Retrieving and setting pixels individually - php

Question

I'm trying to re-create a script I made in JavaScript; it bends an image by changing each pixels positions. I'm currently trying to port this to PHP, except when retrieving pixels and setting them, it doesn't appear correctly (I currently dont change the pixel locations). Below is my attempt:
<?php
header ('Content-Type: image/png');
$url = "https://www.google.co.uk/images/branding/googlelogo/1x/googlelogo_color_272x92dp.png";
list($width, $height, $type, $attr) = getimagesize($url);
$original = imagecreatefrompng($url); //Google's logo
$image = imagecreate($width, $height); // our new image
//loop through all pixels..
for ($x = 0;$x<$width;$x++){
for ($y = 0;$y<$height;$y++){
$rgb = imagecolorat($original, $x,$y); //get colour data from $x $y coordinates
$r = ($rgb >> 16) & 0xFF;
$g = ($rgb >> 8) & 0xFF;
$b = $rgb & 0xFF;
imagesetpixel($image,$x,$y,imagecolorallocate($image,$r,$g,$b));
//set pixel data on our new image at the same location with the same data
}
}
//retain a PNG's transparency
imagecolortransparent($image, imagecolorallocatealpha($image, 0, 0, 0, 127));
imagealphablending($image, false);
imagesavealpha($image, true);
imagepng($image);
imagedestroy($image);
imagedestroy($original);
?>
Here you can see (for testing purposes) I am using Google's logo, and im attempting to re-draw it pixel by pixel.. Below is the result. For some reason it only generates a very small portion of the image.. Any ideas?
Edit:
Here's the solution. As there isn't support for transparency using imagecreatetruecolor() I instead fill the image first with a white rectangle (if there is a solution for transparency, please create an answer).
<?php
header ('Content-Type: image/png');
$url = "https://www.google.co.uk/images/branding/googlelogo/1x/googlelogo_color_272x92dp.png";
list($width, $height, $type, $attr) = getimagesize($url);
$source = imagecreatefrompng($url);
$image = imagecreatetruecolor($width, $height);
imagefilledrectangle($image, 0, 0, $width-1, $height-1, imagecolorallocatealpha($image, 255,255,255,0));
//fill with white rectangle to look transparent, but note that it isn't. Changing alpha channel merely shows
//a black background.
for ($x = 0;$x<$width;$x++){
for ($y = 0;$y<$height;$y++){
$rgb = imagecolorat($source, $x,$y);
$r = ($rgb >> 16) & 0xFF;
$g = ($rgb >> 8) & 0xFF;
$b = $rgb & 0xFF;
$colors = imagecolorsforindex($image, $rgb);
imagesetpixel($image,$x,$y,imagecolorallocatealpha($image,$colors["red"],$colors["green"],$colors["blue"],$colors["alpha"]));
//getting alpha from pixels for a real 'copy'
}
}
imagepng($image);
imagedestroy($image);
imagedestroy($source);
?>