Php image resize only width, auto-adjusting the height - php

Question

There is a system that reshapes images with php. I set the width value. I want it to get the height value automatically. In its current form, there is white space on the right side of some images. how can i lose this space. I want the height value to be scaled automatically.
public function resize(int $width = 0, int $height = 0, $default = '') {
if (!$this->width || !$this->height) {
return;
}
$xpos = 0;
$ypos = 0;
$scale = 1;
$scale_w = $width / $this->width;
$scale_h = 1;
if ($default == 'w') {
$scale = $scale_w;
} elseif ($default == 'h') {
$scale = $scale_h;
} else {
$scale = min($scale_w, $scale_h);
}
if ($scale == 1 && $scale_h == $scale_w && ($this->mime != 'image/png' && $this->mime != 'image/webp')) {
return;
}
$new_width = (int)($this->width * $scale);
$new_height = (int)($this->height * $scale);
$xpos = 0;
$ypos = 0;
$image_old = $this->image;
$this->image = imagecreatetruecolor($width, $new_height);
if ($this->mime == 'image/png') {
imagealphablending($this->image, false);
imagesavealpha($this->image, true);
$background = imagecolorallocatealpha($this->image, 255, 255, 255, 127);
imagecolortransparent($this->image, $background);
} else if ($this->mime == 'image/webp') {
imagealphablending($this->image, false);
imagesavealpha($this->image, true);
$background = imagecolorallocatealpha($this->image, 255, 255, 255, 127);
imagecolortransparent($this->image, $background);
} else {
$background = imagecolorallocate($this->image, 255, 255, 255);
}
imagefilledrectangle($this->image, 0, 0, $width, $new_height, $background);
imagecopyresampled($this->image, $image_old, $xpos, $ypos, 0, 0, $new_width, $new_height, $this->width, $this->height);
imagedestroy($image_old);
$this->width = $width;
$this->height = $new_height;
}

Answer 1

You are most likely missing the $default parameter, it should be 'w'.
As an example:
Let's say you have an image 128 x 128 and want to resize it to 256 (width), it should be scaled up to 256 x 256. The call looks like:
See how the resize scale is calculated:
$scale_w = $width / $this->width; // 256 / 128 = 2
$scale_h = 1;
if ($default == 'w') {
$scale = $scale_w; // = 2
} elseif ($default == 'h') {
$scale = $scale_h; // = 1
} else {
$scale = min($scale_w, $scale_h); // = 1
}
Without 'w' flag $scale becomes 1 and with 'w' flag it becomes 2 - the expected value.
Later on the algorithm uses $width several times instead of $new_width so the new image will be 256w x 128h instead of 128 x 128 due this line:
$this->image = imagecreatetruecolor($width, $new_height);
But imagecopyresampled uses $new_width so you end up with an 256w x 128h image, containing the original 128 x 128 image.