[Ubuntu] PHP, GD and imagerotate() function

The GD library released by the ubuntu team and available in their repository, is not compiled with all options. The imagerotate() function doesn't work at all.

In this case you have two possibilities. Download the sources from the GD official web site and compile it on your own, or use the following function.

<?
// $src_img - a GD image resource
// $angle - degrees to rotate clockwise, in degrees
// returns a GD image resource
// USAGE:
// $im = imagecreatefrompng('test.png');
// $im = imagerotate($im, 15);
// header('Content-type: image/png');
// imagepng($im);
function imageRotateBicubic($src_img, $angle, $bicubic=false) {
  
    // convert degrees to radians
    $angle = $angle + 180;
    $angle = deg2rad($angle);
  
    $src_x = imagesx($src_img);
    $src_y = imagesy($src_img);
  
    $center_x = floor($src_x/2);
    $center_y = floor($src_y/2);
  
    $rotate = imagecreatetruecolor($src_x, $src_y);
    imagealphablending($rotate, false);
    imagesavealpha($rotate, true);

    $cosangle = cos($angle);
    $sinangle = sin($angle);
  
    for ($y = 0; $y < $src_y; $y++) {
      for ($x = 0; $x < $src_x; $x++) {
    // rotate...
    $old_x = (($center_x-$x) * $cosangle + ($center_y-$y) * $sinangle)
      + $center_x;
    $old_y = (($center_y-$y) * $cosangle - ($center_x-$x) * $sinangle)
      + $center_y;
  
    if ( $old_x >= 0 && $old_x < $src_x
         && $old_y >= 0 && $old_y < $src_y ) {
      if ($bicubic == true) {
        $sY  = $old_y + 1;
        $siY  = $old_y;
        $siY2 = $old_y - 1;
        $sX  = $old_x + 1;
        $siX  = $old_x;
        $siX2 = $old_x - 1;
      
        $c1 = imagecolorsforindex($src_img, imagecolorat($src_img, $siX, $siY2));
        $c2 = imagecolorsforindex($src_img, imagecolorat($src_img, $siX, $siY));
        $c3 = imagecolorsforindex($src_img, imagecolorat($src_img, $siX2, $siY2));
        $c4 = imagecolorsforindex($src_img, imagecolorat($src_img, $siX2, $siY));
      
        $r = ($c1['red']  + $c2['red']  + $c3['red']  + $c4['red']  ) << 14;
        $g = ($c1['green'] + $c2['green'] + $c3['green'] + $c4['green']) << 6;
        $b = ($c1['blue']  + $c2['blue']  + $c3['blue']  + $c4['blue'] ) >> 2;
        $a = ($c1['alpha']  + $c2['alpha']  + $c3['alpha']  + $c4['alpha'] ) >> 2;
        $color = imagecolorallocatealpha($src_img, $r,$g,$b,$a);
      } else {
        $color = imagecolorat($src_img, $old_x, $old_y);
      }
    } else {
          // this line sets the background colour
      $color = imagecolorallocatealpha($src_img, 255, 255, 255, 127);
    }
    imagesetpixel($rotate, $x, $y, $color);
      }
    }
    return $rotate;
}
?>

This function has been taken by the official man page of the imagerotate php funciont.