JViewPorts Client not refreshed

Question

hello,
I am sorry for my uncorrect format in the last try to
ask...I am afraid.
I please for some help in following problem...
Starting point:
JScrollPane scrollPane = new JScrollPane();
scrollPane.setPreferredSize(new Dimension(500,450));//viewClient has got a computed mathematical grafic
JComponent viewClient = myExternLibrary.getJComponent();
scrollPane.setViewportView(viewClient); Result:
There is a piece of the mathematical grafic(left,top piece) in the program window. It is all ok.
For example:
scrollPane:
|--------------|
|              |
|           ---|
|           \  |
|            \ |
|             \|
|              |
|<============>|
horizontal scrollbar
Problem:
If I have manipulated the visible area with
buttons,all has been ok.
But if I have manipulated with knob, the JViewPort has
refreshed incompletely.
for example:
I pull knob on the right and allways become(a picture). But b Picture is korrectly.
  (a picture)                 (b picture)
scrollPane:               
|--------------|           |--------------|
|              |           |           ###|
|        ------|           |        ---   |
|        \  \  |           |        \     |
|         \  \ |           |         \    |
|          \  \|           |          \   |
|              |           |           ###|
|<============>|           |<============>|
horizontal scrollbar
Thanks for any help!!
best regards,
Joana

Answer 1

Joana,
i had a similar problem with a chart i was drawing. i overcame it by doing my own double-buffering. but it would require that you have access to your drawing class.
here is what i did:  :
  chartPanel = new JPanel() {
    public void paint(Graphics g) {
      Image img = paintGraph(chartPanel.getWidth(), scroller.getViewport().getHeight());
      g.drawImage(img, 0, 0, Color.white, null);
  protected Image paintGraph(int width, int height) {
    if ((offscreen == null) || (width != offscreensize.width) || (height != offscreensize.height)) {
      offscreen = createImage(width, height);
      offscreensize = new Dimension(width, height);
      offgraphics = (Graphics2D)offscreen.getGraphics();
      try {
        offgraphics.setClip(0, 0, width, height);
        drawChart(offgraphics, width, height);
        drawSelectables(offgraphics, width, height);
      } catch (ArrayIndexOutOfBoundsException e) { /* we have no data */ }
    return offscreen;
  }drawChart() and drawSelectables() are the methods to draw the stuff you need.
thomas