Port FluidSim core and scenarios to C++20

include/FluidSim/AudioOutputStream.hpp

@@ -0,0 +1,30 @@
+#pragma once
+
+#include "FluidSim/SimulationRingBuffer.hpp"
+#include <SFML/Audio/SoundStream.hpp>
+#include <array>
+#include <atomic>
+#include <cstdint>
+
+namespace fluidsim::port {
+
+class AudioOutputStream final : public sf::SoundStream {
+public:
+    explicit AudioOutputStream(SimulationRingBuffer& ring, unsigned int sample_rate = 44100);
+    void set_speed(double speed) { speed_.store(speed, std::memory_order_relaxed); }
+    double speed() const { return speed_.load(std::memory_order_relaxed); }
+
+private:
+    static constexpr std::size_t block_size = 512;
+    SimulationRingBuffer& ring_;
+    std::array<float, block_size> temp_left_{}, temp_right_{};
+    std::array<std::int16_t, block_size * 2> output_{};
+    std::atomic<double> speed_{1.0};
+    float previous_input_left_{}, previous_output_left_{};
+    float previous_input_right_{}, previous_output_right_{};
+
+    bool onGetData(Chunk& data) override;
+    void onSeek(sf::Time time_offset) override;
+};
+
+} // namespace fluidsim::port