[arshidkv12]

Use imageflip() in WP_Image_Editor_GD::flip() instead of imagecopyresampled() with negative dimensions.

This fixes image flipping with PHP 8.6 / GD 2.4.0, where the existing implementation can produce incorrect pixel data.

Trac ticket: https://core.trac.wordpress.org/ticket/66113

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[dhruvang21]

The move from imagecopyresampled() to imageflip() otherwise looks good.

[dhruvang21]

Could we preserve the true|WP_Error return contract here?

imageflip() returns bool, so returning it directly means this method can now return false when the GD operation fails. The parent WP_Image_Editor::flip() contract is true|WP_Error, and the Imagick implementation also converts failures to WP_Error.

I think we should keep @return true|WP_Error and convert a false result from imageflip() into the existing image_flip_error WP_Error, e.g.:

$result = imageflip( ... );

if ( $result ) {
	return true;
}

return new WP_Error( 'image_flip_error', __( 'Image flip failed.' ), $this->file );

[desrosj]

Hi @arshidkv12,

Thank you for opening this PR and contributing to WordPress! ❤️

It seems that there is still unaddressed feedback on here, and #13920 and #13925 are much further along as they have unit tests and documentation about the broader consequences and edge cases from switching to using imageflip().

I'm going to close this out so that efforts can be focused in one place, but please do feel free to continue helping to fix this.

[arshidkv12]

Thank you