jorimt wrote:If that's what you're referring to, it's because 1) G-SYNC + V-SYNC appears to have what could be called a brief "re-initialization" or "re-connection" period (between the module and the GPU) when there is an extremely abrupt transition in the framerate (FYI, there were official reports of a 1ms polling rate on the original modules, and it was never confirmed whether that polling rate either diminished or was entirely eliminated in further module iterations), and 2) since the scanout speed itself on the display is static and unchanging, unavoidable timing misalignments between framerate and scanout progress can occur during these abrupt transitions where the module attempts to adhere to the scanout (to completely avoid tearing), which will create frame delivery delay where the other methods would not, since the module may have to hold the next frame and skip part of (or sometimes, even all of a scanout cycle) before delivery in extreme instances, and thus repeat display of/refresh with the previous frame once or more in the meantime...
From what I am understanding in newer developments:
FreeSync is fundamentally unidirectional, and VRR can be operated unidirectionally. I think some newer GSYNC implementations are now unidirectional from what I'm seeing, e.g. closer to simplified NVIDIA-specific piggyback enhancements onto VESA Adaptive-Sync panels. Further engineering appears to be simplifying VRR implementation. Which may mean that the difference between GSYNC and FreeSync is gradually diminishing on the low-end and mid-range. High end GSYNC probably still require some 2-way behaviours for best operation, but the low end doesn't need it anymore -- in fact, NVIDIA already piggybacks on the VESA Adaptive-Sync with probable simplifications to VRR-based overdrive algorithms that avoids the needs of FPGAs and such. The best FreeSync improved to the point where the venn diagram of quality begins to overlap the cheaper/basic G-SYNC monitors -- and NVIDIA decided it was time to certify certain FreeSync monitors as meeting G-SYNC quality requirements.
Theoretically (if the drivers lets it be precise), the granularity of FreeSync is simply 1 unit of horizontal scanrate, so 160KHz Horizontal Scan Rate (seen in Custom Resolution Utilities) means 1/160000sec granularities in timing your refresh cycle delivery timings.
Picture, this, the GPU simply is in an "infinite loop" of outputting Vertical Back Porch scanlines until the game Present()s the new refresh cycle (that variable-length blanking interval of VRR). Which thereupon the GPU output immediately begins scanning-out at the very next scanline output immediately right after the current Back Porch pixel row (offscreen) is being scanned-out of the GPU output.
So, with proper driver software design, the 1ms granularity can be reduced to just a few microseconds (granularity of horizontal scanrate). All but eliminating the granularity, and making it safer to framerate-cap much closer to VRR max-Hz (e.g. 143.9fps instead of 141fps for 144Hz). Currently, newer VRR displays will have to be lag-tested to see if tighter caps are possible without adding input lag.
In practicality, there are possibly software precision limitations preventing such precision, but theoretically, you can have few-microsecond precision transitioning from VRR to VSYNC ON, and vice versa, and design it in a way that there's never any framebuffer backpressure or monitor refresh-blocking during ultra-tight framerate caps from a good microsecond-accurate framerate capper such as RTSS (e.g. 143.9fps cap during 144Hz VRR operation). That "3fps below" capping is seemed unnecessary, but appeared necessary due to the original 1ms polling granularity. Newer VRR tests will have to determine if tighter caps are becoming lag-free on newer VRR displays.
Basically, graphics drivers and the GPU chip would control repeat-refreshing behaviours (LFC algorithms) instead of the monitor, and high framerates would simply throttle at the driver level, instead of display. So, fundamentally, VRR is optimizeable into a unidirectional protocol, and analog FreeSync also works on certain CRTs