正文
我们知道，在MIDP1.0中，除非我们利用特定厂商的API(比如Nokia),我们是没法对图片的像素进行操作的，但是在MIDP2.0中,Image和Graphics的功能都大大增强了。比如，我们可以获取Image的所有像素值,然后利用程序来修改这些像素(比如说ARGB各自的值),最后再把修改后的像素图绘制出来。通过直接操作图片像素，我们就获得了一种很强大的能力，用编程的方式实现出很多有趣的效果来，而不用额外制作新图片。比如说透明度渐变，颜色反转等。下面就是2个例子，分别实现透明度渐变和颜色反转的功能。
例题一: 透明度渐变效果的实现
给定一张图片，假如我们想实现这么一种效果:图片由全透明状态逐渐清晰，最后达到正常状态。要实现这一个过程，我们首先要获取该图片的所有像素值，逐步让这些像素的alpha值从0转变到正常，每改变图片的所有像素值一次，我们就请求刷屏一次,把最新的像素图画出来，这样我们就能实现透明度渐变的效果了。代码实现如下:
import java.io.IOException;
import javax.microedition.lcdui.Canvas;
import javax.microedition.lcdui.Display;
import javax.microedition.lcdui.Graphics;
import javax.microedition.lcdui.Image;
import javax.microedition.midlet.MIDlet;
import javax.microedition.midlet.MIDletStateChangeException;
/**
*
* @author Jagie
*
*/
public class ShadowMIDlet extends MIDlet {
Canvas c = new ShadowCanvas();
public ShadowMIDlet() {
}
PRotected void startApp() throws MIDletStateChangeException {
Display.getDisplay(this).setCurrent(c);
}
protected void pauseApp() {
// TODO Auto-generated method stub
}
protected void destroyApp(boolean arg0) throws MIDletStateChangeException {
// TODO Auto-generated method stub
}
}
/**
*
* @author Jagie
*
*/
class ShadowCanvas extends Canvas implements Runnable {
int w, h;
// 原始图片
Image srcImage;
// 原始图片的像素数组
int[] srcRgbImage;
// 渐变图片的像素数组
int[] shadowRgbImage;
int imgWidth, imgHeight;
int count;
public ShadowCanvas() {
w = this.getWidth();
h = this.getHeight();
try {
srcImage = Image.createImage("/av.png");
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
imgWidth = srcImage.getWidth();
imgHeight = srcImage.getHeight();
// 制造原始图片的像素数组，用一个int来代表每一个像素,按位表示方式是:0xAARRGGBB
srcRgbImage = new int[imgWidth * imgHeight];
// 获取原始图片的所有像素，参见MIDP APPI文档
srcImage.getRGB(srcRgbImage, 0, imgWidth, 0, 0, imgWidth, imgHeight);
shadowRgbImage = new int[srcRgbImage.length];
System.arraycopy(srcRgbImage, 0, shadowRgbImage, 0,
shadowRgbImage.length);
// 渐变图片的所有像素已开始都是全透明的
for (int i = 0; i < shadowRgbImage.length; i++) {
shadowRgbImage[i] &= 0x00ffffff;
}
new Thread(this).start();
}
public void paint(Graphics g) {
g.setColor(0, 0, 0);
g.fillRect(0, 0, w, h);
// 绘制渐变图片
g.drawRGB(shadowRgbImage, 0, imgWidth, (w - imgWidth) / 2,
(h - imgHeight) / 2, imgWidth, imgHeight, true);
g.setColor(0, 255, 0);
g.drawString("count=" + count, w / 2, 30, Graphics.HCENTER
Graphics.TOP);
}
public void run() {
while (true) {
boolean changed = false;
// 改变渐变图片的每一个像素
for (int i = 0; i < shadowRgbImage.length; i++) {
// 获取渐变图片的某一像素的alpha值
int alpha = (shadowRgbImage[i] & 0xff000000) >>> 24;
// 原始图片的对应像素的alpha值
int oldAlpha = (srcRgbImage[i] & 0xff000000) >>> 24;
if (alpha < oldAlpha) {
// alpha值++
shadowRgbImage[i] = ((alpha + 1) << 24)
(shadowRgbImage[i] & 0x00ffffff);
changed = true;
}
}
try {
Thread.sleep(10);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
count++;
repaint();
// 当所有像素的alpha值都达到原始值后,线程运行结束
if (!changed) {
System.out.println("over");
break;
}
}
}
}
透明度渐变效果如下:
例题二:颜色反转
在手机游戏中,我们经常会碰上这样一种情况,比如我方飞机和敌方飞机外观是完全一样的，唯一的区别就是颜色不同，比如说敌方飞机是红色的，而我方飞机是绿色的。在MIDP1.0中，我们就只好制作2张图片来表示2种飞机，自然，这样会造成jar空间的极大浪费。但是在MIDP2.0中，通过对图片直接进行像素操作，反转RGB中的一个值，我们只需要一张图片就够了，样例代码如下:
ColorMIDlet.java
import java.io.IOException;
import javax.microedition.lcdui.Canvas;
import javax.microedition.lcdui.Display;
import javax.microedition.lcdui.Graphics;
import javax.microedition.lcdui.Image;
import javax.microedition.midlet.MIDlet;
import javax.microedition.midlet.MIDletStateChangeException;
/**
*
* @author Jagie
*
*/
public class ColorMIDlet extends MIDlet {
Canvas c = new ColorCanvas();
public ColorMIDlet() {
super();
// TODO Auto-generated constrUCtor stub
}
protected void startApp() throws MIDletStateChangeException {
Display.getDisplay(this).setCurrent(c);
}
protected void pauseApp() {
// TODO Auto-generated method stub
}
protected void destroyApp(boolean arg0) throws MIDletStateChangeException {
// TODO Auto-generated method stub
}
}
/**
*
* @author Jagie
*
*/
class ColorCanvas extends Canvas {
Image srcImage;
int[] targetImage1;
int[] targetImage2;
public ColorCanvas() {
try {
srcImage = Image.createImage("/av.png");
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
targetImage1 = GraphicsUtil.flipImageColor(srcImage,
GraphicsUtil.SHIFT_RED_TO_BLUE);
targetImage2 = GraphicsUtil.flipImageColor(srcImage,
GraphicsUtil.SHIFT_RED_TO_GREEN);
}
public void paint(Graphics g) {
g.setColor(0, 0, 0);
g.fillRect(0, 0, this.getWidth(), this.getHeight());
g.setColor(0x00ff00);
g.drawString("origin:", getWidth() / 2, 0, Graphics.TOP
Graphics.HCENTER);
g.drawImage(srcImage, 30, 20, Graphics.LEFT Graphics.TOP);
g.drawString("SHIFT_RED_TO_BLUE:", getWidth() / 2,
srcImage.getHeight() + 20, Graphics.TOP Graphics.HCENTER);
g.drawRGB(targetImage1, 0, srcImage.getWidth(), 30, srcImage
.getHeight() + 40, srcImage.getWidth(), srcImage.getHeight(),
true);
g.drawString("SHIFT_RED_TO_GREEN:", getWidth() / 2, srcImage
.getHeight() * 2 + 40, Graphics.TOP Graphics.HCENTER);
g.drawRGB(targetImage2, 0, srcImage.getWidth(), 30, srcImage
.getHeight() * 2 + 60, srcImage.getWidth(), srcImage
.getHeight(), true);
}
}
GraphicsUtil.java
import javax.microedition.lcdui.Image;
/**
*
* @author Jagie
*
*/
public class GraphicsUtil {
public static final int SHIFT_RED_TO_GREEN = 0;
public static final int SHIFT_RED_TO_BLUE = 1;
public static final int SHIFT_GREEN_TO_BLUE = 2;
public static final int SHIFT_GREEN_TO_RED = 3;
public static final int SHIFT_BLUE_TO_RED = 4;
public static final int SHIFT_BLUE_TO_GREEN = 5;
public static int[] flipImageColor(Image source, int shiftType) {
// we start by getting the image data into an int array - the number
// of 32-bit ints is equal to the width multiplied by the height
int[] rgbData = new int[(source.getWidth() * source.getHeight())];
source.getRGB(rgbData, 0, source.getWidth(), 0, 0, source.getWidth(),
source.getHeight());
// now go through every pixel and adjust it's color
for (int i = 0; i < rgbData.length; i++) {
int p = rgbData[i];
// split out the different byte components of the pixel by
// applying
// a mask so we only get what we need, then shift it to make it
// a normal number we can play around with
int a = ((p & 0xff000000) >> 24);
int r = ((p & 0x00ff0000) >> 16);
int g = ((p & 0x0000ff00) >> 8);
int b = ((p & 0x000000ff) >> 0);
int ba = a, br = r, bb = b, bg = g; // backup copies
// flip the colors around according to the Operation required
switch (shiftType) {
case SHIFT_RED_TO_GREEN:
g = r;
r = bg;
break;
case SHIFT_RED_TO_BLUE:
b = r;
r = bb;
break;
case SHIFT_GREEN_TO_BLUE:
g = b;
b = bg;
break;
case SHIFT_GREEN_TO_RED:
g = r;
r = bg;
break;
case SHIFT_BLUE_TO_RED:
b = r;
r = bb;
break;
case SHIFT_BLUE_TO_GREEN:
b = g;
g = bb;
break;
}
// shift all our values back in
rgbData[i] = (a << 24) (r << 16) (g << 8) b;
}
return rgbData;
}
}
（出处：http://www.knowsky.com）
