Certain transparent backgrounds render as blue since SDL_image 2.8.3 on Mac OS X

[tobbi]

I'm sorry for this being rather vague because I'm not sure of the actual cause.
I've installed SDL_image 2.8.3 using Homebrew on my MacOS X 12.7.6 machine and I'm linking SuperTux against it.

Certain previously transparent images now render with a blue background:

2024-12-26.14-41-11.mp4

I then disabled the homebrew formula and compiled 2.8.2 manually and the issue is gone:

2024-12-26.19-21-40.mp4

If there's anything more you need, just tell me.

[slouken]

Do you get the issue if you build 2.8.3 manually? If not, what are the configure options being used by the homebrew formula?

[tobbi]

Do you get the issue if you build 2.8.3 manually? If not, what are the configure options being used by the homebrew formula?

Apparently, linking against a self-built 2.8.3 worked just fine and doesn't show the issue. Here are the homebrew configure flags: https://github.com/Homebrew/homebrew-core/blob/dba938d9df5b2e1fe399ef345d64cfa3df0c1f79/Formula/s/sdl2_image.rb#L43C1-L50C51

[slouken]

Can you link one of the images that is failing?

[tobbi]

The snow particles in question should be https://raw.githubusercontent.com/SuperTux/supertux/refs/heads/master/data/images/particles/snow0.png https://raw.githubusercontent.com/SuperTux/supertux/refs/heads/master/data/images/particles/snow1.png and https://raw.githubusercontent.com/SuperTux/supertux/refs/heads/master/data/images/particles/snow2.png

[slouken]

Can you reproduce it if you build with the same configure options that homebrew uses, and then run showimage on that image?

[sezero]

Reproduces on linux with --disable-stb-image, thus using libpng, in both release-2.8.x and SDL2 branches. Should possibly reproduce in SDL3 (main) branch too.

Commit 0000fb0 (which was cherry-picked to release-2.8.x too) seems to be the culprit.

[tobbi]

Can confirm that by adding the flags from the homebrew formula, the bug re-appears.

[slouken]

Fixed! Thanks for the help tracking this down.