Rewind: Fix subtle off-by-one-frame bugs (only really noticeable when frame advancing).

BizHawk.Client.Common/rewind/Rewinder.cs

@@ -15,6 +15,7 @@ namespace BizHawk.Client.Common
 		private byte[] _lastState;
 		private int _rewindFrequency = 1;
 		private bool _rewindDeltaEnable;
+		private bool _lastRewindLoadedState;
 		private byte[] _deltaBuffer = new byte[0];
 
 		public Rewinder()
@@ -41,11 +42,6 @@ namespace BizHawk.Client.Common
 			get { return _rewindBuffer != null ? _rewindBuffer.Size : 0; }
 		}
 
-		public int BufferCount
-		{
-			get { return _rewindBuffer != null ? _rewindBuffer.Count : 0; }
-		}
-
 		public bool HasBuffer
 		{
 			get { return _rewindBuffer != null; }
@@ -125,26 +121,31 @@ namespace BizHawk.Client.Common
 			}
 		}
 
-		public void Rewind(int frames)
+		public bool Rewind(int frames)
 		{
 			if (!Global.Emulator.HasSavestates() || _rewindThread == null)
 			{
-				return;
+				return false;
 			}
 
 			_rewindThread.Rewind(frames);
+
+			return _lastRewindLoadedState;
 		}
 
 		private void RewindInternal(int frames)
 		{
+			_lastRewindLoadedState = false;
+
 			for (int i = 0; i < frames; i++)
 			{
-				if (_rewindBuffer.Count == 0 || (Global.MovieSession.Movie.IsActive && Global.MovieSession.Movie.InputLogLength == 0))
+				if (_rewindBuffer.Count <= 1 || (Global.MovieSession.Movie.IsActive && Global.MovieSession.Movie.InputLogLength == 0))
 				{
-					return;
+					break;
 				}
 
 				LoadPreviousState();
+				_lastRewindLoadedState = true;
 			}
 		}
 
@@ -351,19 +352,27 @@ namespace BizHawk.Client.Common
 			UpdateLastState(currentState);
 		}
 
-		private void LoadPreviousState()
+		private MemoryStream GetPreviousStateMemoryStream()
 		{
-			using (var reader = new BinaryReader(_rewindBuffer.PopMemoryStream()))
-			{
-				byte[] buf = ((MemoryStream)reader.BaseStream).GetBuffer();
-				var fullState = reader.ReadByte() == 1;
 			if (_rewindDeltaEnable)
 			{
-					using (var lastStateReader = new BinaryReader(new MemoryStream(_lastState)))
+				return _rewindBuffer.PopMemoryStream();
+			}
+			else
 			{
-						Global.Emulator.AsStatable().LoadStateBinary(lastStateReader);
+				_rewindBuffer.Pop();
+				return _rewindBuffer.PeekMemoryStream();
+			}
 		}
 
+		private void LoadPreviousState()
+		{
+			using (var reader = new BinaryReader(GetPreviousStateMemoryStream()))
+			{
+				byte[] buf = ((MemoryStream)reader.BaseStream).GetBuffer();
+				bool fullState = reader.ReadByte() == 1;
+				if (_rewindDeltaEnable)
+				{
 					if (fullState)
 					{
 						UpdateLastState(buf, 1, buf.Length - 1);
@@ -384,6 +393,11 @@ namespace BizHawk.Client.Common
 							index += length;
 						}
 					}
+
+					using (var lastStateReader = new BinaryReader(new MemoryStream(_lastState)))
+					{
+						Global.Emulator.AsStatable().LoadStateBinary(lastStateReader);
+					}
 				}
 				else
 				{

BizHawk.Client.Common/rewind/StreamBlobDatabase.cs

@@ -95,12 +95,20 @@ namespace BizHawk.Client.Common
 		/// </summary>
 		public MemoryStream PopMemoryStream()
 		{
-			var item = Pop();
+			return CreateMemoryStream(Pop());
+		}
+
+		public MemoryStream PeekMemoryStream()
+		{
+			return CreateMemoryStream(Peek());
+		}
+
+		private MemoryStream CreateMemoryStream(ListItem item)
+		{
 			var buf = new byte[item.Length];
 			_mStream.Position = item.Index;
 			_mStream.Read(buf, 0, item.Length);
-			var ret = new MemoryStream(buf, 0, item.Length, false, true);
+			return new MemoryStream(buf, 0, item.Length, false, true);
-			return ret;
 		}
 
 		public long Enqueue(int timestamp, int amount)
@@ -199,6 +207,16 @@ namespace BizHawk.Client.Common
 			return ret;
 		}
 
+		public ListItem Peek()
+		{
+			if (_mHead == null)
+			{
+				throw new InvalidOperationException("Attempted to peek from an empty data structure");
+			}
+
+			return _mHead.Value;
+		}
+
 		public ListItem Dequeue()
 		{
 			if (_mTail == null)

BizHawk.Client.EmuHawk/MainForm.cs

@@ -4186,8 +4186,7 @@ namespace BizHawk.Client.EmuHawk
 
 				if (isRewinding)
 				{
-					Global.Rewinder.Rewind(1);
+					runFrame = Global.Rewinder.Rewind(1);
-					runFrame = Global.Rewinder.Count != 0;
 				}
 			}
 			else