use buffered mode for keyboard input, so that it is impossible for quick keystrokes to get missed. also increase priority of input thread.

BizHawk.Client.EmuHawk/Input/Input.cs

@@ -92,7 +92,11 @@ namespace BizHawk.Client.EmuHawk
 		private Input()
 		{
 #if WINDOWS
-			UpdateThread = new Thread(UpdateThreadProc) {IsBackground = true};
+			UpdateThread = new Thread(UpdateThreadProc)
+			{
+				IsBackground = true, 
+				Priority = ThreadPriority.AboveNormal //why not? this thread shouldn't be very heavy duty, and we want it to be responsive
+			};
 			UpdateThread.Start();
 #endif
 		}
@@ -172,7 +176,8 @@ namespace BizHawk.Client.EmuHawk
 
 		void HandleButton(string button, bool newState)
 		{
-			if (EnableIgnoreModifiers && IgnoreKeys.Contains(button)) return;
+			bool isModifier = IgnoreKeys.Contains(button);
+			if (EnableIgnoreModifiers && isModifier) return;
 			if (LastState[button] && newState) return;
 			if (!LastState[button] && !newState) return;
 			
@@ -185,6 +190,15 @@ namespace BizHawk.Client.EmuHawk
 				return;
 			}
 
+			//apply 
+			//NOTE: this is not quite right. if someone held leftshift+rightshift it would be broken. seems unlikely, though.
+			if (button == "LeftShift") { _Modifiers &= ~ModifierKey.Shift; if (newState) _Modifiers |= ModifierKey.Shift; }
+			if (button == "RightShift") { _Modifiers &= ~ModifierKey.Shift; if (newState) _Modifiers |= ModifierKey.Shift; }
+			if (button == "LeftControl"){  _Modifiers &= ~ModifierKey.Control; if (newState) _Modifiers |= ModifierKey.Control; }
+			if (button == "RightControl"){  _Modifiers &= ~ModifierKey.Control; if (newState) _Modifiers |= ModifierKey.Control; }
+			if (button == "LeftAlt") { _Modifiers &= ~ModifierKey.Alt; if (newState) _Modifiers |= ModifierKey.Alt; }
+			if (button == "RightAlt") { _Modifiers &= ~ModifierKey.Alt; if (newState) _Modifiers |= ModifierKey.Alt; }
+
 			//dont generate events for things like Ctrl+LeftControl
 			ModifierKey mods = _Modifiers;
 			if (button == "LeftShift") mods &= ~ModifierKey.Shift;
@@ -219,7 +233,7 @@ namespace BizHawk.Client.EmuHawk
 					LogicalButton alreadyReleased = ie.LogicalButton;
 					var ieModified = new InputEvent
 						{
-							LogicalButton = (LogicalButton) ModifierState[button],
+							LogicalButton = (LogicalButton)ModifierState[button],
 							EventType = InputEventType.Release
 						};
 					if (ieModified.LogicalButton != alreadyReleased)
@@ -276,26 +290,18 @@ namespace BizHawk.Client.EmuHawk
 		{
 			for (; ; )
 			{
-				KeyInput.Update();
+				var keyEvents = KeyInput.Update();
 				GamePad.UpdateAll();
 				GamePad360.UpdateAll();
 
-				_Modifiers = KeyInput.GetModifierKeysAsKeys();
-
 				//this block is going to massively modify data structures that the binding method uses, so we have to lock it all
 				lock (this)
 				{
 					_NewEvents.Clear();
 
 					//analyze keys
-					var bleh = new HashSet<Key>();
+					foreach (var ke in keyEvents)
-					foreach (var k in KeyInput.State.PressedKeys)
+						HandleButton(ke.Key.ToString(), ke.Pressed);
-						bleh.Add(k);
-					foreach (var k in KeyInput.State.AllKeys)
-						if (bleh.Contains(k))
-							HandleButton(k.ToString(), true);
-						else
-							HandleButton(k.ToString(), false);
 
 					lock (FloatValues)
 					{

BizHawk.Client.EmuHawk/Input/Keyboard.cs

@@ -1,4 +1,5 @@
-using SlimDX;
+using System.Collections.Generic;
+using SlimDX;
 using SlimDX.DirectInput;
 
 namespace BizHawk.Client.EmuHawk
@@ -17,21 +18,45 @@ namespace BizHawk.Client.EmuHawk
 			if (keyboard == null || keyboard.Disposed)
 				keyboard = new Keyboard(dinput);
 			keyboard.SetCooperativeLevel(GlobalWin.MainForm.Handle, CooperativeLevel.Background | CooperativeLevel.Nonexclusive);
+			keyboard.Properties.BufferSize = 8;
 		}
 
-		public static void Update()
+		static List<KeyEvent> EmptyList = new List<KeyEvent>();
+		static List<KeyEvent> EventList = new List<KeyEvent>();
+
+		public static IEnumerable<KeyEvent> Update()
 		{
-			if (keyboard.Acquire().IsFailure)
+			EventList.Clear();
-				return;
-			if (keyboard.Poll().IsFailure)
-				return;
 
-			keyboard.GetCurrentState(ref state);
+			if (keyboard.Acquire().IsFailure)
-			if (Result.Last.IsFailure)
+				return EmptyList;
-				return;
+			if (keyboard.Poll().IsFailure)
+				return EmptyList;
+
+			for (; ; )
+			{
+				var events = keyboard.GetBufferedData();
+				if (Result.Last.IsFailure)
+					return EventList;
+				if (events.Count == 0)
+					break;
+				foreach (var e in events)
+				{
+					foreach (var k in e.PressedKeys)
+						EventList.Add(new KeyEvent { Key = k, Pressed = true });
+					foreach (var k in e.ReleasedKeys)
+					EventList.Add(new KeyEvent { Key = k, Pressed = false });
+				}
+			}
+
+			return EventList;
 		}
 
-		public static KeyboardState State { get { return state; } }
+		public struct KeyEvent
+		{
+			public Key Key;
+			public bool Pressed;
+		}
 
 		
 		public static bool IsPressed(Key key)