Inconsistent Results with imagettfbbox

[oleibman]

Description

The following code (run in a directory containing FreeMono.ttf) gives different results on Linux vs Windows:

<?php
$fontFileName = realpath(__DIR__ . DIRECTORY_SEPARATOR . 'FreeMono.ttf');
var_dump(md5_file($fontFileName)); // to show using same file
var_dump(imagettfbbox(10.0, 0.0, $fontFileName, 'Hello'));

Resulted in this output on Windows:

C:\git\ExactFont\testfont.php:3:
string(32) "ec48e99df5d46035b62ef0d825b43336"
C:\git\ExactFont\testfont.php:4:
array(8) {
  [0] =>
  int(0)
  [1] =>
  int(0)
  [2] =>
  int(39)
  [3] =>
  int(0)
  [4] =>
  int(39)
  [5] =>
  int(-9)
  [6] =>
  int(0)
  [7] =>
  int(-9)
}

But I got this output on a Linux Ubuntu system:

C:\git\ExactFont\testfont.php:3:
string(32) "ec48e99df5d46035b62ef0d825b43336"
C:\git\ExactFont\testfont.php:4:
array(8) {
  [0] =>
  int(0)
  [1] =>
  int(1)
  [2] =>
  int(41)
  [3] =>
  int(1)
  [4] =>
  int(41)
  [5] =>
  int(-9)
  [6] =>
  int(0)
  [7] =>
  int(-9)
}

PHP Version

7.4.3 and 8.1.8 on Linux; 7.4.26 and 8.0.13 and 8.1.0 on Windows

Operating System

Ubuntu 20.04.4 LTS; Windows 10 Enterprise 19044.1826

[oleibman]

And with PHP 8.1.8 on the same Linux Ubuntu system, I get a 3rd result:

/media/sf_git/ExactFont/testfont.php:3:
string(32) "ec48e99df5d46035b62ef0d825b43336"
/media/sf_git/ExactFont/testfont.php:4:
array(8) {
  [0] =>
  int(0)
  [1] =>
  int(0)
  [2] =>
  int(40)
  [3] =>
  int(0)
  [4] =>
  int(40)
  [5] =>
  int(-8)
  [6] =>
  int(0)
  [7] =>
  int(-8)
}
``

[cmb69]

This is most likely due to different versions of libgd. On Windows, usually the bundled libgd is used, while other systems usually use a system libgd. So you should check the versions (e.g. see phpinfo()). Note that "bundled (2.1.0 compatible)" isn't quite right; the bundled libgd contains a lot of newer stuff (than libgd 2.1.0).

Also note that the exact behavior depends on the libfreetype version, too. So also check its version.

[oleibman]

Thank you. As you conjectured, Windows is using "gd bundled (2.1.0 compatible)" and "Freetype 2.9.1"; Linux "gd 2.3.3" but phpinfo doesn't reveal its libFreeType version.

[cmb69]

Linux "gd 2.3.3" but phpinfo doesn't reveal its libFreeType version.

Ah, right; if ext/gd is built against a system libgd, it doesn't know the libfreetype version.

Anyhow, I don't think there is much we can do. A couple of years ago there has been a relevant fix for the bundled libgd, but that has not been backported to upstream libgd, because especially these implementations had diverged earlier. While we could update to use the upstream implementation, I'd be a bit sorry about the lost fix, and the long term goal is to unbundle libgd anyway (we need to wait for libgd/libgd#692, though).

I tend to close this ticket as WONTFIX.