From eb72ff9053bedcbd0b85fec8cce32e129e04c180 Mon Sep 17 00:00:00 2001
From: nattthebear <goyuken@gmail.com>
Date: Sun, 11 Dec 2016 14:07:12 -0500
Subject: [PATCH] Swag up NullSound

---
 BizHawk.Client.EmuHawk/AVOut/AVSync.cs        |  2 +-
 BizHawk.Client.EmuHawk/MainForm.cs            | 11 +---
 .../Base Implementations/NullSound.cs         | 59 +++++++++++++++----
 BizHawk.Emulation.Common/Extensions.cs        | 14 +++++
 4 files changed, 62 insertions(+), 24 deletions(-)

diff --git a/BizHawk.Client.EmuHawk/AVOut/AVSync.cs b/BizHawk.Client.EmuHawk/AVOut/AVSync.cs
index 9f14c85ada..d9139e276f 100644
--- a/BizHawk.Client.EmuHawk/AVOut/AVSync.cs
+++ b/BizHawk.Client.EmuHawk/AVOut/AVSync.cs
@@ -22,7 +22,7 @@ namespace BizHawk.Client.EmuHawk
 			// Sound refactor TODO: we could try set it here, but we want the client to be responsible for mode switching? There may be non-trivial complications with when to switch modes that we don't want this object worrying about
 			if (asyncSoundProvider.SyncMode != SyncSoundMode.Async)
 			{
-				throw new InvalidOperationException("Only sync mode is supported, set sync mode before passing in the sound provider");
+				throw new InvalidOperationException("Only async mode is supported, set async mode before passing in the sound provider");
 			}
 
 			if (!aset || !vset)
diff --git a/BizHawk.Client.EmuHawk/MainForm.cs b/BizHawk.Client.EmuHawk/MainForm.cs
index 589b5d946d..7a06c23288 100644
--- a/BizHawk.Client.EmuHawk/MainForm.cs
+++ b/BizHawk.Client.EmuHawk/MainForm.cs
@@ -734,16 +734,7 @@ namespace BizHawk.Client.EmuHawk
 					_currentVideoProvider = NullVideo.Instance;
 				}
 
-				if (Global.Emulator.HasSoundProvider())
-				{
-					_currentSoundProvider = Global.Emulator.AsSoundProvider();
-				}
-				else
-				{
-					// Set the samples per frame based on VSync rate (which is 60 unless the core states otherwise)
-					// Use 44.1 khz because we like to do that
-					_currentSoundProvider = new NullSound((int)(44100 / Global.Emulator.CoreComm.VsyncRate));
-				}
+				_currentSoundProvider = Global.Emulator.AsSoundProviderOrDefault();
 			}
 		}
 
diff --git a/BizHawk.Emulation.Common/Base Implementations/NullSound.cs b/BizHawk.Emulation.Common/Base Implementations/NullSound.cs
index b785b1f52c..8d34d1bb04 100644
--- a/BizHawk.Emulation.Common/Base Implementations/NullSound.cs	
+++ b/BizHawk.Emulation.Common/Base Implementations/NullSound.cs	
@@ -4,43 +4,76 @@ namespace BizHawk.Emulation.Common
 {
 	public class NullSound : ISoundProvider
 	{
-		private readonly int _spf;
+		private readonly long _spfNumerator;
+		private readonly long _spfDenominator;
+		private long _remainder = 0;
+		private short[] _buff = new short[0];
 
-		public NullSound(int spf)
+		private NullSound()
 		{
-			_spf = spf;
+			SyncMode = SyncSoundMode.Sync;
+		}
+
+		/// <summary>
+		/// create a NullSound that provides an exact number of audio samples per call when in sync mode
+		/// </summary>
+		/// <param name="spf"></param>
+		public NullSound(int spf)
+			:this()
+		{
+			_spfNumerator = spf;
+			_spfDenominator = 1;	
+		}
+
+		/// <summary>
+		/// create a NullSound that exactly matches a given framerate when in sync mode
+		/// </summary>
+		/// <param name="fpsNum"></param>
+		/// <param name="fpsDen"></param>
+		public NullSound(long fpsNum, long fpsDen)
+		{
+			_spfNumerator = fpsDen * 44100;
+			_spfDenominator = fpsNum;
 		}
 
 		public bool CanProvideAsync
 		{
-			get { return false; }
+			get { return true; }
 		}
 
 		public SyncSoundMode SyncMode
 		{
-			get { return SyncSoundMode.Sync; }
+			get;
+			private set;
 		}
 
 		public void GetSamplesSync(out short[] samples, out int nsamp)
 		{
-			short[] ret = new short[_spf * 2];
-			samples = ret;
-			nsamp = _spf;
+			if (SyncMode != SyncSoundMode.Sync)
+				throw new InvalidOperationException("Wrong sound mode");
+
+			int s = (int)((_spfNumerator + _remainder) / _spfDenominator);
+			_remainder = (_spfNumerator + _remainder) % _spfDenominator;
+
+			if (_buff.Length < s * 2)
+				_buff = new short[s * 2];
+
+			samples = _buff;
+			nsamp = s;
 		}
 
 		public void DiscardSamples() { }
 
 		public void SetSyncMode(SyncSoundMode mode)
 		{
-			if (mode == SyncSoundMode.Async)
-			{
-				throw new NotSupportedException("Async mode is not supported.");
-			}
+			SyncMode = mode;
 		}
 
 		public void GetSamplesAsync(short[] samples)
 		{
-			throw new InvalidOperationException("Async mode is not supported.");
+			if (SyncMode != SyncSoundMode.Async)
+				throw new InvalidOperationException("Wrong sound mode");
+			Array.Clear(samples, 0, samples.Length);
 		}
 	}
 }
diff --git a/BizHawk.Emulation.Common/Extensions.cs b/BizHawk.Emulation.Common/Extensions.cs
index 83b97d3342..3ffa04bdaf 100644
--- a/BizHawk.Emulation.Common/Extensions.cs
+++ b/BizHawk.Emulation.Common/Extensions.cs
@@ -2,6 +2,7 @@
 using System.Linq;
 using System.Reflection;
 using BizHawk.Common.ReflectionExtensions;
+using System.Runtime.CompilerServices;
 
 namespace BizHawk.Emulation.Common.IEmulatorExtensions
 {
@@ -48,6 +49,19 @@ namespace BizHawk.Emulation.Common.IEmulatorExtensions
 			return core.ServiceProvider.GetService<ISoundProvider>();
 		}
 
+		private static readonly ConditionalWeakTable<IEmulator, ISoundProvider> CachedNullSoundProviders = new ConditionalWeakTable<IEmulator, ISoundProvider>();
+
+		/// <summary>
+		/// returns the core's SoundProvider, or a suitable dummy provider
+		/// </summary>
+		public static ISoundProvider AsSoundProviderOrDefault(this IEmulator core)
+		{
+			var ret = core.ServiceProvider.GetService<ISoundProvider>();
+			if (ret == null)
+				ret = CachedNullSoundProviders.GetValue(core, e => new NullSound(e.CoreComm.VsyncNum, e.CoreComm.VsyncDen));
+			return ret;
+		}
+
 		public static bool HasMemoryDomains(this IEmulator core)
 		{
 			if (core == null)