MIDP 圖片透明度漸變效果實作：像素級 Alpha 動畫

效果描述

將一張不透明圖片從完全透明（Alpha=0）逐漸變為原始不透明度（Alpha=255），產生淡入動畫。核心同「MIDP 2.0 圖片像素操作」一文的案例一，此處精簡呈現關鍵邏輯。

核心程式碼

public class ShadowMIDlet extends MIDlet {
    Canvas c = new ShadowCanvas();
    protected void startApp() { Display.getDisplay(this).setCurrent(c); }
    protected void pauseApp() {}
    protected void destroyApp(boolean u) {}
}

class ShadowCanvas extends Canvas implements Runnable {
    int w, h;
    Image srcImage;
    int[] srcRgb, shadowRgb;
    int imgW, imgH, count;

    public ShadowCanvas() {
        w = getWidth(); h = getHeight();
        try { srcImage = Image.createImage("/av.png"); }
        catch (IOException e) { e.printStackTrace(); }
        imgW = srcImage.getWidth(); imgH = srcImage.getHeight();
        srcRgb = new int[imgW * imgH];
        srcImage.getRGB(srcRgb, 0, imgW, 0, 0, imgW, imgH);
        shadowRgb = new int[srcRgb.length];
        System.arraycopy(srcRgb, 0, shadowRgb, 0, shadowRgb.length);
        // 全透明初始化
        for (int i=0;i