I have an app that displays stacked rectangular glyphs representing
data in a jscrollpane. It works fine.

Problem: I'd like to add labels to the rows of data glyphs. I'd like
these labels to float as you scroll horizontally, sort of like column
headers in excel, except the other direction. This doesn't work, as
I've coded it. When I scroll, there is some kind of repaint issue and
visual artifacts from the labels trace across the screen.

What I'm doing is calling setBounds on the floating label component in
the data panel paintComponent. I'm assuming this is wrong, but I don't
know what else to do. See code below for a short but full "working"
applet that displays the problem. If it looks hideous in your newreader
here are urls for the code and the applet:

code url:

http://www.everydaysystems.com/testjava/float_in_scroll/FloatInScrollTest.java.txt

applet url:

http://www.everydaysystems.com/testjava/float_in_scroll/FloatInScrollTest.html

I'm hoping this is an embarrassingly simple problem.

Thanks (and embarrassed) in advance,

Reinhard

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import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;

import javax.swing.JApplet;
import javax.swing.JComponent;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JViewport;

public class FloatInScrollTest extends JApplet {

   public void init() {
       setSize(500, 100);
       JPanel dataPanel = new DataPanel();
       JScrollPane scrollPane = new JScrollPane(dataPanel);
       scrollPane

.setHorizontalScrollBarPolicy(JScrollPane.HORIZONTAL_SCROLLBAR_ALWAYS);
       scrollPane

.setVerticalScrollBarPolicy(JScrollPane.VERTICAL_SCROLLBAR_ALWAYS);
       scrollPane.setPreferredSize(new Dimension(500, 100));
       getContentPane().add(scrollPane);
   }

   class FloatingLabelGlyph extends JComponent {
       public FloatingLabelGlyph(String label, Color color) {
           this.color = color;
           this.label = label;
           setVisible(true);
       }

       public void paintComponent(Graphics g) {
           g.setColor(color);
           g.drawString(label, 0, g.getFont().getSize());
       }

       Color color;
       String label;
   }

   class DataGlyph extends JComponent {
       public DataGlyph(Color color, int x, int y, int width) {
           this.color = color;
           setBounds(x, y, width, height);
           setVisible(true);
       }

       public void paintComponent(Graphics g) {
           g.setColor(color);
           g.fillRect(0, 0, getWidth(), getHeight());
       }

       private int height = 10;
       private Color color;
   }

   class DataPanel extends JPanel {
       public DataPanel() {
           super();
           setLayout(null);
           setSize(new Dimension(1000, 1000));
           setPreferredSize(new Dimension(1000, 1000));
           floatingLabels = new FloatingLabelGlyph[labels.length];
           for (int i = 0; i < labels.length; i++) {
               add(floatingLabels[i] = new
FloatingLabelGlyph(labels[i],
                       colors[i]));
           }
           add(new DataGlyph(colors[0], 150, rowYs[0], 50));
           add(new DataGlyph(colors[0], 170, rowYs[1], 75));
           add(new DataGlyph(colors[0], 220, rowYs[0], 100));
           add(new DataGlyph(colors[1], 160, rowYs[2], 55));
           add(new DataGlyph(colors[1], 960, rowYs[2], 35));
           add(new DataGlyph(colors[1], 220, rowYs[2], 25));
           add(new DataGlyph(colors[1], 200, rowYs[3], 33));
           add(new DataGlyph(colors[2], 600, rowYs[4], 100));
           add(new DataGlyph(colors[2], 900, rowYs[4], 88));
           setVisible(true);
       }

       public void paintComponent(Graphics g) {
           // TODO: update label positions. This is the broken part.
           g.clearRect(0,0,getWidth(),getHeight());
           for (int i = 0; i < floatingLabels.length; i++) {
               g.clearRect(floatingLabels[i].getX(),
floatingLabels[i].getY(),
                       floatingLabels[i].getWidth(), floatingLabels[i]
                               .getHeight());
               floatingLabels[i].setBounds((int) ((JViewport)
getParent())
                       .getViewPosition().getX(), labelYs[i], 80, 15);
           }
           super.paintComponent(g);
       }

       private String[] labels = new String[] { "Red Data", "Green
Data",
               "Blue Data" };
       private Color[] colors = new Color[] { Color.RED, Color.GREEN,
               Color.BLUE };
       private FloatingLabelGlyph[] floatingLabels;
       private int[] rowYs = new int[] { 10, 25, 40, 55, 70 };
       private int[] labelYs = new int[] { 10, 40, 70 };
   }

}

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