Fix for state gap when frame advancing and painting input (#2563)

* Fix for state gap when frame advancing and painting input

* simplify

src/BizHawk.Client.EmuHawk/IMainFormForTools.cs

@@ -78,6 +78,8 @@ namespace BizHawk.Client.EmuHawk
 
 		void PauseEmulator();
 
+		bool BlockFrameAdvance { get; set; }
+
 		/// <remarks>only referenced from <see cref="TAStudio"/></remarks>
 		void RelinquishControl(IControlMainform master);
 

src/BizHawk.Client.EmuHawk/MainForm.cs

@@ -768,6 +768,8 @@ namespace BizHawk.Client.EmuHawk
 			}
 		}
 
+		public bool BlockFrameAdvance { get; set; }
+
 		public event Action<bool> OnPauseChanged;
 
 		public string CurrentlyOpenRom { get; private set; } // todo - delete me and use only args instead
@@ -2916,7 +2918,8 @@ namespace BizHawk.Client.EmuHawk
 
 			float atten = 0;
 
-			if (runFrame || force)
+			// BlockFrameAdvance (true when input it being editted in TAStudio) supercedes all other frame advance conditions
+			if ((runFrame || force) && !BlockFrameAdvance)
 			{
 				var isFastForwarding = InputManager.ClientControls["Fast Forward"] || IsTurboing || InvisibleEmulation;
 				var isFastForwardingOrRewinding = isFastForwarding || isRewinding || _unthrottled;

src/BizHawk.Client.EmuHawk/tools/TAStudio/TAStudio.ListView.cs

@@ -619,6 +619,11 @@ namespace BizHawk.Client.EmuHawk
 					_playbackInterrupted = !MainForm.EmulatorPaused;
 					MainForm.PauseEmulator();
 
+					// Pausing the emulator is insufficient to actually stop frame advancing as the frame advance hotkey can
+					// still take effect. This can lead to desyncs by simultaneously changing input and frame advancing.
+					// So we want to block all frame advance operations while the user is changing input in the piano roll
+					MainForm.BlockFrameAdvance = true;
+
 					if (ControllerType.BoolButtons.Contains(buttonName))
 					{
 						_patternPaint = false;
@@ -810,6 +815,8 @@ namespace BizHawk.Client.EmuHawk
 			{
 				CurrentTasMovie.ChangeLog?.EndBatch();
 			}
+
+			MainForm.BlockFrameAdvance = false;
 		}
 
 		private void TasView_MouseUp(object sender, MouseEventArgs e)