Add AudioLowPassFilter component

ProjectObsidian/Components/Audio/AudioLowPassFilter.cs

@@ -0,0 +1,93 @@
+using System;
+using FrooxEngine;
+using Elements.Assets;
+
+namespace Obsidian.Components.Audio;
+
+[Category(new string[] { "Audio" })]
+public class AudioLowPassFilter : Component, IAudioSource, IWorldElement
+{
+    [Range(0f, 1f, "0.00")]
+    public readonly Sync<float> SmoothingFactor;
+
+    public readonly AssetRef<AudioClip> Clip;
+
+    private double lastPos;
+
+    private double nextPos;
+
+    private double lastAudioTime;
+
+    public bool IsActive
+    {
+        get
+        {
+            return Clip.IsAssetAvailable;
+        }
+    }
+
+    public int ChannelCount => (Clip.Asset?.Data?.ChannelCount).GetValueOrDefault();
+
+    public void Read<S>(Span<S> buffer) where S : unmanaged, IAudioSample<S>
+    {
+        var clipData = Clip.Asset?.Data;
+        if (clipData == null)
+        {
+            buffer.Fill(default(S));
+            return;
+        }
+        double dSPTime = base.Engine.AudioSystem.DSPTime;
+        if (lastAudioTime != dSPTime)
+        {
+            lastPos = nextPos;
+            lastAudioTime = dSPTime;
+        }
+        bool flag = false;
+        Span<S> span = stackalloc S[buffer.Length];
+        if (!IsActive)
+        {
+            return;
+        }
+        Span<S> span2 = span;
+        if (!flag)
+        {
+            span2 = buffer;
+        }
+
+        int num = Clip.Asset.Data.Read(span2, lastPos * (double)Clip.Asset.Data.SampleRate, 1f, loop: true);
+
+        EMAIIRSmoothSignal(ref span2, span2.Length, SmoothingFactor);
+
+        nextPos = (lastPos + (double)num * base.Engine.AudioSystem.InvSampleRate * (double)1f) % Clip.Asset.Data.Duration;
+
+        if (flag)
+        {
+            buffer.Add(span2);
+        }
+        flag = true;
+        if (!flag)
+        {
+            buffer.Fill(default(S));
+        }
+    }
+
+    // smoothingFactor is between 0.0 (no smoothing) and 0.9999.. (almost smoothing to DC) - *kind* of the inverse of cutoff frequency
+    public void EMAIIRSmoothSignal<S>(ref Span<S> input, int N, float smoothingFactor = 0.8f) where S : unmanaged, IAudioSample<S>
+    {
+        // forward EMA IIR
+        S acc = input[0];
+        for (int i = 0; i < N; ++i)
+        {
+            acc = input[i].LerpTo(acc, smoothingFactor);
+            input[i] = acc;
+        }
+
+        // backward EMA IIR - required only if we need to preserve the phase (aka make the filter symetric) - we usually want this
+        acc = input[N - 1];
+        for (int i = N - 1; i >= 0; --i)
+        {
+            acc = input[i].LerpTo(acc, smoothingFactor);
+            input[i] = acc;
+        }
+    }
+}

ProjectObsidian/ProjectObsidian.csproj

@@ -72,6 +72,7 @@
     <ProjectReference Include="..\ProjectObsidian.SourceGenerators\SourceGenerators.csproj" OutputItemType="Analyzer" />
     <PackageReference Include="managed-midi" Version="1.10.1" />
     <PackageReference Include="Microsoft.NETFramework.ReferenceAssemblies" Version="1.0.3"> </PackageReference>
+    <PackageReference Include="System.Memory" Version="4.6.0" />
   </ItemGroup>
   <Target Name="PostBuild" AfterTargets="PostBuildEvent">
     <Copy SourceFiles="$(TargetPath)" DestinationFolder="$(ResonitePath)Libraries" />