Add fade in & fade out effects

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

@@ -0,0 +1,10 @@
+#pragma once
+
+#include <psemek/audio/stream.hpp>
+
+namespace psemek::audio
+{
+
+	stream_ptr fade_in(stream_ptr stream, float length, float start = 0.f);
+
+}

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

@@ -0,0 +1,10 @@
+#pragma once
+
+#include <psemek/audio/stream.hpp>
+
+namespace psemek::audio
+{
+
+	stream_ptr fade_out(stream_ptr stream, float length, float start = 0.f);
+
+}

libs/audio/source/effect/fade_in.cpp

@@ -0,0 +1,61 @@
+#include <psemek/audio/effect/fade_in.hpp>
+#include <psemek/audio/constants.hpp>
+
+#include <cmath>
+
+namespace psemek::audio
+{
+
+	namespace
+	{
+
+		struct fade_in_impl
+			: stream
+		{
+			fade_in_impl(stream_ptr stream, float length, float start)
+				: stream_(std::move(stream))
+				, length_(2 * std::round(length * frequency))
+				, start_samples_(2 * std::round(start * frequency))
+			{}
+
+			std::size_t read(float * data, std::size_t sample_count) override
+			{
+				auto const result = stream_->read(data, sample_count);
+				std::fill(data, data + std::min(result, start_samples_), 0.f);
+
+				if (result <= start_samples_)
+				{
+					start_samples_ -= result;
+				}
+				else
+				{
+					for (std::size_t i = start_samples_; i < result; i += 2)
+					{
+						float m = static_cast<float>(std::min(current_, length_)) / length_;
+
+						data[i + 0] *= m;
+						data[i + 1] *= m;
+
+						current_ += 2;
+					}
+					start_samples_ = 0;
+				}
+
+				return result;
+			}
+
+		private:
+			stream_ptr stream_;
+			std::size_t length_;
+			std::size_t current_ = 0;
+			std::size_t start_samples_;
+		};
+
+	}
+
+	stream_ptr fade_in(stream_ptr stream, float length, float start)
+	{
+		return std::make_shared<fade_in_impl>(std::move(stream), length, start);
+	}
+
+}

libs/audio/source/effect/fade_out.cpp

@@ -0,0 +1,63 @@
+#include <psemek/audio/effect/fade_out.hpp>
+#include <psemek/audio/constants.hpp>
+
+#include <cmath>
+
+namespace psemek::audio
+{
+
+	namespace
+	{
+
+		struct fade_out_impl
+			: stream
+		{
+			fade_out_impl(stream_ptr stream, float length, float start)
+				: stream_(std::move(stream))
+				, length_(2 * std::round(length * frequency))
+				, start_samples_(2 * std::round(start * frequency))
+			{}
+
+			std::size_t read(float * data, std::size_t sample_count) override
+			{
+				if (current_ >= length_)
+					return 0;
+
+				auto result = stream_->read(data, sample_count);
+
+				if (result <= start_samples_)
+				{
+					start_samples_ -= result;
+				}
+				else
+				{
+					for (std::size_t i = start_samples_; i < result; i += 2)
+					{
+						float m = static_cast<float>(length_ - std::min(current_, length_)) / length_;
+
+						data[i + 0] *= m;
+						data[i + 1] *= m;
+
+						current_ += 2;
+					}
+					start_samples_ = 0;
+				}
+
+				return result;
+			}
+
+		private:
+			stream_ptr stream_;
+			std::size_t length_;
+			std::size_t current_ = 0;
+			std::size_t start_samples_;
+		};
+
+	}
+
+	stream_ptr fade_out(stream_ptr stream, float length, float start)
+	{
+		return std::make_shared<fade_out_impl>(std::move(stream), length, start);
+	}
+
+}