On Tue, Feb 1, 2022 at 9:34 AM Simon Ser [off-list ref] wrote:

On Tuesday, February 1st, 2022 at 09:26, Geert Uytterhoeven [off-list ref] wrote:

quoted

What's the story with the Rn formats?

The comments say "n bpp Red", while this is a monochrome (even
inverted) display?

I don't think the color matters that much. "Red" was picked just because it was
an arbitrary color, to make the difference with e.g. C8. Or am I mistaken?

The red comes from gl, where with shaders it really doesn't matter
what meaning you attach to channels, but really just how many you
have. So 2-channel formats are called RxGx, 3-channel RxGxBx,
4-channel RxGxBxAx and single-channel Rx. And we use drm_fourcc for
interop in general, hence why these exist.

We should probably make a comment that this really isn't a red channel
when used for display it's a greyscale/intensity format. Aside from
that documentation gap I think reusing Rx formats for
greyscale/intensity for display makes perfect sense.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch