Add ambient music (#16829)

Content.Client/Audio/ContentAudioSystem.cs

@@ -1,8 +1,124 @@
 using Content.Shared.Audio;
+using Robust.Client.GameObjects;
 
 namespace Content.Client.Audio;
 
-public sealed class ContentAudioSystem : SharedContentAudioSystem
+public sealed partial class ContentAudioSystem : SharedContentAudioSystem
 {
+    // Need how much volume to change per tick and just remove it when it drops below "0"
+    private readonly Dictionary<AudioSystem.PlayingStream, float> _fadingOut = new();
 
+    // Need volume change per tick + target volume.
+    private readonly Dictionary<AudioSystem.PlayingStream, (float VolumeChange, float TargetVolume)> _fadingIn = new();
+
+    private readonly List<AudioSystem.PlayingStream> _fadeToRemove = new();
+
+    private const float MinVolume = -32f;
+    private const float DefaultDuration = 2f;
+
+    public override void Initialize()
+    {
+        base.Initialize();
+        UpdatesOutsidePrediction = true;
+        InitializeAmbientMusic();
+    }
+
+    public override void Shutdown()
+    {
+        base.Shutdown();
+        ShutdownAmbientMusic();
+    }
+
+    public override void Update(float frameTime)
+    {
+        base.Update(frameTime);
+
+        if (!_timing.IsFirstTimePredicted)
+            return;
+
+        UpdateAmbientMusic();
+        UpdateFades(frameTime);
+    }
+
+    #region Fades
+
+    public void FadeOut(AudioSystem.PlayingStream? stream, float duration = DefaultDuration)
+    {
+        if (stream == null || duration <= 0f)
+            return;
+
+        // Just in case
+        // TODO: Maybe handle the removals by making it seamless?
+        _fadingIn.Remove(stream);
+        var diff = stream.Volume - MinVolume;
+        _fadingOut.Add(stream, diff / duration);
+    }
+
+    public void FadeIn(AudioSystem.PlayingStream? stream, float duration = DefaultDuration)
+    {
+        if (stream == null || duration <= 0f || stream.Volume < MinVolume)
+            return;
+
+        _fadingOut.Remove(stream);
+        var curVolume = stream.Volume;
+        var change = (curVolume - MinVolume) / duration;
+        _fadingIn.Add(stream, (change, stream.Volume));
+        stream.Volume = MinVolume;
+    }
+
+    private void UpdateFades(float frameTime)
+    {
+        _fadeToRemove.Clear();
+
+        foreach (var (stream, change) in _fadingOut)
+        {
+            // Cancelled elsewhere
+            if (stream.Done)
+            {
+                _fadeToRemove.Add(stream);
+                continue;
+            }
+
+            var volume = stream.Volume - change * frameTime;
+            stream.Volume = MathF.Max(MinVolume, volume);
+
+            if (stream.Volume.Equals(MinVolume))
+            {
+                stream.Stop();
+                _fadeToRemove.Add(stream);
+            }
+        }
+
+        foreach (var stream in _fadeToRemove)
+        {
+            _fadingOut.Remove(stream);
+        }
+
+        _fadeToRemove.Clear();
+
+        foreach (var (stream, (change, target)) in _fadingIn)
+        {
+            // Cancelled elsewhere
+            if (stream.Done)
+            {
+                _fadeToRemove.Add(stream);
+                continue;
+            }
+
+            var volume = stream.Volume + change * frameTime;
+            stream.Volume = MathF.Min(target, volume);
+
+            if (stream.Volume.Equals(target))
+            {
+                _fadeToRemove.Add(stream);
+            }
+        }
+
+        foreach (var stream in _fadeToRemove)
+        {
+            _fadingIn.Remove(stream);
+        }
+    }
+
+    #endregion
 }