Re: [igt-dev] [PATCH i-g-t 08/10] lib: Add support for rendering into packed YCbCr framebuffers

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Thu, May 17, 2018 at 11:41:56PM +0100, Chris Wilson wrote:
> Quoting Ville Syrjala (2018-05-17 20:51:46)
> > +/* { Y0, U, Y1, V } */
> > +static const unsigned char swizzle_yuyv[] = { 0, 1, 2, 3 };
> > +static const unsigned char swizzle_yvyu[] = { 0, 3, 2, 1 };
> > +static const unsigned char swizzle_uyvy[] = { 1, 0, 3, 2 };
> 
> > +static const unsigned char swizzle_vyuy[] = { 1, 2, 3, 0 };
> 
> This one stands out as backwards. Is it a vyuy_rev?

Hmm. I think it's correct.

swizzle[] tells us in which offset in the macropixel we find the
component. The index determines which component we want.

swizzle[0] = offset of Y0
swizzle[1] = offset of U
swizzle[2] = offset of Y1
swizzle[3] = offset of V

so for the vyuy case the macropixel layout will be:

byte: 0          1          2          3
      swizzle[3] swizzel[0] swizzle[1] swizzle[2]
      V          Y0         U          Y1

Seems to make some sense, at least to me.

-- 
Ville Syrjälä
Intel
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