[GTK4] Layout not propagated correctly

[tmssngr]

Describe the bug
For previously invisible Composites, setting the size does not trigger a layout for children like on other platforms or with GTK3.

To Reproduce

import org.eclipse.swt.*;
import org.eclipse.swt.graphics.*;
import org.eclipse.swt.layout.*;
import org.eclipse.swt.widgets.*;

public class Gtk4CardLayoutTest {

	public static void main(String[] args) {
		final Display display = new Display();

		final Shell shell = new Shell(display);
		shell.setLayout(new GridLayout(1, false));

		final Composite buttonBar = new Composite(shell, SWT.NONE);
		buttonBar.setLayoutData(new GridData(SWT.FILL, SWT.FILL, true, false));
		buttonBar.setLayout(new RowLayout());

		final Composite cards = new Composite(shell, SWT.NONE);
		cards.setLayoutData(new GridData(SWT.FILL, SWT.FILL, true, true));
		final CardLayout cardLayout = new CardLayout();
		cards.setLayout(cardLayout);

		createCard("Card 1", buttonBar, cards, cardLayout);
		createCard("Card 2", buttonBar, cards, cardLayout);

		shell.setSize(400, 300);
		shell.open();

		while (!shell.isDisposed()) {
			if (!display.readAndDispatch()) {
				display.sleep();
			}
		}

		display.dispose();
	}

	private static void createCard(String text, Composite buttonBar, Composite cards, CardLayout cardLayout) {
		final boolean isFirst = cards.getChildren().length == 0;

		final Composite card = new Composite(cards, SWT.NONE);
		card.setLayout(new GridLayout());

		final Text textControl = new Text(card, SWT.BORDER);
		textControl.setMessage(text);
		textControl.setLayoutData(new GridData(SWT.FILL, SWT.CENTER, true, true));
		textControl.addListener(SWT.Resize, event -> System.out.println("Resize " + text));

		final Button button = new Button(buttonBar, SWT.RADIO);
		button.setText(text);
		if (isFirst) {
			button.setSelection(true);
			cardLayout.setCurrent(card);
		}
		else {
			card.setVisible(false);
		}
		button.addListener(SWT.Selection, event -> cardLayout.setCurrent(card));
	}

	private static class CardLayout extends Layout {
		private Control current;

		@Override
		protected Point computeSize(Composite composite, int wHint, int hHint, boolean flushCache) {
			final Point size = new Point(0, 0);
			for (Control child : composite.getChildren()) {
				final Point childSize = child.computeSize(SWT.DEFAULT, SWT.DEFAULT);
				size.x = Math.max(size.x, childSize.x);
				size.y = Math.max(size.y, childSize.y);
			}
			return size;
		}

		@Override
		protected void layout(Composite composite, boolean flushCache) {
			System.out.println("current = " + current);
			if (current != null) {
				final Point size = composite.getSize();
				System.out.println("size = " + size);
				current.setSize(size);
			}
		}

		public void setCurrent(Control control) {
			if (current != null) {
				current.setVisible(false);
			}
			current = control;
			if (current != null) {
				current.setVisible(true);
				current.getParent().requestLayout();
			}
		}
	}
}

• launch this snippet with SWT_GTK4=0
• click the "Card 2" radio button -> the "Card 2" text field becomes visible properly at the center
• launch this snippet with SWT_GTK4=1
• click the "Card 2" radio button -> the "Card 2" text field is not resized (though, as the output indicates, setSize() was invoked correctly, but no Resize-event occurs for the second card unless the shell is manually resized)

Expected behavior
It should work like with SWT_GTK4=0 or on other platforms - setSize should trigger a layout. Or it should not trigger a layout on all platforms.

Screenshots
With SWT_GTK4=0:

With SWT_GTK4=1:

Environment:

1. Select the platform(s) on which the behavior is seen:

• • All OS
• • Windows
• • Linux
• • macOS

2. Additional OS info (e.g. OS version, Linux Desktop, etc)
   Ubuntu 26.04

[akurtakov]

Thanks for this one @tmssngr ! It is a very good snippet to debug issue that was making CTabFolder losing content on back and forth between tabs. With this one (to be merged as soon as master opens) - Gtk 4 becomes far more usable!

Keep'em coming!

[tmssngr]

Thanks for the quick fix. It fixes above snippet, but unfortunately not the other bug in SmartGit which I was hoping to reproduce with the above snippet.

[akurtakov]

If you create such a pure SWT snippet to ease debugging the issue - I'll look into it too.

[tmssngr]

Another, very related snippet:

import com.sun.jdi.*;

import org.eclipse.swt.*;
import org.eclipse.swt.layout.*;
import org.eclipse.swt.widgets.*;

public class GTK4DelayedMadeVisible {

	public static void main(String[] args) {
		final Display display = new Display();

		final Shell shell = new Shell(display);
		shell.setLayout(new FillLayout());

		final Composite composite = new Composite(shell, SWT.NONE);
		composite.setVisible(false);
		display.asyncExec(() ->
				                  composite.setVisible(true));

		composite.setLayout(new GridLayout());

		final Button button = new Button(composite, SWT.PUSH);
		button.setText("Exit");
		button.setLayoutData(new GridData(SWT.FILL, SWT.FILL, true, true));
		button.addListener(SWT.Selection, e -> shell.dispose());

		shell.setSize(300, 200);
		shell.open();
		while (!shell.isDisposed()) {
			if (!display.readAndDispatch()) {
				display.sleep();
			}
		}

		display.dispose();
	}
}

With SWT_GTK4=0 it is correct:

However, with SWT_GTK4=1 the layout is not correctly invoked for the composite after becoming visible, even with your commit #3331:

[akurtakov]

@tmssngr Both snippets work now too, let's see whether this will fix your problem or you'll come up with new snippet.