Add simple echo effect

libs/audio/include/psemek/audio/echo.hpp

@@ -0,0 +1,12 @@
+#pragma once
+
+#include <psemek/audio/effect.hpp>
+
+#include <memory>
+
+namespace psemek::audio
+{
+
+	std::shared_ptr<effect> echo(float delay, float volume);
+
+}

libs/audio/include/psemek/audio/utils.hpp

@@ -0,0 +1,18 @@
+#pragma once
+
+#include <cmath>
+#include <limits>
+#include <cstdint>
+
+namespace psemek::audio
+{
+
+	inline std::int16_t clamp(float v)
+	{
+		static auto const min = std::numeric_limits<std::int16_t>::min();
+		static auto const max = std::numeric_limits<std::int16_t>::max();
+
+		return static_cast<std::int16_t>(std::min<int>(max, std::max<int>(min, std::round(v))));
+	}
+
+}

libs/audio/source/echo.cpp

@@ -0,0 +1,68 @@
+#include <psemek/audio/echo.hpp>
+#include <psemek/audio/engine.hpp>
+#include <psemek/audio/utils.hpp>
+
+#include <cmath>
+#include <vector>
+
+namespace psemek::audio
+{
+
+	namespace
+	{
+
+		struct echo_impl
+			: audio::effect
+		{
+			echo_impl(float delay, float volume)
+				: volume_(volume)
+			{
+				int sample_count = std::round(delay * audio::engine::frequency * audio::engine::channels);
+				samples_.reserve(sample_count);
+			}
+
+			std::string_view name() const override
+			{
+				return "echo";
+			}
+
+			void operator()(std::int16_t * data, std::size_t size) override
+			{
+				if (samples_.size() < samples_.capacity())
+				{
+					auto count = std::min(samples_.capacity() - samples_.size(), size);
+					std::copy(data, data + count, std::back_inserter(samples_));
+					pos_ += count;
+					data += count;
+					size -= count;
+
+					if (pos_ == samples_.capacity())
+						pos_ = 0;
+				}
+
+				for (; size > 0; ++data, --size)
+				{
+					float s = clamp((*data) + samples_[pos_] * volume_);
+					samples_[pos_] = *data;
+					*data = s;
+
+					++pos_;
+					if (pos_ == samples_.capacity())
+						pos_ = 0;
+				}
+			}
+
+		private:
+			std::vector<std::int16_t> samples_;
+			std::size_t pos_ = 0;
+			float volume_;
+		};
+
+	}
+
+	std::shared_ptr<effect> echo(float delay, float volume)
+	{
+		return std::make_shared<echo_impl>(delay, volume);
+	}
+
+}