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8 Comments on “Auto-scrolling in Swing applications”

1. 
   1 Alexander Potochkin said at 2:29 pm on March 22nd, 2008:

   Hello Kirill

   It is interesting that I started my own implementation for this feature
   about a month ago, so you are always a step ahead of me :-)

   By the way, could you give more details about why glassPane approach
   “repaints the entire UI on every scroll ”

   What do you mean by the “entire UI”, is it the whole frame ?

   Thanks
   alexp

2. 
   2 Kirill Grouchnikov said at 11:47 pm on March 22nd, 2008:

   Alex,

   It was my understanding that a non-opaque glass pane repaints everything (the whole frame) when it needs to repaint. If the specific glass pane implementation does not have any child elements (just overrides paintComponent()), a repaint of any sub-area of that frame will trigger the repaint of the glass pane which will trigger the repaint of the entire frame. Is my understanding of the scenario incorrect?

   Thanks
   Kirill

3. 
   3 Alexander Potochkin said at 12:03 pm on March 23rd, 2008:

   Hello Kirill

   I wrote a simple test which shows how repainting is changed when glassPane is visible. I’ll add the sources at the end of this message

   When you move the mouse over the checkBox and glassPane is invisible,
   you can see in the console that checkBox is repainted within its bounds

   By clicking on this checkBox you’ll make the glassPane visible,
   move the mouse over it again and you’ll see that painting starts from
   the RootPane now, goes to the checkBox and finally to the GlassPane

   The painting process of Swing is smart enough
   to quickly finds the origin component to be repainted,
   and painting the small part of the transparent glassPane costs nothing

   As you can see all painting are performed within the bounds of the CheckBox,
   so it is very different from the “repainting the entire UI”

   Would you agree?

   Thanks
   alexp

   import javax.swing.*;
   import java.awt.*;
   import java.awt.event.ActionEvent;

   public class GlassPaneRepainting {
   private static void createAndShowGui() {

   final JFrame frame = new JFrame() {
   protected JRootPane createRootPane() {
   JRootPane rp = new JRootPane() {

   public void paint(Graphics g) {
   System.out.println(“”);
   System.out.println(“JRootPane.paint”);
   System.out.println(“g.getClipBounds() = ” + g.getClipBounds());
   super.paint(g);
   }
   };
   rp.setOpaque(true);
   return rp;
   }
   };

   frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
   frame.setLayout(new FlowLayout());

   frame.add(new JCheckBox(“Show the glassPane”) {

   public void paint(Graphics g) {
   System.out.println(“JCheckBox.paint”);
   System.out.println(“g.getClipBounds() = ” + g.getClipBounds());
   super.paint(g);
   }

   protected void fireActionPerformed(ActionEvent event) {
   frame.getGlassPane().setVisible(!frame.getGlassPane().isVisible());
   System.out.println(“”);
   System.out.println(“getGlassPane().isVisible() = ” + frame.getGlassPane().isVisible());
   super.fireActionPerformed(event);
   }
   });

   frame.setGlassPane(new JPanel() {
   {setOpaque(false);}

   public void paint(Graphics g) {
   System.out.println(“GlassPaneRepainting.paint”);
   System.out.println(“g.getClipBounds() = ” + g.getClipBounds());
   super.paint(g);
   }
   });

   frame.setSize(200, 200);
   frame.setLocationRelativeTo(null);
   frame.setVisible(true);
   }

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

4. 
   4 Kirill Grouchnikov said at 2:04 pm on March 23rd, 2008:

   Alex,

   This looks a little surprising to me. What happens when the painting done in glass pane overflows the component bounds (as i did for validation overlays)? When i need to update that painting, i’ll have to force repaint of the entire frame myself?

   And look at the example from Santhosh – the scroller image is drawn centered around the mouse click location. While the test application that he shows only has one scroll pane and he clicked in the middle of that scroll pane, what would happen if you click in the top left corner of the scroll pane? Would the scroller image be cut? And if it would, would you have to force the repaint of the entire frame?

   Thanks
   Kirill

5. 
   5 Alexander Potochkin said at 5:27 am on March 24th, 2008:

   Hello Kirill

   GlassPane is repainted when any component under it is repainted,
   if you place a decoration outside e.g. button and want it to be in sync,
   with the button’s state you certainly need to repaint a glassPane

   but again, one of the key point of the fast painting is not to paint more
   than you need, so in this case you should repaint only small part of the glassPane, which contains that decorations

   About example from Santhosh:

   > what would happen if you click in the top left corner of the scroll pane? > Would the scroller image be cut

   I don’t know, I thought you had tested it :-)

   In my opinion, in the implementation from Santhosh,
   the whole frame is repainted once when
   you press the wheel and the ScrollGlassPane becomes visible

   if you need to move the scrolling indicator,
   you just need to repaint the small area where it was
   and the area where it is now

   I don’t see any reasons why the frame should be repainted during scrolling

   Thanks
   alexp

6. 
   6 Kirill Grouchnikov said at 9:01 pm on March 24th, 2008:

   Alex,

   Thanks for the clarifications. I had the wrong idea that the entire frame is repainted once a non-opaque glass pane is installed.

   Kirill

7. 
   7 Alexander Potochkin said at 5:34 am on March 25th, 2008:

   You are welcome my friend,
   see you in the J1 soon

   alexp

8. 8 Alexander Potochkin's Blog said at 9:42 am on June 24th, 2008:

   JXLayer 3.0 – MouseScrollableUI

   Implementing auto-scrolling feature with JXLayer