Nette\Utils\Image::resize alpha broken (black background)

[josefsabl]

Version:

• Nette/Utils v3.0.1
• PHP 7.3.8 (https://windows.php.net/download/)

GD Support	enabled
GD Version	bundled (2.1.0 compatible)
FreeType Support	enabled
FreeType Linkage	with freetype
FreeType Version	2.9.1
GIF Read Support	enabled
GIF Create Support	enabled
JPEG Support	enabled
libJPEG Version	9 compatible
PNG Support	enabled
libPNG Version	1.6.34
WBMP Support	enabled
XPM Support	enabled
libXpm Version	30512
XBM Support	enabled
WebP Support	enabled

But the same bug can be observed on a production machine with Ubuntu Linux:

GD Support	enabled
GD headers Version	2.2.5
GD library Version	2.2.5
FreeType Support	enabled
FreeType Linkage	with freetype
FreeType Version	2.8.1
GIF Read Support	enabled
GIF Create Support	enabled
JPEG Support	enabled
libJPEG Version	8
PNG Support	enabled
libPNG Version	1.6.34
WBMP Support	enabled
XPM Support	enabled
libXpm Version	30411
XBM Support	enabled
WebP Support	enabled

Bug Description

This (czech language) looks to be an evergreen. I am able to reproduce it with the latest version of package with the EXACT flag and PNG type. However I am positive that I also saw this with WEBP (as I originally had the problem with WEBP and switched to PNG to fix it, it actually helped ! For some time though and now it appeared again!? WTF.)

Steps To Reproduce

\Nette\Utils\Image::fromFile(__DIR__ . '/input.png')
    ->resize(100, 100, \Nette\Utils\Image::EXACT)
    ->save(__DIR__ . '/output.png', null, \Nette\Utils\Image::PNG);

- but also "not works" with other images so I guess it is not the problem with the file.

Expected Behavior

Image with transparency preserved.

Possible Solution

I traced the problem down to this line $this->image = imagecrop($this->image, $r);. Commenting it out fixes the alpha problem, but the image is not cropped, obviously :-)

[josefsabl]

I can confirm that this hack works. I am having this issue on Windows as well as in production on Linux Ubuntu.

[JanTvrdik]

What is you GD version and how is the GD installed (bundled / not-bundled)?

[josefsabl]

What is you GD version and how is the GD installed (bundled / not-bundled)?

I updated the initial post.