On Tue, Feb 1, 2022 at 9:34 AM Simon Ser contact@emersion.fr wrote:
On Tuesday, February 1st, 2022 at 09:26, Geert Uytterhoeven geert@linux-m68k.org wrote:
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