如何在J2ME程序里淡进减出显示图像

本例的代码取自我写的上阳图像处理演示程序（ImageAlbum），自己实现的方法，提供另一种思路。大家应该尽量使用系统内置的API

/*
 * blend方法由下边的作者所写，感谢他所做的工作
 *
 * By: Oscar Wivall Date: 2004-05-06
 *
 * Description: Create cool effects by fading in/out the images in MIDP 2.0.
 * This midlet shows how to change the alpha value of an Image. This MIDlet
 * is tested on Z1010 and K700.
 *
 * This method changes the alpha value of an image array. All the pixels in
 * the image contains Alpha, Red, Green, Blue (ARGB) colors where each of
 * the color is a value from 0 to 255. If Alpha is 255 the pixel will be
 * opaque, if its 0 the pixel is transparent. 0xFFFF0000 = 11111111 11111111
 * 00000000 00000000 - this is a red opaque pixel.
 *
 * To get the RGB values from the array we can use the AND '&' operator.
 * (11111101 & 01111110) = 01111100, only the 1:s where & = 1 will get
 * through.
 *
 * to change 11111111 to 11111111 00000000 00000000 00000000 we can use the
 * shift left operator '<<', (00000001 << 7) = 10000000 in dec (1<<7) =
 * 128
 *
 * To change the alpha value we loop through all the pixels in the image.
 *
 * With the blend method its also possible to mask and dontmask specific
 * colors.
 */
// raw是图像数据
public static void blend(int[] raw, int alphaValue, int maskColor,
                         int dontmaskColor) {
    int len = raw.length;

    // 开始循环，获得图像里每个像素的颜色，然后处理
    for (int i = 0; i < len; i++) {
        int a = 0;
        int color = (raw[i] & 0x00FFFFFF); // 获得像素的颜色
        if (maskColor == color) {
            a = 0;
        } else if (dontmaskColor == color) {
            a = 255;
        } else if (alphaValue > 0) {
            a = alphaValue; // 设置我们希望的alpha值 0-255.
        }

        a = (a << 24); // 把alpha左移24位（left shift the alpha value 24 bits)
        // if color = 00000000 11111111 11111111 00000000
        // and alpha= 01111111 00000000 00000000 00000000
        // then c+a = 01111111 11111111 11111111 00000000
        // and the pixel will be blended.
        color += a;
        raw[i] = color;
    }
}

public void run() {
    // System.out.println("Run IN");
    int stopIndex = 0;
    while (mTrucking) {
        if (mUpdate) {
            // 每循环一次改变一次alpha值 255=不透明, 0=透明
            if (mAlpha >= 255) {
                stopIndex++;
                // System.out.println(stopIndex);
                changeAlphaOff = changeAlphaOff * -1;
            } else if (mAlpha <= 0) {
                changeAlphaOff = changeAlphaOff * -1;
            }
            mAlpha += changeAlphaOff;
            // 使用ImageEffect里的blend方法来改变alphi值并且生成一个新的图象
            ImageEffect.blend(rawInt, mAlpha);
            image = Image.createRGBImage(rawInt, this.image.getWidth(),
                                         this.image.getHeight(), true);

            repaint();
            if (stopIndex == 2) {
                // System.out.println(this.mAlpha);
                // System.out.println(this.changeAlphaOff);
                this.mAlpha = 255;
                this.changeAlphaOff = 15;
                break;
            }

            // mUpdate = false;
        }
    }
    ImageEffect.blend(rawInt, mAlpha);
    image = Image.createRGBImage(rawInt, this.image.getWidth(), this.image
                                 .getHeight(), true);
    repaint();
    // System.out.println("Run OUT");
}

转自: http://blog.csdn.net/the3gwireless