Add volume control effect

examples/audio.cpp

@@ -3,6 +3,7 @@
 #include <psemek/audio/wave/sawtooth.hpp>
 #include <psemek/audio/wave/square.hpp>
 #include <psemek/audio/wave/triangle.hpp>
+#include <psemek/audio/effect/volume.hpp>
 #include <psemek/audio/mixer.hpp>
 #include <psemek/app/app.hpp>
 #include <psemek/app/main.hpp>
@@ -34,6 +35,17 @@ struct audio_app
 	{
 		mixer_ = audio::make_mixer();
 		engine_.output(mixer_);
+
+		auto volume = audio::volume(audio::sine_wave(440.f), 1.f, 0.01f);
+		auto channel = mixer_->add(volume);
+		std::this_thread::sleep_for(std::chrono::seconds{1});
+		volume->gain(0.5f);
+		std::this_thread::sleep_for(std::chrono::seconds{1});
+		volume->gain(0.25f);
+		std::this_thread::sleep_for(std::chrono::seconds{1});
+		volume->gain(0.125f);
+		std::this_thread::sleep_for(std::chrono::seconds{1});
+		channel->stop();
 	}
 
 	void on_key_down(SDL_Keycode key) override
@@ -43,7 +55,8 @@ struct audio_app
 		if (key_to_midi.contains(key) && !channels_.contains(key))
 		{
 			int midi = key_to_midi.at(key);
-			channels_[key] = mixer_->add(audio::sine_wave(440.f * std::pow(2.f, (midi - 69) / 12.f)));
+			auto tone = audio::sine_wave(440.f * std::pow(2.f, (midi - 69) / 12.f));
+			channels_[key] = mixer_->add(audio::volume(tone, 0.5f));
 		}
 	}
 

libs/audio/include/psemek/audio/attack.hpp

@@ -0,0 +1,30 @@
+#pragma once
+
+#include <psemek/audio/constants.hpp>
+
+#include <cmath>
+
+namespace psemek::audio
+{
+
+	inline float attack_to_multiplier(float attack)
+	{
+		if (attack == 0.f)
+			return 1.f;
+		return - std::expm1(- inv_frequency / attack);
+	}
+
+	inline float multiplier_to_attack(float multiplier)
+	{
+		if (multiplier == 1.f)
+			return 0.f;
+
+		return - inv_frequency / std::log1p(- multiplier);
+	}
+
+	inline void attack_update(float & value, float target_value, float multiplier)
+	{
+		value += (target_value - value) * multiplier;
+	}
+
+}

libs/audio/include/psemek/audio/effect/volume.hpp

@@ -0,0 +1,20 @@
+#pragma once
+
+#include <psemek/audio/stream.hpp>
+
+namespace psemek::audio
+{
+
+	struct volume_control
+		: stream
+	{
+		virtual float gain() const = 0;
+		virtual float gain(float value) = 0;
+
+		virtual float attack() const = 0;
+		virtual float attack(float value) = 0;
+	};
+
+	std::shared_ptr<volume_control> volume(stream_ptr stream, float gain = 1.f, float attack = 0.f);
+
+}

libs/audio/include/psemek/audio/effect/volume_base.hpp

@@ -0,0 +1,30 @@
+#pragma once
+
+#include <psemek/audio/stream.hpp>
+
+#include <atomic>
+
+namespace psemek::audio
+{
+
+	struct volume_base
+	{
+		volume_base(float gain, float attack);
+
+		float gain() const { return gain_.load(); }
+		float gain(float value) { return gain_.exchange(value); }
+
+		float attack() const;
+		float attack(float value);
+
+		void apply(float * data, std::size_t sample_count);
+
+	private:
+		std::atomic<float> gain_;
+		std::atomic<float> attack_multiplier_;
+		float real_gain_;
+		float last_sample_src_[2];
+		float last_sample_tgt_[2];
+	};
+
+}

libs/audio/source/effect/volume.cpp

@@ -0,0 +1,43 @@
+#include <psemek/audio/effect/volume.hpp>
+#include <psemek/audio/effect/volume_base.hpp>
+
+namespace psemek::audio
+{
+
+	namespace
+	{
+
+		struct volume_control_impl
+			: volume_control
+		{
+			volume_control_impl(stream_ptr stream, float gain, float attack)
+				: base_(gain, attack)
+				, stream_(std::move(stream))
+			{}
+
+			float gain() const override { return base_.gain(); }
+			float gain(float value) override { return base_.gain(value); }
+
+			float attack() const override { return base_.attack(); }
+			float attack(float value) override { return base_.attack(value); }
+
+			std::size_t read(float * data, std::size_t sample_count) override
+			{
+				auto result = stream_->read(data, sample_count);
+				base_.apply(data, result);
+				return result;
+			}
+
+		private:
+			volume_base base_;
+			stream_ptr stream_;
+		};
+
+	}
+
+	std::shared_ptr<volume_control> volume(stream_ptr stream, float gain, float attack)
+	{
+		return std::make_shared<volume_control_impl>(std::move(stream), gain, attack);
+	}
+
+}

libs/audio/source/effect/volume_base.cpp

@@ -0,0 +1,52 @@
+#include <psemek/audio/effect/volume_base.hpp>
+#include <psemek/audio/constants.hpp>
+#include <psemek/audio/attack.hpp>
+
+#include <cmath>
+
+namespace psemek::audio
+{
+
+	volume_base::volume_base(float gain, float attack)
+		: gain_{gain}
+		, attack_multiplier_{attack_to_multiplier(attack)}
+		, real_gain_{gain}
+		, last_sample_src_{0.f, 0.f}
+		, last_sample_tgt_{0.f, 0.f}
+	{}
+
+	float volume_base::attack() const
+	{
+		return multiplier_to_attack(attack_multiplier_.load());
+	}
+
+	float volume_base::attack(float value)
+	{
+		auto old = attack_multiplier_.exchange(attack_to_multiplier(value));
+		return multiplier_to_attack(old);
+	}
+
+	void volume_base::apply(float * data, std::size_t sample_count)
+	{
+		float gain = gain_.load();
+		float attack_multiplier = attack_multiplier_.load();
+
+		auto apply_impl = [this](float & target, float & last_src, float & last_tgt)
+		{
+			auto old = target;
+			target = last_tgt + (old - last_src) * real_gain_;
+			last_src = old;
+			last_tgt = target;
+		};
+
+		auto end = data + sample_count;
+		for (auto p = data; p < end;)
+		{
+			apply_impl(*p++, last_sample_src_[0], last_sample_tgt_[0]);
+			apply_impl(*p++, last_sample_src_[1], last_sample_tgt_[1]);
+
+			attack_update(real_gain_, gain, attack_multiplier);
+		}
+	}
+
+}