From Forum Nokia Wiki

ID	CS001269	Creation date	January 7, 2009
Platform	S60 3rd Edition, S60 3rd Edition, FP1, S60 3rd Edition, FP2	Tested on devices	Nokia E70, Nokia N78
Category	Java ME	Subcategory	Graphics

Keywords (APIs, classes, methods, functions): javax.microedition.lcdui.Image.createRGBImage,javax.microedition.lcdui.Image

Overview

This code snippet demonstrates how to scale a bitmap in Java ME.

The source image may be included into the project as a resource. The method scaleImage() represents the main part of the functionality.

Source file: ScalingBitmaps.java

import java.io.IOException;
import javax.microedition.lcdui.Command;
import javax.microedition.lcdui.CommandListener;
import javax.microedition.lcdui.Display;
import javax.microedition.lcdui.Displayable;
import javax.microedition.lcdui.Form;
import javax.microedition.lcdui.Image;
import javax.microedition.midlet.MIDlet;
 
 
public class ScalingBitmaps extends MIDlet implements CommandListener {
 
    private Image image;
 
    private Command zoomIn;
    private Command zoomOut;
    private Command exitCommand;
 
    private Form form;
    private Display display;
 
    private double zoomFactor = 1.2;
 
    /**
     * Constructor. Constructs the object and initializes displayables.
     */
    public ScalingBitmaps() {
        try {
            image = Image.createImage("/image.png");
        } catch (IOException e) {
            //TODO: Handle exception.
        }
 
        form = new Form("Scale Bitmap");
        zoomIn = new Command("Zoom In", Command.OK, 1);
        zoomOut = new Command("Zoom Out", Command.OK, 2);
        exitCommand = new Command("Exit", Command.EXIT, 3);
 
 
        form.addCommand(zoomIn);
        form.addCommand(zoomOut);
        form.addCommand(exitCommand);
        form.setCommandListener(this);
 
        form.append(image);
 
        display = Display.getDisplay(this);
        display.setCurrent(form);
    }
 
    /**
     * From CommandListener.
     * Called by the system to indicate that a command has been invoked on a
     * particular displayable.
     * @param cmd the command that was invoked
     * @param displayable the displayable where the command was invoked
     */
    public void commandAction(Command cmd, Displayable displayable) {
        if (cmd == exitCommand) {
            notifyDestroyed();
        } else if (cmd == zoomOut) {
            image = scaleImage(image, (int)(image.getWidth() / zoomFactor), 
                                      (int)(image.getHeight() / zoomFactor));
            form.deleteAll();
            form.append(image);
        } else if (cmd == zoomIn) {
            image = scaleImage(image, (int)(image.getWidth() * zoomFactor), 
                                      (int)(image.getHeight() * zoomFactor));
            form.deleteAll();
            form.append(image);
        }
 
    }
 
    /**
     * Changes size of bitmap.
     * @param sourceImage source image.
     * @param newWidth width of new image.
     * @param newHeight height of new image.
     * @return scaled image.
     */
    private Image scaleImage(Image sourceImage, int newWidth, int newHeight) {
        //Remember image size.
        int oldWidth = sourceImage.getWidth();
        int oldHeight = sourceImage.getHeight();
 
        //Create buffer for input image.
        int[] inputData = new int[oldWidth * oldHeight];
        //Fill it with image data.
        sourceImage.getRGB(inputData, 0, oldWidth, 0, 0, oldWidth, oldHeight);
 
        //Create buffer for output image.
        int[] outputData = new int[newWidth * newHeight];
 
        int YD = (oldHeight / newHeight - 1) * oldWidth;
        int YR = oldHeight % newHeight;
        int XD = oldWidth / newWidth;
        int XR = oldWidth % newWidth;
        //New image buffer offset.
        int outOffset = 0;
        //Source image buffer offset.
        int inOffset = 0;
 
        for (int y = newHeight, YE = 0; y > 0; y--) {
            for (int x = newWidth, XE = 0; x > 0; x--) {
                //Copying pixel from old image to new.
                outputData[outOffset++] = inputData[inOffset];
                inOffset += XD;
                //Calculations for "smooth" scaling in x dimension.
                XE += XR;
                if (XE >= newWidth) {
                    XE -= newWidth;
                    inOffset++;
                }
            }
            inOffset += YD;
            //Calculations for "smooth" scaling in y dimension.
            YE += YR;
            if (YE >= newHeight) {
                YE -= newHeight;
                inOffset += oldWidth;
            }
        }
        //Create image from output buffer.
        return Image.createRGBImage(outputData, newWidth, newHeight, false);
    }
 
    /**
     * From MIDlet.
     * Called when the MIDlet is started.
     */
    public void startApp() {
        // No implementation required.
    }
 
    /**
     * From MIDlet.
     * Called to signal the MIDlet to enter the Paused state.
     */
    public void pauseApp() {
        // No implementation required.
    }
 
    /**
     * From MIDlet.
     * Called to signal the MIDlet to terminate.
     * @param unconditional whether the MIDlet has to be unconditionally
     * terminated
     */
    public void destroyApp(boolean unconditional) {
    }
}

Postconditions=

Image from a resource is displayed on screen. The user can change its size with the "Zoom In" and "Zoom Out" commands.

Supplementary material

You can view the source file and executable application in attached zip archive. The archive is available for download at Media:Scaling_bitmaps_in_J2ME.zip‎‎.