optimize movie recording loop a bit, do not create a new instance of log entry generator every frame, avoids a lot of memory allocations with mnemonic lookups that do not change for the lifetime of the movie, also a slight optikmization in Bk2 controller, co-authored iwth morilli

src/BizHawk.Client.Common/movie/bk2/Bk2Controller.cs

@@ -55,8 +55,9 @@ namespace BizHawk.Client.Common
 
 		public void SetFrom(IController source)
 		{
-			foreach (var button in Definition.BoolButtons)
+			for (int index = 0; index < Definition.BoolButtons.Count; index++)
 			{
+				string button = Definition.BoolButtons[index];
 				_myBoolButtons[button] = source.IsPressed(button);
 			}
 

src/BizHawk.Client.Common/movie/bk2/Bk2LogEntryGenerator.cs

@@ -6,15 +6,25 @@ using BizHawk.Emulation.Common;
 
 namespace BizHawk.Client.Common
 {
+	// Designed to be able to last the lifetime of an IMovie
 	internal class Bk2LogEntryGenerator : ILogEntryGenerator
 	{
 		private readonly string _systemId;
 		private readonly IController _source;
 
+		private readonly Dictionary<string, char> _mnemonics = new();
+
 		public Bk2LogEntryGenerator(string systemId, IController source)
 		{
 			_systemId = systemId;
 			_source = source;
+			foreach (var group in _source.Definition.ControlsOrdered.Where(static c => c.Count is not 0))
+			{
+				foreach (var button in group)
+				{
+					_mnemonics.Add(button, Bk2MnemonicLookup.Lookup(button, _systemId));
+				}
+			}
 		}
 
 		public bool IsEmpty => EmptyEntry == GenerateLogEntry();
@@ -76,7 +86,7 @@ namespace BizHawk.Client.Common
 					else if (_source.Definition.BoolButtons.Contains(button))
 					{
 						sb.Append(!createEmpty && _source.IsPressed(button)
-							? Bk2MnemonicLookup.Lookup(button, _systemId)
+							? _mnemonics[button]
 							: '.');
 					}
 				}

src/BizHawk.Client.Common/movie/bk2/Bk2Movie.cs

@@ -6,7 +6,7 @@ namespace BizHawk.Client.Common
 	public partial class Bk2Movie : BasicMovieInfo, IMovie
 	{
 		private Bk2Controller _adapter;
-
+		private Bk2LogEntryGenerator _logGenerator;
 		public Bk2Movie(IMovieSession session, string filename) : base(filename)
 		{
 			Session = session;
@@ -34,7 +34,14 @@ namespace BizHawk.Client.Common
 
 		public ILogEntryGenerator LogGeneratorInstance(IController source)
 		{
-			return new Bk2LogEntryGenerator(Emulator?.SystemId ?? SystemID, source);
+			// Hack because initial movie loading is a mess, and you will immediate create a file with an undefined controller
+			if (!source.Definition.Any())
+			{
+				return new Bk2LogEntryGenerator(Emulator?.SystemId ?? SystemID, source);
+			}
+
+			_logGenerator ??= new Bk2LogEntryGenerator(Emulator?.SystemId ?? SystemID, source);
+			return _logGenerator;
 		}
 
 		public override int FrameCount => Log.Count;