How to make Java Glasspane sticks to a location even if GUI was resized?

Question

Java Glass pane auto resize when I resize the whole interface,but I want to make it stick to a specific location, it will look like this:

Instead of moving around when I resize it.

Thanks

Answer 1

There's a number of ways this might be achieved, but the basic requirement will require some kind of reference to the component your glass pane content is trying to stick to. This means that when the components are updated and are required to be laid out, you can find the location of the sticky component and update the position of the content on the glass pane.

Remember, the glass pane is a container which occupies the entire content are of a window, it's what's contained within the glass pane that you need to update

import java.awt.AlphaComposite;
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Component;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Point;
import java.util.ArrayList;
import java.util.List;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JTextField;
import javax.swing.SwingUtilities;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;

public class StickyGlassPaneExample {

    public static void main(String[] args) {
        new StickyGlassPaneExample();
    }

    public StickyGlassPaneExample() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
                }

                StickyGlassPane stickyGlassPane = new StickyGlassPane();
                TestPane testPane = new TestPane(stickyGlassPane);

                JFrame frame = new JFrame("Testing");
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.setLayout(new BorderLayout());
                frame.add(testPane);
                frame.setSize(600, 500);
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
                frame.setGlassPane(stickyGlassPane);
                stickyGlassPane.setVisible(true);
            }
        });
    }

    public class TestPane extends JPanel {

        private List<JTextField> fields;

        public TestPane(StickyGlassPane stickyGlassPane) {
            fields = new ArrayList<JTextField>(100);
            for (int index = 0; index < 100; index++) {
                JTextField field = new JTextField(10);
                fields.add(field);
                add(field);
            }
            int fieldIndex = (int)(Math.random() * (fields.size() - 1));
            JTextField sticky = fields.get(fieldIndex);
            sticky.setText("Sticky");
            stickyGlassPane.setStickyComponent(sticky);
        }
    }

    public class StickyGlassPane extends JPanel {

        private Component component;

        private JPanel overlay;

        public StickyGlassPane() {
            setOpaque(false);
            overlay = new JPanel() {

                @Override
                protected void paintComponent(Graphics g) {
                    super.paintComponent(g);
                    Graphics2D g2d = (Graphics2D) g.create();
                    g2d.setColor(Color.RED);
                    g2d.drawRect(0, 0, getWidth(), getHeight());
                    g2d.setComposite(AlphaComposite.SrcOver.derive(0.5f));
                    g2d.fillRect(0, 0, getWidth(), getHeight());
                }

            };
            overlay.setOpaque(false);

            add(overlay);
        }

        @Override
        public void doLayout() {
            if (component != null) {
                Point p = component.getLocation();
                SwingUtilities.convertPoint(component, p, this);
                overlay.setLocation(p);
                overlay.setSize(component.getSize());
            } else {
                overlay.setBounds(0, 0, 0, 0);
            }
        }

        public void setStickyComponent(Component component) {
            this.component = component;
            revalidate();
        }

    }

}