Netplay: Add experimental rollback netplay implementation

Co-authored-by: Jamie Meyer <45072324+HeatXD@users.noreply.github.com>

src/common/layered_settings_interface.h

@@ -10,6 +10,7 @@ class LayeredSettingsInterface final : public SettingsInterface
 public:
   enum Layer : u32
   {
+    LAYER_NETPLAY,
     LAYER_CMDLINE,
     LAYER_GAME,
     LAYER_INPUT,
@@ -61,7 +62,7 @@ public:
   using SettingsInterface::GetUIntValue;
 
 private:
-  static constexpr Layer FIRST_LAYER = LAYER_CMDLINE;
+  static constexpr Layer FIRST_LAYER = LAYER_NETPLAY;
   static constexpr Layer LAST_LAYER = LAYER_BASE;
 
   std::array<SettingsInterface*, NUM_LAYERS> m_layers{};

src/core/CMakeLists.txt

@@ -79,6 +79,9 @@ add_library(core
   multitap.h
   negcon.cpp
   negcon.h
+  netplay.cpp
+  netplay.h
+  netplay_packets.h
   pad.cpp
   pad.h
   pcdrv.cpp
@@ -126,6 +129,10 @@ target_include_directories(core PUBLIC "${CMAKE_CURRENT_SOURCE_DIR}/..")
 target_link_libraries(core PUBLIC Threads::Threads common util zlib)
 target_link_libraries(core PRIVATE stb xxhash imgui rapidjson rcheevos)
 
+if(NOT ANDROID)
+  target_link_libraries(core PRIVATE enet ggpo-x)
+endif()
+
 if(${CPU_ARCH} STREQUAL "x64")
   target_include_directories(core PUBLIC "${CMAKE_CURRENT_SOURCE_DIR}/../../dep/xbyak/xbyak")
   target_compile_definitions(core PUBLIC "XBYAK_NO_EXCEPTION=1" "ENABLE_RECOMPILER=1" "ENABLE_MMAP_FASTMEM=1")

src/core/core.props

@@ -18,4 +18,9 @@
       <AdditionalIncludeDirectories Condition="'$(Platform)'=='ARM' Or '$(Platform)'=='ARM64'">%(AdditionalIncludeDirectories);$(SolutionDir)dep\vixl\include</AdditionalIncludeDirectories>
     </ClCompile>
   </ItemDefinitionGroup>
+  <ItemDefinitionGroup>
+    <Link>
+      <AdditionalDependencies>%(AdditionalDependencies);ws2_32.lib</AdditionalDependencies>
+    </Link>
+  </ItemDefinitionGroup>
 </Project>

src/core/core.vcxproj

@@ -58,6 +58,7 @@
     <ClCompile Include="multitap.cpp" />
     <ClCompile Include="guncon.cpp" />
     <ClCompile Include="negcon.cpp" />
+    <ClCompile Include="netplay.cpp" />
     <ClCompile Include="pad.cpp" />
     <ClCompile Include="controller.cpp" />
     <ClCompile Include="pcdrv.cpp" />
@@ -129,6 +130,8 @@
     <ClInclude Include="multitap.h" />
     <ClInclude Include="guncon.h" />
     <ClInclude Include="negcon.h" />
+    <ClInclude Include="netplay.h" />
+    <ClInclude Include="netplay_packets.h" />
     <ClInclude Include="pad.h" />
     <ClInclude Include="controller.h" />
     <ClInclude Include="pcdrv.h" />
@@ -152,6 +155,12 @@
     <ProjectReference Include="..\..\dep\discord-rpc\discord-rpc.vcxproj">
       <Project>{4266505b-dbaf-484b-ab31-b53b9c8235b3}</Project>
     </ProjectReference>
+    <ProjectReference Include="..\..\dep\enet\enet.vcxproj">
+      <Project>{460a096b-fcc7-465c-8e4b-434af490a9ea}</Project>
+    </ProjectReference>
+    <ProjectReference Include="..\..\dep\ggpo-x\ggpo-x.vcxproj">
+      <Project>{edf3634a-ce8a-4625-92bd-27bad5d30a9a}</Project>
+    </ProjectReference>
     <ProjectReference Include="..\..\dep\imgui\imgui.vcxproj">
       <Project>{bb08260f-6fbc-46af-8924-090ee71360c6}</Project>
     </ProjectReference>
@@ -190,6 +199,7 @@
   <Import Project="core.props" />
   <ItemDefinitionGroup>
     <ClCompile>
+      <AdditionalIncludeDirectories>%(AdditionalIncludeDirectories);$(SolutionDir)dep\enet\include;$(SolutionDir)dep\ggpo-x\include;%(AdditionalIncludeDirectories)</AdditionalIncludeDirectories>
       <PreprocessorDefinitions>ZYDIS_DISABLE_ENCODER;ZYDIS_DISABLE_AVX512;ZYDIS_DISABLE_KNC;ZYDIS_STATIC_BUILD;ZYCORE_STATIC_BUILD;%(PreprocessorDefinitions)</PreprocessorDefinitions>
       <AdditionalIncludeDirectories Condition="'$(Platform)'=='x64'">$(SolutionDir)dep\zydis\include;$(SolutionDir)dep\zydis\dependencies\zycore\include;%(AdditionalIncludeDirectories)</AdditionalIncludeDirectories>
       <ObjectFileName>$(IntDir)/%(RelativeDir)/</ObjectFileName>

src/core/core.vcxproj.filters

@@ -60,6 +60,7 @@
     <ClCompile Include="hotkeys.cpp" />
     <ClCompile Include="gpu_shadergen.cpp" />
     <ClCompile Include="pch.cpp" />
+    <ClCompile Include="netplay.cpp" />
   </ItemGroup>
   <ItemGroup>
     <ClInclude Include="types.h" />
@@ -124,5 +125,7 @@
     <ClInclude Include="shader_cache_version.h" />
     <ClInclude Include="gpu_shadergen.h" />
     <ClInclude Include="pch.h" />
+    <ClInclude Include="netplay.h" />
+    <ClInclude Include="netplay_packets.h" />
   </ItemGroup>
-</Project>
+</Project>

src/core/host.cpp

@@ -217,6 +217,12 @@ void Host::Internal::SetInputSettingsLayer(SettingsInterface* sif)
   s_layered_settings_interface.SetLayer(LayeredSettingsInterface::LAYER_INPUT, sif);
 }
 
+void Host::Internal::SetNetplaySettingsLayer(SettingsInterface* sif)
+{
+  std::unique_lock lock(s_settings_mutex);
+  s_layered_settings_interface.SetLayer(LayeredSettingsInterface::LAYER_NETPLAY, sif);
+}
+
 void Host::ReportFormattedDebuggerMessage(const char* format, ...)
 {
   std::va_list ap;

src/core/host.h

@@ -119,5 +119,8 @@ void SetGameSettingsLayer(SettingsInterface* sif);
 
 /// Sets the input profile settings layer. Called by VMManager when the game changes.
 void SetInputSettingsLayer(SettingsInterface* sif);
+
+/// Sets the netplay settings layer. Use once a session is established.
+void SetNetplaySettingsLayer(SettingsInterface* sif);
 } // namespace Internal
 } // namespace Host

src/core/hotkeys.cpp

@@ -7,6 +7,7 @@
 #include "gpu.h"
 #include "host.h"
 #include "imgui_overlays.h"
+#include "netplay.h"
 #include "pgxp.h"
 #include "settings.h"
 #include "spu.h"
@@ -107,6 +108,17 @@ DEFINE_HOTKEY("OpenPauseMenu", TRANSLATE_NOOP("Hotkeys", "General"), TRANSLATE_N
                 if (!pressed)
                   FullscreenUI::OpenPauseMenu();
               })
+// Netplay on Android? Give me a break....
+DEFINE_HOTKEY("OpenNetplayChat", TRANSLATE_NOOP("Hotkeys", "Netplay"), TRANSLATE_NOOP("Hotkeys", "Open Netplay Chat"),
+              [](s32 pressed) {
+                if (!pressed)
+                  Netplay::OpenChat();
+              })
+DEFINE_HOTKEY("ToggleDesyncNotifications", TRANSLATE_NOOP("Hotkeys", "Netplay"),
+              TRANSLATE_NOOP("Hotkeys", "Toggle Desync Notifications"), [](s32 pressed) {
+                if (!pressed)
+                  Netplay::ToggleDesyncNotifications();
+              })
 #endif
 
 DEFINE_HOTKEY("FastForward", TRANSLATE_NOOP("Hotkeys", "General"), TRANSLATE_NOOP("Hotkeys", "Fast Forward"),

src/core/netplay.h

@@ -0,0 +1,76 @@
+// SPDX-FileCopyrightText: 2023 Connor McLaughlin <stenzek@gmail.com> and contributors.
+// SPDX-License-Identifier: (GPL-3.0 OR CC-BY-NC-ND-4.0)
+
+#pragma once
+
+#include "types.h"
+#include <string>
+
+namespace Netplay {
+
+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,
+
+  // Maximum length of a nickname
+  MAX_NICKNAME_LENGTH = 128,
+
+  // Maximum name of password for session
+  MAX_SESSION_PASSWORD_LENGTH = 128,
+};
+
+enum : u8
+{
+  ENET_CHANNEL_CONTROL = 0,
+  ENET_CHANNEL_GGPO = 1,
+
+  NUM_ENET_CHANNELS,
+};
+
+bool CreateSession(std::string nickname, s32 port, s32 max_players, std::string password, int inputdelay,
+                   bool traversal);
+bool JoinSession(std::string nickname, const std::string& hostname, s32 port, std::string password, bool spectating,
+                 int inputdelay, bool traversal, const std::string& hostcode);
+
+bool IsActive();
+
+/// Frees up resources associated with the current netplay session.
+/// Should only be called by System::ShutdownSystem().
+void SystemDestroyed();
+
+/// Runs the VM and netplay loop. when the netplay loop cancels it switches to normal execute mode.
+void ExecuteNetplay();
+
+/// Called when a frame is completed (System::FrameDone()).
+void FrameDone();
+
+void CollectInput(u32 slot, u32 bind, float value);
+
+void SendChatMessage(const std::string_view& msg);
+
+s32 GetPing();
+u32 GetMaxPrediction();
+std::string_view GetHostCode();
+
+/// Updates the throttle period, call when target emulation speed changes.
+void UpdateThrottlePeriod();
+
+void ToggleDesyncNotifications();
+
+// OSD
+void RenderOverlays();
+void OpenChat();
+
+} // namespace Netplay
+
+namespace Host {
+void OnNetplaySessionOpened(bool is_host);
+void OnNetplaySessionClosed();
+} // namespace Host

src/core/netplay_packets.h

@@ -0,0 +1,319 @@
+// SPDX-FileCopyrightText: 2023 Connor McLaughlin <stenzek@gmail.com> and contributors.
+// SPDX-License-Identifier: (GPL-3.0 OR CC-BY-NC-ND-4.0)
+
+#pragma once
+
+#include "bios.h"
+#include "host.h"
+#include "types.h"
+
+#include "fmt/format.h"
+
+namespace Netplay {
+
+enum class SessionState
+{
+  Inactive,
+  Initializing,
+  Connecting,
+  Resetting,
+  Running,
+  ClosingSession,
+};
+
+enum class ControlMessage : u32
+{
+  // host->player
+  ConnectResponse,
+  JoinResponse,
+  PreReset,
+  Reset,
+  ResumeSession,
+  PlayerJoined,
+  DropPlayer,
+  CloseSession,
+
+  // player->host
+  JoinRequest,
+  ResetComplete,
+  ResetRequest,
+
+  // bi-directional
+  SetNickname,
+  ChatMessage,
+};
+
+enum class DropPlayerReason : u32
+{
+  ConnectTimeout,
+  DisconnectedFromHost,
+};
+
+#pragma pack(push, 1)
+struct ControlMessageHeader
+{
+  ControlMessage type;
+  u32 size;
+};
+
+struct ConnectResponseMessage
+{
+  ControlMessageHeader header;
+
+  s32 num_players;
+  s32 max_players;
+  u64 game_hash;
+  u32 game_serial_length;
+  u32 game_title_length;
+  BIOS::Hash bios_hash;
+
+  struct
+  {
+    ConsoleRegion console_region;
+    CPUExecutionMode cpu_execution_mode;
+    u32 cpu_overclock_numerator;
+    u32 cpu_overclock_denominator;
+    bool cpu_overclock_enable;
+    bool cpu_recompiler_memory_exceptions;
+    bool cpu_recompiler_icache;
+    bool gpu_disable_interlacing;
+    bool gpu_force_ntsc_timings;
+    bool gpu_widescreen_hack;
+    bool gpu_pgxp_enable;
+    bool gpu_pgxp_culling;
+    bool gpu_pgxp_cpu;
+    bool gpu_pgxp_preserve_proj_fp;
+    bool cdrom_region_check;
+    bool disable_all_enhancements;
+    bool use_old_mdec_routines;
+    bool bios_tty_logging;
+    bool was_fast_booted;
+    bool enable_8mb_ram;
+    DisplayAspectRatio display_aspect_ratio;
+    u16 display_aspect_ratio_custom_numerator;
+    u16 display_aspect_ratio_custom_denominator;
+    MultitapMode multitap_mode;
+    TickCount dma_max_slice_ticks;
+    TickCount dma_halt_ticks;
+    u32 gpu_fifo_size;
+    TickCount gpu_max_run_ahead;
+  } settings;
+
+  // <char> * game_serial_length + game_title_length follows
+  // TODO: Include the settings overlays required to match the host config.
+
+  bool Validate() const
+  {
+    return (static_cast<unsigned>(settings.console_region) < static_cast<unsigned>(ConsoleRegion::Count) &&
+            static_cast<unsigned>(settings.cpu_execution_mode) < static_cast<unsigned>(CPUExecutionMode::Count) &&
+            static_cast<unsigned>(settings.display_aspect_ratio) < static_cast<unsigned>(DisplayAspectRatio::Count) &&
+            static_cast<unsigned>(settings.multitap_mode) < static_cast<unsigned>(MultitapMode::Count));
+  }
+
+  std::string_view GetGameSerial() const
+  {
+    return std::string_view(reinterpret_cast<const char*>(this) + sizeof(ConnectResponseMessage), game_serial_length);
+  }
+
+  std::string_view GetGameTitle() const
+  {
+    return std::string_view(reinterpret_cast<const char*>(this) + sizeof(ConnectResponseMessage) + game_serial_length,
+                            game_title_length);
+  }
+
+  static ControlMessage MessageType() { return ControlMessage::ConnectResponse; }
+};
+
+struct JoinRequestMessage
+{
+  enum class Mode
+  {
+    Player,
+    Spectator,
+  };
+
+  ControlMessageHeader header;
+
+  Mode mode;
+  s32 requested_player_id;
+  char nickname[MAX_NICKNAME_LENGTH];
+  char session_password[MAX_SESSION_PASSWORD_LENGTH];
+
+  std::string_view GetNickname() const
+  {
+    const size_t len = strnlen(nickname, std::size(nickname));
+    return std::string_view(nickname, len);
+  }
+
+  std::string_view GetSessionPassword() const
+  {
+    const size_t len = strnlen(session_password, std::size(session_password));
+    return std::string_view(session_password, len);
+  }
+
+  static ControlMessage MessageType() { return ControlMessage::JoinRequest; }
+};
+
+struct JoinResponseMessage
+{
+  enum class Result : u32
+  {
+    Success = 0,
+    ServerFull,
+    PlayerIDInUse,
+    SessionClosed,
+    InvalidPassword,
+  };
+
+  ControlMessageHeader header;
+
+  Result result;
+  s32 player_id;
+
+  static ControlMessage MessageType() { return ControlMessage::JoinResponse; }
+};
+
+struct PreResetMessage
+{
+  ControlMessageHeader header;
+
+  static ControlMessage MessageType() { return ControlMessage::PreReset; }
+};
+
+struct ResetMessage
+{
+  struct PlayerAddress
+  {
+    u32 host;
+    u16 port;
+    s16 controller_port; // -1 if not present
+    char nickname[MAX_NICKNAME_LENGTH];
+
+    std::string_view GetNickname() const
+    {
+      const size_t len = strnlen(nickname, std::size(nickname));
+      return std::string_view(nickname, len);
+    }
+  };
+
+  ControlMessageHeader header;
+  u32 cookie;
+  s32 num_players;
+  PlayerAddress players[MAX_PLAYERS];
+  u32 state_data_size;
+  // state_data_size bytes of state data follows
+
+  static ControlMessage MessageType() { return ControlMessage::Reset; }
+};
+
+struct ResetCompleteMessage
+{
+  ControlMessageHeader header;
+
+  u32 cookie;
+
+  static ControlMessage MessageType() { return ControlMessage::ResetComplete; }
+};
+
+struct ResumeSessionMessage
+{
+  ControlMessageHeader header;
+
+  static ControlMessage MessageType() { return ControlMessage::ResumeSession; }
+};
+
+struct PlayerJoinedMessage
+{
+  ControlMessageHeader header;
+  s32 player_id;
+
+  static ControlMessage MessageType() { return ControlMessage::PlayerJoined; }
+};
+
+struct DropPlayerMessage
+{
+  ControlMessageHeader header;
+  DropPlayerReason reason;
+  s32 player_id;
+
+  static ControlMessage MessageType() { return ControlMessage::DropPlayer; }
+};
+
+struct ResetRequestMessage
+{
+  enum class Reason : u32
+  {
+    ConnectionLost,
+  };
+
+  ControlMessageHeader header;
+  Reason reason;
+  s32 causing_player_id;
+
+  std::string ReasonToString() const
+  {
+    switch (reason)
+    {
+      case Reason::ConnectionLost:
+        return fmt::format(TRANSLATE_FS("Netplay", "Connection lost to player {}."), causing_player_id);
+      default:
+        return "Unknown";
+    }
+  }
+
+  static ControlMessage MessageType() { return ControlMessage::ResetRequest; }
+};
+
+struct CloseSessionMessage
+{
+  enum class Reason : u32
+  {
+    HostRequest,
+    HostShutdown,
+  };
+
+  ControlMessageHeader header;
+  Reason reason;
+
+  std::string_view ReasonToString() const
+  {
+    switch (reason)
+    {
+      case Reason::HostRequest:
+        return TRANSLATE_SV("Netplay", "Session closed due to host request.");
+
+      case Reason::HostShutdown:
+        return TRANSLATE_SV("Netplay", "Session closed due to host shutdown.");
+
+      default:
+        return "Unknown";
+    }
+  }
+
+  static ControlMessage MessageType() { return ControlMessage::CloseSession; }
+};
+
+struct SetNicknameMessage
+{
+  ControlMessageHeader header;
+
+  static ControlMessage MessageType() { return ControlMessage::SetNickname; }
+};
+
+struct ChatMessage
+{
+  ControlMessageHeader header;
+
+  std::string_view GetMessage() const
+  {
+    return (header.size > sizeof(ChatMessage)) ?
+             std::string_view(reinterpret_cast<const char*>(this) + sizeof(ChatMessage),
+                              header.size - sizeof(ChatMessage)) :
+             std::string_view();
+  }
+
+  static ControlMessage MessageType() { return ControlMessage::ChatMessage; }
+};
+#pragma pack(pop)
+
+} // namespace Netplay

src/core/pad.cpp

@@ -7,6 +7,7 @@
 #include "interrupt_controller.h"
 #include "memory_card.h"
 #include "multitap.h"
+#include "netplay.h"
 #include "save_state_version.h"
 #include "system.h"
 #include "types.h"
@@ -159,6 +160,8 @@ void Pad::Reset()
 {
   SoftReset();
 
+  s_last_memory_card_transfer_frame = 0;
+
   for (u32 i = 0; i < NUM_CONTROLLER_AND_CARD_PORTS; i++)
   {
     if (s_controllers[i])
@@ -175,12 +178,12 @@ void Pad::Reset()
 bool Pad::ShouldAvoidSavingToState()
 {
   // Currently only runahead, will also be used for netplay.
-  return g_settings.IsRunaheadEnabled();
+  return g_settings.IsRunaheadEnabled() || Netplay::IsActive();
 }
 
 u32 Pad::GetMaximumRollbackFrames()
 {
-  return g_settings.runahead_frames;
+  return (Netplay::IsActive() ? Netplay::GetMaxPrediction() : g_settings.runahead_frames);
 }
 
 bool Pad::DoStateController(StateWrapper& sw, u32 i)
@@ -251,11 +254,12 @@ bool Pad::DoStateController(StateWrapper& sw, u32 i)
 
 bool Pad::DoStateMemcard(StateWrapper& sw, u32 i, bool is_memory_state)
 {
+  const bool force_load = Netplay::IsActive();
   bool card_present_in_state = static_cast<bool>(s_memory_cards[i]);
 
   sw.Do(&card_present_in_state);
 
-  if (card_present_in_state && !s_memory_cards[i] && g_settings.load_devices_from_save_states)
+  if (card_present_in_state && !s_memory_cards[i] && g_settings.load_devices_from_save_states && !force_load)
   {
     Host::AddFormattedOSDMessage(
       20.0f,
@@ -269,7 +273,7 @@ bool Pad::DoStateMemcard(StateWrapper& sw, u32 i, bool is_memory_state)
 
   if (card_present_in_state)
   {
-    if (sw.IsReading() && !g_settings.load_devices_from_save_states)
+    if (sw.IsReading() && !g_settings.load_devices_from_save_states && !force_load)
     {
       // load memcard into a temporary: If the card datas match, take the one from the savestate
       // since it has other useful non-data state information. Otherwise take the user's card
@@ -281,7 +285,7 @@ bool Pad::DoStateMemcard(StateWrapper& sw, u32 i, bool is_memory_state)
       return false;
   }
 
-  if (sw.IsWriting())
+  if (sw.IsWriting() || force_load)
     return true; // all done as far as writes concerned.
 
   if (card_from_state)
@@ -468,6 +472,9 @@ bool Pad::DoState(StateWrapper& sw, bool is_memory_state)
   }
   else
   {
+    if (sw.IsReading())
+      s_last_memory_card_transfer_frame = 0;
+
     for (u32 i = 0; i < NUM_CONTROLLER_AND_CARD_PORTS; i++)
     {
       if ((sw.GetVersion() < 50) && (i >= 2))

src/core/system.cpp

@@ -24,6 +24,7 @@
 #include "mdec.h"
 #include "memory_card.h"
 #include "multitap.h"
+#include "netplay.h"
 #include "pad.h"
 #include "pcdrv.h"
 #include "pgxp.h"
@@ -71,6 +72,7 @@ Log_SetChannel(System);
 #ifdef _WIN32
 #include "common/windows_headers.h"
 #include <mmsystem.h>
+#include <WinSock2.h>
 #endif
 
 #ifdef ENABLE_DISCORD_PRESENCE
@@ -241,6 +243,12 @@ static TinyString GetTimestampStringForFileName()
 
 void System::Internal::ProcessStartup()
 {
+#if defined(_WIN32)
+  // Setup WinSock
+  WSADATA wd = {};
+  WSAStartup(MAKEWORD(2, 2), &wd);
+#endif
+
   if (!Bus::AllocateMemory())
     Panic("Failed to allocate memory for emulated bus.");
 
@@ -266,6 +274,11 @@ void System::Internal::ProcessShutdown()
   InputManager::CloseSources();
 
   Bus::ReleaseMemory();
+
+#ifdef _WIN32
+  // Cleanup WinSock
+  WSACleanup();
+#endif
 }
 
 void System::Internal::IdlePollUpdate()
@@ -966,7 +979,7 @@ void System::ApplySettings(bool display_osd_messages)
   CheckForSettingsChanges(old_config);
   Host::CheckForSettingsChanges(old_config);
 
-  if (IsValid())
+  if (IsValid() && !Netplay::IsActive())
   {
     ResetPerformanceCounters();
     if (s_system_executing)
@@ -1077,7 +1090,7 @@ void System::ResetSystem()
 
 void System::PauseSystem(bool paused)
 {
-  if (paused == IsPaused() || !IsValid())
+  if (paused == IsPaused() || !IsValid() || Netplay::IsActive())
     return;
 
   SetState(paused ? State::Paused : State::Running);
@@ -1117,7 +1130,7 @@ void System::PauseSystem(bool paused)
 
 bool System::LoadState(const char* filename)
 {
-  if (!IsValid())
+  if (!IsValid() || Netplay::IsActive())
     return false;
 
   if (Achievements::IsHardcoreModeActive() &&
@@ -1748,6 +1761,12 @@ void System::FrameDone()
   PollDiscordPresence();
 #endif
 
+  if (Netplay::IsActive())
+  {
+    Netplay::FrameDone();
+    return;
+  }
+
   if (s_frame_step_request)
   {
     s_frame_step_request = false;
@@ -1855,6 +1874,9 @@ void System::UpdateThrottlePeriod()
   }
 
   ResetThrottler();
+
+  if (Netplay::IsActive())
+    Netplay::UpdateThrottlePeriod();
 }
 
 void System::ResetThrottler()
@@ -2650,7 +2672,7 @@ bool System::IsFastForwardEnabled()
 
 void System::SetFastForwardEnabled(bool enabled)
 {
-  if (!IsValid())
+  if (!IsValid() || Netplay::IsActive())
     return;
 
   s_fast_forward_enabled = enabled;
@@ -2664,7 +2686,7 @@ bool System::IsTurboEnabled()
 
 void System::SetTurboEnabled(bool enabled)
 {
-  if (!IsValid())
+  if (!IsValid() || Netplay::IsActive())
     return;
 
   s_turbo_enabled = enabled;
@@ -2673,7 +2695,7 @@ void System::SetTurboEnabled(bool enabled)
 
 void System::SetRewindState(bool enabled)
 {
-  if (!System::IsValid())
+  if (!System::IsValid() || Netplay::IsActive())
     return;
 
   if (!g_settings.rewind_enable)
@@ -2693,7 +2715,7 @@ void System::SetRewindState(bool enabled)
 
 void System::DoFrameStep()
 {
-  if (!IsValid())
+  if (!IsValid() || Netplay::IsActive())
     return;
 
   if (Achievements::IsHardcoreModeActive() && !Achievements::ConfirmHardcoreModeDisable("Frame stepping"))
@@ -3993,6 +4015,9 @@ void System::ShutdownSystem(bool save_resume_state)
   if (!IsValid())
     return;
 
+  if (Netplay::IsActive())
+    Netplay::SystemDestroyed();
+
   if (save_resume_state)
     SaveResumeState();
 
@@ -4598,6 +4623,8 @@ bool System::PresentDisplay(bool allow_skip_present)
   if (!skip_present)
   {
     FullscreenUI::Render();
+    if (Netplay::IsActive())
+      Netplay::RenderOverlays();
     ImGuiManager::RenderTextOverlays();
     ImGuiManager::RenderOSDMessages();
 

src/duckstation-qt/CMakeLists.txt

@@ -123,6 +123,10 @@ set(SRCS
   memorycardsettingswidget.h
   memoryviewwidget.cpp
   memoryviewwidget.h
+  netplaycreatesessiondialog.ui
+  netplayjoinsessiondialog.ui
+  netplaydialogs.cpp
+  netplaydialogs.h
   postprocessingsettingswidget.cpp
   postprocessingsettingswidget.h
   postprocessingsettingswidget.ui

src/duckstation-qt/duckstation-qt.vcxproj

@@ -45,6 +45,7 @@
     <ClCompile Include="pch.cpp">
       <PrecompiledHeader>Create</PrecompiledHeader>
     </ClCompile>
+    <ClCompile Include="netplaydialogs.cpp" />
     <ClCompile Include="postprocessingsettingswidget.cpp" />
     <ClCompile Include="qttranslations.cpp" />
     <ClCompile Include="qthost.cpp" />
@@ -89,6 +90,7 @@
     <QtMoc Include="memoryviewwidget.h" />
     <QtMoc Include="logwindow.h" />
     <ClInclude Include="pch.h" />
+    <QtMoc Include="netplaydialogs.h" />
     <ClInclude Include="resource.h" />
     <ClInclude Include="settingwidgetbinder.h" />
     <QtMoc Include="consolesettingswidget.h" />
@@ -262,6 +264,7 @@
     <ClCompile Include="$(IntDir)moc_inputbindingwidgets.cpp" />
     <ClCompile Include="$(IntDir)moc_logwindow.cpp" />
     <ClCompile Include="$(IntDir)moc_mainwindow.cpp" />
+    <ClCompile Include="$(IntDir)moc_netplaydialogs.cpp" />
     <ClCompile Include="$(IntDir)moc_memorycardsettingswidget.cpp" />
     <ClCompile Include="$(IntDir)moc_memorycardeditordialog.cpp" />
     <ClCompile Include="$(IntDir)moc_memoryviewwidget.cpp" />
@@ -332,6 +335,12 @@
     <QtUi Include="setupwizarddialog.ui">
       <FileType>Document</FileType>
     </QtUi>
+    <QtUi Include="netplaycreatesessiondialog.ui">
+      <FileType>Document</FileType>
+    </QtUi>
+    <QtUi Include="netplayjoinsessiondialog.ui">
+      <FileType>Document</FileType>
+    </QtUi>
     <None Include="translations\duckstation-qt_es-es.ts" />
     <None Include="translations\duckstation-qt_tr.ts" />
   </ItemGroup>

src/duckstation-qt/duckstation-qt.vcxproj.filters

@@ -96,6 +96,8 @@
     <ClCompile Include="$(IntDir)moc_setupwizarddialog.cpp" />
     <ClCompile Include="logwindow.cpp" />
     <ClCompile Include="$(IntDir)moc_logwindow.cpp" />
+    <ClCompile Include="netplaydialogs.cpp" />
+    <ClCompile Include="$(IntDir)moc_netplaydialogs.cpp" />
   </ItemGroup>
   <ItemGroup>
     <ClInclude Include="qtutils.h" />
@@ -158,6 +160,7 @@
     <QtMoc Include="colorpickerbutton.h" />
     <QtMoc Include="setupwizarddialog.h" />
     <QtMoc Include="logwindow.h" />
+    <QtMoc Include="netplaydialogs.h" />
   </ItemGroup>
   <ItemGroup>
     <QtUi Include="consolesettingswidget.ui" />
@@ -199,6 +202,8 @@
     <QtUi Include="coverdownloaddialog.ui" />
     <QtUi Include="controllerledsettingsdialog.ui" />
     <QtUi Include="setupwizarddialog.ui" />
+    <QtUi Include="netplaycreatesessiondialog.ui" />
+    <QtUi Include="netplayjoinsessiondialog.ui" />
   </ItemGroup>
   <ItemGroup>
     <Natvis Include="qt5.natvis" />
@@ -266,4 +271,4 @@
       <Filter>translations</Filter>
     </QtTs>
   </ItemGroup>
-</Project>
+</Project>

src/duckstation-qt/mainwindow.cpp

@@ -14,6 +14,7 @@
 #include "generalsettingswidget.h"
 #include "logwindow.h"
 #include "memorycardeditordialog.h"
+#include "netplaydialogs.h"
 #include "qthost.h"
 #include "qtutils.h"
 #include "settingsdialog.h"
@@ -84,6 +85,7 @@ static bool s_use_central_widget = false;
 // UI thread VM validity.
 static bool s_system_valid = false;
 static bool s_system_paused = false;
+static bool s_netplay_active = false;
 static QString s_current_game_title;
 static QString s_current_game_serial;
 static QString s_current_game_path;
@@ -654,6 +656,18 @@ void MainWindow::onApplicationStateChanged(Qt::ApplicationState state)
   }
 }
 
+void MainWindow::onNetplaySessionOpened(bool is_host)
+{
+  s_netplay_active = true;
+  updateEmulationActions(false, s_system_valid, false);
+}
+
+void MainWindow::onNetplaySessionClosed()
+{
+  s_netplay_active = false;
+  updateEmulationActions(false, s_system_valid, false);
+}
+
 void MainWindow::onStartFileActionTriggered()
 {
   QString filename = QDir::toNativeSeparators(
@@ -1671,6 +1685,8 @@ void MainWindow::setupAdditionalUi()
 
 void MainWindow::updateEmulationActions(bool starting, bool running, bool cheevos_challenge_mode)
 {
+  const bool netplay_active = s_netplay_active;
+
   m_ui.actionStartFile->setDisabled(starting || running);
   m_ui.actionStartDisc->setDisabled(starting || running);
   m_ui.actionStartBios->setDisabled(starting || running);
@@ -1680,25 +1696,30 @@ void MainWindow::updateEmulationActions(bool starting, bool running, bool cheevo
 
   m_ui.actionPowerOff->setDisabled(starting || !running);
   m_ui.actionPowerOffWithoutSaving->setDisabled(starting || !running);
-  m_ui.actionReset->setDisabled(starting || !running);
-  m_ui.actionPause->setDisabled(starting || !running);
-  m_ui.actionChangeDisc->setDisabled(starting || !running);
-  m_ui.actionCheats->setDisabled(starting || !running || cheevos_challenge_mode);
+  m_ui.actionReset->setDisabled(starting || !running || netplay_active);
+  m_ui.actionPause->setDisabled(starting || !running || netplay_active);
+  m_ui.actionChangeDisc->setDisabled(starting || !running || netplay_active);
+  m_ui.actionCheats->setDisabled(starting || !running || cheevos_challenge_mode || netplay_active);
   m_ui.actionScreenshot->setDisabled(starting || !running);
-  m_ui.menuChangeDisc->setDisabled(starting || !running);
-  m_ui.menuCheats->setDisabled(starting || !running || cheevos_challenge_mode);
-  m_ui.actionCheatManager->setDisabled(starting || !running || cheevos_challenge_mode);
-  m_ui.actionCPUDebugger->setDisabled(starting || !running || cheevos_challenge_mode);
+  m_ui.menuChangeDisc->setDisabled(starting || !running || netplay_active);
+  m_ui.menuCheats->setDisabled(starting || !running || cheevos_challenge_mode || netplay_active);
+  m_ui.actionCheatManager->setDisabled(starting || !running || cheevos_challenge_mode || netplay_active);
+  m_ui.actionCPUDebugger->setDisabled(starting || !running || cheevos_challenge_mode || netplay_active);
   m_ui.actionDumpRAM->setDisabled(starting || !running || cheevos_challenge_mode);
   m_ui.actionDumpVRAM->setDisabled(starting || !running || cheevos_challenge_mode);
   m_ui.actionDumpSPURAM->setDisabled(starting || !running || cheevos_challenge_mode);
 
-  m_ui.actionSaveState->setDisabled(starting || !running);
-  m_ui.menuSaveState->setDisabled(starting || !running);
+  m_ui.actionLoadState->setDisabled(netplay_active);
+  m_ui.menuLoadState->setDisabled(netplay_active);
+  m_ui.actionSaveState->setDisabled(starting || !running || netplay_active);
+  m_ui.menuSaveState->setDisabled(starting || !running || netplay_active);
   m_ui.menuWindowSize->setDisabled(starting || !running);
 
   m_ui.actionViewGameProperties->setDisabled(starting || !running);
 
+  m_ui.actionCreateNetplaySession->setDisabled(!running || cheevos_challenge_mode || netplay_active);
+  m_ui.actionJoinNetplaySession->setDisabled(cheevos_challenge_mode || netplay_active);
+
   if (starting || running)
   {
     if (!m_ui.toolBar->actions().contains(m_ui.actionPowerOff))
@@ -2016,6 +2037,8 @@ void MainWindow::connectSignals()
   connect(g_emu_thread, &EmuThread::achievementsLoginSucceeded, this, &MainWindow::onAchievementsLoginSucceeded);
   connect(g_emu_thread, &EmuThread::achievementsChallengeModeChanged, this,
           &MainWindow::onAchievementsChallengeModeChanged);
+  connect(g_emu_thread, &EmuThread::netplaySessionOpened, this, &MainWindow::onNetplaySessionOpened);
+  connect(g_emu_thread, &EmuThread::netplaySessionClosed, this, &MainWindow::onNetplaySessionClosed);
 
   // These need to be queued connections to stop crashing due to menus opening/closing and switching focus.
   connect(m_game_list_widget, &GameListWidget::refreshProgress, this, &MainWindow::onGameListRefreshProgress);
@@ -2089,6 +2112,10 @@ void MainWindow::connectSignals()
   }
 
   updateMenuSelectedTheme();
+
+  // Netplay UI , TODO
+  connect(m_ui.actionCreateNetplaySession, &QAction::triggered, this, &MainWindow::onCreateNetplaySessionClicked);
+  connect(m_ui.actionJoinNetplaySession, &QAction::triggered, this, &MainWindow::onJoinNetplaySessionClicked);
 }
 
 void MainWindow::setTheme(const QString& theme)
@@ -2550,6 +2577,7 @@ bool MainWindow::requestShutdown(bool allow_confirm /* = true */, bool allow_sav
 
   // If we don't have a serial, we can't save state.
   allow_save_to_state &= !s_current_game_serial.isEmpty();
+  allow_save_to_state &= !s_netplay_active;
   save_state &= allow_save_to_state;
 
   // Only confirm on UI thread because we need to display a msgbox.
@@ -2793,6 +2821,18 @@ void MainWindow::onCPUDebuggerClosed()
   m_debugger_window = nullptr;
 }
 
+void MainWindow::onCreateNetplaySessionClicked()
+{
+  CreateNetplaySessionDialog dlg(this);
+  dlg.exec();
+}
+
+void MainWindow::onJoinNetplaySessionClicked()
+{
+  JoinNetplaySessionDialog dlg(this);
+  dlg.exec();
+}
+
 void MainWindow::onToolsOpenDataDirectoryTriggered()
 {
   QtUtils::OpenURL(this, QUrl::fromLocalFile(QString::fromStdString(EmuFolders::DataRoot)));
@@ -2876,7 +2916,7 @@ MainWindow::SystemLock MainWindow::pauseAndLockSystem()
 #else
   const bool was_fullscreen = false;
 #endif
-  const bool was_paused = !s_system_valid || s_system_paused;
+  const bool was_paused = !s_system_valid || s_system_paused || s_netplay_active;
 
   // We need to switch out of exclusive fullscreen before we can display our popup.
   // However, we do not want to switch back to render-to-main, the window might have generated this event.

src/duckstation-qt/mainwindow.h

@@ -133,6 +133,8 @@ private Q_SLOTS:
                                     quint32 unread_messages);
   void onAchievementsChallengeModeChanged(bool enabled);
   void onApplicationStateChanged(Qt::ApplicationState state);
+  void onNetplaySessionOpened(bool is_host);
+  void onNetplaySessionClosed();
 
   void onStartFileActionTriggered();
   void onStartDiscActionTriggered();
@@ -177,6 +179,9 @@ private Q_SLOTS:
   void openCPUDebugger();
   void onCPUDebuggerClosed();
 
+  void onCreateNetplaySessionClicked();
+  void onJoinNetplaySessionClicked();
+
 protected:
   void showEvent(QShowEvent* event) override;
   void closeEvent(QCloseEvent* event) override;

src/duckstation-qt/mainwindow.ui

@@ -237,8 +237,17 @@
     <addaction name="separator"/>
     <addaction name="actionOpenDataDirectory"/>
    </widget>
+   <widget class="QMenu" name="menuNetplay">
+    <property name="title">
+     <string>Netplay</string>
+    </property>
+    <addaction name="separator"/>
+    <addaction name="actionCreateNetplaySession"/>
+    <addaction name="actionJoinNetplaySession"/>
+   </widget>
    <addaction name="menuSystem"/>
    <addaction name="menuSettings"/>
+   <addaction name="menuNetplay"/>
    <addaction name="menu_View"/>
    <addaction name="menu_Tools"/>
    <addaction name="menuDebug"/>
@@ -976,6 +985,16 @@
     <string>Cover Downloader</string>
    </property>
   </action>
+  <action name="actionCreateNetplaySession">
+   <property name="text">
+    <string>Create Session...</string>
+   </property>
+  </action>
+  <action name="actionJoinNetplaySession">
+   <property name="text">
+    <string>Join Session...</string>
+   </property>
+  </action>
  </widget>
  <resources>
   <include location="resources/resources.qrc"/>

src/duckstation-qt/netplaycreatesessiondialog.ui

@@ -0,0 +1,185 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<ui version="4.0">
+ <class>NetplayCreateSessionDialog</class>
+ <widget class="QDialog" name="NetplayCreateSessionDialog">
+  <property name="windowModality">
+   <enum>Qt::WindowModal</enum>
+  </property>
+  <property name="geometry">
+   <rect>
+    <x>0</x>
+    <y>0</y>
+    <width>496</width>
+    <height>302</height>
+   </rect>
+  </property>
+  <property name="windowTitle">
+   <string comment="Window title">Create Netplay Session</string>
+  </property>
+  <property name="modal">
+   <bool>true</bool>
+  </property>
+  <layout class="QVBoxLayout" name="verticalLayout">
+   <item>
+    <layout class="QHBoxLayout" name="horizontalLayout" stretch="0,1">
+     <item>
+      <widget class="QLabel" name="label">
+       <property name="text">
+        <string/>
+       </property>
+       <property name="pixmap">
+        <pixmap resource="resources/resources.qrc">:/icons/emblem-person-blue.png</pixmap>
+       </property>
+      </widget>
+     </item>
+     <item>
+      <widget class="QLabel" name="label_2">
+       <property name="font">
+        <font>
+         <pointsize>14</pointsize>
+         <bold>false</bold>
+        </font>
+       </property>
+       <property name="text">
+        <string comment="Header text">Create Netplay Session</string>
+       </property>
+       <property name="alignment">
+        <set>Qt::AlignLeading|Qt::AlignLeft|Qt::AlignTop</set>
+       </property>
+      </widget>
+     </item>
+    </layout>
+   </item>
+   <item>
+    <widget class="QLabel" name="label_3">
+     <property name="text">
+      <string>&lt;html&gt;&lt;head/&gt;&lt;body&gt;&lt;p&gt;Select a nickname and port to open your current game session to other players via netplay. A password may optionally be supplied to restrict who can join. The traversal mode option can be enabled to allow other players to join via a host code without needing to portforward.&lt;/p&gt;&lt;/body&gt;&lt;/html&gt;</string>
+     </property>
+     <property name="wordWrap">
+      <bool>true</bool>
+     </property>
+    </widget>
+   </item>
+   <item>
+    <spacer name="verticalSpacer">
+     <property name="orientation">
+      <enum>Qt::Vertical</enum>
+     </property>
+     <property name="sizeHint" stdset="0">
+      <size>
+       <width>20</width>
+       <height>40</height>
+      </size>
+     </property>
+    </spacer>
+   </item>
+   <item>
+    <layout class="QFormLayout" name="formLayout">
+     <item row="0" column="0">
+      <widget class="QLabel" name="label_4">
+       <property name="text">
+        <string>Nickname:</string>
+       </property>
+      </widget>
+     </item>
+     <item row="0" column="1">
+      <widget class="QLineEdit" name="nickname">
+       <property name="text">
+        <string>Netplay Host</string>
+       </property>
+       <property name="maxLength">
+        <number>128</number>
+       </property>
+      </widget>
+     </item>
+     <item row="3" column="0">
+      <widget class="QLabel" name="label_5">
+       <property name="text">
+        <string>Port:</string>
+       </property>
+      </widget>
+     </item>
+     <item row="3" column="1">
+      <widget class="QSpinBox" name="port">
+       <property name="minimum">
+        <number>1</number>
+       </property>
+       <property name="maximum">
+        <number>65535</number>
+       </property>
+       <property name="value">
+        <number>31200</number>
+       </property>
+      </widget>
+     </item>
+     <item row="1" column="0">
+      <widget class="QLabel" name="label_6">
+       <property name="text">
+        <string>Players:</string>
+       </property>
+      </widget>
+     </item>
+     <item row="1" column="1">
+      <widget class="QSpinBox" name="maxPlayers">
+       <property name="minimum">
+        <number>2</number>
+       </property>
+       <property name="maximum">
+        <number>8</number>
+       </property>
+      </widget>
+     </item>
+     <item row="4" column="0">
+      <widget class="QLabel" name="label_7">
+       <property name="text">
+        <string>Password:</string>
+       </property>
+      </widget>
+     </item>
+     <item row="4" column="1">
+      <widget class="QLineEdit" name="password">
+       <property name="maxLength">
+        <number>128</number>
+       </property>
+       <property name="echoMode">
+        <enum>QLineEdit::Password</enum>
+       </property>
+      </widget>
+     </item>
+     <item row="2" column="0">
+      <widget class="QLabel" name="label_8">
+       <property name="text">
+        <string>Input Delay:</string>
+       </property>
+      </widget>
+     </item>
+     <item row="2" column="1">
+      <widget class="QSpinBox" name="inputDelay"/>
+     </item>
+    </layout>
+   </item>
+   <item>
+    <layout class="QHBoxLayout" name="horizontalLayout_2">
+     <item>
+      <widget class="QCheckBox" name="traversal">
+       <property name="text">
+        <string>Enable Traversal Mode</string>
+       </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>
+ <resources>
+  <include location="resources/resources.qrc"/>
+ </resources>
+ <connections/>
+</ui>

src/duckstation-qt/netplaydialogs.cpp

@@ -0,0 +1,129 @@
+// SPDX-FileCopyrightText: 2023 Connor McLaughlin <stenzek@gmail.com> and contributors.
+// SPDX-License-Identifier: (GPL-3.0 OR CC-BY-NC-ND-4.0)
+
+#include "netplaydialogs.h"
+#include "qthost.h"
+
+#include "core/netplay.h"
+
+#include <QtWidgets/QPushButton>
+
+CreateNetplaySessionDialog::CreateNetplaySessionDialog(QWidget* parent) : QDialog(parent)
+{
+  m_ui.setupUi(this);
+
+  connect(m_ui.maxPlayers, &QSpinBox::valueChanged, this, &CreateNetplaySessionDialog::updateState);
+  connect(m_ui.port, &QSpinBox::valueChanged, this, &CreateNetplaySessionDialog::updateState);
+  connect(m_ui.inputDelay, &QSpinBox::valueChanged, this, &CreateNetplaySessionDialog::updateState);
+  connect(m_ui.nickname, &QLineEdit::textChanged, this, &CreateNetplaySessionDialog::updateState);
+  connect(m_ui.password, &QLineEdit::textChanged, this, &CreateNetplaySessionDialog::updateState);
+
+  connect(m_ui.buttonBox->button(QDialogButtonBox::Ok), &QAbstractButton::clicked, this,
+          &CreateNetplaySessionDialog::accept);
+  connect(m_ui.buttonBox->button(QDialogButtonBox::Cancel), &QAbstractButton::clicked, this,
+          &CreateNetplaySessionDialog::reject);
+
+  updateState();
+}
+
+CreateNetplaySessionDialog::~CreateNetplaySessionDialog() = default;
+
+void CreateNetplaySessionDialog::accept()
+{
+  if (!validate())
+    return;
+
+  const int players = m_ui.maxPlayers->value();
+  const int port = m_ui.port->value();
+  const int inputdelay = m_ui.inputDelay->value();
+  const QString& nickname = m_ui.nickname->text();
+  const QString& password = m_ui.password->text();
+  const bool traversal = m_ui.traversal->isChecked();
+  QDialog::accept();
+
+  g_emu_thread->createNetplaySession(nickname.trimmed(), port, players, password, inputdelay, traversal);
+}
+
+bool CreateNetplaySessionDialog::validate()
+{
+  const int players = m_ui.maxPlayers->value();
+  const int port = m_ui.port->value();
+  const int inputdelay = m_ui.inputDelay->value();
+  const QString& nickname = m_ui.nickname->text();
+  return (!nickname.isEmpty() && players >= 2 && players <= Netplay::MAX_PLAYERS && port > 0 && port <= 65535 &&
+          inputdelay >= 0 && inputdelay <= 10);
+}
+
+void CreateNetplaySessionDialog::updateState()
+{
+  m_ui.buttonBox->button(QDialogButtonBox::Ok)->setEnabled(validate());
+}
+
+JoinNetplaySessionDialog::JoinNetplaySessionDialog(QWidget* parent)
+{
+  m_ui.setupUi(this);
+
+  connect(m_ui.port, &QSpinBox::valueChanged, this, &JoinNetplaySessionDialog::updateState);
+  connect(m_ui.inputDelay, &QSpinBox::valueChanged, this, &JoinNetplaySessionDialog::updateState);
+  connect(m_ui.inputDelayTraversal, &QSpinBox::valueChanged, this, &JoinNetplaySessionDialog::updateState);
+  connect(m_ui.nickname, &QLineEdit::textChanged, this, &JoinNetplaySessionDialog::updateState);
+  connect(m_ui.nicknameTraversal, &QLineEdit::textChanged, this, &JoinNetplaySessionDialog::updateState);
+  connect(m_ui.password, &QLineEdit::textChanged, this, &JoinNetplaySessionDialog::updateState);
+  connect(m_ui.passwordTraversal, &QLineEdit::textChanged, this, &JoinNetplaySessionDialog::updateState);
+  connect(m_ui.hostname, &QLineEdit::textChanged, this, &JoinNetplaySessionDialog::updateState);
+  connect(m_ui.hostCode, &QLineEdit::textChanged, this, &JoinNetplaySessionDialog::updateState);
+  connect(m_ui.tabConnectMode, &QTabWidget::currentChanged, this, &JoinNetplaySessionDialog::updateState);
+
+  connect(m_ui.buttonBox->button(QDialogButtonBox::Ok), &QAbstractButton::clicked, this,
+          &JoinNetplaySessionDialog::accept);
+  connect(m_ui.buttonBox->button(QDialogButtonBox::Cancel), &QAbstractButton::clicked, this,
+          &JoinNetplaySessionDialog::reject);
+
+  updateState();
+}
+
+JoinNetplaySessionDialog::~JoinNetplaySessionDialog() = default;
+
+void JoinNetplaySessionDialog::accept()
+{
+  const bool direct_mode = m_ui.tabTraversal->isHidden();
+  const bool valid = direct_mode ? validate() : validateTraversal();
+  if (!valid)
+    return;
+
+  int port = m_ui.port->value();
+  int inputdelay = direct_mode ? m_ui.inputDelay->value() : m_ui.inputDelayTraversal->value();
+  const QString& nickname = direct_mode ? m_ui.nickname->text() : m_ui.nicknameTraversal->text();
+  const QString& password = direct_mode ? m_ui.password->text() : m_ui.passwordTraversal->text();
+  const QString& hostname = m_ui.hostname->text();
+  const QString& hostcode = m_ui.hostCode->text();
+  const bool spectating = m_ui.spectating->isChecked();
+  QDialog::accept();
+
+  g_emu_thread->joinNetplaySession(nickname.trimmed(), hostname.trimmed(), port, password, spectating, inputdelay,
+                                   !direct_mode, hostcode.trimmed());
+}
+
+bool JoinNetplaySessionDialog::validate()
+{
+  const int port = m_ui.port->value();
+  const int inputdelay = m_ui.inputDelay->value();
+  const QString& nickname = m_ui.nickname->text();
+  const QString& hostname = m_ui.hostname->text();
+  return (!nickname.isEmpty() && !hostname.isEmpty() && port > 0 && port <= 65535 && inputdelay >= 0 &&
+          inputdelay <= 10);
+}
+
+bool JoinNetplaySessionDialog::validateTraversal()
+{
+  const int inputdelay = m_ui.inputDelayTraversal->value();
+  const QString& nickname = m_ui.nicknameTraversal->text();
+  const QString& hostcode = m_ui.hostCode->text();
+  return (!nickname.isEmpty() && !hostcode.isEmpty() && inputdelay >= 0 && inputdelay <= 10);
+}
+
+void JoinNetplaySessionDialog::updateState()
+{
+  m_ui.buttonBox->button(QDialogButtonBox::Ok)
+    ->setEnabled(m_ui.tabTraversal->isHidden() ? validate() : validateTraversal());
+}

src/duckstation-qt/netplaydialogs.h

@@ -0,0 +1,51 @@
+// SPDX-FileCopyrightText: 2023 Connor McLaughlin <stenzek@gmail.com> and contributors.
+// SPDX-License-Identifier: (GPL-3.0 OR CC-BY-NC-ND-4.0)
+
+#pragma once
+
+#include "ui_netplaycreatesessiondialog.h"
+#include "ui_netplayjoinsessiondialog.h"
+
+#include <QtWidgets/QDialog>
+
+class CreateNetplaySessionDialog : public QDialog
+{
+  Q_OBJECT
+
+public:
+  CreateNetplaySessionDialog(QWidget* parent);
+  ~CreateNetplaySessionDialog();
+
+public Q_SLOTS:
+  void accept() override;
+
+private Q_SLOTS:
+  void updateState();
+
+private:
+  bool validate();
+
+  Ui::NetplayCreateSessionDialog m_ui;
+};
+
+class JoinNetplaySessionDialog : public QDialog
+{
+  Q_OBJECT
+
+public:
+  JoinNetplaySessionDialog(QWidget* parent);
+  ~JoinNetplaySessionDialog();
+
+public Q_SLOTS:
+  void accept() override;
+
+private Q_SLOTS:
+  void updateState();
+
+private:
+  bool validate();
+  bool validateTraversal();
+
+private:
+  Ui::NetplayJoinSessionDialog m_ui;
+};

src/duckstation-qt/netplayjoinsessiondialog.ui

@@ -0,0 +1,276 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<ui version="4.0">
+ <class>NetplayJoinSessionDialog</class>
+ <widget class="QDialog" name="NetplayJoinSessionDialog">
+  <property name="windowModality">
+   <enum>Qt::WindowModal</enum>
+  </property>
+  <property name="geometry">
+   <rect>
+    <x>0</x>
+    <y>0</y>
+    <width>480</width>
+    <height>308</height>
+   </rect>
+  </property>
+  <property name="windowTitle">
+   <string comment="Window title">Create Netplay Session</string>
+  </property>
+  <property name="modal">
+   <bool>true</bool>
+  </property>
+  <layout class="QVBoxLayout" name="verticalLayout">
+   <item>
+    <layout class="QHBoxLayout" name="horizontalLayout" stretch="0,1">
+     <item>
+      <widget class="QLabel" name="label">
+       <property name="text">
+        <string/>
+       </property>
+       <property name="pixmap">
+        <pixmap resource="resources/resources.qrc">:/icons/emblem-person-blue.png</pixmap>
+       </property>
+      </widget>
+     </item>
+     <item>
+      <widget class="QLabel" name="label_2">
+       <property name="font">
+        <font>
+         <pointsize>14</pointsize>
+         <bold>false</bold>
+        </font>
+       </property>
+       <property name="text">
+        <string comment="Header text">Join Netplay Session</string>
+       </property>
+       <property name="alignment">
+        <set>Qt::AlignLeading|Qt::AlignLeft|Qt::AlignTop</set>
+       </property>
+      </widget>
+     </item>
+    </layout>
+   </item>
+   <item>
+    <widget class="QLabel" name="label_3">
+     <property name="text">
+      <string>Choose a nickname and enter the address/port of the netplay session you wish to join.</string>
+     </property>
+     <property name="wordWrap">
+      <bool>true</bool>
+     </property>
+    </widget>
+   </item>
+   <item>
+    <spacer name="verticalSpacer">
+     <property name="orientation">
+      <enum>Qt::Vertical</enum>
+     </property>
+     <property name="sizeType">
+      <enum>QSizePolicy::Expanding</enum>
+     </property>
+     <property name="sizeHint" stdset="0">
+      <size>
+       <width>20</width>
+       <height>10</height>
+      </size>
+     </property>
+    </spacer>
+   </item>
+   <item>
+    <widget class="QTabWidget" name="tabConnectMode">
+     <property name="minimumSize">
+      <size>
+       <width>0</width>
+       <height>190</height>
+      </size>
+     </property>
+     <property name="currentIndex">
+      <number>0</number>
+     </property>
+     <widget class="QWidget" name="tabDirect">
+      <attribute name="title">
+       <string>Direct Mode</string>
+      </attribute>
+      <layout class="QVBoxLayout" name="verticalLayout_2">
+       <item>
+        <layout class="QFormLayout" name="formLayout">
+         <item row="0" column="0">
+          <widget class="QLabel" name="label_4">
+           <property name="text">
+            <string>Nickname:</string>
+           </property>
+          </widget>
+         </item>
+         <item row="0" column="1">
+          <widget class="QLineEdit" name="nickname">
+           <property name="text">
+            <string>Netplay Peer</string>
+           </property>
+           <property name="maxLength">
+            <number>128</number>
+           </property>
+          </widget>
+         </item>
+         <item row="1" column="0">
+          <widget class="QLabel" name="label_8">
+           <property name="text">
+            <string>Input Delay:</string>
+           </property>
+          </widget>
+         </item>
+         <item row="1" column="1">
+          <widget class="QSpinBox" name="inputDelay"/>
+         </item>
+         <item row="2" column="0">
+          <widget class="QLabel" name="label_6">
+           <property name="text">
+            <string>Hostname:</string>
+           </property>
+          </widget>
+         </item>
+         <item row="2" column="1">
+          <widget class="QLineEdit" name="hostname">
+           <property name="text">
+            <string>localhost</string>
+           </property>
+          </widget>
+         </item>
+         <item row="3" column="0">
+          <widget class="QLabel" name="label_5">
+           <property name="text">
+            <string>Port:</string>
+           </property>
+          </widget>
+         </item>
+         <item row="3" column="1">
+          <widget class="QSpinBox" name="port">
+           <property name="minimum">
+            <number>1</number>
+           </property>
+           <property name="maximum">
+            <number>65535</number>
+           </property>
+           <property name="value">
+            <number>31200</number>
+           </property>
+          </widget>
+         </item>
+         <item row="4" column="0">
+          <widget class="QLabel" name="label_7">
+           <property name="text">
+            <string>Password:</string>
+           </property>
+          </widget>
+         </item>
+         <item row="4" column="1">
+          <widget class="QLineEdit" name="password">
+           <property name="maxLength">
+            <number>128</number>
+           </property>
+           <property name="echoMode">
+            <enum>QLineEdit::Password</enum>
+           </property>
+          </widget>
+         </item>
+        </layout>
+       </item>
+      </layout>
+     </widget>
+     <widget class="QWidget" name="tabTraversal">
+      <attribute name="title">
+       <string>Traversal Mode</string>
+      </attribute>
+      <layout class="QVBoxLayout" name="verticalLayout_3">
+       <item>
+        <layout class="QFormLayout" name="formLayout_2">
+         <item row="0" column="0">
+          <widget class="QLabel" name="label_9">
+           <property name="text">
+            <string>Nickname:</string>
+           </property>
+          </widget>
+         </item>
+         <item row="0" column="1">
+          <widget class="QLineEdit" name="nicknameTraversal">
+           <property name="text">
+            <string>Netplay Peer</string>
+           </property>
+           <property name="maxLength">
+            <number>128</number>
+           </property>
+          </widget>
+         </item>
+         <item row="1" column="1">
+          <widget class="QSpinBox" name="inputDelayTraversal"/>
+         </item>
+         <item row="3" column="0">
+          <widget class="QLabel" name="label_13">
+           <property name="text">
+            <string>Password:</string>
+           </property>
+          </widget>
+         </item>
+         <item row="3" column="1">
+          <widget class="QLineEdit" name="passwordTraversal">
+           <property name="maxLength">
+            <number>128</number>
+           </property>
+           <property name="echoMode">
+            <enum>QLineEdit::Password</enum>
+           </property>
+          </widget>
+         </item>
+         <item row="2" column="0">
+          <widget class="QLabel" name="label_11">
+           <property name="text">
+            <string>Host Code:</string>
+           </property>
+          </widget>
+         </item>
+         <item row="2" column="1">
+          <widget class="QLineEdit" name="hostCode"/>
+         </item>
+         <item row="1" column="0">
+          <widget class="QLabel" name="label_10">
+           <property name="text">
+            <string>Input Delay:</string>
+           </property>
+          </widget>
+         </item>
+        </layout>
+       </item>
+      </layout>
+     </widget>
+    </widget>
+   </item>
+   <item>
+    <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>
+ <resources>
+  <include location="resources/resources.qrc"/>
+ </resources>
+ <connections/>
+</ui>

src/duckstation-qt/qthost.cpp

@@ -20,6 +20,7 @@
 #include "core/host.h"
 #include "core/imgui_overlays.h"
 #include "core/memory_card.h"
+#include "core/netplay.h"
 #include "core/spu.h"
 #include "core/system.h"
 
@@ -106,6 +107,9 @@ static bool s_start_fullscreen_ui = false;
 static bool s_start_fullscreen_ui_fullscreen = false;
 static bool s_run_setup_wizard = false;
 
+// TODO: REMOVE ME
+static int s_netplay_test = -1;
+
 EmuThread* g_emu_thread;
 GDBServer* g_gdb_server;
 
@@ -975,6 +979,62 @@ void EmuThread::updatePostProcessingSettings()
     PostProcessing::UpdateSettings();
 }
 
+void EmuThread::createNetplaySession(const QString& nickname, qint32 port, qint32 max_players, const QString& password, int inputdelay, bool traversal)
+{
+  if (!isOnThread())
+  {
+    QMetaObject::invokeMethod(this, "createNetplaySession", Qt::QueuedConnection, Q_ARG(const QString&, nickname),
+                              Q_ARG(qint32, port), Q_ARG(qint32, max_players), Q_ARG(const QString&, password),
+                              Q_ARG(int, inputdelay), Q_ARG(bool, traversal));
+    return;
+  }
+
+  // need a valid system to make a session
+  if (!System::IsValid())
+    return;
+
+  if (!Netplay::CreateSession(nickname.toStdString(), port, max_players, password.toStdString(), inputdelay, traversal))
+  {
+    errorReported(tr("Netplay Error"), tr("Failed to create netplay session. The log may contain more information."));
+    return;
+  }
+}
+
+void EmuThread::joinNetplaySession(const QString& nickname, const QString& hostname, qint32 port,
+                                   const QString& password, bool spectating, int inputdelay, bool traversal,
+                                   const QString& hostcode)
+{
+  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(bool, spectating), Q_ARG(int, inputdelay), Q_ARG(bool, traversal),
+                              Q_ARG(const QString&, hostcode));
+    return;
+  }
+
+  setInitialState(std::nullopt);
+
+  if (!Netplay::JoinSession(nickname.toStdString(), hostname.toStdString(), port, password.toStdString(), spectating, inputdelay, traversal, hostcode.toStdString()))
+  {
+    errorReported(tr("Netplay Error"), tr("Failed to join netplay session. The log may contain more information."));
+    return;
+  }
+
+  // Exit the event loop, we'll take it from here.
+  g_emu_thread->wakeThread();
+}
+
+void Host::OnNetplaySessionOpened(bool is_host)
+{
+  emit g_emu_thread->netplaySessionOpened(is_host);
+}
+
+void Host::OnNetplaySessionClosed()
+{
+  emit g_emu_thread->netplaySessionClosed();
+}
+
 void EmuThread::clearInputBindStateFromSource(InputBindingKey key)
 {
   if (!isOnThread())
@@ -1327,11 +1387,16 @@ void EmuThread::run()
   // bind buttons/axises
   createBackgroundControllerPollTimer();
   startBackgroundControllerPollTimer();
+  setInitialState(std::nullopt);
 
   // main loop
   while (!m_shutdown_flag)
   {
-    if (System::IsRunning())
+    if (Netplay::IsActive())
+    {
+      Netplay::ExecuteNetplay();
+    }
+    else if (System::IsRunning())
     {
       System::Execute();
     }
@@ -1906,7 +1971,12 @@ bool QtHost::ParseCommandLineParametersAndInitializeConfig(QApplication& app,
 
         continue;
       }
-#ifdef ENABLE_RAINTEGRATION
+      else if (CHECK_ARG_PARAM("-netplay"))
+      {
+        s_netplay_test = StringUtil::FromChars<int>(args[++i].toStdString()).value_or(0);
+        continue;
+      }
+#ifdef WITH_RAINTEGRATION
       else if (CHECK_ARG("-raintegration"))
       {
         Achievements::SwitchToRAIntegration();
@@ -2070,6 +2140,31 @@ int main(int argc, char* argv[])
   else if (!s_nogui_mode)
     main_window->startupUpdateCheck();
 
+  if (s_netplay_test >= 0)
+  {
+    Host::RunOnCPUThread([]() {
+      const bool first = (s_netplay_test == 0);
+      QtHost::RunOnUIThread([first]() { g_main_window->move(QPoint(first ? 300 : 1400, 500)); });
+
+      const int port = 31200;
+      const QString remote = QStringLiteral("127.0.0.1");
+      std::string game = "D:\\PSX\\chd\\padtest.chd";
+      const QString nickname = QStringLiteral("NICKNAME%1").arg(s_netplay_test + 1);
+      if (first)
+      {
+        auto params = std::make_shared<SystemBootParameters>(std::move(game));
+        params->override_fast_boot = true;
+        params->fast_forward_to_first_frame = true;
+        g_emu_thread->bootSystem(std::move(params));
+        g_emu_thread->createNetplaySession(nickname, port, 2, QString(), 0, false);
+      }
+      else
+      {
+        g_emu_thread->joinNetplaySession(nickname, remote, port, QString(), false, 0, false, "");
+      }
+    });
+  }
+
   // This doesn't return until we exit.
   result = app.exec();
 

src/duckstation-qt/qthost.h

@@ -147,6 +147,8 @@ Q_SIGNALS:
   void achievementsRefreshed(quint32 id, const QString& game_info_string);
   void achievementsChallengeModeChanged(bool enabled);
   void cheatEnabled(quint32 index, bool enabled);
+  void netplaySessionOpened(bool is_host);
+  void netplaySessionClosed();
 
 public Q_SLOTS:
   void setDefaultSettings(bool system = true, bool controller = true);
@@ -192,6 +194,10 @@ public Q_SLOTS:
   void applyCheat(quint32 index);
   void reloadPostProcessingShaders();
   void updatePostProcessingSettings();
+  void createNetplaySession(const QString& nickname, qint32 port, qint32 max_players, const QString& password,
+                            int inputdelay, bool traversal);
+  void joinNetplaySession(const QString& nickname, const QString& hostname, qint32 port, const QString& password,
+                          bool spectating, int inputdelay, bool traversal, const QString& hostcode);
   void clearInputBindStateFromSource(InputBindingKey key);
 
 private Q_SLOTS:
@@ -236,6 +242,7 @@ private:
   float m_last_video_fps = std::numeric_limits<float>::infinity();
   u32 m_last_render_width = std::numeric_limits<u32>::max();
   u32 m_last_render_height = std::numeric_limits<u32>::max();
+  u32 m_last_ping = std::numeric_limits<u32>::max();
   RenderAPI m_last_render_api = RenderAPI::None;
   bool m_last_hardware_renderer = false;
 };

src/util/input_manager.cpp

@@ -11,6 +11,7 @@
 #include "core/controller.h"
 #include "core/host.h"
 #include "core/system.h"
+#include "core/netplay.h"
 #include "imgui_manager.h"
 #include "input_source.h"
 
@@ -714,6 +715,12 @@ void InputManager::AddPadBindings(SettingsInterface& si, const std::string& sect
                         if (!System::IsValid())
                           return;
 
+                        if (Netplay::IsActive())
+                        {
+                          Netplay::CollectInput(pad_index, bind_index, value);
+                          return;
+                        }
+
                         Controller* c = System::GetController(pad_index);
                         if (c)
                           c->SetBindState(bind_index, value);