Add support for single-channel colour formats

[vs49688]

Suggestion - add support for single-channel colour formats in SDL3, e.g.

• SDL_PIXELFORMAT_R16 - array of 16-bit uints
• SDL_PIXELFORMAT_R32 - array of 32-bit uints
• SDL_PIXELFORMAT_RF16 - array of 16-bit floats
• SDL_PIXELFORMAT_RF32 - array of 32-bit floats

Specifically, these formats could be (ab)used to have SDL_Surface-backed storage for a depth buffer.

[slouken]

Sure, go ahead and add a PR and tests in testautomation for them. I'm not sure how they would need to be handled in the blitting code, thoughts?

[vs49688]

Sure, go ahead and add a PR and tests in testautomation for them.

I'll give it a crack. I'm not familiar with SDL's internals at all though, so don't expect much soon.

I'm not sure how they would need to be handled in the blitting code, thoughts?

Neither, I'll have to have a think about it.