About that rotating function by david at horizon-nigh not working, I found the bug.
I noticed that the x1 and y1 where not used, so, in the loop through every pixel and transform it, change

$x2 = $x * cos($theta) - $y * sin($theta);
$y2 = $x * sin($theta) + $y * cos($theta);

to:
           
$x2 = $x1 * cos($theta) - $y1 * sin($theta);
$y2 = $x1 * sin($theta) + $y1 * cos($theta);