fxgl-game-lifecycle

name	fxgl-game-lifecycle
description	Bootstrap and structure an FXGL game application — set up GameApplication subclass, configure initSettings, initGameVars, initInput, initGame, initPhysics, initUI, and onUpdate. Use this skill when creating a new FXGL game, adding engine services, configuring window size/title, setting application mode, or wiring the game loop.
triggers	["create FXGL game","GameApplication","initSettings","initGame","game loop","FXGL project setup","engine service","game bootstrap"]
compatibility	Java 17+, FXGL 21.x, Maven or Gradle. JavaFX runtime must be on the module path.
category	fxgl/fundamentals
tags	["fxgl","java","javafx","fundamentals","game","lifecycle"]
metadata	{"author":"fxgl-skills","version":"1.0","fxgl-version":"21.1"}
allowed-tools	["Read","Write","Edit","Bash"]

FXGL Game Lifecycle

Overview

Every FXGL game extends GameApplication and launches via launch(args). The engine calls lifecycle methods in strict order — honour that order or face NPEs.

Lifecycle Order (guaranteed by engine)

launch(args)
  └─ initSettings(GameSettings)      ← configure window, services, achievements
       └─ initGameVars(Map)           ← declare all typed world variables
            └─ initInput()            ← register keyboard/mouse actions
                 └─ initGame()        ← spawn entities, load level, register factories
                      └─ initPhysics() ← set gravity, collision handlers
                           └─ initUI() ← build HUD nodes
                                └─ [game loop starts]
                                     └─ onUpdate(double tpf)  ← runs every frame

Rule: Never call getGameWorld(), getPhysicsWorld(), or getInput() inside initSettings() — those services are not yet initialised.

Minimal Working Game

import com.almasb.fxgl.app.GameApplication;
import com.almasb.fxgl.app.GameSettings;
import static com.almasb.fxgl.dsl.FXGL.*;

public class MyGame extends GameApplication {

    @Override
    protected void initSettings(GameSettings settings) {
        settings.setWidth(1280);
        settings.setHeight(720);
        settings.setTitle("My Game");
        settings.setVersion("0.1");
    }

    @Override
    protected void initGame() {
        entityBuilder()
                .at(400, 300)
                .view(new javafx.scene.shape.Rectangle(, , javafx.scene.paint.Color.BLUE))
                .buildAndAttach();
    }

        {
        launch(args);
    }
}