delegate type for ShowFuture

Author: SuuperW

src/BizHawk.Client.Common/Api/Classes/EmuClientApi.cs

@@ -219,8 +219,14 @@ public void SetWindowSize(int size)
 			}
 		}
 
-		public void ShowFuture(Func<int, bool> preFrameCallback, int maxFrames)
+		public void ShowFuture(ShowFutureCallback/*?*/ preFrameCallback, short maxFrames)
 		{
+			if (maxFrames < 1 && preFrameCallback != null)
+			{
+				_logCallback($"Invalid number of future frames ({maxFrames}); number must be positive.");
+				return;
+			}
+
 			_mainForm.PreFutureFrameCallback = preFrameCallback;
 			_mainForm.MaxFutureFrames = maxFrames;
 		}

src/BizHawk.Client.Common/Api/Interfaces/IEmuClientApi.cs

@@ -145,7 +145,7 @@ public interface IEmuClientApi : IDisposable, IExternalApi
 		/// When the callback returns true, emulation will rewind to the real current frame and the just-run future frame will be displayed.
 		/// <br/>Pass null to disable future frame display.</param>
 		/// <param name="maxFrames">The maximum number of future frames to emulate. Useful to avoid freezing the client UI in case of accidentally never returning true from the callback.</param>
-		void ShowFuture(Func<int, bool> preFrameCallback, int maxFrames);
+		void ShowFuture(ShowFutureCallback/*?*/ preFrameCallback, short maxFrames);
 
 		void SpeedMode(int percent);
 

src/BizHawk.Client.Common/EventTypes.cs

@@ -122,4 +122,11 @@ public StateSavedEventArgs(string stateName)
 	/// <param name="sender">Object that raised the event</param>
 	/// <param name="e">Event arguments</param>
 	public delegate void StateSavedEventHandler(object sender, StateSavedEventArgs e);
+
+	/// <summary>
+	/// Represent a method that will control future emulation.
+	/// </summary>
+	/// <param name="futureFramesEmulated">The number of frames into the future that have been emulated. This is a short purely to help avoid accidentally passing in absurdly large numbers.</param>
+	/// <returns>True to display the current frame, false to continue emulating into the future.</returns>
+	public delegate bool ShowFutureCallback(short futureFramesEmulated);
 }

src/BizHawk.Client.Common/IMainFormForApi.cs

@@ -35,7 +35,7 @@ public interface IMainFormForApi
 		bool PauseAvi { get; set; }
 
 		/// <remarks>only referenced from <see cref="EmuClientApi"/></remarks>
-		public Func<int, bool>/*?*/ PreFutureFrameCallback { get; set; }
+		public ShowFutureCallback/*?*/ PreFutureFrameCallback { get; set; }
 
 		/// <remarks>only referenced from <see cref="EmuClientApi"/></remarks>
 		void ClearHolds();

src/BizHawk.Client.Common/lua/CommonLibs/ClientLuaLibrary.cs

@@ -286,11 +286,17 @@ public void SetWindowSize(int size)
 				"Unregister the callback with event.unregister____ to disable future frame display. " +
 				"No more than `maxFrames` future frames will be emulated. Useful to avoid freezing " +
 				"the client UI in case of accidentally never returning true from the callback.")]
-		public string ShowFuture(LuaFunction luaf, int maxFrames, string name = null)
+		public string ShowFuture(LuaFunction luaf, long maxFrames, string name = null)
 		{
+			if (maxFrames < 1 || maxFrames > short.MaxValue)
+			{
+				Log($"Invalid number of future frames ({maxFrames}); number must be positive and less than 2^15.");
+				return "";
+			}
+
 			INamedLuaFunction nlf = CreateAndRegisterNamedFunction(luaf, NamedLuaFunction.EVENT_TYPE_FUTURE, prohibitedApis: ApiGroup.PROHIBITED_MID_FRAME, name: name);
-			Func<int, bool> FutureCallback = (f) => nlf.Call(f) is [ bool r ] ? r : false;
-			APIs.EmuClient.ShowFuture(FutureCallback, maxFrames);
+			ShowFutureCallback FutureCallback = (f) => nlf.Call(f) is [ bool r ] ? r : false;
+			APIs.EmuClient.ShowFuture(FutureCallback, (short)maxFrames);
 			nlf.OnRemove += () => APIs.EmuClient.ShowFuture(null, 0);
 			return nlf.GuidStr;
 		}

src/BizHawk.Client.EmuHawk/MainForm.cs

@@ -1188,7 +1188,7 @@ private set
 
 		public event StateSavedEventHandler SavestateSaved;
 
-		public Func<int, bool>/*?*/ PreFutureFrameCallback { get; set; }
+		public ShowFutureCallback/*?*/ PreFutureFrameCallback { get; set; }
 
 		public int MaxFutureFrames { get; set; }
 
@@ -3081,7 +3081,7 @@ private void StepRunLoop_Core(bool force = false)
 					statable.SaveStateBinary(new(state));
 
 					int frameCount = 0;
-					while (!PreFutureFrameCallback(frameCount) && frameCount < MaxFutureFrames)
+					while (!PreFutureFrameCallback((short)frameCount) && frameCount < MaxFutureFrames)
 					{
 						frameCount++;
 						MovieSession.HandleFrameBefore();

src/BizHawk.Tests.Client.Common/FakeMainFormForApi.cs

@@ -27,7 +27,7 @@ internal class FakeMainFormForApi : IMainFormForApi
 
 		public bool PauseAvi { get => throw new NotImplementedException(); set => throw new NotImplementedException(); }
 		public int MaxFutureFrames { get => throw new NotImplementedException(); set => throw new NotImplementedException(); }
-		public Func<int, bool> PreFutureFrameCallback { get => throw new NotImplementedException(); set => throw new NotImplementedException(); }
+		public ShowFutureCallback PreFutureFrameCallback { get => throw new NotImplementedException(); set => throw new NotImplementedException(); }
 
 #pragma warning disable CS0067 // Events are never used
 		public event BeforeQuickLoadEventHandler? QuicksaveLoad;