Transparent background of .png not preserved when rotating picture

[frankpw]

Rotating .png picture with transparent background does not preserve transparency. Resulting picture has partially black background.

[frankpw]

Formatting correction to previous patch

[boonebgorges]

Looks like this code has not been touched since at least 3.5. Is the same happening with Imagick?

[frankpw]

I had no chance to test Imagic as GD seems to be more popular and all my servers have GD installed ( but no Imagic ).

[voldemortensen]

I've been doing some testing and it doesn't seem like Imagick is doing it wrong. Created a new instance of WP_Image_Editor_Imagick, rotated it 180˚, saved it, and printed it out in an img. Visually the transparency is the same. Also created new Imagick instances to be able to check the image alpha itself. Long story short the alpha didn't change using Imagick.

[frankpw]

As I said I did not check Imagic. My patch fixes transparency problem in GD.

[voldemortensen]

I was responding to boonebgorges's question since he asked if it did happen with Imagick. I did the testing and reported my findings.

[boonebgorges]

Thanks to both for your feedback. The patch looks fine at a glance. voldemortensen - since you were recently looking at the image unit tests, maybe you can dream up a way to write a test for this?

[voldemortensen]

That one's going to be a nightmare. I will work on them.

[voldemortensen]

Turns out it wasn't as hard as I thought it would be. Just had to use my brain. Patch includes the fix and unit tests for both Imagick and GD keeping alpha on rotate.

[wonderboymusic]

In 31040:

Preserve alpha transparency when rotating a PNG while GD is the active image editor.

Adds unit tests.

Props frankpw, voldemortensen.
Fixes #30596.

[markoheijnen]

Reopening after seeing inconsistency in the usage of imagealphablending. I believe the one in load also should be true.
We could also move the lines into a separate protected method so others could use it too when extended the class. I do wonder if the function_exists is needed. It's there because of wp_imagecreatetruecolor which is from #6005 so quite old.

[DrewAPicture]

@markoheijnen: Can you please follow up here on whether there's still a problem following [31040]? If there is, we're running out of time to fix this in 4.2.

[DrewAPicture]

No meaningful activity in several months, and it seems like we need a new patch. Let's pick this up in a future release. Sorry folks.

[helen]

This was fixed in 4.2. If enhancements are desired for the fix, let's open a new ticket for that.

[mikeschroder]

In 36998:

Media: Fix typo in test_image_preserves_alpha_on_rotate().

peserves -> preserves; introduced in [31040].

See #30596.