On Tue, 13 Jul 2021 09:54:35 -0400 Harry Wentland <harry.wentland@xxxxxxx> wrote: > On 2021-07-13 3:52 a.m., Pekka Paalanen wrote: > > On Mon, 12 Jul 2021 12:15:59 -0400 > > Harry Wentland <harry.wentland@xxxxxxx> wrote: > > > >> On 2021-07-12 4:03 a.m., Pekka Paalanen wrote: > >>> On Fri, 9 Jul 2021 18:23:26 +0200 > >>> Raphael Gallais-Pou <raphael.gallais-pou@xxxxxxxxxxx> wrote: > >>> > >>>> On 7/9/21 10:04 AM, Pekka Paalanen wrote: > >>>>> On Wed, 7 Jul 2021 08:48:47 +0000 > >>>>> Raphael GALLAIS-POU - foss <raphael.gallais-pou@xxxxxxxxxxx> wrote: > >>>>> > >>>>>> Some display controllers can be programmed to present non-black colors > >>>>>> for pixels not covered by any plane (or pixels covered by the > >>>>>> transparent regions of higher planes). Compositors that want a UI with > >>>>>> a solid color background can potentially save memory bandwidth by > >>>>>> setting the CRTC background property and using smaller planes to display > >>>>>> the rest of the content. > >>>>>> > >>>>>> To avoid confusion between different ways of encoding RGB data, we > >>>>>> define a standard 64-bit format that should be used for this property's > >>>>>> value. Helper functions and macros are provided to generate and dissect > >>>>>> values in this standard format with varying component precision values. > >>>>>> > >>>>>> Signed-off-by: Raphael Gallais-Pou <raphael.gallais-pou@xxxxxxxxxxx> > >>>>>> Signed-off-by: Matt Roper <matthew.d.roper@xxxxxxxxx> > >>>>>> --- > >>>>>> drivers/gpu/drm/drm_atomic_state_helper.c | 1 + > >>>>>> drivers/gpu/drm/drm_atomic_uapi.c | 4 +++ > >>>>>> drivers/gpu/drm/drm_blend.c | 34 +++++++++++++++++++++-- > >>>>>> drivers/gpu/drm/drm_mode_config.c | 6 ++++ > >>>>>> include/drm/drm_blend.h | 1 + > >>>>>> include/drm/drm_crtc.h | 12 ++++++++ > >>>>>> include/drm/drm_mode_config.h | 5 ++++ > >>>>>> include/uapi/drm/drm_mode.h | 28 +++++++++++++++++++ > >>>>>> 8 files changed, 89 insertions(+), 2 deletions(-) > > > > ... > > > >>>>> The question about full vs. limited range seems unnecessary to me, as > >>>>> the background color will be used as-is in the blending stage, so > >>>>> userspace can just program the correct value that fits the pipeline it > >>>>> is setting up. > >>>>> > >>>>> One more question is, as HDR exists, could we need background colors > >>>>> with component values greater than 1.0? > >>>> > >>>> AR4H color format should cover that case, isn't it ? > >>> > >>> Yes, but with the inconvenience I mentioned. > >>> > >>> This is a genuine question though, would anyone actually need > >>> background color values > 1.0. I don't know of any case yet where it > >>> would be required. It would imply that plane blending happens in a > >>> color space where >1.0 values are meaningful. I'm not even sure if any > >>> hardware supporting that exists. > >>> > >>> Maybe it would be best to assume that only [0.0, 1.0] pixel value range > >>> is useful, and mention in the commit message that if someone really > >>> needs values outside of that, they should create another background > >>> color property. Then, you can pick a simple unsigned integer pixel > >>> format, too. (I didn't see any 16 bit-per-channel formats like that in > >>> drm_fourcc.h though.) > >>> > >> > >> I don't think we should artificially limit this to [0.0, 1.0]. As you > >> mentioned above when talking about full vs limited, the userspace > >> understands what's the correct value that fits the pipeline. If that > >> pipeline is FP16 with > 1.0 values then it would make sense that the > >> background color can be > 1.0. > > > > Ok. The standard FP32 format then for ease of use and guaranteed enough > > range and precision for far into the future? > > > > I don't have a strong preference for FP16 vs FP32. My understanding is > that FP16 is enough to represent linearly encoded data in a way that > looks smooth to humans. > > scRGB uses FP16 with linear encoding in a range of [-0.5, 7.4999]. > > > Or do you want to keep it in 64 bits total, so the UABI can pack > > everything into a u64 instead of needing to create a blob? > > > > I don't mind as long as it's clearly documented what it is and how it > > works, and it carries enough precision. > > > > But FP16 with its 10 bits of precision might be too little for integer > > 12-16 bpc pipelines and sinks? The 10 bits worries me still. If you have a pipeline that works in [0.0, 1.0] range only, then FP16 limits precision to 10 bits (in the upper half of the range?). > > > > If the values can go beyond [0.0, 1.0] range, then does the blending > > hardware and the degamma/ctm/gamma coming afterwards cope with them, or > > do they get clamped anyway? > > > > That probably depends on the HW and how it's configured. AMD HW can handle > values above and below [0.0, 1.0]. Right, so how would userspace know what will happen? Or do we need to specify that while values outside that unit range are expressable, it is hardware-specific on how they will behave, so generic userspace should not attempt to use values outside of the unit range? I guess this caveat should be documented for everything, not just for background color? LUT inputs and outputs, CTM input and output ranges, FB formats... Thanks, pq
Attachment:
pgp_1akmfWMZm.pgp
Description: OpenPGP digital signature
