Stage Management System

Screens and Stages in LibGDX

Screen and Stage classes are used to manage different parts of a game, such as menus, levels, and UI interactions.

Screen

The Screen interface represents a game state or scene. It defines lifecycle methods like show(), render(), resize(), hide(), and dispose(), allowing developers to manage transitions between different parts of the game. The Game class in LibGDX uses Screens to switch between different game states efficiently. Each screen can contain logic for rendering, updating, and handling input. In ColdCase our Main Class implements the Game interface, which comes with the Screen field.

Stage

A Stage is a container for UI elements and actors that helps manage input and rendering. It simplifies handling complex UI elements like buttons, labels, and animations. Stages use LibGDX’s Scene2D system, making it easier to organize UI and game objects. We can add actors to a stage, update them, and let the stage manage rendering and input processing.

StageManager

The StageManager class acts as the central controller for screen transitions. It allows the game to switch between different screens, such as the main menu, gameplay, settings, and multiplayer connection screens.

It also initialises an InputMultiplexer. This allows both the AbstractStage and the PlayerController, which is part of an MapActor, to listen to input events. This way the users can interact with the game world as the player and the UI.

Stages Enum

The Stages enum defines all possible game screens, including the main menu, gameplay, multiplayer hosting and joining screens. These screens are implementations of the AbstractStage class, each with its own UI elements and actors.

The GameStage class is the class responsible for the game world. It initializes the map, the inventory, and the pause menu as separate actors (MapActor, InventoryActor, PauseMenu). These actors initiate there respective UI and Game elements - the map, the inventory, and the pause menu. The MapActor gets the correct level it is supposed to load from the LevelManager.

The MainMenuStage class is the class responsible for the main menu. It initializes the main menu buttons and their click listeners. The buttons are created using the LibGDX Scene2D UI system. The main menu buttons are Host, Join, Settings, and Exit. The Host button starts a new game session, the Join button connects to an existing game session and the Exit button closes the game.

The JoinStage class is the class responsible for the multiplayer connection screen. It allows players to connect to a game session using a session ID. The screen contains a text field for entering the session ID, a connection status label, a connect button, and a back button. The connection status label shows whether the player is connected or not. The connect button triggers the connection process, and the back button returns to the main menu.

The HostStage class is the class responsible for the host screen. It allows the host player to start a game session, view the session ID, and manage the connection. The screen contains a session ID field, a copy button, a start button, and a back button. The session ID field displays the session ID, the copy button copies the session ID to the clipboard, the start button starts the game, and the back button returns to the main menu.

The SettingsStage class is supposed to be responsible for the settings screen. But do to a lack of time and there being no settings to change, this screen is not implemented.

AbstractStage

The AbstractStage class provides a common base for all stages in the game. It extends LibGDX’s Stage class and implements the Screen interface, ensuring that every stage follows the same lifecycle. It is responsible for rendering, input handling, and resizing. Each specific stage in the game must extend this class and implement the buildStage() method, where UI elements and actors are set up. This method is called from the StageManager when a new Stage is loaded. The render method is there to propagate the render call down to its actors (this in case of the GameStage includes the Map), while onConnected and onDisconnected methods allow handling network events when applicable.

Interaction Between the Classes

The StageManager controls the active screen and ensures smooth transitions. When a screen change is requested, it retrieves the correct screen from the Stages enum and sets it in the game. Each stage is an instance of AbstractStage, which provides the rendering and input structure needed for the game. This system ensures that screen management is modular and efficient, making it easy to add new screens or modify existing ones without disrupting the core game loop.