Fill png transparency with background color - php

Question

I'm refactoring an old image crop/resize library i wrote about 5 years ago and i'm stuck trying to restore one of it's functionalities. The funny part is that i'm not even sure it worked back then since i probably never actually used it.
I need to be able to work on png images while keeping transparency (which works), but i also wan't to be able to fill the transparent part of the image with a color.
Creating a blank image and filling it with a color works fine, but when i try to paste my png over it, the background is transparent again.
Here's a simplified version of my code:
<?php
$src = imagecreatefrompng($pathToSomePngFile);
imagealphablending($src, false);
imagesavealpha($src, true);
$output = imagecreatetruecolor($width, $height);
if ($backgroundColor) {
$fillColor = imagecolorallocate(
$output,
$backgroundColor['r'],
$backgroundColor['g'],
$backgroundColor['b']
);
imagefilledrectangle(
$output,
0,
0,
$width,
$height,
$fillColor
);
} else {
imagealphablending($output, false);
imagesavealpha($output, true);
}
imagecopyresampled(
$output,
$src,
0,
0,
0,
0,
$width,
$height,
$width,
$height
);
imagepng($output, $pathToWhereImageIsSaved);
UPDATE
Updated with delboy1978uk's solution to get it to work without changing my other settings.

Answer 1

Something like this should work.
<?php
// open original image
$img = imagecreatefrompng($originalTransparentImage);
$width = imagesx($img);
$height = imagesy($img);
// make a plain background with the dimensions
$background = imagecreatetruecolor($width, $height);
$color = imagecolorallocate($background, 127, 127, 127); // grey background
imagefill($background, 0, 0, $color);
// place image on top of background
imagecopy($background, $img, 0, 0, 0, 0, $width, $height);
//save as png
imagepng($background, '/path/to/new.png', 0);