What are the barriers of GSync and Freesync being employed in HMDs?

With all this frustration that comes with Motion smoothing, Compulsive Smoothing, I wondered if something like FreeSync had ever been considered for an HMD. I mean, we’re trying to squeeze every last frame out of our PCs and I thought…well with my PC I truly love GSync, in fact I miss it terribly when I play games that get 35-55 FPS on my TV where my display is 60 hz and I have to VSync 30 fps.
There must be some barriers, just curious if anyone has ideas of what they are, or if there’s examples of attempts to infuse that somewhere. I mean after all Pimax is putting all these chips on their future HMDs…
Links and thoughts appreciated.

I suppose given things can “kick down” the frame rate, the interaction between VR runtime and application must already allow for varying predicteded times for the next frame, that the game needs to try to adhere to, on a per-frame basis, but I don’t know…

As long as we are doing low persistence, the illumination duty cycle needs to be adjusted for the duration between two frames, when this duration is dynamic, in order to avoid fluctuations in the perceived light level, but that occurs to me like a strictly driver-side matter, so that should present no blocker…

(EDIT: …as to whether the screens are wired up for external sync; Who knows…)

As a bit of curiousity, even if off-topic: On the opposite end of the sync-spectrum, Doc_Ok, with whom I’m sure you are familiar, mentioned in passing in a reddit thread the other day, that back with the RiftDK2 he made a little experiment where much like Carmack also had been thinging about, he took advantage of the rolling shutter (before we got global), and updated the cameras- and rendered out each raster line on its own, on the fly as the screen drew it, instead of finishing the frame first, and the resulting responsiveness was apparently really nice. (Note that he does not use any of the commercial VR runtimes, but his own university-work-focussed system, which runs on Linux.)

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