fxgl-idle-clicker

name	fxgl-idle-clicker
description	Build an incremental idle or clicker game in FXGL — click for resources, buy auto-producers, scale costs exponentially, show passive income in the HUD, unlock upgrades by milestones, calculate capped offline progress on load, format very large numbers, and implement prestige resets with permanent bonuses.
triggers	["idle game","clicker","incremental","passive income","offline progress","prestige","big number formatting","auto producer"]
compatibility	Java 17+, FXGL 21.x. Pairs naturally with fxgl-save-load, fxgl-progression, and fxgl-ui-scenes.
category	fxgl/game-types
tags	["fxgl","java","javafx","game-types","idle","clicker"]
metadata	{"author":"fxgl-skills","version":"1.0","fxgl-version":"21.1"}
allowed-tools	["Read","Write","Edit","Bash"]

FXGL Idle / Clicker Game

Core Variables

@Override
protected void initGameVars(Map<String, Object> vars) {
    vars.put("coins", 0.0);
    vars.put("clickValue", 1.0);
    vars.put("passivePerSecond", 0.0);
    vars.put("prestigeBonus", 1.0);
}

Track producers separately in a model rather than scattering values across many globals.

public record Producer(String id, double baseRate, double baseCost, IntegerProperty owned) {
    public double currentCost() {
        return baseCost * Math.pow(1.15, owned.get());
    }
}

Click Loop

private void onMainClick() {
    double gain = getd("clickValue") * getd("prestigeBonus");
    set("coins", getd("coins") + gain);
}

Bind the main click to a large button or main resource sprite in initUI().

Passive Income

private final List<Producer> producers = List.of(
        new Producer("cursor", 0.2, 15, new SimpleIntegerProperty()),
        new Producer("farm", 3.0, 100, new SimpleIntegerProperty()),
        new Producer("factory", 20.0, 750, new SimpleIntegerProperty())
);

@Override
protected void initGame() {
    run(() -> {
        set("coins", getd("coins") + getd("passivePerSecond"));
    }, Duration.seconds(1));
}

private void recalculatePassiveRate() {
    double rate = producers.stream()
            .mapToDouble(p -> p.owned().get() * p.baseRate())
            .sum();

    set("passivePerSecond", rate * getd("prestigeBonus"));
}

Buying Producers

private boolean tryBuyProducer(Producer p) {
    double cost = p.currentCost();
    if (getd("coins") < cost)
        return false;

    set("coins", getd("coins") - cost);
    p.owned().set(p.owned().get() + 1);
    recalculatePassiveRate();
    return true;
}

Offline Progress

Use save data to store the last save timestamp. On load:

private double calculateOfflineGain(Instant lastSaveTime) {
    long elapsedSeconds = Duration.between(lastSaveTime, Instant.now()).getSeconds();
    long capped = Math.min(elapsedSeconds, 8 * 60 * 60);   // 8-hour cap

    return getd("passivePerSecond") * capped * 0.5;        // 50% offline efficiency
}

Show the result in a popup after applying it:

double offlineGain = calculateOfflineGain(lastSaveTime);
set("coins", getd("coins") + offlineGain);
showMessage("You earned " + formatBig(offlineGain) + " while away!");

Big Number Formatting

private String formatBig(double value) {
    if (value < 1_000) return String.format("%.0f", value);
    if (value < 1_000_000) return String.format("%.1fK", value / 1_000.0);
    if (value < 1_000_000_000) return String.format("%.1fM", value / 1_000_000.0);
    if (value < 1_000_000_000_000L) return String.format("%.1fB", value / 1_000_000_000.0);
    return String.format("%.1fT", value / 1_000_000_000_000.0);
}

Prestige Reset

private void doPrestige() {
    double coins = getd("coins");
    if (coins < 1_000_000)
        return;

    double bonus = 1.0 + Math.max(0, Math.floor(Math.log10(coins) - 5) * 0.02);
    set("prestigeBonus", getd("prestigeBonus") * bonus);

    set("coins", 0.0);
    set("clickValue", 1.0);

    producers.forEach(p -> p.owned().set(0));
    recalculatePassiveRate();
}

Unlocks and Upgrades

Use milestone predicates instead of hardcoding UI visibility everywhere.

public record Upgrade(String id, double cost, BooleanSupplier isUnlocked, Runnable effect) {}

Upgrade cursorDouble = new Upgrade(
        "cursor-double",
        250,
        () -> producers.get(0).owned().get() >= 10,
        () -> set("clickValue", getd("clickValue") * 2)
);

HUD Pattern

Text coinsText = getUIFactoryService().newText("", Color.GOLD, 28);
coinsText.textProperty().bind(Bindings.createStringBinding(
        () -> "Coins: " + formatBig(getd("coins")),
        getdp("coins")
));

Text incomeText = getUIFactoryService().newText("", Color.LIGHTGREEN, 20);
incomeText.textProperty().bind(Bindings.createStringBinding(
        () -> "Per second: " + formatBig(getd("passivePerSecond")),
        getdp("passivePerSecond")
));

Gotchas

• Store progression in model objects — dozens of separate globals become impossible to balance.
• Always cap offline progress — uncapped offline gain breaks progression curves.
• Recalculate passive rate after every buy, upgrade, and prestige — stale cached values are the most common idle-game bug.
• Double precision is enough early, not forever — late-game incremental designs may need BigDecimal or scientific-notation storage if numbers grow extremely large.