Merge pull request #2982 from HeatXD/spectating

Netplay / GGPO: Spectating up to 4 players

dep/ggpo-x/src/backends/p2p.cpp

@@ -294,7 +294,7 @@ Peer2PeerBackend::AddPlayer(GGPOPlayer *player,
    }
 
    // no other players in this session?
-   if (player->type == GGPO_PLAYERTYPE_LOCAL && _num_players == 1)
+   if (player->type == GGPO_PLAYERTYPE_LOCAL && _num_players == 1 && _num_spectators == 0)
      _synchronizing = false;
 
    return GGPO_OK;

dep/ggpo-x/src/backends/spectator.cpp

@@ -21,13 +21,13 @@ SpectatorBackend::SpectatorBackend(GGPOSessionCallbacks* cb, int num_players, in
     * Initialize the UDP port
     */
    // FIXME
-   abort();
+   //abort();
    //_udp.Init(localport, &_poll, this);
 
    /*
     * Init the host endpoint
     */
-   //_host.Init(&_udp, _poll, 0, hostip, hostport, NULL);
+   _host.Init(peer, 0, NULL);
    _host.Synchronize();
 }
   

src/core/netplay.cpp

@@ -90,6 +90,12 @@ static void ShowChatMessage(s32 player_id, const std::string_view& message);
 static void RequestReset(ResetRequestMessage::Reason reason, s32 causing_player_id = 0);
 static void SendConnectRequest();
 
+// Spectators
+static bool IsSpectator(const ENetPeer* peer);
+static s32 GetFreeSpectatorSlot();
+static s32 GetSpectatorSlotForPeer(const ENetPeer* peer);
+static void DropSpectator(s32 slot_id, DropPlayerReason reason);
+
 // Controlpackets
 static void HandleMessageFromNewPeer(ENetPeer* peer, const ENetPacket* pkt);
 static void HandleControlMessage(s32 player_id, const ENetPacket* pkt);
@@ -159,6 +165,12 @@ static std::bitset<MAX_PLAYERS> s_reset_players;
 static Common::Timer s_reset_start_time;
 static Common::Timer s_last_host_connection_attempt;
 
+// Spectators
+static std::array<Peer, MAX_SPECTATORS> s_spectators;
+static std::bitset<MAX_SPECTATORS> s_reset_spectators;
+static s32 s_num_spectators = 0;
+static bool s_local_spectating;
+
 /// GGPO
 static std::string s_local_nickname;
 static std::string s_local_session_password;
@@ -238,26 +250,17 @@ static bool SendControlPacket(s32 player_id, const PacketWrapper<T>& pkt)
   return SendControlPacket<T>(s_peers[player_id].peer, pkt);
 }
 template<typename T>
-static void SendControlPacketToAll(const PacketWrapper<T>& pkt)
+static void SendControlPacketToAll(const PacketWrapper<T>& pkt, bool send_to_spectators)
 {
-  for (s32 i = 0; i < MAX_PLAYERS; i++)
+  const s32 total_peers = send_to_spectators ? MAX_PLAYERS + MAX_SPECTATORS : MAX_PLAYERS;
+  for (s32 i = 0; i < total_peers; i++)
   {
-    if (!s_peers[i].peer)
+    ENetPeer* peer_to_send = i < MAX_PLAYERS ? s_peers[i].peer : s_spectators[i - MAX_PLAYERS].peer;
+    if (!peer_to_send)
       continue;
 
-    // last one?
-    bool last = true;
-    for (s32 j = i + 1; j < MAX_PLAYERS; j++)
-    {
-      if (s_peers[j].peer)
-      {
-        last = false;
-        break;
-      }
-    }
-
-    ENetPacket* pkt_to_send = last ? pkt.pkt : enet_packet_create(pkt.pkt->data, pkt.pkt->dataLength, pkt.pkt->flags);
-    const int rc = enet_peer_send(s_peers[i].peer, ENET_CHANNEL_CONTROL, pkt_to_send);
+    ENetPacket* pkt_to_send = enet_packet_create(pkt.pkt->data, pkt.pkt->dataLength, pkt.pkt->flags);
+    const int rc = enet_peer_send(peer_to_send, ENET_CHANNEL_CONTROL, pkt_to_send);
     if (rc != 0)
     {
       Log_ErrorPrintf("enet_peer_send() to player %d failed: %d", i, rc);
@@ -339,7 +342,7 @@ bool Netplay::Start(bool is_hosting, std::string nickname, const std::string& re
   ENetAddress server_address;
   server_address.host = ENET_HOST_ANY;
   server_address.port = is_hosting ? static_cast<u16>(port) : ENET_PORT_ANY;
-  s_enet_host = enet_host_create(&server_address, MAX_PLAYERS - 1, NUM_ENET_CHANNELS, 0, 0);
+  s_enet_host = enet_host_create(&server_address, MAX_PLAYERS + MAX_SPECTATORS - 1, NUM_ENET_CHANNELS, 0, 0);
   if (!s_enet_host)
   {
     Log_ErrorPrintf("Failed to create enet host.");
@@ -351,6 +354,7 @@ bool Netplay::Start(bool is_hosting, std::string nickname, const std::string& re
   s_local_delay = ldelay;
   s_reset_cookie = 0;
   s_reset_players.reset();
+  s_reset_spectators.reset();
 
   // If we're the host, we can just continue on our merry way, the others will join later.
   if (is_hosting)
@@ -358,7 +362,9 @@ bool Netplay::Start(bool is_hosting, std::string nickname, const std::string& re
     // Starting session with a single player.
     s_player_id = 0;
     s_num_players = 1;
+    s_num_spectators = 0;
     s_reset_players = 1;
+    s_reset_spectators = 0;
     s_peers[s_player_id].nickname = s_local_nickname;
     CreateGGPOSession();
     s_state = SessionState::Running;
@@ -451,10 +457,16 @@ void Netplay::RequestCloseSession(CloseSessionMessage::Reason reason)
     // Notify everyone
     auto pkt = NewControlPacket<CloseSessionMessage>();
     pkt->reason = reason;
-    SendControlPacketToAll(pkt);
+    SendControlPacketToAll(pkt, true);
+    // close spectator connections
+    for (s32 i = 0; i < MAX_SPECTATORS; i++)
+    {
+      if (s_spectators[i].peer)
+        enet_peer_disconnect(s_spectators[i].peer, 0);
+    }
   }
 
-  // Close all connections
+  // Close player connections
   DestroyGGPOSession();
   for (s32 i = 0; i < MAX_PLAYERS; i++)
   {
@@ -486,7 +498,14 @@ void Netplay::RequestCloseSession(CloseSessionMessage::Reason reason)
         {
           const s32 player_id = GetPlayerIdForPeer(event.peer);
           if (player_id >= 0)
+          {
             s_peers[player_id].peer = nullptr;
+            return;
+          }
+
+          const s32 spectator_slot = GetSpectatorSlotForPeer(event.peer);
+          if (spectator_slot >= 0)
+            s_spectators[spectator_slot].peer = nullptr;
         }
         break;
 
@@ -542,6 +561,14 @@ void Netplay::ShutdownEnetHost()
     s_peers[i] = {};
   }
 
+  for (u32 i = 0; i < MAX_SPECTATORS; i++)
+  {
+    if (s_spectators[i].peer)
+      enet_peer_reset(s_spectators[i].peer);
+
+    s_spectators[i] = {};
+  }
+
   enet_host_destroy(s_enet_host);
   s_enet_host = nullptr;
 }
@@ -572,7 +599,9 @@ void Netplay::HandleEnetEvent(const ENetEvent* event)
 
     case ENET_EVENT_TYPE_DISCONNECT:
     {
+      const s32 spectator_slot = GetSpectatorSlotForPeer(event->peer);
       const s32 player_id = GetPlayerIdForPeer(event->peer);
+
       if (s_state == SessionState::Connecting)
       {
         Assert(player_id == s_host_player_id);
@@ -586,6 +615,12 @@ void Netplay::HandleEnetEvent(const ENetEvent* event)
         return;
       }
 
+      if (spectator_slot >= 0)
+      {
+        DropSpectator(spectator_slot, DropPlayerReason::DisconnectedFromHost);
+        return;
+      }
+
       Log_WarningPrintf("ENet player %d disconnected", player_id);
       if (IsValidPlayerId(player_id))
       {
@@ -599,8 +634,10 @@ void Netplay::HandleEnetEvent(const ENetEvent* event)
 
     case ENET_EVENT_TYPE_RECEIVE:
     {
-      const s32 player_id = GetPlayerIdForPeer(event->peer);
-      if (player_id < 0)
+      s32 player_id = GetPlayerIdForPeer(event->peer);
+      const s32 spectator_slot = GetSpectatorSlotForPeer(event->peer);
+
+      if (player_id < 0 && spectator_slot < 0)
       {
         // If it's a new connection, we need to handle connection request messages.
         if (event->channelID == ENET_CHANNEL_CONTROL && IsHost())
@@ -611,6 +648,9 @@ void Netplay::HandleEnetEvent(const ENetEvent* event)
 
       if (event->channelID == ENET_CHANNEL_CONTROL)
       {
+        if (player_id < 0)
+          player_id = spectator_slot + MAX_PLAYERS + 1;
+
         HandleControlMessage(player_id, event->packet);
       }
       else if (event->channelID == ENET_CHANNEL_GGPO)
@@ -736,8 +776,36 @@ void Netplay::CreateGGPOSession()
   cb.free_buffer = NpFreeBuffCb;
   cb.on_event = NpOnEventCb;
 
+  if (s_local_spectating)
+  {
+    ggpo_start_spectating(&s_ggpo, &cb, s_num_players, sizeof(Netplay::Input), s_peers[s_host_player_id].peer);
+    return;
+  }
+
   ggpo_start_session(&s_ggpo, &cb, s_num_players, sizeof(Netplay::Input), MAX_ROLLBACK_FRAMES);
 
+  // if you are the host be sure to add the needed spectators to the session before the players 
+  // this way we prevent the session finishing to synchronize before adding the spectators.
+  if (IsHost())
+  {
+    for (s32 i = 0; i < MAX_SPECTATORS; i++)
+    {
+      // slot filled?
+      if (!s_spectators[i].peer)
+        continue;
+
+      GGPOErrorCode result;
+      GGPOPlayer player = {sizeof(GGPOPlayer)};
+
+      player.type = GGPO_PLAYERTYPE_SPECTATOR;
+      player.u.remote.peer = s_spectators[i].peer;
+      result = ggpo_add_player(s_ggpo, &player, &s_spectators[i].ggpo_handle);
+
+      // It's a new session, this should always succeed...
+      Assert(GGPO_SUCCEEDED(result));
+    }
+  }
+
   int player_num = 1;
   for (s32 i = 0; i < MAX_PLAYERS; i++)
   {
@@ -890,7 +958,8 @@ void Netplay::HandleConnectResponseMessage(s32 player_id, const ENetPacket* pkt)
 
   Log_InfoPrintf("Received session details from host: ");
   Log_InfoPrintf("  Console Region: %s", Settings::GetConsoleRegionDisplayName(msg->settings.console_region));
-  Log_InfoPrintf("  BIOS Hash: %s%s", msg->bios_hash.ToString().c_str(), msg->settings.was_fast_booted ? " (fast booted)" : "");
+  Log_InfoPrintf("  BIOS Hash: %s%s", msg->bios_hash.ToString().c_str(),
+                 msg->settings.was_fast_booted ? " (fast booted)" : "");
   Log_InfoPrintf("  Game Serial: %.*s", msg->game_serial_length, msg->GetGameSerial().data());
   Log_InfoPrintf("  Game Title: %.*s", msg->game_title_length, msg->GetGameTitle().data());
   Log_InfoPrintf("  Game Hash: %" PRIX64, msg->game_hash);
@@ -947,10 +1016,11 @@ void Netplay::SendConnectRequest()
 {
   DebugAssert(!IsHost());
 
-  Log_DevPrintf("Sending connect request to host with player id %d", s_player_id);
+  std::string req = s_local_spectating ? "as a spectator" : fmt::format("with player id {}", s_player_id);
+  Log_DevPrintf("Sending connect request to host %s", req.c_str());
 
   auto pkt = NewControlPacket<JoinRequestMessage>();
-  pkt->mode = JoinRequestMessage::Mode::Player;
+  pkt->mode = s_local_spectating ? JoinRequestMessage::Mode::Spectator : JoinRequestMessage::Mode::Player;
   pkt->requested_player_id = s_player_id;
   std::memset(pkt->nickname, 0, sizeof(pkt->nickname));
   std::memset(pkt->session_password, 0, sizeof(pkt->session_password));
@@ -959,6 +1029,55 @@ void Netplay::SendConnectRequest()
   SendControlPacket(s_peers[s_host_player_id].peer, pkt);
 }
 
+bool Netplay::IsSpectator(const ENetPeer* peer)
+{
+  for (s32 i = 0; i < MAX_SPECTATORS; i++)
+  {
+    if (s_spectators[i].peer == peer)
+      return true;
+  }
+  return false;
+}
+
+s32 Netplay::GetFreeSpectatorSlot()
+{
+  for (s32 i = 0; i < MAX_SPECTATORS; i++)
+  {
+    if (!s_spectators[i].peer)
+      return i;
+  }
+  return -1;
+}
+
+s32 Netplay::GetSpectatorSlotForPeer(const ENetPeer* peer)
+{
+  for (s32 i = 0; i < MAX_SPECTATORS; i++)
+  {
+    if (s_spectators[i].peer == peer)
+      return i;
+  }
+  return -1;
+}
+
+void Netplay::DropSpectator(s32 slot_id, DropPlayerReason reason)
+{
+  Assert(IsHost());
+  DebugAssert(s_spectators[slot_id].peer);
+  Log_InfoPrintf("Dropping Spectator %d: %s", slot_id, s_spectators[slot_id].nickname.c_str());
+
+  Host::OnNetplayMessage(
+    fmt::format(Host::TranslateString("Netplay", "Spectator {} left the session: {}").GetCharArray(), slot_id,
+                s_spectators[slot_id].nickname, DropPlayerReasonToString(reason)));
+
+  enet_peer_disconnect_now(s_spectators[slot_id].peer, 0);
+  s_spectators[slot_id] = {};
+  s_num_spectators--;
+  // sadly we have to reset here. this really sucks for the active players since you dont really want to halt for a spectator.
+  // not resetting seems to be creating index out of bounds errors in the ringbuffer.
+  // TODO ? 
+  Reset();
+}
+
 void Netplay::UpdateConnectingState()
 {
   if (s_reset_start_time.GetTimeSeconds() >= MAX_CONNECT_TIME)
@@ -1011,11 +1130,34 @@ void Netplay::HandleMessageFromNewPeer(ENetPeer* peer, const ENetPacket* pkt)
     return;
   }
 
-  // TODO: Spectators shouldn't get assigned a real player ID, they should go into a separate peer list.
-  if (msg->mode != JoinRequestMessage::Mode::Player)
+  if (msg->mode == JoinRequestMessage::Mode::Spectator)
   {
-    response->result = JoinResponseMessage::Result::SessionClosed;
+    // something is really wrong if this isn't the host.
+    Assert(IsHost());
+
+    const s32 spectator_slot = GetFreeSpectatorSlot();
+    // no free slots? notify the peer.
+    if (spectator_slot < 0)
+    {
+      response->result = JoinResponseMessage::Result::ServerFull;
+      SendControlPacket(peer, response);
+      return;
+    }
+
+    Assert(s_num_spectators < MAX_SPECTATORS);
+    response->result = JoinResponseMessage::Result::Success;
+    response->player_id = MAX_PLAYERS + 1 + spectator_slot;
     SendControlPacket(peer, response);
+    // continue and add peer to the list.
+    s_spectators[spectator_slot].peer = peer;
+    s_spectators[spectator_slot].nickname = msg->GetNickname();
+    s_num_spectators++;
+    // Force everyone to resync for now. sadly since ggpo currently only supports adding spectators during setup..
+    Reset();
+    // notify host that the spectator joined
+    Host::OnNetplayMessage(
+      fmt::format(Host::TranslateString("Netplay", "{} is joining the session as a Spectator.").GetCharArray(),
+                  msg->GetNickname()));
     return;
   }
 
@@ -1123,6 +1265,7 @@ void Netplay::HandleJoinResponseMessage(s32 player_id, const ENetPacket* pkt)
   s_player_id = msg->player_id;
   s_state = SessionState::Resetting;
   s_reset_players.reset();
+  s_reset_spectators.reset();
   s_reset_start_time.Reset();
 }
 
@@ -1197,9 +1340,10 @@ void Netplay::Reset()
   // Any GGPO packets will get dropped, since the session's gone temporarily.
   DestroyGGPOSession();
 
-  for (s32 i = 0; i < MAX_PLAYERS; i++)
+  for (s32 i = 0; i < MAX_PLAYERS + MAX_SPECTATORS; i++)
   {
-    if (!s_peers[i].peer)
+    ENetPeer* peer_to_send = i < MAX_PLAYERS ? s_peers[i].peer : s_spectators[i - MAX_PLAYERS].peer;
+    if (!peer_to_send)
       continue;
 
     ENetPacket* pkt = enet_packet_create(nullptr, sizeof(header) + state_data_size, ENET_PACKET_FLAG_RELIABLE);
@@ -1207,7 +1351,7 @@ void Netplay::Reset()
     std::memcpy(pkt->data + sizeof(header), state.GetMemoryPointer(), state_data_size);
 
     // This should never fail, we get errors back later..
-    const int rc = enet_peer_send(s_peers[i].peer, ENET_CHANNEL_CONTROL, pkt);
+    const int rc = enet_peer_send(peer_to_send, ENET_CHANNEL_CONTROL, pkt);
     if (rc != 0)
       Log_ErrorPrintf("enet_peer_send() for synchronization request failed: %d", rc);
   }
@@ -1222,6 +1366,7 @@ void Netplay::Reset()
 
   s_state = SessionState::Resetting;
   s_reset_players.reset();
+  s_reset_spectators.reset();
   s_reset_players.set(s_player_id);
   s_reset_start_time.Reset();
 }
@@ -1246,11 +1391,15 @@ void Netplay::HandleResetMessage(s32 player_id, const ENetPacket* pkt)
   DestroyGGPOSession();
 
   // Make sure we're connected to all players.
-  Assert(msg->num_players > 1);
+  Assert(msg->num_players > 1 || s_local_spectating);
   Log_DevPrintf("Checking connections");
   s_num_players = msg->num_players;
   for (s32 i = 0; i < MAX_PLAYERS; i++)
   {
+    // We are already connected to the host as a spectator we dont need any other connections
+    if (s_local_spectating)
+      continue;
+
     Peer& p = s_peers[i];
     if (msg->players[i].controller_port < 0)
     {
@@ -1314,6 +1463,15 @@ void Netplay::HandleResetMessage(s32 player_id, const ENetPacket* pkt)
   s_state = SessionState::Resetting;
   s_reset_cookie = msg->cookie;
   s_reset_players.reset();
+  s_reset_spectators.reset();
+
+  if (s_local_spectating)
+  {
+    s_reset_spectators.set(s_player_id - (MAX_PLAYERS + 1));
+    s_reset_start_time.Reset();
+    return;
+  }
+
   s_reset_players.set(s_player_id);
   s_reset_start_time.Reset();
 }
@@ -1329,6 +1487,13 @@ void Netplay::HandleResetCompleteMessage(s32 player_id, const ENetPacket* pkt)
     Log_ErrorPrintf("Received unexpected reset complete from player %d", player_id);
     return;
   }
+  else if (player_id > MAX_PLAYERS && player_id <= MAX_PLAYERS + MAX_SPECTATORS)
+  {
+    const s32 spectator_slot = player_id - (MAX_PLAYERS + 1);
+    s_reset_spectators.set(spectator_slot);
+    Log_DevPrintf("Spectator %d is now reset and ready", spectator_slot);
+    return;
+  }
   else if (s_reset_players.test(player_id))
   {
     Log_ErrorPrintf("Received double reset from player %d", player_id);
@@ -1363,12 +1528,14 @@ void Netplay::HandleResumeSessionMessage(s32 player_id, const ENetPacket* pkt)
 
 void Netplay::UpdateResetState()
 {
+  const s32 num_players = (s_local_spectating ? 1 : s_num_players);
   if (IsHost())
   {
-    if (static_cast<s32>(s_reset_players.count()) == s_num_players)
+    if (static_cast<s32>(s_reset_players.count()) == num_players &&
+        static_cast<s32>(s_reset_spectators.count()) == s_num_spectators)
     {
-      Log_VerbosePrintf("All players synchronized, resuming!");
-      SendControlPacketToAll(NewControlPacket<ResumeSessionMessage>());
+      Log_VerbosePrintf("All players and spectators synchronized, resuming!");
+      SendControlPacketToAll(NewControlPacket<ResumeSessionMessage>(), true);
       CreateGGPOSession();
       s_state = SessionState::Running;
       return;
@@ -1388,11 +1555,21 @@ void Netplay::UpdateResetState()
         Log_DevPrintf("Dropping player %d because they didn't connect in time", i);
         DropPlayer(i, DropPlayerReason::ConnectTimeout);
       }
+
+      for (s32 i = 0; i < MAX_SPECTATORS; i++)
+      {
+        if (s_reset_spectators.test(i))
+          continue;
+
+        // we'll check if we're done again next loop
+        Log_DevPrintf("Dropping Spectator %d because they didn't connect in time", i);
+        DropSpectator(i, DropPlayerReason::ConnectTimeout);
+      }
     }
   }
   else
   {
-    if (static_cast<s32>(s_reset_players.count()) != s_num_players)
+    if (static_cast<s32>(s_reset_players.count()) != num_players)
     {
       for (s32 i = 0; i < MAX_PLAYERS; i++)
       {
@@ -1403,7 +1580,7 @@ void Netplay::UpdateResetState()
           s_reset_players.set(i);
       }
 
-      if (static_cast<s32>(s_reset_players.count()) == s_num_players)
+      if (static_cast<s32>(s_reset_players.count()) == num_players)
       {
         // now connected to all!
         Log_InfoPrintf("Connected to %d players, waiting for host...", s_num_players);
@@ -1421,8 +1598,14 @@ void Netplay::UpdateResetState()
     }
   }
 
+  // Log_InfoPrintf("p:%d/s:%d", num_players, s_num_spectators);
+
+  const s32 min_progress = IsHost() ? static_cast<int>(s_reset_players.count() + s_reset_spectators.count()) :
+                                      static_cast<int>(s_reset_players.count());
+  const s32 max_progress = IsHost() ? s_num_players + s_num_spectators : num_players;
+
   PollEnet(Common::Timer::GetCurrentValue() + Common::Timer::ConvertMillisecondsToValue(16));
-  Host::DisplayLoadingScreen("Netplay synchronizing", 0, static_cast<int>(s_reset_players.count()), s_num_players);
+  Host::DisplayLoadingScreen("Netplay synchronizing", 0, min_progress, max_progress);
   Host::PumpMessagesOnCPUThread();
 }
 
@@ -1454,7 +1637,7 @@ void Netplay::NotifyPlayerJoined(s32 player_id)
   {
     auto pkt = NewControlPacket<PlayerJoinedMessage>();
     pkt->player_id = player_id;
-    SendControlPacketToAll(pkt);
+    SendControlPacketToAll(pkt, false);
   }
 
   Host::OnNetplayMessage(
@@ -1498,7 +1681,7 @@ void Netplay::DropPlayer(s32 player_id, DropPlayerReason reason)
     auto pkt = NewControlPacket<DropPlayerMessage>();
     pkt->reason = reason;
     pkt->player_id = player_id;
-    SendControlPacketToAll(pkt);
+    SendControlPacketToAll(pkt, false);
 
     // resync with everyone who's left
     Reset();
@@ -1830,7 +2013,8 @@ void Netplay::SendChatMessage(const std::string_view& msg)
 
   auto pkt = NewControlPacket<ChatMessage>(sizeof(ChatMessage) + static_cast<u32>(msg.length()));
   std::memcpy(pkt.pkt->data + sizeof(ChatMessage), msg.data(), msg.length());
-  SendControlPacketToAll(pkt);
+  // TODO: turn chat on for spectators? it's kind of weird to handle. probably has to go through the host and be relayed to the players.
+  SendControlPacketToAll(pkt, false); 
 
   // add own netplay message locally to netplay messages
   ShowChatMessage(s_player_id, msg);
@@ -1876,7 +2060,7 @@ bool Netplay::CreateSession(std::string nickname, s32 port, s32 max_players, std
   // TODO: This is going to blow away our memory cards, because for sync purposes we want all clients
   // to have the same data, and we don't want to trash their local memcards. We should therefore load
   // the memory cards for this game (based on game/global settings), and copy that to the temp card.
-  
+
   // TODO: input delay. GGPO Should support changing it on the fly.
   const s32 input_delay = 1;
 
@@ -1894,9 +2078,11 @@ bool Netplay::CreateSession(std::string nickname, s32 port, s32 max_players, std
   return true;
 }
 
-bool Netplay::JoinSession(std::string nickname, const std::string& hostname, s32 port, std::string password)
+bool Netplay::JoinSession(std::string nickname, const std::string& hostname, s32 port, std::string password,
+                          bool spectating)
 {
   s_local_session_password = std::move(password);
+  s_local_spectating = spectating;
 
   // TODO: input delay. GGPO Should support changing it on the fly.
   const s32 input_delay = 1;

src/core/netplay.h

@@ -10,6 +10,9 @@ enum : s32
   // Maximum number of emulated controllers.
   MAX_PLAYERS = 2,
 
+  // Maximum number of spectators allowed to watch the session.
+  MAX_SPECTATORS = 4,
+
   // Maximum netplay prediction frames
   MAX_ROLLBACK_FRAMES = 8,
 
@@ -29,7 +32,7 @@ enum : u8
 };
 
 bool CreateSession(std::string nickname, s32 port, s32 max_players, std::string password);
-bool JoinSession(std::string nickname, const std::string& hostname, s32 port, std::string password);
+bool JoinSession(std::string nickname, const std::string& hostname, s32 port, std::string password, bool spectating);
 
 bool IsActive();
 

src/duckstation-qt/joinnetplaysessiondialog.ui

@@ -10,7 +10,7 @@
     <x>0</x>
     <y>0</y>
     <width>480</width>
-    <height>220</height>
+    <height>226</height>
    </rect>
   </property>
   <property name="windowTitle">
@@ -146,11 +146,28 @@
     </layout>
    </item>
    <item>
-    <widget class="QDialogButtonBox" name="buttonBox">
-     <property name="standardButtons">
-      <set>QDialogButtonBox::Cancel|QDialogButtonBox::Ok</set>
-     </property>
-    </widget>
+    <layout class="QHBoxLayout" name="horizontalLayout_2">
+     <item>
+      <widget class="QCheckBox" name="spectating">
+       <property name="layoutDirection">
+        <enum>Qt::LeftToRight</enum>
+       </property>
+       <property name="text">
+        <string>Enable Spectator Mode</string>
+       </property>
+       <property name="checkable">
+        <bool>true</bool>
+       </property>
+      </widget>
+     </item>
+     <item>
+      <widget class="QDialogButtonBox" name="buttonBox">
+       <property name="standardButtons">
+        <set>QDialogButtonBox::Cancel|QDialogButtonBox::Ok</set>
+       </property>
+      </widget>
+     </item>
+    </layout>
    </item>
   </layout>
  </widget>

src/duckstation-qt/netplaydialogs.cpp

@@ -82,9 +82,10 @@ void JoinNetplaySessionDialog::accept()
   const QString& nickname = m_ui.nickname->text();
   const QString& hostname = m_ui.hostname->text();
   const QString& password = m_ui.password->text();
+  const bool spectating = m_ui.spectating->isChecked();
   QDialog::accept();
 
-  g_emu_thread->joinNetplaySession(nickname.trimmed(), hostname.trimmed(), port, password);
+  g_emu_thread->joinNetplaySession(nickname.trimmed(), hostname.trimmed(), port, password, spectating);
 }
 
 bool JoinNetplaySessionDialog::validate()

src/duckstation-qt/qthost.cpp

@@ -1092,16 +1092,17 @@ void EmuThread::createNetplaySession(const QString& nickname, qint32 port, qint3
 }
 
 void EmuThread::joinNetplaySession(const QString& nickname, const QString& hostname, qint32 port,
-                                   const QString& password)
+                                   const QString& password, bool spectating)
 {
   if (!isOnThread())
   {
     QMetaObject::invokeMethod(this, "joinNetplaySession", Qt::QueuedConnection, Q_ARG(const QString&, nickname),
-                              Q_ARG(const QString&, hostname), Q_ARG(qint32, port), Q_ARG(const QString&, password));
+                              Q_ARG(const QString&, hostname), Q_ARG(qint32, port), Q_ARG(const QString&, password),
+                              Q_ARG(bool, spectating));
     return;
   }
 
-  if (!Netplay::JoinSession(nickname.toStdString(), hostname.toStdString(), port, password.toStdString()))
+  if (!Netplay::JoinSession(nickname.toStdString(), hostname.toStdString(), port, password.toStdString(), spectating))
   {
     errorReported(tr("Netplay Error"), tr("Failed to join netplay session. The log may contain more information."));
     return;
@@ -2246,7 +2247,7 @@ int main(int argc, char* argv[])
       }
       else
       {
-        g_emu_thread->joinNetplaySession(nickname, remote, port, QString());
+        g_emu_thread->joinNetplaySession(nickname, remote, port, QString(), false);
       }
     });
   }

src/duckstation-qt/qthost.h

@@ -188,7 +188,8 @@ public Q_SLOTS:
   void applyCheat(quint32 index);
   void reloadPostProcessingShaders();
   void createNetplaySession(const QString& nickname, qint32 port, qint32 max_players, const QString& password);
-  void joinNetplaySession(const QString& nickname, const QString& hostname, qint32 port, const QString& password);
+  void joinNetplaySession(const QString& nickname, const QString& hostname, qint32 port, const QString& password,
+                          bool spectating);
 
 private Q_SLOTS:
   void stopInThread();