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fxgl-game-lifecycle 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.
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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(40
40
public
static
void
main
(String[] args)
initSettings — Key Options @Override
protected void initSettings (GameSettings settings) {
settings.setWidth(1280 );
settings.setHeight(720 );
settings.setTitle("My Game" );
settings.setVersion("1.0" );
settings.setMainMenuEnabled(true );
settings.setGameMenuEnabled(true );
settings.setEnabledMenuItems(EnumSet.of(MenuItem.NEW_GAME, MenuItem.SAVE, MenuItem.LOAD, MenuItem.EXIT));
settings.setApplicationMode(ApplicationMode.DEVELOPER);
settings.setDeveloperMenuEnabled(true );
settings.setProfilingEnabled(true );
settings.setFullScreenAllowed(true );
settings.setFullScreenFromStart(false );
settings.addEngineService(QuestService.class);
settings.addEngineService(SaveLoadService.class);
settings.getAchievements().add(new Achievement ("First Kill" , "Kill an enemy" , "kills" , 1 ));
}
initGameVars — World Variable Declaration All variables used elsewhere must be declared here. Missing a variable declaration
causes IllegalArgumentException on first access.
@Override
protected void initGameVars (Map<String, Object> vars) {
vars.put("score" , 0 );
vars.put("lives" , 3 );
vars.put("speed" , 200.0 );
vars.put("paused" , false );
vars.put("playerName" , "" );
}
initInput — Binding Actions @Override
protected void initInput () {
onKey(KeyCode.A, () -> getPlayer().translateX(-5 ));
onKey(KeyCode.D, () -> getPlayer().translateX(5 ));
onKeyDown(KeyCode.SPACE, () -> shoot());
onKeyUp(KeyCode.SHIFT, () -> stopSprint());
onBtnDownPrimary(() -> spawnProjectile());
}
initGame — Entity & World Setup @Override
protected void initGame () {
getGameWorld().addEntityFactory(new MyEntityFactory ());
setLevelFromMap("level1.tmx" );
spawn("player" , 100 , 100 );
spawn("enemy" , 500 , 300 );
entityBuilder().buildScreenBoundsAndAttach(40 );
Entity player = getGameWorld().getSingleton(e -> e.isType(EntityType.PLAYER));
getGameScene().getViewport().bindToEntity(player, getAppWidth() / 2.0 , getAppHeight() / 2.0 );
}
initPhysics — Gravity & Collision Handlers @Override
protected void initPhysics () {
getPhysicsWorld().setGravity(0 , 1200 );
onCollisionBegin(EntityType.PLAYER, EntityType.COIN, (player, coin) -> {
coin.removeFromWorld();
inc("score" , +10 );
});
onCollisionBegin(EntityType.PLAYER, EntityType.ENEMY, (player, enemy) -> {
inc("lives" , -1 );
if (geti("lives" ) <= 0 ) showGameOver();
});
}
initUI — HUD @Override
protected void initUI () {
Text scoreText = getUIFactoryService().newText("" , Color.WHITE, 24 );
scoreText.textProperty().bind(getip("score" ).asString("Score: %d" ));
addUINode(scoreText, 20 , 40 );
Text livesText = getUIFactoryService().newText("" , Color.RED, 24 );
livesText.textProperty().bind(getip("lives" ).asString("Lives: %d" ));
addUINode(livesText, 20 , 70 );
}
onUpdate — Game Loop @Override
protected void onUpdate (double tpf) {
spawnTimer += tpf;
if (spawnTimer > 3.0 ) {
spawn("enemy" , random(0 , getAppWidth()), -50 );
spawnTimer = 0 ;
}
}
private double spawnTimer = 0 ;
Custom Engine Services
public class ScoreService extends EngineService {
private int highScore = 0 ;
@Override
public void onGameReady () { }
public int getHighScore () { return highScore; }
public void updateHighScore (int score) { highScore = Math.max(highScore, score); }
}
settings.addEngineService(ScoreService.class);
FXGL.getService(ScoreService.class).updateHighScore(geti("score" ));
Gotchas
Asset directory : all assets must be under src/main/resources/assets/. FXGL
auto-prefixes this path. Writing getAssetLoader().loadTexture("textures/player.png")
resolves to assets/textures/player.png on the classpath.launch(args) is finalinitSettings runs before JavaFX Application.start()Kotlin DSL : use import com.almasb.fxgl.dsl.* and GameApplication() — same hooks,
same order. The FXGLForKt file provides Kotlin-specific extension functions.Application mode : always ship with ApplicationMode.RELEASE. The developer menu
and profiler are disabled automatically.Module path for JavaFX : add --module-path and --add-modules javafx.controls,javafx.fxml
to JVM args in your build file if running outside a module-aware launcher.initGameVars is mandatory for reactive properties : getip("score") throws
IllegalArgumentException if "score" was not declared in initGameVars.World reset : calling getGameController().startNewGame() re-runs all init* hooks.
Avoid storing state in instance fields unless you reset it in initGameVars.
Quick Reference DSL method Description getApp()Returns the GameApplication instance getAppWidth() / getAppHeight()Window dimensions in pixels getAppCenter()Point2D of the window centregetSettings()Read-only settings snapshot getGameController()Control game state (startNewGame, exit, pause) tpf()Time per frame of the last frame (seconds)
