Whiteboard

Whiteboard is a free-hand drawing area using finger/mouse — the classic case is signature capture. It already handles the touch events and accumulates the strokes internally.

Complete example (copy, paste and run)

package com.exemplo;

import dev.crossfly.ui.*;
import dev.crossfly.ui.layout.*;
import dev.crossfly.ui.image.*;       // Image

/** 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());

      // Signature area filling the remaining space (LAY_FILL).
      Whiteboard board = new Whiteboard();
      board.setPenColor(0xFF000000);   // black pen
      board.thick = true;              // thick stroke
      add(LAY_FILL, board);

      // Button to clear the drawing.
      Button limpar = new Button("Limpar");
      limpar.onAction(c -> board.clear());
      add(LAY_AUTO, limpar);

      // Button to capture the drawing as an image (e.g., to persist it).
      Button salvar = new Button("Salvar");
      salvar.onAction(c -> {
         Image img = board.getImage();   // the current drawing as an Image (may be null if empty)
         // … persist img (e.g., PNG) …
      });
      add(LAY_AUTO, salvar);
   }
}

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

Basic usage (signature)

Whiteboard assinatura = new Whiteboard();
assinatura.setPenColor(0xFF000000);   // black pen
assinatura.thick = true;              // thick stroke
painel.add(0.5f, assinatura);         // 50% of the height

Button limpar = new Button("Limpar");
limpar.onAction(c -> assinatura.clear());

Button salvar = new Button("Salvar");
salvar.onAction(c -> {
   Image img = assinatura.getImage();   // the drawing as an image
   // … persist img (e.g., PNG) …
});

API

Best practices

• Give it generous height (a fraction of the container or autoHeight) — a signature needs space.
• Always offer a Clear button.
• When saving, use getImage() and handle exceptions when converting/persisting.

Common mistakes

• Area too small → illegible signature.
• Forgetting that setImage(Image) throws ImageException (checked).
• Confusing it with ImageView (only displays) — Whiteboard captures drawing.

See also

• Images · Custom drawing
• Catalog: Whiteboard · Reference: Chapter 18 — Images