Port FluidSim core and scenarios to C++20

include/FluidSim/TwoStrokeScenario.hpp

@@ -0,0 +1,53 @@
+#pragma once
+
+#include "FluidSim/AudioProcessing.hpp"
+#include "FluidSim/Crankcase.hpp"
+#include "FluidSim/Fluid.hpp"
+#include "FluidSim/OutdoorExhaustReverb.hpp"
+#include "FluidSim/Solver.hpp"
+#include "FluidSim/TwoStrokeCylinder.hpp"
+#include <cstdint>
+#include <vector>
+
+namespace fluidsim::port {
+
+struct TwoStrokeSnapshot {
+    float rpm{}, cylinder_pressure{}, crankcase_pressure{}, intake_pressure{};
+    float throttle{}, transfer_area{}, exhaust_area{};
+    bool reed_open{};
+};
+
+// Port of the C# 125 cc crankcase-scavenged two-stroke scenario. It retains
+// the plenum / reed / crankcase / transfer / cylinder / exhaust topology.
+class TwoStrokeScenario {
+public:
+    explicit TwoStrokeScenario(int sample_rate = 44100);
+    AudioFrame process();
+    void set_throttle(float value);
+    TwoStrokeSnapshot snapshot() const;
+
+    float throttle{};
+    Crankshaft crankshaft{};
+    TwoStrokeCylinder cylinder;
+    Crankcase crankcase;
+    Volume0D intake_plenum{0.5e-3f, 101325.0f, 300.0f};
+    std::vector<Pipe1D> pipes;
+
+private:
+    float dt_{}, max_throttle_area_{};
+    float reed_in_area_{}, reed_out_area_{}, transfer_pipe_area_{}, transfer_valve_area_{}, exhaust_valve_area_{};
+    bool reed_open_{};
+    std::uint64_t step_count_{};
+    Port* plenum_inlet_{};
+    Port* plenum_outlet_{};
+    BoundarySystem boundaries_;
+    Solver solver_;
+    SoundProcessor intake_sound_;
+    SoundProcessor exhaust_sound_;
+    OutdoorExhaustReverb reverb_;
+
+    static float area_for_diameter(float diameter);
+    static std::vector<Pipe1D> create_pipes();
+};
+
+} // namespace fluidsim::port