Android 倒影

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private Bitmap revertBitmap() {
    //1.倒立图
    Matrix matrix = new Matrix();
    matrix.preScale(1, -1);   //以X轴向下翻转
    int width = mSourceBitmap.getWidth();
    int height = mSourceBitmap.getHeight();

    //生成倒立图，宽度和原图一致，高度为原图的一半
    mRevertBitmap = Bitmap.createBitmap(mSourceBitmap, 0, height / 2, width, height / 2, matrix, false);

    //2.要生成原图加上倒立图，先生成一个可变空的Bitmap, 高度为原图高度的1.5倍（包括原图和倒立图的高度）
    int gap = 10; //间隙空白
    Bitmap bitmap = Bitmap.createBitmap(width, height + height / 2, Bitmap.Config.ARGB_8888);
    Paint paint = new Paint();
    Canvas canvas = new Canvas(bitmap);
    canvas.drawBitmap(mSourceBitmap, 0, 0, paint);  //绘制原图
    canvas.drawBitmap(mRevertBitmap, 0, height + gap, paint);  //绘制倒立图

    //3.画笔使用LinearGradient 线性渐变渲染
    LinearGradient lg = new LinearGradient(0, height + gap, width, bitmap.getHeight(), 0xabff0000, 0x00ffff00, Shader.TileMode.MIRROR);
    paint.setShader(lg);

    //4.指定画笔的Xfermode 即绘制的模式（不同的模式，绘制的区域不同）
    paint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.DST_ATOP));

    //5.在倒立图区，绘制矩形渲染图层
    canvas.drawRect(0, height + gap, width, bitmap.getHeight(), paint);
    paint.setXfermode(null);
    return bitmap;
}