update for split-screen mode

This includes splitting GameRunner (the main game instance) from Game1 (now a per-screen game state), adding a PerScreen<T> utility to simplify per-screen values, adding separate per-screen input handling and events, adding new Context fields for split-screen, and logging the screen ID in split-screen mode to distinguish log entries.

16 files changed, 624 insertions, 255 deletions

diff --git a/docs/release-notes.md b/docs/release-notes.md
index 00445832..176961d4 100644
--- a/docs/release-notes.md
+++ b/docs/release-notes.md
@@ -9,7 +9,11 @@
 
 ## Upcoming release
 * For players:
-  * Updated for Stardew Valley 1.5.
+  * Updated for Stardew Valley 1.5, including split-screen support.
+
+* For modders:
+  * Added `PerScreen<T>` utility and new `Context` fields to simplify split-screen support in mods.
+  * Added screen ID to log when playing in split-screen mode.
 
 ## 3.7.6
 Released 21 November 2020 for Stardew Valley 1.4.1 or later.
diff --git a/src/SMAPI.Web/Framework/LogParsing/LogMessageBuilder.cs b/src/SMAPI.Web/Framework/LogParsing/LogMessageBuilder.cs
index 42e283a9..992876ef 100644
--- a/src/SMAPI.Web/Framework/LogParsing/LogMessageBuilder.cs
+++ b/src/SMAPI.Web/Framework/LogParsing/LogMessageBuilder.cs
@@ -16,6 +16,9 @@ namespace StardewModdingAPI.Web.Framework.LogParsing
         /// <summary>The log level for the next log message.</summary>
         public LogLevel Level { get; set; }
 
+        /// <summary>The screen ID in split-screen mode.</summary>
+        public int ScreenId { get; set; }
+
         /// <summary>The mod name for the next log message.</summary>
         public string Mod { get; set; }
 
@@ -36,10 +39,11 @@ namespace StardewModdingAPI.Web.Framework.LogParsing
         /// <summary>Start accumulating values for a new log message.</summary>
         /// <param name="time">The local time when the log was posted.</param>
         /// <param name="level">The log level.</param>
+        /// <param name="screenId">The screen ID in split-screen mode.</param>
         /// <param name="mod">The mod name.</param>
         /// <param name="text">The initial log text.</param>
         /// <exception cref="InvalidOperationException">A log message is already started; call <see cref="Clear"/> before starting a new message.</exception>
-        public void Start(string time, LogLevel level, string mod, string text)
+        public void Start(string time, LogLevel level, int screenId, string mod, string text)
         {
             if (this.Started)
                 throw new InvalidOperationException("Can't start new message, previous log message isn't done yet.");
@@ -48,6 +52,7 @@ namespace StardewModdingAPI.Web.Framework.LogParsing
 
             this.Time = time;
             this.Level = level;
+            this.ScreenId = screenId;
             this.Mod = mod;
             this.Text.Append(text);
         }
@@ -74,6 +79,7 @@ namespace StardewModdingAPI.Web.Framework.LogParsing
             {
                 Time = this.Time,
                 Level = this.Level,
+                ScreenId = this.ScreenId,
                 Mod = this.Mod,
                 Text = this.Text.ToString()
             };
diff --git a/src/SMAPI.Web/Framework/LogParsing/LogParser.cs b/src/SMAPI.Web/Framework/LogParsing/LogParser.cs
index 227dcd89..f69d4b6f 100644
--- a/src/SMAPI.Web/Framework/LogParsing/LogParser.cs
+++ b/src/SMAPI.Web/Framework/LogParsing/LogParser.cs
@@ -14,7 +14,7 @@ namespace StardewModdingAPI.Web.Framework.LogParsing
         ** Fields
         *********/
         /// <summary>A regex pattern matching the start of a SMAPI message.</summary>
-        private readonly Regex MessageHeaderPattern = new Regex(@"^\[(?<time>\d\d[:\.]\d\d[:\.]\d\d) (?<level>[a-z]+) +(?<modName>[^\]]+)\] ", RegexOptions.Compiled | RegexOptions.IgnoreCase);
+        private readonly Regex MessageHeaderPattern = new Regex(@"^\[(?<time>\d\d[:\.]\d\d[:\.]\d\d) (?<level>[a-z]+)(?: +screen_(?<screen>\d+))? +(?<modName>[^\]]+)\] ", RegexOptions.Compiled | RegexOptions.IgnoreCase);
 
         /// <summary>A regex pattern matching SMAPI's initial platform info message.</summary>
         private readonly Regex InfoLinePattern = new Regex(@"^SMAPI (?<apiVersion>.+) with Stardew Valley (?<gameVersion>.+) on (?<os>.+)", RegexOptions.Compiled | RegexOptions.IgnoreCase);
@@ -304,9 +304,11 @@ namespace StardewModdingAPI.Web.Framework.LogParsing
                         builder.Clear();
                     }
 
+                    var screenGroup = header.Groups["screen"];
                     builder.Start(
                         time: header.Groups["time"].Value,
                         level: Enum.Parse<LogLevel>(header.Groups["level"].Value, ignoreCase: true),
+                        screenId: screenGroup.Success ? int.Parse(screenGroup.Value) : 0, // main player is always screen ID 0
                         mod: header.Groups["modName"].Value,
                         text: line.Substring(header.Length)
                     );
diff --git a/src/SMAPI.Web/Framework/LogParsing/Models/LogMessage.cs b/src/SMAPI.Web/Framework/LogParsing/Models/LogMessage.cs
index f7c99d02..1e08be78 100644
--- a/src/SMAPI.Web/Framework/LogParsing/Models/LogMessage.cs
+++ b/src/SMAPI.Web/Framework/LogParsing/Models/LogMessage.cs
@@ -12,6 +12,9 @@ namespace StardewModdingAPI.Web.Framework.LogParsing.Models
         /// <summary>The log level.</summary>
         public LogLevel Level { get; set; }
 
+        /// <summary>The screen ID in split-screen mode.</summary>
+        public int ScreenId { get; set; }
+
         /// <summary>The mod name.</summary>
         public string Mod { get; set; }
 
diff --git a/src/SMAPI.Web/Views/LogParser/Index.cshtml b/src/SMAPI.Web/Views/LogParser/Index.cshtml
index d4ff4f10..fd472673 100644
--- a/src/SMAPI.Web/Views/LogParser/Index.cshtml
+++ b/src/SMAPI.Web/Views/LogParser/Index.cshtml
@@ -13,6 +13,8 @@
         .ToDictionary(level => level.ToString().ToLower(), level => level != LogLevel.Trace);
 
     string curPageUrl = this.Url.PlainAction("Index", "LogParser", new { id = Model.PasteID }, absoluteUrl: true);
+
+    ISet<int> screenIds = new HashSet<int>(Model.ParsedLog?.Messages?.Select(p => p.ScreenId) ?? new int[0]);
 }
 
 @section Head {
@@ -35,7 +37,8 @@
                 showMods: @this.ForJson(Model.ParsedLog?.Mods?.Select(p => Model.GetSlug(p.Name)).Distinct().ToDictionary(slug => slug, slug => true)),
                 showSections: @this.ForJson(Enum.GetNames(typeof(LogSection)).ToDictionary(section => section, section => false)),
                 showLevels: @this.ForJson(defaultFilters),
-                enableFilters: @this.ForJson(!Model.ShowRaw)
+                enableFilters: @this.ForJson(!Model.ShowRaw),
+                screenIds: @this.ForJson(screenIds)
             }, '@this.Url.PlainAction("Index", "LogParser", values: null)');
         });
     </script>
@@ -305,6 +308,10 @@ else if (Model.ParsedLog?.IsValid == true)
                         @if (message.IsStartOfSection) { <text> v-on:click="toggleSection('@message.Section')" </text> }
                         v-show="filtersAllow('@Model.GetSlug(message.Mod)', '@levelStr') @sectionFilter">
                         <td v-pre>@message.Time</td>
+                        @if (screenIds.Count > 1)
+                        {
+                            <td v-pre>screen_@message.ScreenId</td>
+                        }
                         <td v-pre>@message.Level.ToString().ToUpper()</td>
                         <td v-pre data-title="@message.Mod">@message.Mod</td>
                         <td>
@@ -325,7 +332,7 @@ else if (Model.ParsedLog?.IsValid == true)
                     if (message.Repeated > 0)
                     {
                         <tr class="@levelStr mod mod-repeat" v-show="filtersAllow('@Model.GetSlug(message.Mod)', '@levelStr') @sectionFilter">
-                            <td colspan="3"></td>
+                            <td colspan="4"></td>
                             <td v-pre><i>repeats [@message.Repeated] times.</i></td>
                         </tr>
                     }
diff --git a/src/SMAPI/Constants.cs b/src/SMAPI/Constants.cs
index 5ff324b0..d0f34cee 100644
--- a/src/SMAPI/Constants.cs
+++ b/src/SMAPI/Constants.cs
@@ -39,6 +39,9 @@ namespace StardewModdingAPI
 
         /// <summary>The game's assembly name.</summary>
         internal static string GameAssemblyName => EarlyConstants.Platform == GamePlatform.Windows ? "Stardew Valley" : "StardewValley";
+
+        /// <summary>The <see cref="Context.ScreenId"/> value which should appear in the SMAPI log, if any.</summary>
+        internal static int? LogScreenId { get; set; }
     }
 
     /// <summary>Contains SMAPI's constants and assumptions.</summary>
diff --git a/src/SMAPI/Context.cs b/src/SMAPI/Context.cs
index a7238b32..b1b33cd6 100644
--- a/src/SMAPI/Context.cs
+++ b/src/SMAPI/Context.cs
@@ -1,5 +1,7 @@
+using System.Collections.Generic;
 using StardewModdingAPI.Enums;
 using StardewModdingAPI.Events;
+using StardewModdingAPI.Utilities;
 using StardewValley;
 using StardewValley.Menus;
 
@@ -9,16 +11,49 @@ namespace StardewModdingAPI
     public static class Context
     {
         /*********
+        ** Fields
+        *********/
+        /// <summary>Whether the player has loaded a save and the world has finished initializing.</summary>
+        private static readonly PerScreen<bool> IsWorldReadyForScreen = new PerScreen<bool>();
+
+        /// <summary>The current stage in the game's loading process.</summary>
+        private static readonly PerScreen<LoadStage> LoadStageForScreen = new PerScreen<LoadStage>();
+
+        /// <summary>Whether a player save has been loaded.</summary>
+        internal static bool IsSaveLoaded => Game1.hasLoadedGame && !(Game1.activeClickableMenu is TitleMenu);
+
+        /// <summary>Whether the game is currently writing to the save file.</summary>
+        internal static bool IsSaving => Game1.activeClickableMenu is SaveGameMenu || Game1.activeClickableMenu is ShippingMenu; // saving is performed by SaveGameMenu, but it's wrapped by ShippingMenu on days when the player shipping something
+
+        /// <summary>The active split-screen instance IDs.</summary>
+        internal static readonly ISet<int> ActiveScreenIds = new HashSet<int>();
+
+        /// <summary>The last screen ID that was removed from the game, used to synchronize <see cref="PerScreen{T}"/>.</summary>
+        internal static int LastRemovedScreenId = -1;
+
+        /// <summary>The current stage in the game's loading process.</summary>
+        internal static LoadStage LoadStage
+        {
+            get => Context.LoadStageForScreen.Value;
+            set => Context.LoadStageForScreen.Value = value;
+        }
+
+
+        /*********
         ** Accessors
         *********/
         /****
-        ** Public
+        ** Game/player state
         ****/
         /// <summary>Whether the game has performed core initialization. This becomes true right before the first update tick.</summary>
         public static bool IsGameLaunched { get; internal set; }
 
         /// <summary>Whether the player has loaded a save and the world has finished initializing.</summary>
-        public static bool IsWorldReady { get; internal set; }
+        public static bool IsWorldReady
+        {
+            get => Context.IsWorldReadyForScreen.Value;
+            set => Context.IsWorldReadyForScreen.Value = value;
+        }
 
         /// <summary>Whether <see cref="IsWorldReady"/> is true and the player is free to act in the world (no menu is displayed, no cutscene is in progress, etc).</summary>
         public static bool IsPlayerFree => Context.IsWorldReady && Game1.currentLocation != null && Game1.activeClickableMenu == null && !Game1.dialogueUp && (!Game1.eventUp || Game1.isFestival());
@@ -29,22 +64,36 @@ namespace StardewModdingAPI
         /// <summary>Whether the game is currently running the draw loop. This isn't relevant to most mods, since you should use <see cref="IDisplayEvents"/> events to draw to the screen.</summary>
         public static bool IsInDrawLoop { get; internal set; }
 
-        /// <summary>Whether <see cref="IsWorldReady"/> and the player loaded the save in multiplayer mode (regardless of whether any other players are connected).</summary>
-        public static bool IsMultiplayer => Context.IsWorldReady && Game1.multiplayerMode != Game1.singlePlayer;
-
-        /// <summary>Whether <see cref="IsWorldReady"/> and the current player is the main player. This is always true in single-player, and true when hosting in multiplayer.</summary>
-        public static bool IsMainPlayer => Context.IsWorldReady && Game1.IsMasterGame;
-
         /****
-        ** Internal
+        ** Multiplayer
         ****/
-        /// <summary>Whether a player save has been loaded.</summary>
-        internal static bool IsSaveLoaded => Game1.hasLoadedGame && !(Game1.activeClickableMenu is TitleMenu);
+        /// <summary>The unique ID of the current screen in split-screen mode. A screen is always assigned a new ID when it's opened (so a player who quits and rejoins has a new screen ID).</summary>
+        public static int ScreenId => Game1.game1?.instanceId ?? 0;
 
-        /// <summary>Whether the game is currently writing to the save file.</summary>
-        internal static bool IsSaving => Game1.activeClickableMenu is SaveGameMenu || Game1.activeClickableMenu is ShippingMenu; // saving is performed by SaveGameMenu, but it's wrapped by ShippingMenu on days when the player shipping something
+        /// <summary>Whether the game is running in multiplayer or split-screen mode (regardless of whether any other players are connected). See <see cref="IsSplitScreen"/> and <see cref="HasRemotePlayers"/> for more specific checks.</summary>
+        public static bool IsMultiplayer => Context.IsSplitScreen || (Context.IsWorldReady && Game1.multiplayerMode != Game1.singlePlayer);
 
-        /// <summary>The current stage in the game's loading process.</summary>
-        internal static LoadStage LoadStage { get; set; }
+        /// <summary>Whether this player is running on the main player's computer. This is true for both the main player and split-screen players.</summary>
+        public static bool IsOnHostComputer => Context.IsMainPlayer || Context.IsSplitScreen;
+
+        /// <summary>Whether the current player is playing in a split-screen. This is only applicable when <see cref="IsOnHostComputer"/> is true, since split-screen players on another computer are just regular remote players.</summary>
+        public static bool IsSplitScreen => LocalMultiplayer.IsLocalMultiplayer();
+
+        /// <summary>Whether there are players connected over the network.</summary>
+        public static bool HasRemotePlayers => Context.IsMultiplayer && !Game1.hasLocalClientsOnly;
+
+        /// <summary>Whether the current player is the main player. This is always true in single-player, and true when hosting in multiplayer.</summary>
+        public static bool IsMainPlayer => Game1.IsMasterGame && !(TitleMenu.subMenu is FarmhandMenu);
+
+
+        /*********
+        ** Public methods
+        *********/
+        /// <summary>Get whether a screen ID is still active.</summary>
+        /// <param name="id">The screen ID.</param>
+        public static bool HasScreenId(int id)
+        {
+            return Context.ActiveScreenIds.Contains(id);
+        }
     }
 }
diff --git a/src/SMAPI/Framework/Logging/LogManager.cs b/src/SMAPI/Framework/Logging/LogManager.cs
index 1e484709..a2c0125e 100644
--- a/src/SMAPI/Framework/Logging/LogManager.cs
+++ b/src/SMAPI/Framework/Logging/LogManager.cs
@@ -84,10 +84,11 @@ namespace StardewModdingAPI.Framework.Logging
         /// <param name="writeToConsole">Whether to output log messages to the console.</param>
         /// <param name="isVerbose">Whether verbose logging is enabled. This enables more detailed diagnostic messages than are normally needed.</param>
         /// <param name="isDeveloperMode">Whether to enable full console output for developers.</param>
-        public LogManager(string logPath, ColorSchemeConfig colorConfig, bool writeToConsole, bool isVerbose, bool isDeveloperMode)
+        /// <param name="getScreenIdForLog">Get the screen ID that should be logged to distinguish between players in split-screen mode, if any.</param>
+        public LogManager(string logPath, ColorSchemeConfig colorConfig, bool writeToConsole, bool isVerbose, bool isDeveloperMode, Func<int?> getScreenIdForLog)
         {
             // init construction logic
-            this.GetMonitorImpl = name => new Monitor(name, this.IgnoreChar, this.LogFile, colorConfig, isVerbose)
+            this.GetMonitorImpl = name => new Monitor(name, this.IgnoreChar, this.LogFile, colorConfig, isVerbose, getScreenIdForLog)
             {
                 WriteToConsole = writeToConsole,
                 ShowTraceInConsole = isDeveloperMode,
diff --git a/src/SMAPI/Framework/ModHelpers/DataHelper.cs b/src/SMAPI/Framework/ModHelpers/DataHelper.cs
index 41612387..0fe3209f 100644
--- a/src/SMAPI/Framework/ModHelpers/DataHelper.cs
+++ b/src/SMAPI/Framework/ModHelpers/DataHelper.cs
@@ -69,8 +69,8 @@ namespace StardewModdingAPI.Framework.ModHelpers
         {
             if (Context.LoadStage == LoadStage.None)
                 throw new InvalidOperationException($"Can't use {nameof(IMod.Helper)}.{nameof(IModHelper.Data)}.{nameof(this.ReadSaveData)} when a save file isn't loaded.");
-            if (!Game1.IsMasterGame)
-                throw new InvalidOperationException($"Can't use {nameof(IMod.Helper)}.{nameof(IModHelper.Data)}.{nameof(this.ReadSaveData)} because this isn't the main player. (Save files are stored on the main player's computer.)");
+            if (!Context.IsOnHostComputer)
+                throw new InvalidOperationException($"Can't use {nameof(IMod.Helper)}.{nameof(IModHelper.Data)}.{nameof(this.ReadSaveData)} when connected to a remote host. (Save files are stored on the main player's computer.)");
 
 
             string internalKey = this.GetSaveFileKey(key);
@@ -87,8 +87,8 @@ namespace StardewModdingAPI.Framework.ModHelpers
         {
             if (Context.LoadStage == LoadStage.None)
                 throw new InvalidOperationException($"Can't use {nameof(IMod.Helper)}.{nameof(IModHelper.Data)}.{nameof(this.WriteSaveData)} when a save file isn't loaded.");
-            if (!Game1.IsMasterGame)
-                throw new InvalidOperationException($"Can't use {nameof(IMod.Helper)}.{nameof(IModHelper.Data)}.{nameof(this.WriteSaveData)} because this isn't the main player. (Save files are stored on the main player's computer.)");
+            if (!Context.IsOnHostComputer)
+                throw new InvalidOperationException($"Can't use {nameof(IMod.Helper)}.{nameof(IModHelper.Data)}.{nameof(this.WriteSaveData)} when connected to a remote host. (Save files are stored on the main player's computer.)");
 
             string internalKey = this.GetSaveFileKey(key);
             string data = model != null
diff --git a/src/SMAPI/Framework/ModHelpers/InputHelper.cs b/src/SMAPI/Framework/ModHelpers/InputHelper.cs
index 09ce3c65..e1317544 100644
--- a/src/SMAPI/Framework/ModHelpers/InputHelper.cs
+++ b/src/SMAPI/Framework/ModHelpers/InputHelper.cs
@@ -1,3 +1,4 @@
+using System;
 using StardewModdingAPI.Framework.Input;
 
 namespace StardewModdingAPI.Framework.ModHelpers
@@ -8,8 +9,8 @@ namespace StardewModdingAPI.Framework.ModHelpers
         /*********
         ** Accessors
         *********/
-        /// <summary>Manages the game's input state.</summary>
-        private readonly SInputState InputState;
+        /// <summary>Manages the game's input state for the current player instance. That may not be the main player in split-screen mode.</summary>
+        private readonly Func<SInputState> CurrentInputState;
 
 
         /*********
@@ -17,41 +18,41 @@ namespace StardewModdingAPI.Framework.ModHelpers
         *********/
         /// <summary>Construct an instance.</summary>
         /// <param name="modID">The unique ID of the relevant mod.</param>
-        /// <param name="inputState">Manages the game's input state.</param>
-        public InputHelper(string modID, SInputState inputState)
+        /// <param name="currentInputState">Manages the game's input state for the current player instance. That may not be the main player in split-screen mode.</param>
+        public InputHelper(string modID, Func<SInputState> currentInputState)
             : base(modID)
         {
-            this.InputState = inputState;
+            this.CurrentInputState = currentInputState;
         }
 
         /// <inheritdoc />
         public ICursorPosition GetCursorPosition()
         {
-            return this.InputState.CursorPosition;
+            return this.CurrentInputState().CursorPosition;
         }
 
         /// <inheritdoc />
         public bool IsDown(SButton button)
         {
-            return this.InputState.IsDown(button);
+            return this.CurrentInputState().IsDown(button);
         }
 
         /// <inheritdoc />
         public bool IsSuppressed(SButton button)
         {
-            return this.InputState.IsSuppressed(button);
+            return this.CurrentInputState().IsSuppressed(button);
         }
 
         /// <inheritdoc />
         public void Suppress(SButton button)
         {
-            this.InputState.OverrideButton(button, setDown: false);
+            this.CurrentInputState().OverrideButton(button, setDown: false);
         }
 
         /// <inheritdoc />
         public SButtonState GetState(SButton button)
         {
-            return this.InputState.GetState(button);
+            return this.CurrentInputState().GetState(button);
         }
     }
 }
diff --git a/src/SMAPI/Framework/ModHelpers/ModHelper.cs b/src/SMAPI/Framework/ModHelpers/ModHelper.cs
index d9fc8621..058bff83 100644
--- a/src/SMAPI/Framework/ModHelpers/ModHelper.cs
+++ b/src/SMAPI/Framework/ModHelpers/ModHelper.cs
@@ -51,7 +51,7 @@ namespace StardewModdingAPI.Framework.ModHelpers
         /// <summary>Construct an instance.</summary>
         /// <param name="modID">The mod's unique ID.</param>
         /// <param name="modDirectory">The full path to the mod's folder.</param>
-        /// <param name="inputState">Manages the game's input state.</param>
+        /// <param name="currentInputState">Manages the game's input state for the current player instance. That may not be the main player in split-screen mode.</param>
         /// <param name="events">Manages access to events raised by SMAPI.</param>
         /// <param name="contentHelper">An API for loading content assets.</param>
         /// <param name="contentPackHelper">An API for managing content packs.</param>
@@ -63,7 +63,7 @@ namespace StardewModdingAPI.Framework.ModHelpers
         /// <param name="translationHelper">An API for reading translations stored in the mod's <c>i18n</c> folder.</param>
         /// <exception cref="ArgumentNullException">An argument is null or empty.</exception>
         /// <exception cref="InvalidOperationException">The <paramref name="modDirectory"/> path does not exist on disk.</exception>
-        public ModHelper(string modID, string modDirectory, SInputState inputState, IModEvents events, IContentHelper contentHelper, IContentPackHelper contentPackHelper, ICommandHelper commandHelper, IDataHelper dataHelper, IModRegistry modRegistry, IReflectionHelper reflectionHelper, IMultiplayerHelper multiplayer, ITranslationHelper translationHelper)
+        public ModHelper(string modID, string modDirectory, Func<SInputState> currentInputState, IModEvents events, IContentHelper contentHelper, IContentPackHelper contentPackHelper, ICommandHelper commandHelper, IDataHelper dataHelper, IModRegistry modRegistry, IReflectionHelper reflectionHelper, IMultiplayerHelper multiplayer, ITranslationHelper translationHelper)
             : base(modID)
         {
             // validate directory
@@ -77,7 +77,7 @@ namespace StardewModdingAPI.Framework.ModHelpers
             this.Content = contentHelper ?? throw new ArgumentNullException(nameof(contentHelper));
             this.ContentPacks = contentPackHelper ?? throw new ArgumentNullException(nameof(contentPackHelper));
             this.Data = dataHelper ?? throw new ArgumentNullException(nameof(dataHelper));
-            this.Input = new InputHelper(modID, inputState);
+            this.Input = new InputHelper(modID, currentInputState);
             this.ModRegistry = modRegistry ?? throw new ArgumentNullException(nameof(modRegistry));
             this.ConsoleCommands = commandHelper ?? throw new ArgumentNullException(nameof(commandHelper));
             this.Reflection = reflectionHelper ?? throw new ArgumentNullException(nameof(reflectionHelper));
diff --git a/src/SMAPI/Framework/Monitor.cs b/src/SMAPI/Framework/Monitor.cs
index 533420a5..04e67d68 100644
--- a/src/SMAPI/Framework/Monitor.cs
+++ b/src/SMAPI/Framework/Monitor.cs
@@ -30,6 +30,9 @@ namespace StardewModdingAPI.Framework
         /// <summary>A cache of messages that should only be logged once.</summary>
         private readonly HashSet<string> LogOnceCache = new HashSet<string>();
 
+        /// <summary>Get the screen ID that should be logged to distinguish between players in split-screen mode, if any.</summary>
+        private readonly Func<int?> GetScreenIdForLog;
+
 
         /*********
         ** Accessors
@@ -56,7 +59,8 @@ namespace StardewModdingAPI.Framework
         /// <param name="logFile">The log file to which to write messages.</param>
         /// <param name="colorConfig">The colors to use for text written to the SMAPI console.</param>
         /// <param name="isVerbose">Whether verbose logging is enabled. This enables more detailed diagnostic messages than are normally needed.</param>
-        public Monitor(string source, char ignoreChar, LogFileManager logFile, ColorSchemeConfig colorConfig, bool isVerbose)
+        /// <param name="getScreenIdForLog">Get the screen ID that should be logged to distinguish between players in split-screen mode, if any.</param>
+        public Monitor(string source, char ignoreChar, LogFileManager logFile, ColorSchemeConfig colorConfig, bool isVerbose, Func<int?> getScreenIdForLog)
         {
             // validate
             if (string.IsNullOrWhiteSpace(source))
@@ -68,6 +72,7 @@ namespace StardewModdingAPI.Framework
             this.ConsoleWriter = new ColorfulConsoleWriter(Constants.Platform, colorConfig);
             this.IgnoreChar = ignoreChar;
             this.IsVerbose = isVerbose;
+            this.GetScreenIdForLog = getScreenIdForLog;
         }
 
         /// <inheritdoc />
@@ -143,7 +148,9 @@ namespace StardewModdingAPI.Framework
         private string GenerateMessagePrefix(string source, ConsoleLogLevel level)
         {
             string levelStr = level.ToString().ToUpper().PadRight(Monitor.MaxLevelLength);
-            return $"[{DateTime.Now:HH:mm:ss} {levelStr} {source}]";
+            int? playerIndex = this.GetScreenIdForLog();
+
+            return $"[{DateTime.Now:HH:mm:ss} {levelStr}{(playerIndex != null ? $" screen_{playerIndex}" : "")} {source}]";
         }
     }
 }
diff --git a/src/SMAPI/Framework/SCore.cs b/src/SMAPI/Framework/SCore.cs
index 1b4c32bb..a7f8fbed 100644
--- a/src/SMAPI/Framework/SCore.cs
+++ b/src/SMAPI/Framework/SCore.cs
@@ -85,17 +85,14 @@ namespace StardewModdingAPI.Framework
         private readonly CommandManager CommandManager = new CommandManager();
 
         /// <summary>The underlying game instance.</summary>
-        private SGame Game;
-
-        /// <summary>Manages input visible to the game.</summary>
-        private SInputState Input => SGame.Input;
-
-        /// <summary>The game's core multiplayer utility.</summary>
-        private SMultiplayer Multiplayer => SGame.Multiplayer;
+        private SGameRunner Game;
 
         /// <summary>SMAPI's content manager.</summary>
         private ContentCoordinator ContentCore;
 
+        /// <summary>The game's core multiplayer utility for the main player.</summary>
+        private SMultiplayer Multiplayer;
+
         /// <summary>Tracks the installed mods.</summary>
         /// <remarks>This is initialized after the game starts.</remarks>
         private readonly ModRegistry ModRegistry = new ModRegistry();
@@ -103,11 +100,6 @@ namespace StardewModdingAPI.Framework
         /// <summary>Manages SMAPI events for mods.</summary>
         private readonly EventManager EventManager;
 
-        /// <summary>Monitors the entire game state for changes.</summary>
-        private WatcherCore Watchers;
-
-        /// <summary>A snapshot of the current <see cref="Watchers"/> state.</summary>
-        private readonly WatcherSnapshot WatcherSnapshot = new WatcherSnapshot();
 
         /****
         ** State
@@ -127,25 +119,15 @@ namespace StardewModdingAPI.Framework
         /// <summary>Whether post-game-startup initialization has been performed.</summary>
         private bool IsInitialized;
 
+        /// <summary>Whether the player just returned to the title screen.</summary>
+        public bool JustReturnedToTitle { get; set; }
+
         /// <summary>The maximum number of consecutive attempts SMAPI should make to recover from an update error.</summary>
         private readonly Countdown UpdateCrashTimer = new Countdown(60); // 60 ticks = roughly one second
 
-        /// <summary>The number of ticks until SMAPI should notify mods that the game has loaded.</summary>
-        /// <remarks>Skipping a few frames ensures the game finishes initializing the world before mods try to change it.</remarks>
-        private readonly Countdown AfterLoadTimer = new Countdown(5);
-
         /// <summary>Whether custom content was removed from the save data to avoid a crash.</summary>
         private bool IsSaveContentRemoved;
 
-        /// <summary>Whether the game is saving and SMAPI has already raised <see cref="IGameLoopEvents.Saving"/>.</summary>
-        private bool IsBetweenSaveEvents;
-
-        /// <summary>Whether the game is creating the save file and SMAPI has already raised <see cref="IGameLoopEvents.SaveCreating"/>.</summary>
-        private bool IsBetweenCreateEvents;
-
-        /// <summary>Whether the player just returned to the title screen.</summary>
-        private bool JustReturnedToTitle;
-
         /// <summary>Asset interceptors added or removed since the last tick.</summary>
         private readonly List<AssetInterceptorChange> ReloadAssetInterceptorsQueue = new List<AssetInterceptorChange>();
 
@@ -191,7 +173,7 @@ namespace StardewModdingAPI.Framework
             if (File.Exists(Constants.ApiUserConfigPath))
                 JsonConvert.PopulateObject(File.ReadAllText(Constants.ApiUserConfigPath), this.Settings);
 
-            this.LogManager = new LogManager(logPath: logPath, colorConfig: this.Settings.ConsoleColors, writeToConsole: writeToConsole, isVerbose: this.Settings.VerboseLogging, isDeveloperMode: this.Settings.DeveloperMode);
+            this.LogManager = new LogManager(logPath: logPath, colorConfig: this.Settings.ConsoleColors, writeToConsole: writeToConsole, isVerbose: this.Settings.VerboseLogging, isDeveloperMode: this.Settings.DeveloperMode, getScreenIdForLog: this.GetScreenIdForLog);
 
             SCore.PerformanceMonitor = new PerformanceMonitor(this.Monitor);
             this.EventManager = new EventManager(this.ModRegistry, SCore.PerformanceMonitor);
@@ -250,22 +232,22 @@ namespace StardewModdingAPI.Framework
                 LocalizedContentManager.OnLanguageChange += locale => this.OnLocaleChanged();
 
                 // override game
-                var multiplayer = new SMultiplayer(this.Monitor, this.EventManager, this.Toolkit.JsonHelper, this.ModRegistry, this.Reflection, this.OnModMessageReceived, this.Settings.LogNetworkTraffic);
-                var modHooks = new SModHooks(this.OnNewDayAfterFade);
+                this.Multiplayer = new SMultiplayer(this.Monitor, this.EventManager, this.Toolkit.JsonHelper, this.ModRegistry, this.Reflection, this.OnModMessageReceived, this.Settings.LogNetworkTraffic);
                 SGame.CreateContentManagerImpl = this.CreateContentManager; // must be static since the game accesses it before the SGame constructor is called
-                this.Game = new SGame(
+                this.Game = new SGameRunner(
                     monitor: this.Monitor,
                     reflection: this.Reflection,
                     eventManager: this.EventManager,
-                    modHooks: modHooks,
-                    multiplayer: multiplayer,
+                    modHooks: new SModHooks(this.OnNewDayAfterFade),
+                    multiplayer: this.Multiplayer,
                     exitGameImmediately: this.ExitGameImmediately,
 
                     onGameContentLoaded: this.OnGameContentLoaded,
                     onGameUpdating: this.OnGameUpdating,
+                    onPlayerInstanceUpdating: this.OnPlayerInstanceUpdating,
                     onGameExiting: this.OnGameExiting
                 );
-                StardewValley.Program.gamePtr = this.Game;
+                StardewValley.GameRunner.instance = this.Game;
 
                 // apply game patches
                 new GamePatcher(this.Monitor).Apply(
@@ -422,12 +404,6 @@ namespace StardewModdingAPI.Framework
         /// <summary>Raised after the game finishes initializing.</summary>
         private void OnGameInitialized()
         {
-            // set initial state
-            this.Input.TrueUpdate();
-
-            // init watchers
-            this.Watchers = new WatcherCore(this.Input, this.Game.GetObservableLocations());
-
             // validate XNB integrity
             if (!this.ValidateContentIntegrity())
                 this.Monitor.Log("SMAPI found problems in your game's content files which are likely to cause errors or crashes. Consider uninstalling XNB mods or reinstalling the game.", LogLevel.Error);
@@ -460,8 +436,6 @@ namespace StardewModdingAPI.Framework
         /// <param name="runGameUpdate">Invoke the game's update logic.</param>
         private void OnGameUpdating(GameTime gameTime, Action runGameUpdate)
         {
-            var events = this.EventManager;
-
             try
             {
                 /*********
@@ -471,15 +445,6 @@ namespace StardewModdingAPI.Framework
                 SCore.DeprecationManager.PrintQueued();
                 SCore.PerformanceMonitor.PrintQueuedAlerts();
 
-                // reapply overrides
-                if (this.JustReturnedToTitle)
-                {
-                    if (!(Game1.mapDisplayDevice is SDisplayDevice))
-                        Game1.mapDisplayDevice = this.GetMapDisplayDevice();
-
-                    this.JustReturnedToTitle = false;
-                }
-
                 /*********
                 ** First-tick initialization
                 *********/
@@ -490,25 +455,151 @@ namespace StardewModdingAPI.Framework
                 }