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20 years ago
Here's a neat function for those of us who don't have imagerotate() on our servers.  It's based on a comment from ron at korving dot demon dot nl on the manual page for imagecopyresampled.



I'm still not 100% on coping with transparency, but this function seems to cope okay.  It doesn't resize to fit within bounds, it just rotates and you lose anything outside the image box.  



The bicubic mode is slooow.



If you want to be able to change the background colour, pass in a colour and use it where indicated.  The line I used just sets it transparent.



<?php

// $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;

}

?>
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