imagerotate will turn the picture all black, when rotated 90

[xuncanzhe]

Description

When using imagerotate to rotate the barcode image, setting the rotation angle to 90 will cause the image to be completely filled with black. but angle 90.01 is working

The following code:

<?php
$img_debug = imagecreatefrompng("D:/7701202301090006.png");
$img_debug = imagerotate($img_debug, 90.00, 0, -1);
imagepng($img_debug, "D:/output.png");

PHP Version

PHP 7.3.4

Operating System

windows

[nielsdos]

I can't reproduce this on my system with PHP 8.1+.
Also please note that your PHP version is outdated and longer supported. It could be possible that the bug you are encountering was fixed in more recent versions of PHP.

[KapitanOczywisty]

If image uses transparency you may need to thinker with alpha options e.g.

imagealphablending($img_debug, false);
imagesavealpha($img_debug, true);

It would be helpful if you can share image which causes this issue.

[xuncanzhe]

I'm using php 8.2.3 version again and the problem still exists. Attached is an image of what I tested. The strange thing is that its economy is only abnormal when rotates is 90.

[xuncanzhe]

By the way, normal multicolor images don't have this problem either. At present, it is only abnormal on the barcode image.

[KapitanOczywisty]

@xuncanzhe White on that image has alpha channel and this is the problem. I've tested on my end and adding imagesavealpha after imagerotate solves the issue:

$img_debug = imagecreatefrompng("D:/7701202301090006.png");
$img_debug = imagerotate($img_debug, 90.00, 0, -1);
imagesavealpha($img_debug, true);
imagepng($img_debug, "D:/output.png");

The strange thing is that its economy is only abnormal when rotates is 90.

90, 180 and 270 rotations are done using other functions, but you're correct, in other rotation there is saveAlphaFlag = 1 set. I'd say it's a bug.

By the way, normal multicolor images don't have this problem either. At present, it is only abnormal on the barcode image.

This is problem with transparent colors.

[xuncanzhe]

Thanks a lot, it worked fine after adding imagesavealpha($img_debug, true);

[KapitanOczywisty]

@xuncanzhe I'd leave this open, since missing saveAlphaFlag for 90 deg rotation seems to be an oversight.

[nielsdos]

Yeah I agree. This needs to be fixed in libgd itself though. @KapitanOczywisty do you want to make a patch, or shall I do it? (with appropriate credit to you ofc)

[KapitanOczywisty]

@nielsdos go ahead, It would take me ages to do that :)

This needs to be fixed in libgd itself though.

I think it has to be fixed in both php-src and libgd repositories. I know there is desire to unbundle libgd from php, but for now bundled is used by default. /cc @cmb69

[nielsdos]

Ok, it's on my todo list for today :)

[nielsdos]

Created a PR here: libgd/libgd#862