multiplayer stage 2: peer identity, stable vehicle ids and a session lobby

TTrain::id() numbers cabs with a local counter, in the order each peer happens
to create them, so it cannot address a vehicle across the session. Neither was
there any way for a player to see what is available to drive.

- network/entities: PeerId (the host is peer 1, remote peers are numbered from
  2, so it is a participant rather than a special case) and NetworkEntityId,
  plus a registry that numbers the drivable vehicles of the loaded scenario in
  name order and resolves ids back to TDynamicObject
- the server owns the numbering and publishes it as VEHICLE_LIST - name, crew
  occupancy, crew capacity, AI state, availability - on every change and at
  least every 120 frames, out of band so it stays out of the replay backbuffer;
  a client binds the received ids to its own copy of the scenario by name
- SERVER_HELLO hands the joining peer its PeerId
- a multiplayer lobby listing that roster, with vehicles taken by other players
  shown as such rather than hidden; entering one goes through the existing
  entervehicle command, the vehicle is never moved

The lobby lives inside the driver mode instead of a mode of its own: the world
has to keep running while somebody is choosing (a client stops consuming the
server's frames the moment its mode is not a command processor), and the same
screen is what a player needs to change vehicles later on.

Crew occupancy is still derived from the presence of a cab instance; the real
crew model, claim handshake and AI takeover follow in stage 3.

application/application.cpp

@@ -1517,6 +1517,11 @@ bool eu07_application::init_network()
 	{
 		// create network manager
 		m_network.emplace();
+
+		// the host takes part in the session like any other peer, with an identity of its
+		// own, so that crew and permission handling needs no special case for it
+		if (!Global.network_client)
+			Global.network_peer_id = network::PEER_HOST;
 	}
 
 	for (auto const &pair : Global.network_servers)
@@ -1526,14 +1531,15 @@ bool eu07_application::init_network()
 		m_network->create_server(pair.first, pair.second);
 	}
 
+	if (!Global.local_start_vehicle_override && (Global.network_client || !Global.network_servers.empty()))
+	{
+		// in a multiplayer session the vehicle is picked in the lobby, so both the host
+		// and the joining clients start out as observers rather than in a random cab
+		Global.local_start_vehicle = "ghostview";
+	}
+
 	if (Global.network_client)
 	{
-		if (!Global.local_start_vehicle_override)
-		{
-			// in a multiplayer session the vehicle is assigned by the server;
-			// until the lobby exists the client simply starts out as an observer
-			Global.local_start_vehicle = "ghostview";
-		}
 
 		Global.network_status = "Connecting to " + Global.network_client->second + "...";
 		WriteLog("net: connecting to " + Global.network_client->second + " (" + Global.network_client->first + ")", logtype::net);

application/drivermode.cpp

@@ -266,6 +266,14 @@ bool driver_mode::update()
 
 		// variable step simulation time routines
 
+		if (change_train.empty() && !Global.network_pending_vehicle.empty())
+		{
+			// vehicle picked in the multiplayer lobby; the cab itself is built by the
+			// replicated entervehicle command, we only have to move in once it exists
+			change_train = Global.network_pending_vehicle;
+			Global.network_pending_vehicle.clear();
+		}
+
 		if (!change_train.empty())
 		{
 			TTrain *train = simulation::Trains.find(change_train);
@@ -452,6 +460,15 @@ void driver_mode::enter()
 		Error("Bad scenario: failed to locate player train, \"" + Global.local_start_vehicle + "\"");
 	}
 
+	if (Application.is_server() || Application.is_client())
+	{
+		// in a multiplayer session nobody is dropped into a random vehicle: the roster
+		// published by the server is offered instead, and stays available for later switches
+		auto ui = std::dynamic_pointer_cast<driver_ui>(m_userinterface);
+		if (ui != nullptr)
+			ui->show_multiplayer_lobby(nPlayerTrain == nullptr);
+	}
+
 	// if (!Global.bMultiplayer) //na razie włączone
 	{ // eventy aktywowane z klawiatury tylko dla jednego użytkownika
 		KeyEvents[0] = simulation::Events.FindEvent("keyctrl00");

application/driveruilayer.cpp

@@ -37,6 +37,7 @@ driver_ui::driver_ui()
 	add_external_panel(&m_logpanel);
 	add_external_panel(&m_perfgraphpanel);
 	add_external_panel(&m_cameraviewpanel);
+	add_external_panel(&m_multiplayerlobby);
 	m_logpanel.is_open = false;
 
 	m_aidpanel.title = STR("Driving Aid");
@@ -87,10 +88,18 @@ void driver_ui::render_menu_contents()
 		if (ImGui::MenuItem(m_timepanel.name().c_str()))
 			m_timepanel.open();
 
+		if (Application.is_server() || Application.is_client())
+			ImGui::MenuItem(m_multiplayerlobby.name().c_str(), nullptr, &m_multiplayerlobby.is_open);
+
 		ImGui::EndMenu();
 	}
 }
 
+void driver_ui::show_multiplayer_lobby(bool const Show)
+{
+	m_multiplayerlobby.is_open = Show;
+}
+
 void driver_ui::showDebugUI()
 {
 	m_debugpanel.is_open = !m_debugpanel.is_open;

application/driveruilayer.h

@@ -20,6 +20,7 @@ http://mozilla.org/MPL/2.0/.
 #include "widgets/trainingcard.h"
 #include "widgets/perfgraphs.h"
 #include "widgets/cameraview_extcam.h"
+#include "widgets/multiplayer_lobby.h"
 
 class driver_ui : public ui_layer {
 
@@ -40,6 +41,9 @@ public:
     // updates state of UI elements
     void
         update() override;
+    // opens or closes the multiplayer lobby
+    void
+        show_multiplayer_lobby( bool const Show );
 
 protected:
     void render_menu_contents() override;
@@ -69,4 +73,5 @@ private:
 	ui::map_panel m_mappanel;
 	ui::time_panel m_timepanel;
 	ui::cameraview_panel m_cameraviewpanel;
+	ui::multiplayer_lobby_panel m_multiplayerlobby;
 };

application/scenarioloadermode.cpp

@@ -19,6 +19,7 @@ http://mozilla.org/MPL/2.0/.
 #include "rendering/renderer.h"
 #include "utilities/Logs.h"
 #include "utilities/translation.h"
+#include "network/entities.h"
 
 scenarioloader_mode::scenarioloader_mode() {
     m_userinterface = std::make_shared<scenarioloader_ui>();
@@ -61,6 +62,11 @@ bool scenarioloader_mode::update() {
 		Application.pop_mode();
 	}
 
+	if( Application.is_server() ) {
+		// the server owns the vehicle numbering for the whole session and publishes it
+		network::Entities.build();
+	}
+
 	WriteLog( "Scenario loading time: " + std::to_string( std::chrono::duration_cast<std::chrono::seconds>( std::chrono::system_clock::now() - timestart ).count() ) + " seconds" );
 	// TODO: implement and use next mode cue