Implement audio pause control

examples/audio.cpp

@@ -8,6 +8,7 @@
 #include <psemek/audio/effect/fade_in.hpp>
 #include <psemek/audio/effect/fade_out.hpp>
 #include <psemek/audio/effect/compressor.hpp>
+#include <psemek/audio/effect/pause.hpp>
 #include <psemek/audio/duplicate.hpp>
 #include <psemek/audio/stereo.hpp>
 #include <psemek/audio/mixer.hpp>
@@ -69,7 +70,9 @@ struct audio_app
 	{
 		mixer_ = audio::make_mixer();
 		volume_control_ = audio::volume_stereo(mixer_, 0.5f, 0.5f, 0.1f);
-		engine_.output()->stream(audio::compressor(volume_control_, audio::from_db(-2.f), 0.95f, 0.002f, 1.f, audio::from_db(1.f)));
+		auto compressor = audio::compressor(volume_control_, audio::from_db(-2.f), 0.95f, 0.002f, 1.f, audio::from_db(1.f));
+		pause_control_ = audio::pause(compressor, false, 0.01f);
+		engine_.output()->stream(pause_control_);
 	}
 
 	void on_key_down(SDL_Keycode key) override
@@ -80,7 +83,12 @@ struct audio_app
 		{
 			int midi = key_to_midi.at(key);
 			auto tone = audio::sine_wave(440.f * std::pow(2.f, (midi - 69) / 12.f));
-			channels_[key] = mixer_->add(audio::fade_in(tone, 0.01f));
+			channels_[key] = mixer_->add(audio::fade_in(tone, 0.002f));
+		}
+
+		if (key == SDLK_SPACE)
+		{
+			pause_control_->paused(!pause_control_->paused());
 		}
 	}
 
@@ -131,6 +139,7 @@ private:
 	audio::engine engine_;
 	audio::mixer_ptr mixer_;
 	std::shared_ptr<audio::volume_control_stereo> volume_control_;
+	std::shared_ptr<audio::pause_control> pause_control_;
 	std::map<SDL_Keycode, audio::channel_ptr> channels_;
 
 	util::clock<> clock_;

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

@@ -0,0 +1,21 @@
+#pragma once
+
+#include <psemek/audio/stream.hpp>
+#include <psemek/audio/duration.hpp>
+
+namespace psemek::audio
+{
+
+	struct pause_control
+		: stream
+	{
+		virtual bool paused() const = 0;
+		virtual bool paused(bool value) = 0;
+
+		virtual void pause() { paused(true); }
+		virtual void resume() { paused(false); }
+	};
+
+	std::shared_ptr<pause_control> pause(stream_ptr stream, bool paused = false, duration length = 0.01f);
+
+}

libs/audio/source/effect/pause.cpp

@@ -0,0 +1,95 @@
+#include <psemek/audio/effect/pause.hpp>
+#include <psemek/audio/smooth.hpp>
+
+#include <atomic>
+
+namespace psemek::audio
+{
+
+	namespace
+	{
+
+		struct pause_control_impl
+			: pause_control
+		{
+			pause_control_impl(stream_ptr stream,  bool paused, duration length)
+				: stream_(std::move(stream))
+				, paused_{paused}
+				, length_(length)
+				, level_(paused ? 0 : length_.samples())
+			{}
+
+			bool paused() const override
+			{
+				return paused_.load();
+			}
+
+			bool paused(bool value) override
+			{
+				return paused_.exchange(value);
+			}
+
+			std::optional<std::size_t> length() const override
+			{
+				return stream_->length();
+			}
+
+			std::size_t read(float * data, std::size_t sample_count) override
+			{
+				bool const paused = paused_.load();
+
+				if (paused)
+				{
+					auto result = stream_->read(data, std::min(sample_count, level_));
+
+					for (std::size_t i = 0; i < result; i += 2)
+					{
+						float gain = static_cast<float>(level_) / length_.samples();
+						data[i + 0] *= gain;
+						data[i + 1] *= gain;
+						level_ -= 2;
+					}
+
+					std::fill(data + result, data + sample_count, 0.f);
+					return sample_count;
+				}
+				else
+				{
+					auto result = stream_->read(data, sample_count);
+
+					auto const max_level = static_cast<std::size_t>(length_.samples());
+
+					for (std::size_t i = 0; i < result; i += 2)
+					{
+						float gain = static_cast<float>(level_) / max_level;
+						data[i + 0] *= gain;
+						data[i + 1] *= gain;
+
+						if (level_ < max_level)
+							level_ += 2;
+					}
+
+					return result;
+				}
+			}
+
+			std::size_t played() const override
+			{
+				return stream_->played();
+			}
+
+		private:
+			stream_ptr stream_;
+			std::atomic<bool> paused_;
+			duration length_;
+			std::size_t level_;
+		};
+
+	}
+
+	std::shared_ptr<pause_control> pause(stream_ptr stream,  bool paused, duration length)
+	{
+		return std::make_shared<pause_control_impl>(std::move(stream), paused, length);
+	}
+
+}