Java working with jpanel and jscrollpane while drawing lines

Question

I developed a software solution to connect Java components visually and it works fine. My only problem now is that my dashboard is surrounded by a jscrollpane and thats good. But if i get out of the dashboard so that the jscrollpane have to grow, all the lines drawed to connect the components are moving from they position. I have search for methods to get the real screen size of the jscollpane but found nothing.

To grow the jscrollpane if needed i use:

Point p = (mainPanel.getMousePosition());
if(mainPanel.getWidth() - (p.x) < tmp.getWidth() && mainPanel.getHeight() - (p.y) < tmp.getHeight())
{
    dim = new Dimension(dim.width+(mainPanel.getWidth()-p.x),dim.height+mainPanel.getHeight() - (p.y));
}
else if(mainPanel.getHeight() - (p.y) < tmp.getHeight())
{
    dim = new Dimension(dim.width,dim.height+mainPanel.getHeight() - (p.y));
}
else if(mainPanel.getWidth() - (p.x) < tmp.getWidth())
{
    dim = new Dimension(dim.width+(mainPanel.getWidth()-p.x),dim.height);
}
mainPanel.setPreferredSize(dim);

While the mouse is dragged.

So i need to get the coordinates of the left top point in the jscrollpane to calculate the new coordinates or something that shifts the lines correct back.

To draw the lines i use:

@Override
public void paint(Graphics g) {
    super.paint(g);
    Graphics2D g2d = (Graphics2D) g;

    g2d.setRenderingHint(RenderingHints.KEY_ANTIALIASING,
            RenderingHints.VALUE_ANTIALIAS_ON);

    // test
    Line2D tmp_line;
    for (int i = 0; i < abuttons.size(); i++) {
        // System.out.println(abuttons.get(i).out);
        if (abuttons.get(i).out != null) {
            int x1 = abuttons.get(i).getLocation().x
                    + abuttons.get(i).connectBtn_right.getLocation().x 
                    + 12;
            int y1 = abuttons.get(i).getLocation().y
                    + abuttons.get(i).connectBtn_right.getLocation().y 
                    + 9 + 75;
            int x2 = abuttons.get(i).out.getLocation().x
                    + abuttons.get(i).out.connectBtn_left.getLocation().x
                    + 12;
            int y2 = abuttons.get(i).out.getLocation().y
                    + abuttons.get(i).out.connectBtn_left.getLocation().y
                    + 9 + 75;

            tmp_line = new Line2D.Double(x1, y1, x2, y2);
            g2d.setPaint(Color.BLACK);
            g2d.setStroke(new BasicStroke(1.5f));
            g2d.draw(tmp_line);
        }
    }
    if (point1 != null && point2 != null) {
        line2d = new Line2D.Double(point1, point2);
        g2d.setPaint(Color.RED);
        g2d.setStroke(new BasicStroke(1.5f));// set stroke size
        g2d.draw(line2d);
    }
}

Thanks for any help

Here the SSCCE:

import java.awt.BorderLayout;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.Point;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.border.EmptyBorder;
import javax.swing.JScrollPane;
import javax.swing.JButton;


public class LineDraw extends JFrame {

private JPanel contentPane;
JScrollPane scrollPane = new JScrollPane();
JPanel panel = new JPanel();
JButton btnNewButton = new JButton("New button");
JButton btnNewButton_1 = new JButton("New button");

/**
 * Launch the application.
 */
public static void main(String[] args) {
    EventQueue.invokeLater(new Runnable() {
        public void run() {
            try {
                LineDraw frame = new LineDraw();
                frame.setVisible(true);
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    });
}

/**
 * Create the frame.
 */
public LineDraw() {
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    setBounds(100, 100, 450, 300);
    contentPane = new JPanel();
    contentPane.setBorder(new EmptyBorder(5, 5, 5, 5));
    setContentPane(contentPane);
    contentPane.setLayout(null);

    scrollPane.setBounds(0, 0, 424, 251);
    contentPane.add(scrollPane);

    scrollPane.setViewportView(panel);
    panel.setLayout(null);

    btnNewButton.setBounds(27, 98, 89, 23);
    panel.add(btnNewButton);

    btnNewButton_1.setBounds(213, 137, 89, 23);
    panel.add(btnNewButton_1);
    initListener();
}

private void initListener()
{
    btnNewButton.addMouseMotionListener(new MouseAdapter() {
            @Override
            public void mouseDragged(MouseEvent me) {
                super.mouseDragged(me);
                Point pos = panel.getMousePosition();
                System.out.println(pos);
                if(panel.getWidth()-pos.x<50 && panel.getHeight()-pos.y<50)
                {
                    panel.setPreferredSize(new Dimension(panel.getWidth()+50,panel.getHeight()+50));
                }
                else if(panel.getHeight()-pos.y<50)
                {
                    panel.setPreferredSize(new Dimension(panel.getWidth(),panel.getHeight()+50));
                }                   
                else if(panel.getWidth()-pos.x<50)
                {
                    panel.setPreferredSize(new Dimension(panel.getWidth()+50,panel.getHeight()));
                }
                btnNewButton.setLocation(pos);
                repaint();
                validate();
            }
        });
    btnNewButton_1.addMouseMotionListener(new MouseAdapter() {
        @Override
        public void mouseDragged(MouseEvent me) {
            super.mouseDragged(me);
            Point pos = panel.getMousePosition();
            if(panel.getWidth()-pos.x<50 && panel.getHeight()-pos.y<50)
            {
                panel.setPreferredSize(new Dimension(panel.getWidth()+50,panel.getHeight()+50));
            }
            else if(panel.getHeight()-pos.y<50)
            {
                panel.setPreferredSize(new Dimension(panel.getWidth(),panel.getHeight()+50));
            }                   
            else if(panel.getWidth()-pos.x<50)
            {
                panel.setPreferredSize(new Dimension(panel.getWidth()+50,panel.getHeight()));
            }
            btnNewButton_1.setLocation(panel.getMousePosition());
            repaint();
            validate();
        }
    });
}

@Override
public void paint(Graphics g)
{
    super.paint(g);
    g.drawLine(btnNewButton.getLocation().x+10,btnNewButton.getLocation().y+32, btnNewButton_1.getLocation().x+10,btnNewButton_1.getLocation().y+32);
}
}

Answer 1

OVerride paintComponent() of panel instead of paint() of JFrame

import javax.swing.*;
import javax.swing.border.EmptyBorder;
import java.awt.*;
import java.awt.event.*;


public class LineDraw extends JFrame {

    private JPanel contentPane;
    JScrollPane scrollPane = new JScrollPane();
    JPanel panel = new JPanel(){
        @Override
        public void paintComponent(Graphics g)
        {
            super.paintComponent(g);
            g.drawLine(btnNewButton.getLocation().x,btnNewButton.getLocation().y, btnNewButton_1.getLocation().x,btnNewButton_1.getLocation().y);
        }

    };
    JButton btnNewButton = new JButton("New button");
    JButton btnNewButton_1 = new JButton("New button");

    /**
     * Launch the application.
     */
    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {
            public void run() {
                try {
                    LineDraw frame = new LineDraw();
                    frame.setVisible(true);
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        });
    }

    /**
     * Create the frame.
     */
    public LineDraw() {
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setBounds(100, 100, 450, 300);
        contentPane = new JPanel();
        contentPane.setBorder(new EmptyBorder(5, 5, 5, 5));
        setContentPane(contentPane);
        contentPane.setLayout(null);

        scrollPane.setBounds(0, 0, 424, 251);
        contentPane.add(scrollPane);

        scrollPane.setViewportView(panel);
        panel.setLayout(null);

        btnNewButton.setBounds(27, 98, 89, 23);
        panel.add(btnNewButton);

        btnNewButton_1.setBounds(213, 137, 89, 23);
        panel.add(btnNewButton_1);
        initListener();
    }

    private void initListener()
    {
        btnNewButton.addMouseMotionListener(new MouseAdapter() {
            @Override
            public void mouseDragged(MouseEvent me) {
                super.mouseDragged(me);
                Point pos = panel.getMousePosition();
                System.out.println(pos);
                if(panel.getWidth()-pos.x<50 && panel.getHeight()-pos.y<50)
                {
                    panel.setPreferredSize(new Dimension(panel.getWidth()+50,panel.getHeight()+50));
                }
                else if(panel.getHeight()-pos.y<50)
                {
                    panel.setPreferredSize(new Dimension(panel.getWidth(),panel.getHeight()+50));
                }
                else if(panel.getWidth()-pos.x<50)
                {
                    panel.setPreferredSize(new Dimension(panel.getWidth()+50,panel.getHeight()));
                }
                btnNewButton.setLocation(pos);
                validate();
                repaint();
            }
        });
        btnNewButton_1.addMouseMotionListener(new MouseAdapter() {
            @Override
            public void mouseDragged(MouseEvent me) {
                super.mouseDragged(me);
                Point pos = panel.getMousePosition();
                if(panel.getWidth()-pos.x<50 && panel.getHeight()-pos.y<50)
                {
                    panel.setPreferredSize(new Dimension(panel.getWidth()+50,panel.getHeight()+50));
                }
                else if(panel.getHeight()-pos.y<50)
                {
                    panel.setPreferredSize(new Dimension(panel.getWidth(),panel.getHeight()+50));
                }
                else if(panel.getWidth()-pos.x<50)
                {
                    panel.setPreferredSize(new Dimension(panel.getWidth()+50,panel.getHeight()));
                }
                btnNewButton_1.setLocation(panel.getMousePosition());
                validate();
                repaint();
            }
        });
    }

}

And remove the paint() method entirely.