FluidSim/Program.cs

using SFML.Graphics;
using SFML.Window;
using SFML.System;
using System.Diagnostics;
using FluidSim.Core;

namespace FluidSim;

public class Program
{
    private const int SampleRate = 44100;
    private const double DrawFrequency = 60.0;
    private static Scenario scenario;

    // Speed control
    //private static double desiredSpeed = 1.0;
    private static double desiredSpeed = 0.0001;
    private static double currentSpeed = desiredSpeed;
    private const double MinSpeed = 0.0001;
    private const double MaxSpeed = 1.0;
    private const double ScrollFactor = 1.1;

    // Space‑toggle state
    private static double lastDesiredSpeed = 0.1;   // remembers the last non‑1.0 scroll speed
    private static bool isRealTime = true;          // true when desiredSpeed == 1.0

    private static volatile bool running = true;

    public static void Main()
    {
        var mode = new VideoMode(new Vector2u(1280, 720));
        var window = new RenderWindow(mode, "Pipe Resonator");
        window.SetVerticalSyncEnabled(true);
        window.Closed += (_, _) => { running = false; window.Close(); };
        window.MouseWheelScrolled += OnMouseWheel;
        window.KeyPressed += OnKeyPressed;

        var soundEngine = new SoundEngine(bufferCapacity: 16384);
        soundEngine.Volume = 70;
        soundEngine.Start();

        //scenario = new PipeResonatorScenario();
        //scenario = new HelmholtzResonatorScenario();
        scenario = new SodShockTubeScenario();

        scenario.Initialize(SampleRate);

        var stopwatch = Stopwatch.StartNew();
        double lastDrawTime = 0.0;
        double drawInterval = 1.0 / DrawFrequency;
        double lastSpeedUpdateTime = stopwatch.Elapsed.TotalSeconds;

        // Resampling buffer
        List<float> simBuffer = new List<float>(4096);
        double readIndex = 0.0;

        for (int i = 0; i < 4; i++)
            simBuffer.Add(scenario.Process());

        long totalSimSteps = simBuffer.Count;
        long totalOutputSamples = 0;

        double lastRealTime = stopwatch.Elapsed.TotalSeconds;
        const int outputChunk = 256;
        float[] outputBuf = new float[outputChunk];

        while (window.IsOpen)
        {
            window.DispatchEvents();

            double currentRealTime = stopwatch.Elapsed.TotalSeconds;
            double dtSpeed = currentRealTime - lastSpeedUpdateTime;
            lastSpeedUpdateTime = currentRealTime;

            // Smoothly transition currentSpeed → desiredSpeed
            // When toggling, desiredSpeed jumps, but currentSpeed follows with a smooth lerp
            double smoothingRate = 8.0;   // higher = faster catch‑up
            currentSpeed += (desiredSpeed - currentSpeed) * (1.0 - Math.Exp(-smoothingRate * dtSpeed));

            // ---------- Generate audio ----------
            double targetAudioClock = currentRealTime + 0.05;

            while (totalOutputSamples < targetAudioClock * SampleRate && running)
            {
                int toGenerate = (int)Math.Min(
                    (long)outputChunk,
                    (long)(targetAudioClock * SampleRate) - totalOutputSamples
                );
                if (toGenerate <= 0) break;

                double maxIndex = readIndex + (toGenerate - 1) * currentSpeed + 2;
                int requiredSimIndex = (int)Math.Ceiling(maxIndex);
                while (simBuffer.Count - 1 < requiredSimIndex)
                {
                    simBuffer.Add(scenario.Process());
                    totalSimSteps++;
                }

                for (int i = 0; i < toGenerate; i++)
                {
                    int i0 = (int)readIndex;
                    int i1 = i0 + 1;
                    double frac = readIndex - i0;

                    float y0 = simBuffer[Math.Clamp(i0, 0, simBuffer.Count - 1)];
                    float y1 = simBuffer[Math.Clamp(i1, 0, simBuffer.Count - 1)];
                    outputBuf[i] = (float)(y0 + (y1 - y0) * frac);

                    readIndex += currentSpeed;

                    while (readIndex >= 1.0 && simBuffer.Count > 2)
                    {
                        simBuffer.RemoveAt(0);
                        readIndex -= 1.0;
                    }
                }

                int accepted = soundEngine.WriteSamples(outputBuf, toGenerate);
                totalOutputSamples += accepted;

                if (accepted < toGenerate)
                    break;
            }

            // ---------- Drawing & title ----------
            if (currentRealTime - lastDrawTime >= drawInterval)
            {
                double actualSpeed = totalOutputSamples / (currentRealTime * SampleRate);
                double simTime = totalSimSteps / (double)SampleRate;
                string toggleHint = isRealTime ? "[Space] slow mo" : "[Space] real time";
                window.SetTitle(
                    $"{toggleHint}  Sim: {simTime:F2}s | " +
                    $"Speed: {currentSpeed:F4}x → {desiredSpeed:F4}x | " +
                    $"Actual: {actualSpeed:F2}x"
                );

                window.Clear(Color.Black);
                scenario.Draw(window);
                window.Display();
                lastDrawTime = currentRealTime;
            }
        }

        soundEngine.Dispose();
        window.Dispose();
    }

    private static void OnMouseWheel(object? sender, MouseWheelScrollEventArgs e)
    {
        bool wasRealTime = Math.Abs(desiredSpeed - 1.0) < 1e-6;

        if (e.Delta > 0)
            desiredSpeed *= ScrollFactor;
        else if (e.Delta < 0)
            desiredSpeed /= ScrollFactor;

        desiredSpeed = Math.Clamp(desiredSpeed, MinSpeed, MaxSpeed);

        // Update the remembered slow-mo speed (unless we are exactly at 1.0)
        if (!wasRealTime || Math.Abs(desiredSpeed - 1.0) > 1e-6)
            lastDesiredSpeed = desiredSpeed;

        // Update isRealTime flag
        isRealTime = Math.Abs(desiredSpeed - 1.0) < 1e-6;
    }

    private static void OnKeyPressed(object? sender, KeyEventArgs e)
    {
        if (e.Code == Keyboard.Key.Space)
        {
            if (isRealTime)
            {
                // Switch to the remembered slow speed
                desiredSpeed = lastDesiredSpeed;
            }
            else
            {
                // Switch back to real time
                desiredSpeed = 1.0;
            }
            isRealTime = !isRealTime;
        }
    }
}