GLUI menu driver doesn't support alpha channel images

[zach-morris]

First and foremost consider this:

• Only RetroArch bugs should be filed here. Not core bugs or game bugs
• This is not a forum or a help section, this is strictly developer oriented

When developing the PR https://github.com/libretro/RetroArch/pull/17216, it was noticed when testing the glui menu driver does not support alpha channel images. See here.

Expected behavior

glui menu driver supports alpha channel images

Actual behavior

glui menu driver does not support alpha channel images

Steps to reproduce the bug

1. Place alpha channel image in place of a Boxart or Snapshot or Title image
2. Change to the glui driver
3. Note it shows black background instead of alpha channel

Bisect Results

I think it's always happened, but never noticed with Boxart, Snapshot or Titles. If logos are introduced as the PR suggests, it will be noticeable.

Version/Commit

You can find this information under Information/System Information

• RetroArch: 1.19.1

Environment information

• OS: Winx64
• Compiler: libretro-build-mxe-win64-cross

[i30817]

You're lucky you see it as black, in certain Linux systems it's shown in the classic gray-white checkerboard pattern.

It sometimes happens in some cover images which were improperly prepared.

Glui, not sure if only by default, also does show a placeholder for a missing image in that part of the gui if any is missing, instead of showing the bare background. I got used to it, and I suppose both things are to minimize laying out reflow problems and performance for limited systems, like frankly a large minority of the people that use RetroArch instead of cemu, yuzu or that PS3 emulator.