谁能解释这个加扰功能是如何工作的？

I'm working with a function taken from Corrupt (a web based piece of software used to get "glitchy" effects using jpeg images). This function can be found in the corrupt.php file on line 23. At the moment it's not making the files glitchy enough. I made this images to show you how I want the images to look. This was made by opening the jpeg in a text editor and cutting certain lines and pasting them in other places.

I want this function to do a similar thing but at the moment it doesn't. Any ideas? Is there a better way of doing this maybe?

function scramble($content, $size) {
    $sStart = 10;
    $sEnd = $size-1;
    $nReplacements = rand(1, 30);

    for($i = 0; $i < $nReplacements; $i++) {
        $PosA = rand($sStart, $sEnd);
        $PosB = rand($sStart, $sEnd);

        $tmp = $content[$PosA];
        $content[$PosA] = $content[$PosB];
        $content[$PosB] = $tmp;
    }

    return($content);
}

It is randomly swapping information around in the data arrays loaded from your image. This causes a valid image to come out with invalid image information in some sectors. Also, image files sometimes contain additional information at the front/end of the file; this does not look like it takes that into account and could corrupt that information as well.

To increase the amount of swaps you will want to increase the number of replacements. The bit of code you are particularly interested in is rand(1, 30);; I would suggest increasing the minimum amount of scramble first and then the upper range if you still do not get the desired effect.

The function does random swaps between the elements of the array. The number of swaps is a randomly generated number from 1 to 30.