mikechi2 wrote:A big challenge with rotation is inefficient memory access compared to regular readout. I'm not going to say rotation is off the table. There's probably enough memory bandwidth to do rotation for 240p sources, but it probably won't be slated for the initial release. Again, don't want to overpromise and under-deliver
Have you done any latency testing? I'm just curious - despite my earlier comments I don't really want to see a useful feature deep-sixed for no good reason =)
orange808 wrote:Here's the thing: with a zero lag sample and hold display that refreshes instantly, I get the frame on screen without display lag or raster/scanout latency. In this case, that means one total frame of latency from video processing and the display. The display still finishes "drawing" each frame at the same time a CRT would, because the "scanout" takes microseconds instead of ~17ms (faster than electron gun scanout).
TL;DR of my take - VRR doesn't seem to add much outside of specialized retrogaming contexts except a lot of cost for no benefit.
Grey-to-grey transition in newer panels is almost nothing, but MPRT measurements are higher. There also is a big impact from resolution and refresh (scanout is still done in CRT order, and
it's not instant anyway), as input latency measurements scale with resolution (on average). Rtings in a February review:
Sadly, like most high refresh rate monitors, it has a low native resolution [...]
Rtings is upping their lag measurement methology to a new version coming soon to public articles (from version 1.1 to 1.2). Modern lag isn't dramatic compared to older tech with multi-frame latency, but 1 frame is the floor for rotation - and the panel is going to add its own latency to that, as always, in various ways. See the link to Blurbusters' high framerate captures above.
I'm not sure how VRR snuck into this discussion. When talking about scalers, I think we need to focus mainly on 60Hz modes and 4K resolution to get the best idea of the normal operating margins for retrogaming. Of course, if there's inconsistent frame pacing then it's helpful even for scaling. But if frame pacing is consistent it's not going to do much. And, of course, the inconsistent frame pacing has to be in the video signal - a classic system having slowdown doesn't matter if the actual delivered frame output is still at a consistent rate.
If you compare, say, a 120Hz VRR monitor with a 60Hz monitor, the VRR panel comes out on top for input lag because 120Hz has a faster cadence than 60Hz, not because of VRR. Instead look at the 120Hz numbers versus 60Hz, look at 60Hz numbers all the way across, and also look at 60Hz across different resolutions.
VRR has also been a value-add for the fastest modern panels (and hardware) which obscures that VRR only reduces latency from inconsistent frame pacing. After all it adds some additional communication overhead, although it's almost nothing. Even with VRR in the new HDMI spec I think it is well out of the reach of hobbyists and small shops for a good time to come. But, thankfully, it probably won't affect most retrogamer scaling either.
Not sure where "faster scanout than an electron gun" is coming from either. Doesn't seem plausible or even physically possible. Sure, 120Hz+ modern framerates can transition away from a color faster than some old slow-decay CRT phosphors but once again this doesn't look like much of an apples-to-apples comparison because the CRT probably has a better MPRT.