Value animations

The three animators interpolate a number over time. They do not draw anything: in the onUpdate you read getValue() and apply it wherever you want (alpha, position, color…). Since rendering is on demand, call Component.repaint() in the callback.

Comparison

Complete example (copy, paste and run)

package com.exemplo;

import dev.crossfly.ui.*;
import dev.crossfly.ui.layout.*;
import dev.crossfly.ui.animation.*;   // AlphaAnimation, PositionAnimation, LoopAnimation
import dev.crossfly.util.*;           // Debug

/** Runnable main screen. Point the launcher (classname) and run: gradlew :lwjgl3:run */
public class MainWindow extends Window
{
   @Override
   public void onShow() throws Exception
   {
      super.onShow();
      setLayout(new VerticalLayout());

      // AlphaAnimation — fade-in of a label (0→1 in 0.3s)
      Label card = new Label("Olá");
      add(LAY_AUTO, card);
      AlphaAnimation fade = new AlphaAnimation(0f, 1f, 0.3f);
      fade.onUpdate(() -> { card.alpha(fade.getValue()); Component.repaint(); })
          .onComplete(() -> Debug.log("fade concluído"))
          .start();

      // PositionAnimation — slides a panel in from the right (in pixels, free)
      Label painel = new Label("Painel");
      add(LAY_AUTO, painel);
      int y0 = painel.y, w = painel.width, h = painel.height;
      PositionAnimation slide = new PositionAnimation(Screen.width, 0, 0.4f);
      slide.onUpdate(() -> { painel.setBounds((int) slide.getValue(), y0, w, h); Component.repaint(); })
           .start();

      // LoopAnimation — continuous opacity pulse (1s cycle, smoothed, infinite)
      Label ponto = new Label("●");
      add(LAY_AUTO, ponto);
      LoopAnimation pulse = new LoopAnimation(1.0f, 60f, true);
      pulse.onUpdate(() -> { ponto.alpha(0.4f + 0.6f * pulse.getValue()); Component.repaint(); })
           .start();
   }
}

The snippets below show only the core (what goes inside onShow()). To run them, place them in the MainWindow skeleton above.

AlphaAnimation — fade-in

Label card = new Label("Olá");
AlphaAnimation fade = new AlphaAnimation(0f, 1f, 0.3f);   // 0→1 in 0.3s
fade.onUpdate(() -> { card.alpha(fade.getValue()); Component.repaint(); })
    .onComplete(() -> Debug.log("fade concluído"))
    .start();

Constructors: AlphaAnimation(start, end, duration) (60 FPS) or (start, end, duration, fps).

PositionAnimation — slide a panel (in pixels)

int y0 = painel.y, w = painel.width, h = painel.height;
PositionAnimation slide = new PositionAnimation(Screen.width, 0, 0.4f);  // enters from the right
slide.onUpdate(() -> { painel.setBounds((int) slide.getValue(), y0, w, h); Component.repaint(); })
     .start();

It is not limited to [0,1] and is linear — ideal for coordinates.

LoopAnimation — continuous pulse

LoopAnimation pulse = new LoopAnimation(1.0f, 60f, true);   // 1s cycle, 60 FPS, smoothed
pulse.onUpdate(() -> { float v = 0.4f + 0.6f * pulse.getValue(); ponto.alpha(v); Component.repaint(); })
     .start();
// pulse.stop();   // stop when leaving the screen

Constructors: LoopAnimation(duration) (linear, 60 FPS) or (duration, fps, easeInOut). It does not have onComplete (runs forever until stop()).

Common control

start() · stop() (fires onComplete on Alpha/Position) · cancel() (does not fire) · isRunning() · getValue().

Best practices

• Always Component.repaint() in onUpdate — rendering is on demand.
• Stop loops (stop()) when leaving the screen (in onRemove()), otherwise the Timer keeps running.
• Store the animation in a variable/field so you can stop()/cancel() it later.

Common mistakes

• Using PositionAnimation expecting a [0,1] range — it is free; the one that clamps is AlphaAnimation.
• Forgetting the repaint() and “the animation doesn’t show up”.
• Calling setAlpha(...) (from the old Javadoc) — the real method is alpha(float).

See also

• Screen transitions · Press and feedback