On Thursday, January 23rd, 2025 at 21:06, Harry Wentland <harry.wentland@xxxxxxx> wrote: > On 2025-01-15 03:00, Simon Ser wrote: > > > Is this 125 magic number something we can expect other hardware to > > implement as well? > > It's based on MS's CCCS interpretation of 80 nits as 1.0f [1]. Based on > this definition one needs to use 125.0f to represent 10,000 nits, > the maximum value PQ can represent. > > It's hard to say whether other HW will implement it the same way, > though most drivers for HW that supports HDR on Windows might have > a similar concept somewhere. I see, thanks for the explanation! > > Could AMD use the HDR multiplier or another block to behave as if > > the multiplier didn't exist? > > Gamescope makes use of this scaled PQ EOTF and its inverse, so I'd > like to expose at least one color pipeline that we can use to move > gamescope from the AMD-private color properties to the color pipeline > API. > > We only have a single HDR multiplier but three curves (1 and 3 are EOTF, > curve 2 is the inverse). We could only mode a PQ curve in the range of > 0 to MAX_VALUE (1.0, 255, 1024, etc.) for the 1st EOTF, not for the 2nd or > 3rd curves. I'm not sure how useful that would be. Yeah, I don't see a good way out of this. I was hoping there could be a way to expose something more generic. Then maybe this curve ends up only being exposed by AMD, but as we discussed in the past that's fine.
