RFC for a render API to support adaptive sync and VRR

[Cyr, Aric]

> -----Original Message-----
> From: Michel Dänzer [mailto:michel at daenzer.net]
> Sent: Tuesday, April 10, 2018 13:16
> 
> On 2018-04-10 07:13 PM, Cyr, Aric wrote:
> >> -----Original Message-----
> >> From: Michel Dänzer [mailto:michel at daenzer.net]
> >> Sent: Tuesday, April 10, 2018 13:06
> >> On 2018-04-10 06:26 PM, Cyr, Aric wrote:
> >>> From: Koenig, Christian Sent: Tuesday, April 10, 2018 11:43
> >>>
> >>>> For video games we have a similar situation where a frame is rendered
> >>>> for a certain world time and in the ideal case we would actually
> >>>> display the frame at this world time.
> >>>
> >>> That seems like it would be a poorly written game that flips like
> >>> that, unless they are explicitly trying to throttle the framerate for
> >>> some reason.  When a game presents a completed frame, they’d like
> >>> that to happen as soon as possible.
> >>
> >> What you're describing is what most games have been doing traditionally.
> >> Croteam's research shows that this results in micro-stuttering, because
> >> frames may be presented too early. To avoid that, they want to
> >> explicitly time each presentation as described by Christian.
> >
> > Yes, I agree completely.  However that's only truly relevant for fixed
> > refreshed rate displays.
> 
> No, it also affects variable refresh; possibly even more in some cases,
> because the presentation time is less predictable.

Yes, and that's why you don't want to do it when you have variable refresh.  The hardware in the monitor and GPU will do it for you, so why bother?
The input to their algorithms will be noisy causing worst estimations.  If you just present as fast as you can, it'll just work (within reason).
The majority of gamers want maximum FPS for their games, and there's quite frequently outrage at a particular game when they are limited to something lower that what their monitor could otherwise support (i.e. I don't want my game limited to 30Hz if I have a shiny 144Hz gaming display I paid good money for).   Of course, there's always exceptions... but in our experience those are few and far between.