NetPlay host input authority mode

Currently, each player buffers their own inputs and sends them to the
host. The host then relays those inputs to everyone else. Every player
waits on inputs from all players to be buffered before continuing. What
this means is all clients run in lockstep, and the total latency of
inputs cannot be lower than the sum of the 2 highest client ping times
in the game (in 3+ player sessions with people across the world, the
latency can be very high).

Host input authority mode changes it so players no longer buffer their
own inputs, and only send them to the host. The host stores only the
most recent input received from a player. The host then sends inputs
for all pads at the SI poll interval, similar to the existing code. If
a player sends inputs to slowly, their last received input is simply
sent again. If they send too quickly, inputs are dropped. This means
that the host has full control over what inputs are actually read by
the game, hence the name of the mode. Also, because the rate at which
inputs are received by SI is decoupled from the rate at which players
are sending inputs, clients are no longer dependent on each other. They
only care what the host is doing. This means that they can set their
buffer individually based on their latency to the host, rather than the
highest latency between any 2 players, allowing someone with lower ping
to the host to have less latency than someone else.

This is a catch to this: as a necessity of how the host's input sending
works, the host has 0 latency. There isn't a good way to fix this, as
input delay is now solely dependent on the real latency to the host's
server. Having differing latency between players would be considered
unfair for competitive play, but for casual play we don't really care.
For this reason though, combined with the potential for a few inputs to
be dropped on a bad connection, the old mode will remain and this new
mode is entirely optional.

Source/Core/Core/NetPlayClient.cpp

@@ -60,6 +60,7 @@ namespace NetPlay
 static std::mutex crit_netplay_client;
 static NetPlayClient* netplay_client = nullptr;
 static std::unique_ptr<IOS::HLE::FS::FileSystem> s_wii_sync_fs;
+static bool s_si_poll_batching;
 
 // called from ---GUI--- thread
 NetPlayClient::~NetPlayClient()
@@ -407,6 +408,22 @@ unsigned int NetPlayClient::OnData(sf::Packet& packet)
   }
   break;
 
+  case NP_MSG_PAD_FIRST_RECEIVED:
+  {
+    PadMapping map;
+    packet >> map;
+    packet >> m_first_pad_status_received[map];
+    m_first_pad_status_received_event.Set();
+  }
+  break;
+
+  case NP_MSG_HOST_INPUT_AUTHORITY:
+  {
+    packet >> m_host_input_authority;
+    m_dialog->OnHostInputAuthorityChanged(m_host_input_authority);
+  }
+  break;
+
   case NP_MSG_CHANGE_GAME:
   {
     {
@@ -532,7 +549,9 @@ unsigned int NetPlayClient::OnData(sf::Packet& packet)
 
       packet >> m_net_settings.m_SyncSaveData;
       packet >> m_net_settings.m_SaveDataRegion;
-      m_net_settings.m_IsHosting = m_dialog->IsHosting();
+
+      m_net_settings.m_IsHosting = m_local_player->IsHost();
+      m_net_settings.m_HostInputAuthority = m_host_input_authority;
     }
 
     m_dialog->OnMsgStartGame();
@@ -636,7 +655,7 @@ unsigned int NetPlayClient::OnData(sf::Packet& packet)
 
     case SYNC_SAVE_DATA_RAW:
     {
-      if (m_dialog->IsHosting())
+      if (m_local_player->IsHost())
         return 0;
 
       bool is_slot_a;
@@ -660,7 +679,7 @@ unsigned int NetPlayClient::OnData(sf::Packet& packet)
 
     case SYNC_SAVE_DATA_GCI:
     {
-      if (m_dialog->IsHosting())
+      if (m_local_player->IsHost())
         return 0;
 
       bool is_slot_a;
@@ -696,7 +715,7 @@ unsigned int NetPlayClient::OnData(sf::Packet& packet)
 
     case SYNC_SAVE_DATA_WII:
     {
-      if (m_dialog->IsHosting())
+      if (m_local_player->IsHost())
         return 0;
 
       const auto game = m_dialog->FindGameFile(m_selected_game);
@@ -1118,6 +1137,8 @@ bool NetPlayClient::StartGame(const std::string& path)
 
   ClearBuffers();
 
+  m_first_pad_status_received.fill(false);
+
   if (m_dialog->IsRecording())
   {
     if (Movie::IsReadOnly())
@@ -1366,7 +1387,7 @@ void NetPlayClient::OnConnectFailed(u8 reason)
 }
 
 // called from ---CPU--- thread
-bool NetPlayClient::GetNetPads(const int pad_nb, GCPadStatus* pad_status)
+bool NetPlayClient::GetNetPads(const int pad_nb, const bool batching, GCPadStatus* pad_status)
 {
   // The interface for this is extremely silly.
   //
@@ -1385,11 +1406,17 @@ bool NetPlayClient::GetNetPads(const int pad_nb, GCPadStatus* pad_status)
   // The slot number is the "local" pad number, and what player
   // it actually means is the "in-game" pad number.
 
-  // When the 1st in-game pad is polled, we assume the others will
-  // will be polled as well. To reduce latency, we poll all local
-  // controllers at once and then send the status to the other
+  // When the 1st in-game pad is polled and batching is set, the
+  // others will be polled as well. To reduce latency, we poll all
+  // local controllers at once and then send the status to the other
   // clients.
-  if (IsFirstInGamePad(pad_nb))
+  //
+  // Batching is enabled when polled from VI. If batching is not
+  // enabled, the poll is probably from MMIO, which can poll any
+  // specific pad arbitrarily. In this case, we poll just that pad
+  // and send it.
+
+  if (IsFirstInGamePad(pad_nb) && batching)
   {
     sf::Packet packet;
     packet << static_cast<MessageId>(NP_MSG_PAD_DATA);
@@ -1398,34 +1425,44 @@ bool NetPlayClient::GetNetPads(const int pad_nb, GCPadStatus* pad_status)
     const int num_local_pads = NumLocalPads();
     for (int local_pad = 0; local_pad < num_local_pads; local_pad++)
     {
-      switch (SConfig::GetInstance().m_SIDevice[local_pad])
-      {
-      case SerialInterface::SIDEVICE_WIIU_ADAPTER:
-        *pad_status = GCAdapter::Input(local_pad);
-        break;
-      case SerialInterface::SIDEVICE_GC_CONTROLLER:
-      default:
-        *pad_status = Pad::GetStatus(local_pad);
-        break;
-      }
-
-      int ingame_pad = LocalPadToInGamePad(local_pad);
-
-      // adjust the buffer either up or down
-      // inserting multiple padstates or dropping states
-      while (m_pad_buffer[ingame_pad].Size() <= m_target_buffer_size)
-      {
-        // add to buffer
-        m_pad_buffer[ingame_pad].Push(*pad_status);
-
-        // add to packet
-        AddPadStateToPacket(ingame_pad, *pad_status, packet);
-        send_packet = true;
-      }
+      send_packet = PollLocalPad(local_pad, packet) || send_packet;
     }
 
     if (send_packet)
       SendAsync(std::move(packet));
+
+    if (m_host_input_authority)
+      SendPadHostPoll(-1);
+  }
+
+  if (!batching)
+  {
+    int local_pad = InGamePadToLocalPad(pad_nb);
+    if (local_pad < 4)
+    {
+      sf::Packet packet;
+      packet << static_cast<MessageId>(NP_MSG_PAD_DATA);
+      if (PollLocalPad(local_pad, packet))
+        SendAsync(std::move(packet));
+    }
+
+    if (m_host_input_authority)
+      SendPadHostPoll(pad_nb);
+  }
+
+  if (m_host_input_authority && !m_local_player->IsHost())
+  {
+    const bool buffer_over_target = m_pad_buffer[pad_nb].Size() > m_target_buffer_size + 1;
+    if (!buffer_over_target)
+      m_buffer_under_target_last = std::chrono::steady_clock::now();
+
+    std::chrono::duration<double> time_diff =
+        std::chrono::steady_clock::now() - m_buffer_under_target_last;
+    if (time_diff.count() >= 1.0 || !buffer_over_target)
+    {
+      // run fast if the buffer is overfilled, otherwise run normal speed
+      SConfig::GetInstance().m_EmulationSpeed = buffer_over_target ? 0.0f : 1.0f;
+    }
   }
 
   // Now, we either use the data pushed earlier, or wait for the
@@ -1534,6 +1571,86 @@ bool NetPlayClient::WiimoteUpdate(int _number, u8* data, const u8 size, u8 repor
   return true;
 }
 
+bool NetPlayClient::PollLocalPad(const int local_pad, sf::Packet& packet)
+{
+  GCPadStatus pad_status;
+
+  switch (SConfig::GetInstance().m_SIDevice[local_pad])
+  {
+  case SerialInterface::SIDEVICE_WIIU_ADAPTER:
+    pad_status = GCAdapter::Input(local_pad);
+    break;
+  case SerialInterface::SIDEVICE_GC_CONTROLLER:
+  default:
+    pad_status = Pad::GetStatus(local_pad);
+    break;
+  }
+
+  const int ingame_pad = LocalPadToInGamePad(local_pad);
+  bool data_added = false;
+
+  if (m_host_input_authority)
+  {
+    // add to packet
+    AddPadStateToPacket(ingame_pad, pad_status, packet);
+    data_added = true;
+  }
+  else
+  {
+    // adjust the buffer either up or down
+    // inserting multiple padstates or dropping states
+    while (m_pad_buffer[ingame_pad].Size() <= m_target_buffer_size)
+    {
+      // add to buffer
+      m_pad_buffer[ingame_pad].Push(pad_status);
+
+      // add to packet
+      AddPadStateToPacket(ingame_pad, pad_status, packet);
+      data_added = true;
+    }
+  }
+
+  return data_added;
+}
+
+void NetPlayClient::SendPadHostPoll(const PadMapping pad_num)
+{
+  if (!m_local_player->IsHost())
+    return;
+
+  if (pad_num < 0)
+  {
+    for (size_t i = 0; i < m_pad_map.size(); i++)
+    {
+      if (m_pad_map[i] <= 0)
+        continue;
+
+      while (!m_first_pad_status_received[i])
+      {
+        if (!m_is_running.IsSet())
+          return;
+
+        m_first_pad_status_received_event.Wait();
+      }
+    }
+  }
+  else if (m_pad_map[pad_num] > 0)
+  {
+    while (!m_first_pad_status_received[pad_num])
+    {
+      if (!m_is_running.IsSet())
+        return;
+
+      m_first_pad_status_received_event.Wait();
+    }
+  }
+
+  sf::Packet packet;
+  packet << static_cast<MessageId>(NP_MSG_PAD_HOST_POLL);
+  packet << pad_num;
+  SendAsync(std::move(packet));
+}
+
 // called from ---GUI--- thread and ---NETPLAY--- thread (client side)
 bool NetPlayClient::StopGame()
 {
@@ -1542,6 +1659,7 @@ bool NetPlayClient::StopGame()
   // stop waiting for input
   m_gc_pad_event.Set();
   m_wii_pad_event.Set();
+  m_first_pad_status_received_event.Set();
 
   NetPlay_Disable();
 
@@ -1564,6 +1682,7 @@ void NetPlayClient::Stop()
   // stop waiting for input
   m_gc_pad_event.Set();
   m_wii_pad_event.Set();
+  m_first_pad_status_received_event.Set();
 
   // Tell the server to stop if we have a pad mapped in game.
   if (LocalPlayerHasControllerMapped())
@@ -1719,6 +1838,12 @@ const PadMappingArray& NetPlayClient::GetWiimoteMapping() const
   return m_wiimote_map;
 }
 
+void NetPlayClient::AdjustPadBufferSize(const unsigned int size)
+{
+  m_target_buffer_size = size;
+  m_dialog->OnPadBufferChanged(size);
+}
+
 bool IsNetPlayRunning()
 {
   return netplay_client != nullptr;
@@ -1750,6 +1875,11 @@ void ClearWiiSyncFS()
   s_wii_sync_fs.reset();
 }
 
+void SetSIPollBatching(bool state)
+{
+  s_si_poll_batching = state;
+}
+
 void NetPlay_Enable(NetPlayClient* const np)
 {
   std::lock_guard<std::mutex> lk(crit_netplay_client);
@@ -1767,12 +1897,12 @@ void NetPlay_Disable()
 
 // called from ---CPU--- thread
 // Actual Core function which is called on every frame
-bool SerialInterface::CSIDevice_GCController::NetPlay_GetInput(int numPAD, GCPadStatus* PadStatus)
+bool SerialInterface::CSIDevice_GCController::NetPlay_GetInput(int pad_num, GCPadStatus* status)
 {
   std::lock_guard<std::mutex> lk(NetPlay::crit_netplay_client);
 
   if (NetPlay::netplay_client)
-    return NetPlay::netplay_client->GetNetPads(numPAD, PadStatus);
+    return NetPlay::netplay_client->GetNetPads(pad_num, NetPlay::s_si_poll_batching, status);
 
   return false;
 }