Consider BGRA instead of RGBA

[nigeltao]

Speaking of Windows (#24)... IIUC the default Windows color order is BGRA (not RGBA) and likewise for Linux (X11) and I think MacOS / iOS too. Can't remember what Android is.

Anway, if we're talking of finalizing the file format (#28), consider QOI producing BGRA, not RGBA. Especially as QOI is about being fast to decode, this would avoid what libpng calls the PNG_TRANSFORM_BGR step.

Transforming BGRA <-> RGBA is cheap, especially with SIMD, but it's not free.

[dougallj]

As far as I can tell RGBA isn't part of the format? Looking at the decoder, I think you could just change unsigned char r, g, b, a; to unsigned char b, g, r, a; in the qoi_rgba_t definition to decode straight to BGRA, without changing the format, and presumably for free.

[floooh]

I'd suggest keeping the (default) color channel order as it is, as it's the same as in stb_image.h, and (more importantly) some older 3D APIs (like WebGL) don't directly support creating textures in BGRA format.

[phoboslab]

The file format for QOI will not change anymore. See #37 for more info.

Ideas for a successor to QOI should be discussed here: https://github.com/nigeltao/qoi2-bikeshed/issues