Unable to fully comprehend some php codes

Question

I am trying to use the following script to fit a paragraph into a box. I cannot understand the following parts of the script. It will be helpful if you explain these lines in brief. An earnest request to my fellow expert PHP developers.

$result .= ($result == '' ? '' : "\n") . $word;
$result .= ($result == '' ? '' : ' ') . $word;

Here is the complete script

//Fits a string into box with given width

function wrapText($string, $fontfile, $fontsize, $angle, $width)
{
    $result = '';
    $words = explode(' ', $string);
    foreach ($words as $word) {
        $teststring = $result . ' ' . $word;
        $testbox = imagettfbbox($fontsize, $angle, $fontfile, $teststring);
        if ($testbox[2] > $width) {
            $result .= ($result == '' ? '' : "\n") . $word;
        } else {
            $result .= ($result == '' ? '' : ' ') . $word;
        }
    }

    return $result;
}