Project-M/Assets/_Project/Scripts/Client/Presentation/AmbientAudioSystem.cs

using ProjectM.Simulation;
using Unity.Entities;
using Unity.NetCode;
using UnityEngine;

namespace ProjectM.Client
{
    /// <summary>
    /// Client-only AMBIENT audio + cycle-phase stingers. A managed presentation <see cref="SystemBase"/>
    /// (<see cref="PresentationSystemGroup"/>, main thread, no Burst) that OBSERVES the replicated
    /// <see cref="CycleState"/> and never touches the simulation. On start it plays a low, seamless-looping
    /// procedural drone (asset-free, <c>AudioClip.Create</c> like <c>CombatFeedbackSystem.MakeClip</c>); each
    /// time the cycle phase changes it plays a short procedural stinger and eases the drone's intensity by phase
    /// (calmer at base, tenser during Defend / "wave incoming"). Lives only in the client world, so the server
    /// never creates audio and nothing here affects determinism. Volumes are deliberately conservative + tunable.
    /// </summary>
    [WorldSystemFilter(WorldSystemFilterFlags.ClientSimulation)]
    [UpdateInGroup(typeof(PresentationSystemGroup))]
    public partial class AmbientAudioSystem : SystemBase
    {
        AudioSource _ambient;
        AudioClip _ambientClip;
        AudioClip _stingExpedition;
        AudioClip _stingDefend;
        AudioClip _stingBuild;
        GameObject _root;

        byte _lastPhase;
        bool _phaseInit;

        const float AmbientBaseVolume = 0.10f; // low bed; Defend eases up to ~1.7x

        protected override void OnCreate()
        {
            _ambientClip = MakeDrone();
            _stingExpedition = MakeSting(520f, 880f, 0.45f, 0.30f); // airy rising "deploy"
            _stingDefend = MakeSting(300f, 140f, 0.55f, 0.42f);     // tense falling "wave incoming"
            _stingBuild = MakeSting(440f, 660f, 0.40f, 0.26f);      // soft confirm
        }

        protected override void OnStartRunning()
        {
            if (_root != null) return;
            _root = new GameObject("~AmbientAudio");
            _ambient = _root.AddComponent<AudioSource>();
            _ambient.clip = _ambientClip;
            _ambient.loop = true;
            _ambient.playOnAwake = false;
            _ambient.spatialBlend = 0f; // 2D bed
            _ambient.volume = AmbientBaseVolume * GameVolume.Music;
            _ambient.Play();
        }

        protected override void OnDestroy()
        {
            if (_root != null) Object.Destroy(_root);
        }

        protected override void OnUpdate()
        {
            if (_ambient == null) return;
            if (!SystemAPI.TryGetSingleton<CycleState>(out var cyc)) return;

            byte phase = cyc.Phase;
            if (!_phaseInit)
            {
                _lastPhase = phase; // adopt the current phase silently (no stinger on first observe)
                _phaseInit = true;
            }
            else if (phase != _lastPhase)
            {
                PlaySting(phase);
                _lastPhase = phase;
            }

            // Ease the drone intensity toward the phase target (tenser during Defend).
            float target = phase == CyclePhase.Siege ? AmbientBaseVolume * 1.7f : AmbientBaseVolume;
            _ambient.volume = Mathf.MoveTowards(_ambient.volume, target * GameVolume.Music, SystemAPI.Time.DeltaTime * 0.25f);
        }

        void PlaySting(byte phase)
        {
            AudioClip clip = phase == CyclePhase.Siege ? _stingDefend : _stingBuild;
            if (clip != null && _ambient != null)
                _ambient.PlayOneShot(clip, 0.6f * GameVolume.Music);
        }

        // ---- Procedural audio (asset-free; mirrors CombatFeedbackSystem.MakeClip) ----

        // A low, seamless-looping pad: each partial completes an integer number of cycles over the buffer
        // (freq snapped to k/duration) so the loop point has no click. A slow tremolo adds motion.
        static AudioClip MakeDrone()
        {
            const int rate = 44100;
            const float dur = 4f;
            int len = (int)(dur * rate);
            var clip = AudioClip.Create("ambient_drone", len, 1, rate, false);
            var data = new float[len];
            float f0 = Snap(55f, dur);     // sub
            float f1 = Snap(110f, dur);    // root
            float f2 = Snap(164.81f, dur); // fifth-ish
            float f3 = Snap(220f, dur);
            float trem = Snap(0.5f, dur);  // slow amplitude wobble
            for (int i = 0; i < len; i++)
            {
                float t = i / (float)rate;
                float s = 0.50f * Mathf.Sin(2f * Mathf.PI * f0 * t)
                        + 0.35f * Mathf.Sin(2f * Mathf.PI * f1 * t)
                        + 0.18f * Mathf.Sin(2f * Mathf.PI * f2 * t)
                        + 0.10f * Mathf.Sin(2f * Mathf.PI * f3 * t);
                float amp = 0.75f + 0.25f * Mathf.Sin(2f * Mathf.PI * trem * t);
                data[i] = s * amp * 0.5f; // peak ~0.57, no clipping
            }
            clip.SetData(data, 0);
            return clip;
        }

        // freq snapped so freq*dur is an integer -> the waveform closes seamlessly at the loop point.
        static float Snap(float freq, float dur)
        {
            float cycles = Mathf.Max(1f, Mathf.Round(freq * dur));
            return cycles / dur;
        }

        // Short one-shot tone sweeping f0->f1 with an exponential decay envelope.
        static AudioClip MakeSting(float f0, float f1, float dur, float vol)
        {
            const int rate = 44100;
            int len = Mathf.Max(16, (int)(dur * rate));
            var clip = AudioClip.Create("sting", len, 1, rate, false);
            var data = new float[len];
            float phase = 0f;
            for (int i = 0; i < len; i++)
            {
                float t = i / (float)len;
                float env = Mathf.Exp(-3.5f * t);
                float freq = Mathf.Lerp(f0, f1, t);
                phase += 2f * Mathf.PI * freq / rate;
                data[i] = Mathf.Sin(phase) * env * vol;
            }
            clip.SetData(data, 0);
            return clip;
        }
    }
}