j2me中drawRGB()步骤的用法

import javax.microedition.midlet.*;import javax.microedition.lcdui.*;public class AlphaBlending extends MIDlet implements CommandListener {        private Display display;    private Form. form;    private Command exitCommand;    private Command startCommand;    private Command backCommand;    private AlphaCanvas alphaCanvas;        private static final String IMAGE_NAME = "/image.png";            public AlphaBlending() {        display = Display.getDisplay(this);        exitCommand = new Command("Exit", Command.EXIT, 2);        startCommand = new Command("Start", Command.SCREEN, 1);        backCommand = new Command("Back", Command.BACK, 1);        alphaCanvas = new AlphaCanvas(IMAGE_NAME);        form. = new Form("Alpha Blending Demo");        form.append(new StringItem(null, "Press 'Start' to run demo."));        form.addCommand(exitCommand);        form.addCommand(startCommand);        form.setCommandListener(this);    }            public void startApp() {        display.setCurrent(form);    }            public void pauseApp() {}            public void destroyApp(boolean unconditional) {}            public void commandAction(Command c, Displayable d) {        if (c == exitCommand) {            destroyApp(false);            notifyDestroyed();        }else if (c == startCommand) {            display.setCurrent(alphaCanvas);            alphaCanvas.addCommand(backCommand);            alphaCanvas.setCommandListener(this);                        Thread t = new Thread(alphaCanvas);            t.start();        }else if (c == backCommand) {                        display.setCurrent(form);        }    }        } import javax.microedition.midlet.*;import javax.microedition.lcdui.*;import java.io.*;public class AlphaCanvas extends Canvas implements Runnable {        private Image backgroundImage;    private int[] maskArray;    private int imageWidth;    private int imageHeight;    private int x;    private int y;    private int maskHeight = 0;        public AlphaCanvas(String imageName) {        //create the background image        try {            backgroundImage = Image.createImage(imageName);        }catch(IOException ioe) {            ioe.printStackTrace() ;        }        imageWidth = backgroundImage.getWidth();        imageHeight = backgroundImage.getHeight();                //create a semi-transparent red mask to cover the background image        maskArray = new int[imageWidth*imageHeight];        for (int i = 0; i < imageWidth*imageHeight; i++) {            maskArray[i] = 0x11FFF000;//alpha coefficient set to 0.3        }                x = (getWidth() - imageWidth)/2;        y = (getHeight() - imageHeight)/2;    }        public void paint(Graphics g) {        g.setColor(255, 255, 255);        g.fillRect(0, 0, getWidth(), getHeight());//paint Canvas background white        g.drawImage(backgroundImage, x, y, Graphics.TOP|Graphics.LEFT);                //render the semi-transparent mask        if (maskHeight != 0){            g.drawRGB(maskArray, 0, imageWidth, x, y, imageWidth, maskHeight, true);        }    }        public void run() {        for(int i = 1; i <= imageHeight; i++) {            maskHeight = i;            repaint();            try {                Thread.sleep(50);            }catch(InterruptedException ie) {}        }    }    }

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