Extending

Your own widgets, properties, events, layouts and tags.

Everything is extended with plain code, without reflection or annotations.

Your own widget

public class StripeBar extends Widget<StripeBar> {
    public static final StyleKey<Integer> STRIPE = StyleKey.builder("stripe-color", Integer.class)
            .defaultValue(0xFFFFFFFF).animated(Interpolator.COLOR).register();

    private float value;

    public StripeBar() {
        super("stripe-bar");                     // theme class
        setFocusable(true);
    }

    public StripeBar value(float v) {
        value = v;
        return this;
    }

    @Override
    protected void measureContent(float maxWidth, float maxHeight) {
        setContentSize(120, 8);                  // natural size without padding
    }

    @Override
    protected void paintContent(Canvas canvas, float partialTick) {
        canvas.fillRoundRect(0, 0, width() * value, height(), Radii.all(4),
                Brush.solid(style.get(STRIPE)));
    }

    @Override
    protected void handleEvent(UiEvent event) {
        if (event.type() == PointerEvent.CLICK) {
            value(((PointerEvent) event).localX() / width());
            event.consume();
        }
    }
}

Useful UiElement hooks: onAttach / onDetach (signal subscriptions and animations), onLayout (after a size change), onStateChanged, paintBackground, paintForeground, paintOverlay. Custom states use bits starting at State.FIRST_CUSTOM.

Everything else

What	How
Style property	`StyleKey.builder(name, type).defaultValue(...).inherited().affectsLayout().animated(...).register()`
Theme token	`ThemeVar.of("brand", Integer.class, 0xFF00FF00)`
Event	`EventType.create("name", bubbles)`
Layout	`implements Layout`
Markup tag	`Markup.tag("card", (node, ctx) -> ...)`
CSS property	`CssProperties.register(...)`
Effect	`FxRegistry.register("mymod:effect", ...)`
Translation source	`I18n.addSource((lang, key) -> ...)`

Platform hooks

`Platform` method	Default	Purpose
`dataDirectory()`	`config/luminaui`	folder for theme files
`readFile/writeFile/listFiles`	via `java.nio`	files inside `dataDirectory()`
`dayTime()`	`-1` (no world)	world time in ticks 0–24000
`biomeId()`	`null`	biome id under the player
`narrate(text)`	nothing	narration for the screen reader
`isShiftDown()`	`false`	Shift+click on a slot (quick move)
`playSound(id, volume, pitch)`	nothing	UI sounds
`pollGameData(GameState out)`	`false` (no world)	player snapshot for `GameData`, every client tick
`hudState()`	`0`	F1 / F3 / chat / screen flags for HUD visibility rules, every frame
`createTexture(key, w, h, argb)`	`null`	a texture from pixels (GIF frames, minimap)
`sampleMap(radius)`	`null`	map colors around the player for `MiniMap`
`worldBlocks()`	`null`	client world blocks one by one for `StructurePreview` and `WorldCapture`
`captureWorld(x0, y0, z0, x1, y1, z1)`	via `worldBlocks()`	a world box at once as one structure
`pollGamepad()`	`null`	gamepad state for navigation