On 10.04.2018 19:25, Cyr, Aric wrote: >> -----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, theyâ??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? I think Michel's point is that the monitor and GPU hardware *cannot* really do this, because there's synchronization with audio to take into account, which the GPU or monitor don't know about. Also, as I wrote separately, there's the case of synchronizing multiple monitors. > 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. I agree that games most likely shouldn't try to be smart. I'm curious about the Croteam findings, but even if they did a really clever thing that works better than just telling the display driver "display ASAP please", chances are that *most* developers won't do that. And they'll most likely get it wrong, so our guidance should really be "games should ask for ASAP presentation, and nothing else". However, there *are* legitimate use cases for requesting a specific presentation time, and there *is* precedent of APIs that expose such features. Are there any real problems with exposing an absolute target present time? Cheers, Nicolai
