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README.md

Software Engineering Project - Wizard

Welcome to Wizard, a C++ implementation of the classic card game. Compete with your friends in exciting multiplayer gameplay!

Wizard Logo Cards

🚀 Features

  • 🌐 Multiplayer Gameplay: Play with 3 to 6 players.
  • 🔄 Synchronized Game State: Real-time updates for all players.
  • 🖼️ Elegant User Interface: A visually appealing UI powered by wxWidgets.

You can read the game's rules here. The implementation features a client/server architecture for multiplayer scenarios. It uses wxWidgets for the GUI, sockpp for the network interface, rapidjson for object serialization, and googletest for the unit tests.

1 Overview

The game and source files is available on GitLab on the main branch. The game was developed based on the provided LAMA example project game. This project consists of a server and a client, each with their own main.cpp file. Each player can run his client and connect to the server in the same local network.

2 Compile Instructions

3 Run the Game

4 Play the Game

4.1 Connection Panel

The client renders the GUI that is presented to the player, whereas the server is a console application without a user interface. Every action a player performs in the client application (for example playing a card) is sent as a formatted message to the server application, which processes the request.

  • If the player's move was valid, the server will update the game state (e.g. move a card from the player's hand to the discard pile) and broadcast this new game state to all players of the game. Whenever the client application receives a game state update, it will re-render the GUI accordingly and allow new interactions.
  • If the move was invalid, the game state will not be updated and only the requesting player will get a response containing the error message.

Network Interface

Everything that is passed between client and server are objects of type client_request and server_response. Since the underlying network protocol works with TCP, these client_request and server_response objects are transformed into a JSON string, which can then be sent over the network. The receiving end reads the JSON string and constructs an object of type client_request resp. server_response that reflects the exact parameters that are specified in the JSON string. This process is known as serialization (object to string) and deserialization (string to object). If you want to read more about serialization, read me on Wikipedia.

client-server-diagram

Serialization & Deserialization of messages

Both, the client_request and server_response base classes, implement the abstract class serializable with its write_into_json(...) function. It allows to serialize the object instance into a JSON string. Additionally, they have a static function from_json(...), which allows creating an object instance from a JSON string.

// All request types of your imlementation
// IMPORTANT: Add your own types here (and remove unused ones)
enum RequestType {
    join_game,
    start_game,
    estimate_tricks,
    decide_trump_color,
    leave_game,
    play_card,
};

class client_request : public serializable {
protected:
    RequestType _type;   // stores the type of request, such that the receiving end knows how to deserialize it
    std::string _req_id; // unique id of this request
    std::string _player_id; // id of the player sending the request
    std::string _game_id;   // id of the game this request is for

    ...
private:
    // for deserializing RequestType (contains mappings from string to RequestType)
    // IMPORTANT: Add mapping for your own RequestTypes to this unordered_map
    static const std::unordered_map<std::string, RequestType> _string_to_request_type;
    
    // for serializing RequestType (contains mappings from RequestType to string)
    // IMPORTANT: Add mapping for your own RequestTypes to this unordered_map
    static const std::unordered_map<RequestType, std::string> _request_type_to_string;

public:
    // DESERIALIZATION: Attempts to create the specific client_request from the provided json.
    static client_request* from_json(const rapidjson::Value& json);

    // SERIALIZATION: Serializes the client_request into a json object that can be sent over the network
    virtual void write_into_json(rapidjson::Value& json, rapidjson::Document::AllocatorType& allocator) const override;
};
Serialization

When you implement your own specializations of client_request (and server_response, if necessary) you will have to implement the write_into_json(...) functions yourself. Your subclass always has to call the write_into_json(...) function of its base-class, such that the parameters of the base-class are written into the JSON document:

Here is the base-class implementation:

// Implementation in the base-class client_request
void client_request::write_into_json(rapidjson::Value &json,
                                     rapidjson::MemoryPoolAllocator<rapidjson::CrtAllocator> &allocator) const {
    // Look up string value of this client_request's RequestType and store it in the json document
    rapidjson::Value type_val(_request_type_to_string.at(this->_type).c_str(), allocator);
    json.AddMember("type", type_val, allocator);

    // Save player_id in the JSON document
    rapidjson::Value player_id_val(_player_id.c_str(), allocator);
    json.AddMember("player_id", player_id_val, allocator);

    // Save game_id in the JSON document
    rapidjson::Value game_id_val(_game_id.c_str(), allocator);
    json.AddMember("game_id", game_id_val, allocator);
    ...
}

And here is the subclass implementation (for the play_card_request class), where an additional field _card_id is serialized.

// Implementation in the subclass play_card_request 
void play_card_request::write_into_json(rapidjson::Value &json,
                                        rapidjson::MemoryPoolAllocator<rapidjson::CrtAllocator> &allocator) const {
    // IMPORTANT: call base-class, such that the parameters of the base-class are written into the 'json' variable
    client_request::write_into_json(json, allocator);

    // Add parameters to the JSON that are unique to the play_card_request
    rapidjson::Value card_id_val(_card_id.c_str(), allocator);
    json.AddMember("card_id", card_id_val,allocator);
}
Deserialization

The deserialization of client_request JSONs always goes through the from_json(...) function of the client_request class. In this function, the "type" field, stored in the JSON, is inspected to determine, which subclass should be called to perform the deserialization:

if (json.HasMember("type") && json["type"].IsString()) {
        // Get the RequestType stored as a string in the JSON
        const std::string type = json["type"].GetString();
        // Lookup the actual RequestType per string from a pre-defined unordered_map
        const RequestType request_type = client_request::_string_to_request_type.at(type);

        // Call the correct from_json() specialization
        if (request_type == RequestType::play_card) {
            return play_card_request::from_json(json);
        }
        else if (request_type == RequestType::draw_card) {
            return draw_card_request::from_json(json);
        }
        else if (...) {
            ...
        } else {
            throw WizardException("Encountered unknown ClientRequest type " + type);
        }
    }
    throw WizardException("Could not determine type of ClientRequest. JSON was:\n" + json_utils::to_string(&json));

Therefore, when you implement your own client_request subclasses, remember to add a new element into the RequestType enum to define your new request type. You will also have to add an entry for this new RequestType in the two unordered_maps _string_to_request_type, resp. _request_type_to_string in the client_request base-class. Once this is done, you can add a check for your new RequestType element in the from_json(...) function of the client_request base-class and call the specialized from_json(...) function of your subclass from there.

Also, don't forget to set the correct RequestType in the public constructor of your new client_request subclass, here examplified at the play_card_request class:

// Public constructor
play_card_request::play_card_request(std::string game_id, std::string player_id, std::string card_id)
        : client_request(client_request::create_base_class_properties(  // call base-class constructor
                                                    RequestType::play_card, // IMPORTANT: set the RequestType of your subclass
                                                    uuid_generator::generate_uuid_v4(), 
                                                    player_id, 
                                                    game_id) ),
        _card_id(card_id)   // set subclass specific parameters
{ }

The deserialization in your subclass will look something like this:

// private constructor for deserialization
play_card_request::play_card_request(client_request::base_class_properties props, std::string card_id) :
        client_request(props),  // call base-class constructor
        _card_id(card_id)   // set subclass specific parameters
{ }

// Deserialization
play_card_request* play_card_request::from_json(const rapidjson::Value& json) {
    // extract base-class properties from the json
    base_class_properties props = client_request::extract_base_class_properties(json);

    // get subclass specific properties
    if (json.HasMember("card_id")) {
        // invoke deserialization constructor
        return new play_card_request(props, json["card_id"].GetString());
    } else {
        throw WizardException("Could not find 'card_id' in play_card_request");
    }
}

There are plenty of examples of subclasses in the network/requests folder, where you can see how the serialization/deserialization scheme works.

4.2.2 Sending messages

Client -> Server:

All you have to do is use the static class ClientNetworkManager on the client side and then invoke its sendRequest(const client_request& request) function with the client_request that you want to send. The server's response will arrive as an object of type request_response and the ClientNetworkManager will invoke the Process() function of that request_response object automatically.

Server -> Client:

All messages arriving at the server are being deserialized and then passed on to the handle_request(client_request* req) function of the request_handler singleton class. This function returns a pointer to an object of type request_response (a subclass of server_response), which is then automatically sent back to the requesting client. In your game implementation you should extend the handle_request(client_request* req) function of the request_handler, such that it can handle the client_request that you add to your game and return an object of type request_response with all parameters you want to send.

If the client_request causes an update of the game_state you should also update all other players of that game about the game_state change. This happens in the game_instance class, here examplified at the case where a start_game_request calls the start_game(...) function on the respective game_instance on the server side:

bool game_instance::start_game(player* player, std::string &err) {
    modification_lock.lock();   // make sure only one request can modify the game_state at a time

    // Try to start the game
    if (_game_state->start_game(err)) { 
        // create a full_state_response (subclass of server_response) with the full game_state inside
        full_state_response state_update_msg = full_state_response(this->get_id(), *_game_state);
        // BROADCAST new game_state to all other players
        server_network_manager::broadcast_message(state_update_msg, _game_state->get_players(), player);

        modification_lock.unlock(); // allow other threads to modify the game_state
        return true;
    }
    modification_lock.unlock();
    return false;
}

4.2.3 Debugging Messages

By default, the server (specifically, the server_network_manager) will print every valid message that it receives to the console. In order for this to work in your project as well, you have to make sure that your CMake file contains a line, where the preprocessor variable PRINT_NETWORK_MESSAGES is defined for your server executable.

target_compile_definitions(Wizard-server PRIVATE PRINT_NETWORK_MESSAGES=1)

If a wrongly formatted message arrives at the server, it will print an error message with the received message string to the console, no matter if PRINT_NETWORK_MESSAGES is defined or not.

If you want to manually print one of your serialized messages (or any other serialized object for that matter), you can use the helper function json_utils::to_string(const rapidjson::Value* json) as follows.

#include "src/common/serialization/json_utils.h"
#include "rapidjson/include/rapidjson/document.h"

...
// Create a request to serialize
join_game_request* req = new join_game_request(player->get_id(), player->get_player_name());

// serialize the request object
rapidjson::Document* req_json = req->to_json();

// print serialization to the console.
std::cout << json_utils::to_string(req_json) << std::endl;

4.3 Game State

The game_state class stores all parameters that are required to represent the game on the client (resp. server) side. In order to synchronize this game_state among all players, the game_state can also be serialized and deserialized. If a client_request was successfully executed on the server, then the request_response that is sent back to the client contains a serialized version of the updated game_state. All other players receive the updated game_state at the same time through a full_state_response.

To serialize the game_state, the same write_into_json(...) function is used as for the client_request.

class game_state : public unique_serializable {
private:
    // Properties
    std::vector<player*> _players;
    draw_pile* _draw_pile;
    discard_pile* _discard_pile;
    serializable_value<bool>* _is_started;
    serializable_value<bool>* _is_finished;
    serializable_value<int>* _round_number;
    serializable_value<int>* _current_player_idx;
    serializable_value<int>* _starting_player_idx;

    // deserialization constructor
    game_state(
            std::string id,
            draw_pile* draw_pile,
            discard_pile* discard_pile,
            std::vector<player*>& players,
            serializable_value<bool>* is_started,
            serializable_value<bool>* is_finished,
            serializable_value<int>* current_player_idx,
            serializable_value<int>* round_number,
            serializable_value<int>* starting_player_idx);

public:
    game_state();

    ...
    // SERIALIZATION
    virtual void write_into_json(rapidjson::Value& json, rapidjson::Document::AllocatorType& allocator) const override;
    // DESERIALIZATION
    static game_state* from_json(const rapidjson::Value& json);
};

The game_state inherits from unique_serializable, which essentially requires the write_into_json() function and adds a unique id to the object, such that it can be uniquely identified. Similarly, each parameter nested inside the game_state (e.g. players, draw_pile, etc.) also inherit from unique_serializable and therefore have their own id and serialization, resp. deserialization functions.

On the client side, the new game_state is then passed to the updateGameState(game_state*) function of the GameController class, which performs a redraw of the GUI.

Since you will have to add your own properties to the game_state class (and probably create other classes that inherit from unique_serializable to add to your game_state), we want to shortly elaborate how the serialization and deserialization works for subclasses of unique_serializable. It's very similar to the client_request class discussed earlier. Here is how the write_into_json(...) function is implemented in the game_state class of Wizard. Don't be shocked by the lengthy code. It's only a lot of repetition for each class property :

void game_state::write_into_json(rapidjson::Value &json,
                                 rapidjson::MemoryPoolAllocator<rapidjson::CrtAllocator> &allocator) const {
    // call base-class to write id and object name into the json
    unique_serializable::write_into_json(json, allocator);

    // write all properties of this game_state instance into the JSON
    rapidjson::Value is_finished_val(rapidjson::kObjectType);   // create an empty rapidjson::Value that can hold an ObjectType
    _is_finished->write_into_json(is_finished_val, allocator);  // write class property '_is_finished' into the created rapidjson::Value
    json.AddMember("is_finished", is_finished_val, allocator);  // add the rapidjson::Value 'is_finished_val' to the game_state json

    rapidjson::Value is_started_val(rapidjson::kObjectType);
    _is_started->write_into_json(is_started_val, allocator);
    json.AddMember("is_started", is_started_val, allocator);

    rapidjson::Value current_player_idx_val(rapidjson::kObjectType);
    _current_player_idx->write_into_json(current_player_idx_val, allocator);
    json.AddMember("current_player_idx", current_player_idx_val, allocator);

    rapidjson::Value starting_player_idx_val(rapidjson::kObjectType);
    _starting_player_idx->write_into_json(starting_player_idx_val, allocator);
    json.AddMember("starting_player_idx", starting_player_idx_val, allocator);

    rapidjson::Value round_number_val(rapidjson::kObjectType);
    _round_number->write_into_json(round_number_val, allocator);
    json.AddMember("round_number", round_number_val, allocator);

    rapidjson::Value draw_pile_val(rapidjson::kObjectType);
    _draw_pile->write_into_json(draw_pile_val, allocator);
    json.AddMember("draw_pile", draw_pile_val, allocator);

    rapidjson::Value discard_pile_val(rapidjson::kObjectType);
    _discard_pile->write_into_json(discard_pile_val, allocator);
    json.AddMember("discard_pile", discard_pile_val, allocator);

    // Special helper function to serialize vector of pointers
    // The pointers inside the vector have to inherit from serializable (or unique_serializable)
    json.AddMember("players", vector_utils::serialize_vector(_players, allocator), allocator);
}

For deserialization, the from_json(...) function is used, which is implemented as follows:

// DESERIALIZATION CONSTRUCTOR receives pointers for all its properties and stores them
game_state::game_state(std::string id, draw_pile *draw_pile, discard_pile *discard_pile,
                       std::vector<player *> &players, serializable_value<bool> *is_started,
                       serializable_value<bool> *is_finished, serializable_value<int> *current_player_idx,
                       serializable_value<int>* round_number, serializable_value<int> *starting_player_idx)
        : unique_serializable(id),  // initialize the unique_serializable base-class
          _draw_pile(draw_pile),
          _discard_pile(discard_pile),
          _players(players),
          _is_started(is_started),
          _is_finished(is_finished),
          _current_player_idx(current_player_idx),
          _round_number(round_number),
          _starting_player_idx(starting_player_idx)
{ }

// DESERIALIZATION 
// returns a pointer to the new game_state
game_state* game_state::from_json(const rapidjson::Value &json) {
    // Make sure the json contains all required information
    if (json.HasMember("is_finished")
        && json.HasMember("is_started")
        && json.HasMember("current_player_idx")
        && json.HasMember("round_number")
        && json.HasMember("starting_player_idx")
        && json.HasMember("players")
        && json.HasMember("draw_pile")
        && json.HasMember("discard_pile"))
    {
        // deserialize all players
        std::vector<player*> deserialized_players;
        for (auto &serialized_player : json["players"].GetArray()) {
            deserialized_players.push_back(player::from_json(serialized_player.GetObject()));
        }
        // Invoke deserialization constructor
        return new game_state(unique_serializable::extract_id(json),   // extract base_params from JSON
                              draw_pile::from_json(json["draw_pile"].GetObject()),  // deserialize the draw_pile
                              discard_pile::from_json(json["discard_pile"].GetObject()),
                              deserialized_players,
                              serializable_value<bool>::from_json(json["is_started"].GetObject()),
                              serializable_value<bool>::from_json(json["is_finished"].GetObject()),
                              serializable_value<int>::from_json(json["current_player_idx"].GetObject()),
                              serializable_value<int>::from_json(json["round_number"].GetObject()),
                              serializable_value<int>::from_json(json["starting_player_idx"].GetObject()));
    } else {
        throw WizardException("Failed to deserialize game_state. Required entries were missing.");
    }
}

A similar scheme is applied in all other objects that inherit from unique_serializable. Namely, these are:

  • player
  • hand
  • card
  • draw_pile
  • discard_pile
  • serializable_value

4.4 GUI with wxWidgets

The GUI of the example project was built using the cross-platform GUI library wxWidgets. In order to build a project using wxWidget elements, you will first need to install wxWidgets on your system (see Section 1.1 above).

4.4.1 Structure & Important Classes

Here is a list of the most important elements that you will need to create your GUI. This is just meant as an overview, you will need to look up their correct usage in wxWidget's documentation.

  • Application core
    • wxIMPLEMENT_APP(): In order to properly interact with the operating system's GUI, wxWidgets takes over the control flow of your application. wxWidgets therefore has its own main() function, that you can reference with the macro wxIMPLEMENT_APP(wxApp*).
    • wxApp: The core class of your application must inherit from the wxApp class. wxWidgets will call the OnInit() function when starting the application. You can find the example project's implementation in src/client/app/Wizard.
  • Windows
    • wxFrame: Each window of your application must inherit from the wxFrame class. The example project has one window which you can find here: src/client/windows/GameWindow
  • GUI elements
    • wxPanel: Panels serve as containers for elements within a window. All panels must instantiate or inherit from the wxPanel class. A panel can contain one or more subpanels.
    • wxBoxSizer: Box sizers allow you to layout your panels within a window, either horizontally or vertically. By nesting box sizers, you can create complex layouts. Have a look at src/client/panels/ConnectionPanel for an example.
    • wxStaticText: This class displays text in your GUI.
    • wxButton: This class creates a clickable button in your GUI.
  • Pop-ups
    • wxMessageBox(): You can use this function to display a small pop-up window with text in front of the your current main window. This is useful to display error or status messages.

4.4.2 Events

Like in most GUI environments, objects in wxWidgets trigger events when they are interacted with by the user. For instance, a button will trigger a wxEVT_BUTTON event when clicked. Similarly, a panel will trigger a wxEVT_LEFT_UP event when clicked. There are many other events that can be triggered - for example when a keyboard key is pressed, when a window is resized, or when the cursor moves over an element.

In order to make the GUI interactive, we must specify the effect of an event. The easiest way is to bind an event to a lambda function. A lambda function is an unnamed function that can be used as an r-value. In C++, lambda functions have the following syntax:

[ external_variables... ]( function_parameters ... ) {
    function_body...
}

Here is an example which binds a lambda function to a button click event:

wxButton* myButton = new wxButton(parentPanel, wxID_ANY, "Click me!");
int myVariable = 42;
myButton->Bind(wxEVT_BUTTON, [myVariable](wxCommandEvent& event) {
    doSomething(myVariable, event);
});

In C++, we need to specify which variables from outside the lambda function's scope should be accessible within it. In the example above, myVariable is declared outside of the lambda function but is used by the doSomething() function call within the lambda function. We must therefore list myVariable within the square brackets at the beginning of the lambda function definition, in order to make it accessible from within the lambda function's scope.