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? > > 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]. Harry > > Thanks, > pq >
