In response to pilot at myupb dot com on 31-May-2008 02:23
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I am not sure why you would be defining your own PI, instead of using the built-in constant, and why you do the degrees to radian conversion manually. There might be a speed issue, however here is the exact same code with that small difference.

<?php
if(!function_exists("imagerotate")) {
    function imagerotate(&$srcImg, $angle, $transparentColor = null) {
        $srcw = imagesx($srcImg);
        $srch = imagesy($srcImg);
       
        if($angle == 0) return $srcImg;
       
        // Convert the angle to radians
        $theta = deg2rad ($angle);
       
        // Get the origin (center) of the image
        $originx = $srcw / 2;
        $originy = $srch / 2;
       
        // The pixels array for the new image
        $pixels = array();
        $minx = 0;
        $maxx = 0;
        $miny = 0;
        $maxy = 0;
        $dstw = 0;
        $dsth = 0;
       
        // Loop through every pixel and transform it
        for($x=0;$x<$srcw;$x++) {
            for($y=0;$y<$srch;$y++) {
                list($x1, $y1) = translateCoordinate($originx, $originy, $x, $y, false);
               
                $x2 = $x * cos($theta) - $y * sin($theta);
                $y2 = $x * sin($theta) + $y * cos($theta);
               
                // Store the pixel color
                $pixels[] = array($x2, $y2, imagecolorat($srcImg, $x, $y));
               
                // Check our boundaries
                if($x2 > $maxx) $maxx = $x2;
                if($x2 < $minx) $minx = $x2;
                if($y2 > $maxy) $maxy = $y2;
                if($y2 < $miny) $miny = $y2;
            }
        }
       
        // Determine the new image size
        $dstw = $maxx - $minx + 1;
        $dsth = $maxy - $miny + 1;
       
        // Create our new image
        $dstImg = imagecreatetruecolor($dstw, $dsth);
       
        // Fill the background with our transparent color
        if($transparentColor == null) $transparentColor = imagecolorallocate($dstImg, 1, 2, 3);
        imagecolortransparent($dstImg, $transparentColor);
        imagefilledrectangle($dstImg, 0, 0, $dstw + 1, $dsth + 1, $transparentColor);
       
        // Get the new origin
        $neworiginx = -$minx;
        $neworiginy = -$miny;
       
        // Fill in the pixels
        foreach($pixels as $data) {
            list($x, $y, $color) = $data;
            list($newx, $newy) = translateCoordinate($neworiginx, $neworiginy, $x, $y);
            imagesetpixel($dstImg, $newx, $newy, $color);
        }
       
        return $dstImg;
    }
   
    /**
     * Translates from mathematical coordinate system to computer coordinate system using
     * origin coordinates from the computer system or visa versa
     *
     * @param int $originx
     * @param int $originy
     * @param int $x
     * @param int $y
     * @param bool $toComp
     * @return array(int $x, int $y)
     */
    function translateCoordinate($originx, $originy, $x, $y, $toComp=true) {
        if($toComp) {
            $newx = $originx + $x;
            $newy = $originy - $y;
        } else {
            $newx = $x - $originx;
            $newy = $originy - $y;
        }
       
        return array($newx, $newy);
    }
}
?>