Hello,

I am trying to write a simple image viewer which will center the image if
the image is smaller than the APPLET size, but otherwise load the image as
the content of a JScrollPane. The code attached works, but has an
unfortunate side-effect which is that the image seems to flicker if the
image is smaller than the applet. It seems to repaint twice, the first
time with the image located in the upper left corner, then quickly it
appears centered. I have debug code which indicates that the
paintComponent member is only called once. I have googled this one and
come up empty handed. Any suggestions would be appreciated...

Thank you,
Michael Uman
Software Magician

/*
    MODULE        :    ScrollPaneApp.java
    PROJECT        :    Java Based image viewer
    PROGRAMMER    :    Michael Uman
*/

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

public class ScrollPaneApp extends JApplet {
    String         filename = "image.jpg";
    JScrollPane scrollPane;
    int            debug = 0;
   
    public void start() {
        if (debug == 1)
            System.out.println("start()");
    }

    public void stop() {
        if (debug == 1)
            System.out.println("stop()");
    }

    public void init() {
//        System.out.println("init()");
        String    tmp;

//    --    Get Applet parameters...

          if ((tmp = getParameter("debug")) != null) {
            debug = Integer.parseInt(tmp);
        }
        if ((tmp = getParameter("image")) != null) {
            filename = tmp;
        }
           
        if (debug == 1)
            System.out.println("Filename = " + filename);

          try {
            URL url = new URL(getCodeBase(), filename);

            Image image = getImage(url);

            int w = getWidth();
            int h = getHeight();

            scrollPane = new JScrollPane(new ImageComponent(image, w, h));

            this.getContentPane().add(scrollPane);
        } catch (MalformedURLException e) {
        }

    }

    public String getAppletInfo() {
        return "ScrollPaneApplet (C) 2005 Softwaremagic.net";
    }

    public String[][] getParameterInfo() {
        String    param_info[][] = {
            {    "debug", "0..1", "0 = no debug, 1 = debug messages", },
            {    "image", "String", "Name of image to load", },
        };

        return param_info;
    }
}

------------------------------------------------------------------
/*
    MODULE        :    ImageComponent.java
    PROJECT        :    Java Based image viewer
    PROGRAMMER    :    Michael Uman
*/

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

public class ImageComponent extends JComponent {
    Image image;
    Dimension size;
    int            parent_w, parent_h;

    public ImageComponent(Image image, int w, int h) {
        this.image = image;

        this.parent_w = w;
        this.parent_h = h;

        MediaTracker mt = new MediaTracker(this);

        mt.addImage(image, 0);
        try {
            mt.waitForAll();
        }
        catch (InterruptedException e) {
        }

        size = new Dimension(image.getWidth(this), image.getHeight(this));
        setPreferredSize(size);
    }

    public void paintComponent(Graphics g) {

//        System.out.println("oh paint()");
        int off_x = 0,
            off_y = 0;

        if (parent_w > size.getWidth()) {
            off_x = (int)((parent_w - size.getWidth()) / 2);
        }
        if (parent_h > size.getHeight()) {
            off_y = (int)((parent_h - size.getHeight()) / 2);
        }
   
//        System.out.println("X offset = " + off_x + " Y offset = " + off_y);

        g.drawImage(image,
            off_x,
            off_y,
            this);
    }

    public Dimension getPreferredSize() {
        return size;
    }
}