From 1f5128bf6bbd817b6f7381cef63af70978c8b2fd Mon Sep 17 00:00:00 2001
From: RetroEdit <30182911+RetroEdit@users.noreply.github.com>
Date: Fri, 14 Aug 2020 16:00:56 +0000
Subject: [PATCH] zwinder: Make GetStateClosestToFrame actually get closest
 state. (#2291)

* zwinder: Make GetStateClosestToFrame actually get closest state.

* Clarify docs
---
 .../movie/tasproj/IStateManager.cs                  |  2 +-
 .../movie/tasproj/ZwinderStateManager.cs            |  6 +++---
 .../tools/TAStudio/TAStudio.Navigation.cs           |  4 +---
 .../tools/TAStudio/TAStudio.cs                      | 13 +++++++++++--
 .../Client.Common/Movie/ZwinderStateManagerTests.cs |  4 ++--
 5 files changed, 18 insertions(+), 11 deletions(-)

diff --git a/src/BizHawk.Client.Common/movie/tasproj/IStateManager.cs b/src/BizHawk.Client.Common/movie/tasproj/IStateManager.cs
index 2b7087e74e..6fcd012262 100644
--- a/src/BizHawk.Client.Common/movie/tasproj/IStateManager.cs
+++ b/src/BizHawk.Client.Common/movie/tasproj/IStateManager.cs
@@ -33,7 +33,7 @@ namespace BizHawk.Client.Common
 		void Clear();
 
 		/// <summary>
-		/// Get a nearby state.  The returned frame must be less (but not equal to???) the passed frame.
+		/// Get a nearby state.  The returned frame must be less than or equal to the passed frame.
 		/// This may not fail; the StateManager strongly holds a frame 0 state to ensure there's always a possible result.
 		/// </summary>
 		/// <param name="frame"></param>
diff --git a/src/BizHawk.Client.Common/movie/tasproj/ZwinderStateManager.cs b/src/BizHawk.Client.Common/movie/tasproj/ZwinderStateManager.cs
index 9a6d99bfac..1bf75ef95f 100644
--- a/src/BizHawk.Client.Common/movie/tasproj/ZwinderStateManager.cs
+++ b/src/BizHawk.Client.Common/movie/tasproj/ZwinderStateManager.cs
@@ -68,7 +68,7 @@ namespace BizHawk.Client.Common
 		{
 			get
 			{
-				var kvp = GetStateClosestToFrame(frame + 1);
+				var kvp = GetStateClosestToFrame(frame);
 				if (kvp.Key != frame)
 					return NonState;
 				var ms = new MemoryStream();
@@ -221,10 +221,10 @@ namespace BizHawk.Client.Common
 
 		public KeyValuePair<int, Stream> GetStateClosestToFrame(int frame)
 		{
-			if (frame <= 0)
+			if (frame < 0)
 				throw new ArgumentOutOfRangeException(nameof(frame));
 
-			var si = AllStates().First(s => s.Frame < frame);
+			var si = AllStates().First(s => s.Frame <= frame);
 			return new KeyValuePair<int, Stream>(si.Frame, si.Read());
 		}
 
diff --git a/src/BizHawk.Client.EmuHawk/tools/TAStudio/TAStudio.Navigation.cs b/src/BizHawk.Client.EmuHawk/tools/TAStudio/TAStudio.Navigation.cs
index 1d23922fdc..ebfdd928a0 100644
--- a/src/BizHawk.Client.EmuHawk/tools/TAStudio/TAStudio.Navigation.cs
+++ b/src/BizHawk.Client.EmuHawk/tools/TAStudio/TAStudio.Navigation.cs
@@ -52,9 +52,7 @@ namespace BizHawk.Client.EmuHawk
 				{
 					TastudioPlayMode();
 
-					// Simply getting the last state doesn't work if that state is the frame.
-					// display isn't saved in the state, need to emulate to frame
-					var lastState = CurrentTasMovie.TasStateManager.GetStateClosestToFrame(frame <= 0 ? 1 : frame);
+					var lastState = GetPriorStateForFramebuffer(frame);
 					if (lastState.Key > Emulator.Frame)
 					{
 						LoadState(lastState);
diff --git a/src/BizHawk.Client.EmuHawk/tools/TAStudio/TAStudio.cs b/src/BizHawk.Client.EmuHawk/tools/TAStudio/TAStudio.cs
index cb17cd58fa..cf481468c0 100644
--- a/src/BizHawk.Client.EmuHawk/tools/TAStudio/TAStudio.cs
+++ b/src/BizHawk.Client.EmuHawk/tools/TAStudio/TAStudio.cs
@@ -601,7 +601,7 @@ namespace BizHawk.Client.EmuHawk
 
 			tasMovie.GreenzoneInvalidated = GreenzoneInvalidated;
 			tasMovie.PropertyChanged += TasMovie_OnPropertyChanged;
-			
+
 			tasMovie.PopulateWithDefaultHeaderValues(
 				Emulator,
 				Game,
@@ -901,6 +901,15 @@ namespace BizHawk.Client.EmuHawk
 			}
 		}
 
+		/// <summary>
+		/// Get a savestate prior to the previous frame so code following the call can frame advance and have a framebuffer.
+		/// If frame is 0, return the initial state.
+		/// </summary>
+		private KeyValuePair<int,Stream> GetPriorStateForFramebuffer(int frame)
+		{
+			return CurrentTasMovie.TasStateManager.GetStateClosestToFrame(frame > 0 ? frame - 1 : 0);
+		}
+
 		private void StartAtNearestFrameAndEmulate(int frame, bool fromLua, bool fromRewinding)
 		{
 			if (frame == Emulator.Frame)
@@ -910,7 +919,7 @@ namespace BizHawk.Client.EmuHawk
 
 			_unpauseAfterSeeking = (fromRewinding || WasRecording) && !MainForm.EmulatorPaused;
 			TastudioPlayMode();
-			var closestState = CurrentTasMovie.TasStateManager.GetStateClosestToFrame(frame <= 0 ? 1 : frame);
+			var closestState = GetPriorStateForFramebuffer(frame);
 			if (closestState.Value.Length > 0 && (frame < Emulator.Frame || closestState.Key > Emulator.Frame))
 			{
 				LoadState(closestState);
diff --git a/src/BizHawk.Tests/Client.Common/Movie/ZwinderStateManagerTests.cs b/src/BizHawk.Tests/Client.Common/Movie/ZwinderStateManagerTests.cs
index ad7b0e3f17..33849f090b 100644
--- a/src/BizHawk.Tests/Client.Common/Movie/ZwinderStateManagerTests.cs
+++ b/src/BizHawk.Tests/Client.Common/Movie/ZwinderStateManagerTests.cs
@@ -62,7 +62,7 @@ namespace BizHawk.Tests.Client.Common.Movie
 		}
 
 		[TestMethod]
-		public void SomethingSomething()
+		public void StateBeforeFrame()
 		{
 			var ss = new StateSource { PaddingData = new byte[1000] };
 			var zw = new ZwinderStateManager(new ZwinderStateManagerSettings
@@ -90,7 +90,7 @@ namespace BizHawk.Tests.Client.Common.Movie
 			var kvp = zw.GetStateClosestToFrame(10440);
 			var actual = StateSource.GetFrameNumberInState(kvp.Value);
 			Assert.AreEqual(kvp.Key, actual);
-			Assert.IsTrue(actual < 10440);
+			Assert.IsTrue(actual <= 10440);
 		}
 
 		private class StateSource : IStatable