GUI: Discord Rich Presence (#73)

Publish launcher status to Discord over its local IPC named pipe with
no external dependency: framed-JSON handshake and SET_ACTIVITY, a
background worker with reconnection and latest-state dedup, and silent
no-op behavior when Discord is not running.

- "Browsing the library" (game count, session elapsed) while idle;
  "Playing <game>" with title id and elapsed time during emulation.
  Activities always carry timestamps: Discord accepts but does not
  render activities without them
- Presence flips back to browsing immediately on Stop instead of
  waiting for process exit: a game wedged in a GPU driver call can
  outlive termination for a while. Stop also terminates the job
  object so the whole child tree dies even in that state
- Toggle in the Options panel (persisted); client id configurable in
  gui-settings.json; SHARPEMU_LOG_DISCORD=1 traces queue/send/failure

src/SharpEmu.GUI/DiscordRichPresence.cs

@@ -0,0 +1,252 @@
+// Copyright (C) 2026 SharpEmu Emulator Project
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+using System.IO.Pipes;
+using System.Text;
+using System.Text.Json;
+
+namespace SharpEmu.GUI;
+
+/// <summary>
+/// Minimal Discord Rich Presence client. Speaks Discord's local IPC
+/// protocol (framed JSON over the discord-ipc-N named pipe) directly, so no
+/// external dependency is needed. All failures are silent: no Discord, no
+/// presence, no impact on the launcher.
+/// </summary>
+public sealed class DiscordRichPresence : IDisposable
+{
+    private const int OpHandshake = 0;
+    private const int OpFrame = 1;
+    private const int MaxFrameBytes = 64 * 1024;
+
+    private static readonly JsonSerializerOptions JsonOptions = new()
+    {
+        DefaultIgnoreCondition = System.Text.Json.Serialization.JsonIgnoreCondition.WhenWritingNull,
+    };
+
+    private readonly object _gate = new();
+    private readonly string _clientId;
+    private readonly AutoResetEvent _signal = new(false);
+    private readonly Thread _worker;
+
+    private NamedPipeClientStream? _pipe;
+    private PresenceState? _desired;
+    private PresenceState? _sent;
+    private volatile bool _disposed;
+
+    private sealed record PresenceState(string Details, string? State, long? StartUnixSeconds);
+
+    public DiscordRichPresence(string clientId)
+    {
+        _clientId = clientId;
+        _worker = new Thread(WorkerLoop)
+        {
+            IsBackground = true,
+            Name = "DiscordRichPresence",
+        };
+        _worker.Start();
+    }
+
+    /// <summary>
+    /// Requests the given presence; the worker applies it asynchronously and
+    /// retries (with reconnection) until it is delivered or replaced.
+    /// </summary>
+    public void SetPresence(string details, string? state = null, long? startUnixSeconds = null)
+    {
+        lock (_gate)
+        {
+            _desired = new PresenceState(details, state, startUnixSeconds);
+        }
+
+        Trace($"queued details=\"{details}\" state=\"{state}\"");
+        _signal.Set();
+    }
+
+    public void Dispose()
+    {
+        _disposed = true;
+        _signal.Set();
+        ClosePipe();
+    }
+
+    private void WorkerLoop()
+    {
+        while (!_disposed)
+        {
+            // Woken immediately on presence changes; the periodic tick
+            // retries after connection failures (e.g. Discord starts later).
+            _signal.WaitOne(TimeSpan.FromSeconds(15));
+            if (_disposed || _clientId.Length == 0)
+            {
+                continue;
+            }
+
+            PresenceState? desired;
+            lock (_gate)
+            {
+                desired = _desired;
+            }
+
+            if (desired is null || desired == _sent)
+            {
+                continue;
+            }
+
+            try
+            {
+                EnsureConnected();
+                SendActivity(desired);
+                _sent = desired;
+                Trace($"sent details=\"{desired.Details}\" state=\"{desired.State}\"");
+            }
+            catch (Exception exception)
+            {
+                // Connection died (or never existed); reconnect on a later tick.
+                Trace($"send failed: {exception.Message}");
+                ClosePipe();
+                _sent = null;
+            }
+        }
+    }
+
+    private void EnsureConnected()
+    {
+        if (_pipe is { IsConnected: true })
+        {
+            return;
+        }
+
+        ClosePipe();
+        Exception? lastError = null;
+        for (var index = 0; index < 10; index++)
+        {
+            var pipe = new NamedPipeClientStream(
+                ".",
+                $"discord-ipc-{index}",
+                PipeDirection.InOut,
+                PipeOptions.Asynchronous);
+            try
+            {
+                pipe.Connect(500);
+                _pipe = pipe;
+                WriteFrame(OpHandshake, JsonSerializer.Serialize(new
+                {
+                    v = 1,
+                    client_id = _clientId,
+                }));
+
+                // Discord replies with a READY (or error) frame; consume it
+                // so the pipe buffer stays drained.
+                _ = ReadFrame();
+                return;
+            }
+            catch (Exception exception)
+            {
+                lastError = exception;
+                pipe.Dispose();
+                _pipe = null;
+            }
+        }
+
+        throw lastError ?? new IOException("Discord IPC pipe not found.");
+    }
+
+    private void SendActivity(PresenceState presence)
+    {
+        var payload = new Dictionary<string, object?>
+        {
+            ["cmd"] = "SET_ACTIVITY",
+            ["nonce"] = Guid.NewGuid().ToString(),
+            ["args"] = new Dictionary<string, object?>
+            {
+                ["pid"] = Environment.ProcessId,
+                ["activity"] = new Dictionary<string, object?>
+                {
+                    ["details"] = presence.Details,
+                    ["state"] = presence.State,
+                    ["timestamps"] = presence.StartUnixSeconds is { } start
+                        ? new Dictionary<string, object?> { ["start"] = start }
+                        : null,
+                    ["assets"] = new Dictionary<string, object?>
+                    {
+                        ["large_image"] = "logo",
+                        ["large_text"] = "SharpEmu",
+                    },
+                },
+            },
+        };
+
+        WriteFrame(OpFrame, JsonSerializer.Serialize(payload, JsonOptions));
+
+        // Consume Discord's acknowledgement to keep the pipe drained.
+        _ = ReadFrame();
+    }
+
+    private void WriteFrame(int opcode, string json)
+    {
+        var pipe = _pipe ?? throw new IOException("Discord IPC pipe is not connected.");
+        var payload = Encoding.UTF8.GetBytes(json);
+        var frame = new byte[8 + payload.Length];
+        BitConverter.TryWriteBytes(frame.AsSpan(0, 4), opcode);
+        BitConverter.TryWriteBytes(frame.AsSpan(4, 4), payload.Length);
+        payload.CopyTo(frame, 8);
+        pipe.Write(frame, 0, frame.Length);
+        pipe.Flush();
+    }
+
+    private string ReadFrame()
+    {
+        var pipe = _pipe ?? throw new IOException("Discord IPC pipe is not connected.");
+        var header = ReadExactly(pipe, 8);
+        var length = BitConverter.ToInt32(header, 4);
+        if (length is < 0 or > MaxFrameBytes)
+        {
+            throw new IOException($"Discord IPC frame length {length} is out of range.");
+        }
+
+        return Encoding.UTF8.GetString(ReadExactly(pipe, length));
+    }
+
+    private static byte[] ReadExactly(NamedPipeClientStream pipe, int count)
+    {
+        var buffer = new byte[count];
+        var read = 0;
+        while (read < count)
+        {
+            var chunk = pipe.Read(buffer, read, count - read);
+            if (chunk <= 0)
+            {
+                throw new IOException("Discord IPC pipe closed.");
+            }
+
+            read += chunk;
+        }
+
+        return buffer;
+    }
+
+    private static void Trace(string message)
+    {
+        if (string.Equals(
+                Environment.GetEnvironmentVariable("SHARPEMU_LOG_DISCORD"),
+                "1",
+                StringComparison.Ordinal))
+        {
+            Console.Error.WriteLine($"[DISCORD] {message}");
+        }
+    }
+
+    private void ClosePipe()
+    {
+        var pipe = _pipe;
+        _pipe = null;
+        try
+        {
+            pipe?.Dispose();
+        }
+        catch (Exception)
+        {
+            // Best effort; the pipe may already be broken.
+        }
+    }
+}

src/SharpEmu.GUI/EmulatorProcess.cs

@@ -85,6 +85,14 @@ internal sealed class EmulatorProcess : IDisposable
                 return;
             }
 
+            // Prefer terminating the job: it kills the whole tree, including
+            // any children the emulator spawned, even when the main process
+            // is wedged in a GPU driver call.
+            if (_jobHandle != 0)
+            {
+                _ = TerminateJobObject(_jobHandle, 1);
+            }
+
             if (_processHandle != 0)
             {
                 _ = TerminateProcess(_processHandle, 1);
@@ -639,6 +647,10 @@ internal sealed class EmulatorProcess : IDisposable
     [return: MarshalAs(UnmanagedType.Bool)]
     private static extern bool TerminateProcess(nint process, uint exitCode);
 
+    [DllImport("kernel32.dll", SetLastError = true)]
+    [return: MarshalAs(UnmanagedType.Bool)]
+    private static extern bool TerminateJobObject(nint job, uint exitCode);
+
     [DllImport("kernel32.dll", SetLastError = true)]
     [return: MarshalAs(UnmanagedType.Bool)]
     private static extern bool CloseHandle(nint handle);

src/SharpEmu.GUI/GuiSettings.cs

@@ -31,6 +31,16 @@ public sealed class GuiSettings
 
     public string? EmulatorPath { get; set; }
 
+    /// <summary>Publish launcher/game status to Discord Rich Presence.</summary>
+    public bool DiscordRichPresence { get; set; } = true;
+
+    /// <summary>
+    /// Discord application ID used for Rich Presence; the default is the
+    /// SharpEmu application. Override to rebrand what Discord shows as
+    /// "Playing …" (register at discord.com/developers/applications).
+    /// </summary>
+    public string DiscordClientId { get; set; } = "1525606762248540221";
+
     // The emulator is portable and keeps its data next to the executable;
     // the GUI follows the same convention.
     public static string SettingsPath => Path.Combine(AppContext.BaseDirectory, "gui-settings.json");

src/SharpEmu.GUI/MainWindow.axaml

@@ -252,10 +252,14 @@ SPDX-License-Identifier: GPL-2.0-or-later
               <TextBlock Classes="fieldLabel" Text="Log to file" />
               <ToggleSwitch x:Name="LogToFileToggle" OnContent="On" OffContent="Off" />
             </StackPanel>
-            <StackPanel>
+            <StackPanel Margin="0,0,24,0">
               <TextBlock Classes="fieldLabel" Text="Title music" />
               <ToggleSwitch x:Name="TitleMusicToggle" OnContent="On" OffContent="Off" IsChecked="True" />
             </StackPanel>
+            <StackPanel>
+              <TextBlock Classes="fieldLabel" Text="Discord presence" />
+              <ToggleSwitch x:Name="DiscordToggle" OnContent="On" OffContent="Off" />
+            </StackPanel>
           </WrapPanel>
         </StackPanel>
       </Border>

src/SharpEmu.GUI/MainWindow.axaml.cs

@@ -44,6 +44,13 @@ public partial class MainWindow : Window
     private string? _emulatorExePath;
     private bool _isRunning;
     private int _autoScrollTicks;
+
+    // Discord Rich Presence state.
+    private readonly long _launcherStartUnixSeconds = DateTimeOffset.UtcNow.ToUnixTimeSeconds();
+    private DiscordRichPresence? _discord;
+    private string? _runningGameName;
+    private string? _runningGameTitleId;
+    private long _runningSinceUnixSeconds;
     private int _detailLoadGeneration;
     private int _backdropGeneration;
 
@@ -82,12 +89,17 @@ public partial class MainWindow : Window
         RescanButton.Click += async (_, _) => await RescanLibraryAsync();
         OpenFileButton.Click += async (_, _) => await OpenFileAsync();
         LaunchButton.Click += (_, _) => LaunchSelected();
-        StopButton.Click += (_, _) => _emulator?.Stop();
+        StopButton.Click += (_, _) => StopEmulator();
         ClearLogButton.Click += (_, _) => _consoleLines.Clear();
         CopyLogButton.Click += async (_, _) => await CopyConsoleAsync();
         OptionsToggle.IsCheckedChanged += (_, _) => OptionsPanel.IsVisible = OptionsToggle.IsChecked == true;
         ConsoleToggle.IsCheckedChanged += (_, _) => ConsolePanel.IsVisible = ConsoleToggle.IsChecked == true;
         TitleMusicToggle.IsCheckedChanged += (_, _) => OnTitleMusicToggled();
+        DiscordToggle.IsCheckedChanged += (_, _) =>
+        {
+            _settings.DiscordRichPresence = DiscordToggle.IsChecked == true;
+            UpdateDiscordPresence();
+        };
 
         GameList.AddHandler(ContextRequestedEvent, OnGameContextRequested, RoutingStrategies.Tunnel);
         CtxLaunch.Click += (_, _) => LaunchSelected();
@@ -164,7 +176,7 @@ public partial class MainWindow : Window
 
         if ((pressed & 0x2000) != 0) // Circle
         {
-            _emulator?.Stop();
+            StopEmulator();
         }
 
         _previousPadButtons = pad.Buttons;
@@ -235,9 +247,45 @@ public partial class MainWindow : Window
         _settings = GuiSettings.Load();
         ApplySettingsToControls();
         LocateEmulator();
+        UpdateDiscordPresence();
         await RescanLibraryAsync();
     }
 
+    // ---- Discord Rich Presence ----
+
+    /// <summary>
+    /// Publishes the launcher state to Discord: browsing while idle, the
+    /// running game (with elapsed time) during emulation. No-ops when
+    /// disabled or when no Discord application ID is configured.
+    /// </summary>
+    private void UpdateDiscordPresence()
+    {
+        if (!_settings.DiscordRichPresence || _settings.DiscordClientId.Length == 0)
+        {
+            _discord?.Dispose();
+            _discord = null;
+            return;
+        }
+
+        _discord ??= new DiscordRichPresence(_settings.DiscordClientId);
+        if (_isRunning && _runningGameName is { } gameName)
+        {
+            _discord.SetPresence(
+                $"Playing {gameName}",
+                _runningGameTitleId,
+                _runningSinceUnixSeconds);
+        }
+        else
+        {
+            // Discord does not render activities without timestamps, so the
+            // browsing state carries the launcher's start time.
+            _discord.SetPresence(
+                "Browsing the library",
+                $"{_allGames.Count} game(s)",
+                _launcherStartUnixSeconds);
+        }
+    }
+
     private void OnWindowClosing()
     {
         ReadControlsIntoSettings();
@@ -245,6 +293,7 @@ public partial class MainWindow : Window
         _consoleFlushTimer.Stop();
         _gamepadTimer.Stop();
         _sndPreview.Stop();
+        _discord?.Dispose();
         _emulator?.Dispose();
         DropFileLog();
     }
@@ -275,6 +324,7 @@ public partial class MainWindow : Window
         StrictToggle.IsChecked = _settings.StrictDynlibResolution;
         LogToFileToggle.IsChecked = _settings.LogToFile;
         TitleMusicToggle.IsChecked = _settings.PlayTitleMusic;
+        DiscordToggle.IsChecked = _settings.DiscordRichPresence;
     }
 
     private void ReadControlsIntoSettings()
@@ -284,6 +334,7 @@ public partial class MainWindow : Window
         _settings.StrictDynlibResolution = StrictToggle.IsChecked == true;
         _settings.LogToFile = LogToFileToggle.IsChecked == true;
         _settings.PlayTitleMusic = TitleMusicToggle.IsChecked == true;
+        _settings.DiscordRichPresence = DiscordToggle.IsChecked == true;
     }
 
     private string SelectedLogLevel()
@@ -382,6 +433,7 @@ public partial class MainWindow : Window
         _allGames.AddRange(games);
         RefreshVisibleGames();
         LoadGameDetailsInBackground(games);
+        UpdateDiscordPresence();
         StatusBarRight.Text = folders.Length == 0
             ? "Add a game folder to populate the library."
             : $"Library scanned: {games.Count} game(s) in {folders.Length} folder(s).";
@@ -1009,10 +1061,38 @@ public partial class MainWindow : Window
 
         _emulator = emulator;
         _isRunning = true;
+        _runningGameName = displayName;
+        _runningGameTitleId = _allGames
+            .FirstOrDefault(game => game.Path.Equals(ebootPath, StringComparison.OrdinalIgnoreCase))?
+            .TitleId;
+        _runningSinceUnixSeconds = DateTimeOffset.UtcNow.ToUnixTimeSeconds();
         StatusDot.Fill = SuccessLineBrush;
         StatusText.Text = $"Running — {displayName}";
         StatusBarRight.Text = $"Running {displayName}";
         UpdateRunButtons();
+        UpdateDiscordPresence();
+    }
+
+    /// <summary>
+    /// Stops the running game and updates status/presence immediately. The
+    /// process-exit path still runs when the corpse is collected, but a game
+    /// wedged in a GPU driver call can keep its process alive for a long
+    /// time after termination — the launcher should not look (or tell
+    /// Discord it is) "playing" during that window.
+    /// </summary>
+    private void StopEmulator()
+    {
+        if (!_isRunning)
+        {
+            return;
+        }
+
+        _emulator?.Stop();
+        _runningGameName = null;
+        _runningGameTitleId = null;
+        StatusText.Text = "Stopping…";
+        StatusBarRight.Text = "Stopping…";
+        UpdateDiscordPresence();
     }
 
     /// <summary>
@@ -1069,7 +1149,10 @@ public partial class MainWindow : Window
         StatusDot.Fill = exitCode == 0 ? (IBrush)SuccessLineBrush : ErrorLineBrush;
         StatusText.Text = $"Exited with code {exitCode} ({meaning})";
         StatusBarRight.Text = "Idle";
+        _runningGameName = null;
+        _runningGameTitleId = null;
         UpdateRunButtons();
+        UpdateDiscordPresence();
     }
 
     private void UpdateRunButtons()