On Wed, Nov 10, 2021 at 10:49:24AM +0200, Pekka Paalanen wrote: > On Wed, 10 Nov 2021 00:02:16 +0200 > Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx> wrote: > > > On Tue, Nov 09, 2021 at 03:47:58PM -0500, Harry Wentland wrote: > > > On 2021-11-08 04:54, Pekka Paalanen wrote: > > > > On Thu, 4 Nov 2021 12:27:56 -0400 > > > > Harry Wentland <harry.wentland@xxxxxxx> wrote: > > > > > > > >> On 2021-11-04 04:38, Pekka Paalanen wrote: > > > >>> On Wed, 3 Nov 2021 11:08:13 -0400 > > > >>> Harry Wentland <harry.wentland@xxxxxxx> wrote: > > > >>> > > > >>>> On 2021-09-06 17:38, Uma Shankar wrote: > > > >>>>> Existing LUT precision structure is having only 16 bit > > > >>>>> precision. This is not enough for upcoming enhanced hardwares > > > >>>>> and advance usecases like HDR processing. Hence added a new > > > >>>>> structure with 32 bit precision values. > > > >>>>> > > > >>>>> This also defines a new structure to define color lut ranges, > > > >>>>> along with related macro definitions and enums. This will help > > > >>>>> describe multi segmented lut ranges in the hardware. > > > >>>>> > > > >>>>> Signed-off-by: Uma Shankar <uma.shankar@xxxxxxxxx> > > > >>>>> --- > > > >>>>> include/uapi/drm/drm_mode.h | 58 +++++++++++++++++++++++++++++++++++++ > > > >>>>> 1 file changed, 58 insertions(+) > > ... > > > > >> If the framebuffer is not in FP16 the question then becomes how > > > >> the integer pixel values relate to LUT addressing. > > > > > > > > Traditionally, and in any API I've seen (GL, Vulkan), a usual mapping > > > > is to match minimum unsigned integer value to 0.0, and unsigned maximum > > > > integer value to 1.0. This is how things work on the cable too, right? > > > > (Also taking full vs. limited range video signal into account. And > > > > conversion to cable-YUV if that happens.) > > > > > > > > If you want integer format FB values to map to something else, then you > > > > have to tag the FB with that range information, somehow. New UAPI. > > > > > > > > > > On the cable we send integer values, not floating point. AMD HW uses > > > floating point internally, though, and the PWL API defines floating > > > point entries, so on some level we need to be clear what the floating > > > point entries mean. Either we document that to be [0.0, 1.0] or we > > > have some UAPI to define it. I'm leaning toward the latter but have > > > to think about it some more. > > > > As for Intel hw if you have an integer pixel value of 0xff... (with > > however many bits you have with a specific pixel format) it will get > > extended to 0.fff... (to whatever precision the pipe has internally). > > So if we go by that a fixed point 1.0 value in the proposed > > drm_color_lut_range would be considered just outside the gamut. And > > pretty sure fp16 input of 1.0 should also result in a 0.fff... internal > > value as well [1]. I think that definition pretty much matches how GL > > UNORM<->float conversion works as well. > > Does it work that way in GL though? > > I've always thought that with GL_UNSIGNED_BYTE, 0xff maps to 1.0, not > 255.0/256.0. > > Taking a random spec: OpenGL ES 2.0.25 > > Section 2.1.2 Data Conversions says: > > Normalized unsigned integers represent numbers in the range > [0, 1]. The conversion from a normalized unsigned integer c to > the corresponding floating-point f is defined as > f = c / (2^b - 1) > > Note how the divisor has -1. That seems to match what I said, or at least tried to say (~0 <-> 1.0 in float). drm_color_lut_range being fixed point would follow the ~0 side of that. Or at least that interpretation would very easily map to our hw. -- Ville Syrjälä Intel
