Small window preview question

Question

Hi all,
In some graph/diagram drawing applications there is the possibility of showing the whole "diagram"
in a small window in a corner even if in the main window only a portion of its is visible. This small window
shows also the visible part of the diagram inside a red rectangle (something like Acrobat thumbnail view).
Does anyone know how this small window is called and if it is possible to create one in Java?
Thanks.

Answer 1

That's not hard to do. Say _diagramPanel is a reference to a JScrollPane containing the component rendering your diagram:
public class PreviewPanel extends JPanel {
   protected void paintComponent(final Graphics g) {
      final Graphics2D g2 = (Graphics2D) g.create();
      g2.scale(0.2,0.2); //here, of course, you should compute a proper scale factor
      _diagramPanel.paint(g2);
      g2.setColor(Color.RED);
      g2.draw(_diagramPanel.getViewport().getViewRect());
      g2.dispose();
}...and you're pretty much done. All you have to do then is make sure that the PreviewPanel is being repainted whenever the diagram panel updates in any way.