[Mesa-dev] [Intel-gfx] [PATCH] dri3, i915, i965: Add __DRI_IMAGE_FOURCC_SARGB8888

[Geert Uytterhoeven]

On Sat, Nov 23, 2013 at 2:10 AM, Ville Syrjälä
<ville.syrjala at linux.intel.com> wrote:
> On Fri, Nov 22, 2013 at 03:43:13PM -0800, Keith Packard wrote:
>> Ville Syrjälä <ville.syrjala at linux.intel.com> writes:
>>
>> > What is this format anyway? -ENODOCS
>>
>> Same as MESA_FORMAT_SARGB8 and __DRI_IMAGE_FORMAT_SARGB8 :-)
>>
>> > If its just an srgb version of ARGB8888, then I wouldn't really want it
>> > in drm_fourcc.h. I expect colorspacy stuff will be handled by various
>> > crtc/plane properties in the kernel so we don't need to encode that
>> > stuff into the fb format.
>>
>> It's not any different from splitting YUV codes from RGB codes;
>
> Not really. Saying something is YUV (or rather Y'CbCr) doesn't
> actually tell you the color space. It just tells you whether the
> information is encoded as R+G+B or Y+Cb+Cr. How you convert between
> them is another matter. You need to know the gamma, color primaries,
> chroma siting for sub-sampled YCbCr formats, etc.

Yep. Fbdev has a separation of type (how pixel values are laid out in memory),
fb_bitfield structs (how tuples are formed into pixels), and visual (how to
interprete the tuples).

The fb_bitfield structs do have RGB-centric names, but you could use them
for e.g. Y, Cb, Cr, and alpha, giving a proper visual. Unfortunately the
YCbCr visuals haven't made it into mainline.

FOURCC unifies all of that in (not so) unique 32-bit IDs.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert at linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds