Image_GD::_do_rotate PHP Method

    protected function _do_rotate($degrees)
    {
        if (!function_exists('imagerotate')) {
            throw new CException('This method requires imagerotate, which is only available in the bundled version of GD');
        }
        // Loads image if not yet loaded
        $this->_load_image();
        // Transparent black will be used as the background for the uncovered region
        $transparent = imagecolorallocatealpha($this->_image, 0, 0, 0, 127);
        // Rotate, setting the transparent color
        $image = imagerotate($this->_image, 360 - $degrees, $transparent, 1);
        // Save the alpha of the rotated image
        imagesavealpha($image, TRUE);
        // Get the width and height of the rotated image
        $width = imagesx($image);
        $height = imagesy($image);
        if (imagecopymerge($this->_image, $image, 0, 0, 0, 0, $width, $height, 100)) {
            // Swap the new image for the old one
            imagedestroy($this->_image);
            $this->_image = $image;
            // Reset the width and height
            $this->width = $width;
            $this->height = $height;
        }
    }