Line not drawing at the correct location.

Question

I have a JPanel inside a JScrollPane I am drawing on and drawing is going good except for one problem. At the very end of my paint method, I want to draw a vertical line on the panel that is exactly in the middle of the current visible rectangle. From what I can tell, it should be repainting in the dead center every time repaint is called, but for some reason it isn't.
Here is my paintComponent method:
    public void paintComponent(Graphics g)
        int wordWidth = 0;
        int wordHeight = 0;
        int duration = 0;       
        super.paintComponent(g);       
        g2d = (Graphics2D) g;
        g2d.setFont(font);
        /* draw a gradient background */
        g2d.setPaint(new GradientPaint(0, 0, new Color(100, 100, 100), 0, this.getSize().height, new Color(255, 255, 255)));
        g2d.fillRect(0, 0, this.getSize().width, this.getSize().height);
        /* draw lines for each note */
        g2d.setColor(Color.BLACK);
        for (int i = 0; i < GuiConstants.notes.values().length; i++)
            g2d.drawLine(0, (int) (GuiConstants.SONG_DISPLAY_HEIGHT - ((GuiConstants.SONG_DISPLAY_HEIGHT / 24) * (i))), this.getSize().width, (int) (GuiConstants.SONG_DISPLAY_HEIGHT - ((GuiConstants.SONG_DISPLAY_HEIGHT / 24) * (i))));
        synchronized (words)
            for (int i = 0; i < words.size(); i++)
                /* get the width and height of the text so we can draw a box around it */
                wordWidth = g.getFontMetrics().stringWidth(words.get(i).getLyric());
                wordHeight = g.getFontMetrics().getHeight();
                /* get the duration of the word */
                duration = ((words.get(i).getEndSample() / 200) - (words.get(i).getStartSample() / 200));
                /* draw the main box that the text sits in */
                g2d.setColor(Color.DARK_GRAY);
                g2d.fillRoundRect(words.get(i).getPoint().x, words.get(i).getPoint().y, wordWidth, wordHeight, 3, 3);
                /* draw a box that will be a duration */
                if ((i % 2) == 0)
                    g2d.setColor(Color.BLUE);
                else
                    g2d.setColor(Color.ORANGE);
                g2d.fillRoundRect(words.get(i).getPoint().x, words.get(i).getPoint().y, duration, wordHeight, 3, 3);
                /* draw the text in the box */
                g2d.setColor(Color.WHITE);
                g2d.drawString(words.get(i).getLyric(), words.get(i).getPoint().x, words.get(i).getPoint().y + 16);
        /* draw vertical line in the middle of the panel */
        int x = ((int) this.getVisibleRect().getX()) + ((int) this.getVisibleRect().getWidth() / 2);
        System.out.println("Drawing line at " + x);
        g2d.setColor(Color.RED);
        g2d.drawLine(x, 0, x, GuiConstants.SONG_DISPLAY_HEIGHT);
    }This section is the other part I am having problems with.
/* draw vertical line in the middle of the panel */
        int x = ((int) this.getVisibleRect().getX()) + ((int) this.getVisibleRect().getWidth() / 2);
        System.out.println("Drawing line at " + x);
        g2d.setColor(Color.RED);
        g2d.drawLine(x, 0, x, GuiConstants.SONG_DISPLAY_HEIGHT);When the panel displays for the first time, the line is painted directly in the center. When I click the right arrow on my JScrollPane, the output to the console says that is it drawing at the correct point, but actually the is never repainted and it moves with the panel as I scroll across. Now, if I click in the middle off the scrollbar to force the scrollbar indicator to scroll to where my mouse is pressed, it actually repaints correctly.
I am just confused on how I can be printing to the console the correct location where it "says" it's painting, but it doesn't actually repaint. Any ideas?

Answer 1

so wouldn't putting a panel in front of it prevent me from being able to main panel I am painting to?wouldn't it be easier to whip up a simple app, to test?
(take only 5 minutes)
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
class Testing
  int xPos, yPos;
  public void buildGUI()
    JPanel overlayPanel = new JPanel();
    OverlayLayout overlay = new OverlayLayout(overlayPanel);
    overlayPanel.setLayout(overlay);
    JPanel draggingPanel = new JPanel(null);
    final JLabel label = new JLabel("Drag me");
    label.setBorder(BorderFactory.createLineBorder(Color.BLACK));
    Dimension dim = label.getPreferredSize();
    label.setBounds(50,50,dim.width,dim.height);
    draggingPanel.add(label);
    final JPanel linePanel = new JPanel(){
      public void paintComponent(Graphics g){
        super.paintComponent(g);
        g.drawLine(getWidth()/2,0,getWidth()/2,getHeight());
    linePanel.setOpaque(false);
    overlayPanel.add(linePanel);
    overlayPanel.add(draggingPanel);
    JFrame f = new JFrame();
    f.getContentPane().add(overlayPanel);
    f.setSize(400,300);
    f.setLocationRelativeTo(null);
    f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    f.setVisible(true);
     label.addMouseListener(new MouseAdapter(){
      public void mousePressed(MouseEvent me){
        xPos = me.getX();
        yPos = me.getY();
    label.addMouseMotionListener(new MouseMotionAdapter(){
      public void mouseDragged(MouseEvent me){
        Point me_p = me.getPoint();
        Point l_p = label.getLocation();
        label.setLocation(l_p.x + me_p.x - xPos,l_p.y + me_p.y - yPos);
        linePanel.repaint();
  public static void main(String[] args)
    SwingUtilities.invokeLater(new Runnable(){
      public void run(){
        new Testing().buildGUI();
}