android-discuss, Scamble a Bitmap image

 I am new to android development. I have been asked to write an
function to scramble a bitmap image. A user can then enter a password
and the image will unscramble.

I have managed to write the following code that works but takes way to
long to execute due to the setPixels call.

I was thinking of an alternate solution of just drawing the original
unscrambled image and then making some sort of transparent overlay
bitmap with some sort of distortion effect. When the user enters the
correct password the overlay fades away.

Please help!

@Override
protected void onDraw(Canvas canvas)
{
        //Some of the variables are global but I left out that code. This
successfully runs.

                int w = bitmap.getWidth();
        int h = bitmap.getHeight();

        Bitmap scrambled = Bitmap.createBitmap(w, h,
Bitmap.Config.ARGB_8888);
        int[]pixels = new int[w*h];

        bitmap.getPixels(pixels, 0, w, 0, 0, w, h);

        int color = 0;
        Random random = new Random();

        Paint paint = new Paint();

        for (int i = 0; i < pixels.length; i++)
        {
                pixels[i] = pixels[random.nextInt(pixels.length - 1)];
        }

        scrambled.setPixels(pixels, 0, w, 0, 0, w, h);
        canvas.drawBitmap(scrambled, 0, 0, paint);
}

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