator a single step, given the current state of the low-frequency oscillator, @c oscillator.
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*/
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void update(const LowFrequencyOscillator &oscillator);
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/*!
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@returns The current attenuation from this envelope generator.
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*/
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int attenuation() const;
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/*!
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Enables or disables damping on this envelope generator. If damping is enabled then this envelope generator will
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use the damping phase when necessary (i.e. when transitioning to key on if attenuation is not already at maximum)
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and in any case will call @c will_attack before transitioning from any other state to attack.
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@param will_attack Supply a will_attack callback to enable damping mode; supply nullopt to disable damping mode.
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*/
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void set_should_damp(const std::optional<std::function<void(void)>> &will_attack);
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/*!
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Sets the current state of the key-on input.
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*/
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void set_key_on(bool);
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/*!
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Sets the attack rate, which should be in the range 0–15.
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*/
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void set_attack_rate(int);
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/*!
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Sets the decay rate, which should be in the range 0–15.
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*/
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void set_decay_rate(int);
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/*!
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Sets the release rate, which should be in the range 0–15.
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*/
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void set_release_rate(int);
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/*!
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Sets the sustain level, which should be in the range 0–15.
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*/
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void set_sustain_level(int);
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/*!
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Enables or disables use of the sustain level. If this is disabled, the envelope proceeds
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directly from decay to release.
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*/
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void set_use_sustain_level(bool);
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/*!
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Enables or disables key-rate scaling.
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*/
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void set_key_rate_scaling_enabled(bool enabled);
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/*!
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Enables or disables application of the low-frequency oscillator's tremolo.
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*/
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void set_tremolo_enabled(bool enabled);
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/*!
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Sets the current period associated with the channel that owns this envelope generator;
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this is used to select a key scaling rate if key-rate scaling is enabled.
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*/
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void set_period(int period, int octave);
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private:
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enum class ADSRPhase {
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Attack, Decay, Sustain, Release, Damp
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} adsr_phase_ = ADSRPhase::Attack;
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int adsr_attenuation_ = 511;
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bool key_on_ = false;
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std::optional<std::function<void(void)>> will_attack_;
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};
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}
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}
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#endif /* EnvelopeGenerator_h */
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