[Pixman] [PATCH 1/2] pixman: Add support for argb/xrgb float formats, v3.

[Bill Spitzak]

I think an indicator for float can double as indicating the size is
multiplied by 8. All float formats I am familiar with take a mulitple of 8
bits, including an 8-bit format that is sometimes used in CG.


On Mon, Oct 29, 2018 at 2:18 AM Maarten Lankhorst <
maarten.lankhorst at linux.intel.com> wrote:

> Op 29-10-18 om 09:16 schreef Siarhei Siamashka:
> > On Wed, 03 Oct 2018 10:11:46 +0100
> > Chris Wilson <chris at chris-wilson.co.uk> wrote:
> >
> >> Quoting Maarten Lankhorst (2018-08-01 13:41:33)
> >>> diff --git a/pixman/pixman.h b/pixman/pixman.h
> >>> index 509ba5e534a8..c9bf4faa80d4 100644
> >>> --- a/pixman/pixman.h
> >>> +++ b/pixman/pixman.h
> >>> @@ -647,19 +647,24 @@ struct pixman_indexed
> >>>   * sample implementation allows only packed RGB and GBR
> >>>   * representations for data to simplify software rendering,
> >>>   */
> >>> -#define PIXMAN_FORMAT(bpp,type,a,r,g,b)        (((bpp) << 24) |  \
> >>> +#define PIXMAN_FORMAT_PACKC(val) ((val) <= 10 ? (val) : \
> >>> +                                (val) == 32 ? 11 : 0)
> >>> +#define PIXMAN_FORMAT_UNPACKC(val) ((val) <= 10 ? (val) : \
> >>> +                                   (val) == 11 ? 32 : 0)
> >> We have 4bits, why not reserve 0xf for float32? Certainly you
> >> want space for
> >>
> >> #define PIXMAN_FORMAT_PACKED_FLOAT16 0xb
> >> #define PIXMAN_FORMAT_PACKED_FLOAT32 0xc
> >> #define PIXMAN_FORMAT_PACKED_FLOAT64 0xd
> >>
> >> I just wonder if we may have 12bpc one day as well, so leaving 0xc clear
> >> has some some appeal.
> > We could probably also try to do something like this:
> >
> > /*
> >  * While the protocol is generous in format support, the
> >  * sample implementation allows only packed RGB and GBR
> >  * representations for data to simplify software rendering,
> >  *
> >  * Bit 23 selects the granularity of channel color depth
> >  *  0: 1-bit granularity (allows up to 15 bits per channel)
> >  *  1: 1-byte granularity (allows up to 120 bits per channel)
> >  */
> > #define PIXMAN_FORMAT(bpp,type,a,r,g,b)       \
> >       (((bpp) << 24) |  \
> >       ((type) << 16) | \
> >       (((a) < 16) ? ((a) << 12) : (((a / 8) << 12) | (1 << 23))) | \
> >       (((r) < 16) ? ((r) << 8)  : (((r / 8) << 8)  | (1 << 23))) | \
> >       (((g) < 16) ? ((g) << 4)  : (((g / 8) << 4)  | (1 << 23))) | \
> >       (((b) < 16) ? ((b))       : (((b / 8))       | (1 << 23))))
> >
> > /* 0 for 1-bit granularity and 3 for 1-byte granularity */
> > #define PIXMAN_FORMAT_CHANDEPTH_SHIFT(f) \
> >       ((((f) >> 23) & 1) | ((((f) >> 23) & 1) << 1))
> I would use 2 bits then, 6 is still plenty for the rest of the type.
>
> Perhaps make a separate PIXMAN_FORMAT_TYPE_RGBA_FLOAT and
> PIXMAN_FORMAT_TYPE_RGB_FLOAT?
>
> > #define PIXMAN_FORMAT_A(f) \
> >       ((((f) >> 12) & 0x0f) << PIXMAN_FORMAT_CHANDEPTH_SHIFT(f))
> > #define PIXMAN_FORMAT_R(f) \
> >       ((((f) >>  8) & 0x0f) << PIXMAN_FORMAT_CHANDEPTH_SHIFT(f))
> > #define PIXMAN_FORMAT_G(f) \
> >       ((((f) >>  4) & 0x0f) << PIXMAN_FORMAT_CHANDEPTH_SHIFT(f))
> > #define PIXMAN_FORMAT_B(f) \
> >       ((((f)      ) & 0x0f) << PIXMAN_FORMAT_CHANDEPTH_SHIFT(f))
> >
> > #define PIXMAN_FORMAT_BPP(f)  (((uint32_t)(f)) >> 24)
> > #define PIXMAN_FORMAT_TYPE(f) (((f) >> 16) & 0x7f)
> > #define PIXMAN_FORMAT_RGB(f)  (((f)      ) & 0xfff)
> > #define PIXMAN_FORMAT_VIS(f)  (((f)      ) & 0xffff)
> > #define PIXMAN_FORMAT_DEPTH(f)        (PIXMAN_FORMAT_A(f) +   \
> >                                PIXMAN_FORMAT_R(f) +   \
> >                                PIXMAN_FORMAT_G(f) +   \
> >                                PIXMAN_FORMAT_B(f))
> >
> >
> > Right now the format type occupies 8 bits. The highest bit could be
> > repurposed as a flag for storing channel depth as bytes instead
> > of bits. This way 16-bit and 64-bit per color component will be
> > also supported. The limitation of this approach is that the depth
> > of every color component has to be a multiple of 8 bits if any of
> > them is 16 bits or larger.
> >
> > I don't feel very comfortable about the fact that some applications
> > are using the PIXMAN_FORMAT_A/R/G/B macros and this code gets compiled
> > as part of these application binaries.
> >
> > Are there any other interesting >32bpp formats that we may need
> > to support in the future?
> >
> Doubt it, pixman doesn't have that accuracy currently, but F16 might be
> interesting at some point..
>
> ~Maarten
>
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