o3dcon-2022-multiplayer-workshop

A repository with code to complement 2022 O3DCon Multiplayer Workspace

Multiplayer Workshop Walkthrough: This walkthrough will roughly outline each step of the process in making this multiplayer demo. Each branch of this repository will have an updated README.md so that the code contained in the branch matches up to the last step of the walkthrough.

Step 1: Project creation using project template (20 minutes)

1. Create a new game called MyMultiplayerGame using Project Manager's Remote Template System a. Open Project Manager (Aka O3DE.exe) b. Select "New Project..." > "Create New Project" c. Click the "Add Remote Template Button" and provide the O3DE-extra's git URL: https://github.com/o3de/o3de-extras.git d. Select the Multiplayer Template and "Download Template" e. Once downloaded you can proceed to use Multiplayer Template to create a new game called "MyMultiplayerGame"
2. Compile using the "Build Now" option in Project Manager
3. Open Editor and let Asset Processor finish (this will take about 15 minutes)
4. Play around with the demo level a. Notice that pressing CTRL+G shows network connection status b. The server is automatically spawned and hidden by default, expose it by setting cvars: i. editorsv_hidden false ii. editorsv_rhi_override "" c. The Editor CTRL+G experience can only spawn one player. Try spawning multiple players, by spawning a server and 2 clients by hand i. Use the cmd files at the root of your project. launch_server.cmd (1x) and launch_client.cmd (2x)

Step 2: Create a new mutliplayer component

1. Create a new Multiplayer Component under Gem/Code/Source/AutoGen called O3DConPlayer.AutoComponent.xml

<NetworkInput Type="int" Name="ButtonsMashed" Init="0" />    

2. Add the XML to Gem/Code/MyMultiplayerGame_files.cmake 3. Compile and open Editor

Step 3: Open Editor and make a new player

1. Open editor
2. Create a new level called O3DConLevel
3. Add a new entity called O3DConPlayer
4. Add our new multiplayer component O3DEConPlayer component
5. Add the missing required components a. Local Predicition Play Input b. Network Binding
6. Save out the O3DConPlayer prefab
7. Add at least 2 PlayerSpawner.prefabs to the level
8. CTRL+G and make sure the O3DConPlayer spawns Important Note: Use network.spawnable not .spawnables
9. Notice the player position is still at <0,0,0> and not where you've placed the PlayerSpawner
10. Add NetworkTransformComponent to O3DConPlayer.prefab and now the player position is fixed

Step 4: Adding a custom multiplayer controller code File

1. Update O3DConPlayer.AutoComponent.xml to enable custom controller logic <Component Name="O3DConPlayer" OverrideController="true" OverrideInclude="Source/Components/O3DConPlayer.h"

2. Compile. Notice compiler error. Cannot open include file: 'Source/Components/O3DConPlayer.h': No such file or directory This is because we never made that file!

3. Open Visual Studio and find the generated multiplayer base class code a. Solution Explorer > Project.Static > GeneratedFiles > O3DConPlayer.AutoComponent.h

4. The generated auto-component comes with boilerplate code that's commented out for you to use inside of your new MyMultiplayerGame\Gem\Code\Source\Components\O3DConPlayer.cpp/.h files. a. Copy and paste the "Place in your .h" section and "Place in your .cpp" section into your .h and .cpp respectively

5. Update MyMultiplayerGame_files.cmake with the new .cpp/.h files

6. Compile successfully

Step 5: Keyboard Input Update O3DConPlayer.h/.cpp to gather keyboard input and send it across the network. We won't do anything with the input yet except print a log anytime we press a key and process it via the network input system.

// O3DConPlayer.h updates
#include <Source/AutoGen/O3DConPlayer.AutoComponent.h>
#include <AzFramework/Input/Events/InputChannelEventListener.h>
namespace MyMultiplayerGame
{
    class O3DConPlayerController
        : public O3DConPlayerControllerBase
        , protected AzFramework::InputChannelEventListener //< could use StartingPointInput::InputEventNotificationBus::MultiHandler instead
    {
    public:

        //! AzFramework::InputChannelEventListener overrides
        bool OnInputChannelEventFiltered(const AzFramework::InputChannel& inputChannel) override;

    private:
        int m_keysPressed = 0;
        bool m_isPressing = false;
    };
}

// O3DConPlayerController.cpp updates
namespace MyMultiplayerGame
{
    void O3DConPlayerController::OnActivate([[maybe_unused]] Multiplayer::EntityIsMigrating entityIsMigrating)
    {
        if(IsNetEntityRoleAutonomous())
        {
            InputChannelEventListener::Connect();
        }
    }

    void O3DConPlayerController::OnDeactivate([[maybe_unused]] Multiplayer::EntityIsMigrating entityIsMigrating)
    {
        if (IsNetEntityRoleAutonomous())
        {
            InputChannelEventListener::Disconnect();
        }
    }

    // Called by the player on the player's machine
    void O3DConPlayerController::CreateInput([[maybe_unused]] Multiplayer::NetworkInput& input, [[maybe_unused]] float deltaTime)
    {
        O3DConPlayerNetworkInput* playerInput = input.FindComponentInput<O3DConPlayerNetworkInput>();
        playerInput->m_buttonsMashed = m_keysPressed;
        m_keysPressed = 0;
    }

    // Called by the player on the player's machine
    // Called on the server with the information we need
    void O3DConPlayerController::ProcessInput([[maybe_unused]] Multiplayer::NetworkInput& input, [[maybe_unused]] float deltaTime)
    {
        const auto* playerInput = input.FindComponentInput<O3DConPlayerNetworkInput>();
        if (playerInput->m_buttonsMashed > 0)
        {
            AZLOG_WARN("Player pressed %i keys this network frame!", playerInput->m_buttonsMashed);
        }
    }

    bool O3DConPlayerController::OnInputChannelEventFiltered(const AzFramework::InputChannel& inputChannel)
    {
        // only accept keyboard input
        if (inputChannel.GetInputDevice().GetInputDeviceId().GetNameCrc32() != AZ_CRC("keyboard"))
        {
            return false;
        }

        const bool isPressed = inputChannel.GetValue() > 0.0f;
        if( !m_isPressing && isPressed )
        {
            m_isPressing = true;
            ++m_keysPressed;
        }
        else if(inputChannel.GetValue() == 0.0f)
        {
            m_isPressing = false;
        }

        return true;
    }
}

Step 6: Moving the player transform

1. Update ProcessInput()

   void O3DConPlayerController::ProcessInput(Multiplayer::NetworkInput& input, [[maybe_unused]] float deltaTime)
   {
       const auto* playerInput = input.FindComponentInput<O3DConPlayerNetworkInput>();
   
       const float movementPerButtonPress = 0.1f;
       const AZ::Vector3 delta = AZ::Vector3::CreateAxisY(movementPerButtonPress * playerInput->m_buttonsMashed);
   
       GetEntity()->GetTransform()->SetWorldTranslation(GetEntity()->GetTransform()->GetWorldTranslation() + delta);
   }
   

The player will now move forward everytime you press a key.

Step 7: Moving the player properly with a PhysX Character Controller

1. Add some NetworkRigidBody.prefabs to the level in front of the player spawner and notice that the player moves through the boxes like a ghost
2. Open O3DConPlayer.prefab and add a "Network Character" component i. Add the PhysX Character Controller dependency ii. Save O3DConPlayer.prefab and exit Editor.exe
3. Update O3DConPlayer.AutoComponent.xml. This will make NetworkCharacterComponent a component dependency as well as create a helper function GetNetworkCharacterComponentController()

     <ComponentRelation Constraint="Required" HasController="true" Name="NetworkCharacterComponent" Namespace="Multiplayer" Include="Multiplayer/Components/NetworkCharacterComponent.h" />
   

4. Update the O3DConPlayer.cpp ProcessInput() code to move the NetworkCharacterComponent

     const auto* playerInput = input.FindComponentInput<O3DConPlayerNetworkInput>();
     const AZ::Vector3 MovementPerButtonPress = AZ::Vector3::CreateAxisY(10.0f);
     const AZ::Vector3 delta = MovementPerButtonPress * aznumeric_cast<float>(playerInput->m_buttonsMashed);
     GetNetworkCharacterComponentController()->TryMoveWithVelocity(delta, deltaTime);
   

5. Compile, open Editor, run the game, and notice that the player now pushes the boxes around

Step 8: Report a win!

1. Add a new RPC and new network property to O3DConPlayer.AutoComponent.xml

   <NetworkProperty Type="int" Name="TotalButtonsMashed" Init="0" ReplicateFrom="Authority" ReplicateTo="Client" Container="Object" IsPublic="false" IsRewindable="true" IsPredictable="false" ExposeToEditor="false" ExposeToScript="false" GenerateEventBindings="false" Description="" />
   <RemoteProcedure Name="PlayerFinishedRPC" InvokeFrom="Authority" HandleOn="Client" IsPublic="false" IsReliable="true" GenerateEventBindings="false" Description="">
       <Param Type="Multiplayer::HostFrameId" Name="NetworkFrameTime" />
   </RemoteProcedure>
   

2. Update O3DConPlayerController::ProcessInput to send the PlayerFinsihedRPC if the total buttons pressed reaches a certain count.

   a) Update O3DConPlayer.h O3DConPlayerController to store the network host time the player crossed the finish line

    class O3DConPlayerController
    {
        ...
        Multiplayer::HostFrameId m_finishedFrame = Multiplayer::InvalidHostFrameId;
   

   b) Update O3DConPlayerController::ProcessInput to check if the finish line was crossed

   void O3DConPlayerController::ProcessInput([[maybe_unused]] Multiplayer::NetworkInput& input, [[maybe_unused]] float deltaTime)
   {
       ...
       
       if(IsNetEntityRoleAuthority())
       {
           const int buttonPressesToFinish = 20;
           SetTotalButtonsMashed(GetTotalButtonsMashed() + playerInput->m_buttonsMashed);
   
           const Multiplayer::HostFrameId currentNetworkFrame = Multiplayer::GetNetworkTime()->GetHostFrameId();
           if (GetTotalButtonsMashed() >= buttonPressesToFinish && currentNetworkFrame < m_finishedFrame)
           {
               m_finishedFrame = currentNetworkFrame;
               PlayerFinishedRPC(m_finishedFrame);
           }
       }
   }
   

3. Update O3DConPlayer Component a) Update O3DConPlayer.h to declare the HandlePlayerFinishedRPC function

    class O3DConPlayer
    { 
        ...
        void HandlePlayerFinishedRPC(AzNetworking::IConnection* invokingConnection, const Multiplayer::HostFrameId& networkFrameTime) override;
   

   b) Implement the handler in O3DConPlayer.cpp

   void O3DConPlayer::HandlePlayerFinishedRPC([[maybe_unused]] AzNetworking::IConnection* invokingConnection, const Multiplayer::HostFrameId& networkFrameTime)
   {
       AZLOG_ERROR("Player %i finished at network frame: %i", GetPlayerId(), static_cast<uint32_t>(networkFrameTime));
   }
   

4. Play the game, and check the console log and see that a message is sent to the client when a player crosses the finish line