Repaint JComponent on res

  To: comp.lang.java.gui
Hi,
   Hope someone can help.

I'm drawing in a JComponent.
Initially the JComponent is sized at 200 x 200
and an origin point is set at getWidth()/2,
and getHeight()/2. A cross is drawn at the origin.

Now, I use the mouse to move the origin
(hence the cross drawn at the origin) to approx.
3 * getWidth()/4, and 3 * getHeight()/4. Fine.

Now, I wish to resize the JComponent and have the
cross drawn at the same relative location in the
resized component as it was in the old sized component.
i.e.
old location = 75% width, 75% height of old component size.
new location = 75% width, 75% height of new component size.
The origin may be outside the visible area of the component,
for instance it may be located at -10X, 500Y because I will
be drawing more things that just this example cross.

It seems like such a simple thing but I can't seem to get
a before ComponentResize size and an after ComponentResize size
at the same time so that I can compare them.

Thanks for any help.
BV

package scratch;

import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.event.ComponentAdapter;
import java.awt.event.ComponentEvent;
import java.awt.event.ComponentListener;
import java.awt.event.MouseEvent;

import javax.swing.JComponent;
import javax.swing.JFrame;
import javax.swing.SwingUtilities;
import javax.swing.event.MouseInputAdapter;

public class Scratch
extends JComponent {

   private static final long
   serialVersionUID = 1L;
   boolean unPainted = true;
   private int originXOffset;
   private int originYOffset;

   public static void main(String[] args) {
     SwingUtilities.invokeLater(new Runnable() {
       public void run() {
         createAndShowGUI();
       }
     });
   }

   private static void createAndShowGUI() {
     JFrame f = new JFrame("Scratch");
     Scratch scratch = new Scratch();
     f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
     f.add(scratch);
     f.pack();
     f.setVisible(true);
   }

   public Scratch() {
     setPreferredSize(new Dimension(200, 200));
     addComponentListener(resizer);
     addMouseListener(mouser);
     addMouseMotionListener(mouser);
   }

   @Override
   protected void paintComponent(Graphics g) {
     super.paintComponent(g);
     Graphics2D g2 = (Graphics2D)g;

     if (unPainted) {
       originXOffset = getWidth()/2;
       originYOffset = getHeight()/2;
       unPainted = false;
     }

     Color startingColor = g2.getColor();
     g2.setColor(Color.RED);
     g2.drawLine(
         originXOffset - 10, originYOffset,
         originXOffset + 10, originYOffset);
     g2.drawLine(
         originXOffset, originYOffset - 10,
         originXOffset, originYOffset + 10);
     g2.setColor(startingColor);
   }

   private ComponentListener resizer =
     new ComponentAdapter() {

     public void componentResized(ComponentEvent e) {
       // TODO Shift originXOffset and originYOffset
       // so that the cross is drawn at the same relative
       // location in the newly sized component.
     }
   };

   private MouseInputAdapter mouser =
     new MouseInputAdapter() {

     int startX;
     int startY;
     boolean inDrag = false;

     @Override
     public void mousePressed(MouseEvent e) {
       super.mousePressed(e);
       startX = e.getX();
       startY = e.getY();
       inDrag = true;
     }

     @Override
     public void mouseReleased(MouseEvent e) {
       super.mouseReleased(e);
       inDrag = false;
     }

     @Override
     public void mouseDragged(MouseEvent e) {
       int currentX = e.getX();
       int currentY = e.getY();

       if (currentX < startX) {
         originXOffset =
           originXOffset - (startX - currentX);
         startX = currentX;
       }
       else {
         originXOffset =
           originXOffset + (currentX - startX);
         startX = currentX;
       }
       if (currentY < startY) {
         originYOffset =
           originYOffset - (startY - currentY);
         startY = currentY;
       }
       else {
         originYOffset =
           originYOffset + (currentY - startY);
         startY = currentY;
       }
       if (inDrag) {
         repaint();
       }
     }
   };
}

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