SDL2 - UpdateYUVTexture on `opengles2` flips red/blue channels

[itsmattkc]

My app uses SDL_UpdateYUVTexture extensively for uploading video frames to an SDL_Texture. With the opengl backend, everything displays fine and as expected. However, with the opengles2 backend, the red and blue channels are inexplicably flipped.

✅ Correct result using opengl

❌ Incorrect result using opengles2:

This is particularly problematic on Android (and other embedded/low power systems) where opengles2 is the default/only option.

I'm using SDL 2.32.0 self-compiled as part of my CMake build system. The issue is tracked on our end at vanilla-wiiu/vanilla#133.

I tried investigating but my only guess was some kind of conflict between RGBA and BGRA textures. I couldn't find anything that seemed to definitively solve it. Any help with this issue would be great.

[ccawley2011]

It might be a regression from this commit: 9f7ccbe

SDL_PIXELFORMAT_ABGR32 isn't handled elsewhere in the file, while SDL_PIXELFORMAT_BGRA32 is handled by using a shader to swap the R and B components. SDL_PIXELFORMAT_RGBA32 is the pixel format that corresponds to the standard layout, but it's unclear why it was removed.

[itsmattkc]

Thanks for getting back to me so soon. Indeed, it seems that commit started the issue because I just tested 643437f and it works fine.

[slouken]

@icculus, can you take a look at this?

[icculus]

Yep!

[icculus]

Just realizing this is an SDL2 thing because this code is all gone in SDL3. 🤦‍♀️

I'm going to revert my previous commit on the topic. We might need to deal with #11031 again, but this is clearly more important.