Paul wrote:If you want to avoid tearing at the bottom of your screen while using Gsync (and Vsync off) on a 180Hz monitor, you have to cap the fps around 152. It's been explained pretty well in this topic:
link
However if you're fine with a little tearing at the bottom, feel free to cap the fps a little higher, maybe around 170+ fps.
Usually, VSYNC ON at 170-175 won't add appreciable lag. The tearing at the bottom edge of the screen is only microseconds away.
Mathematically, at 1080p@144Hz, using 160KHz horizontal scan rate (pixel rows per second, scanlines per second), the extra input lag of VSYNC OFF GSYNC versus VSYNC ON GSYNC based on tearline position -- a tearline 10 pixels above the bottom edge of the screen is only an additional 10/160,000th of a second of input lag. Waiting for VSYNC in a situation of a tearline 10 pixels from bottom edge -- 0.06ms input lag. That's six hundredths of a single millisecond!
You can find your scanrate (also known as "horizontal refresh") in Custom Resolution Utility. To calculate the mathematical input lag, that is how many fractions of a second for every pixel row the tearline is above the bottom edge of the screen (VSYNC ON relative to VSYNC OFF). If the tearline was very high up on the screen like near the beginning of the screen -- yes, you can have several milliseconds less lag. But if it's only a few pixels from the bottom edge, that's MICROSECONDS of input lag. And besides, stuff above the tearline is unaffected (no input lag difference) -- it's only stuff below the tearline that genuinely has less input lag. Is there any enemies showing below the tearline? No? Then use VSYNC ON with GSYNC.
The way the screen scans out, one pixel at a time serialized over a video cable, and onto the screen (at the pixel dotclock) -- the pixels start at the top and ends at the bottom. So if you're already near the bottom, you're only microseconds away from finishing the refresh cycle (wait on VSYNC). If you've programmed raster interrupts in the old days as I have (e.g. Commodore 64), you gain the ability to precision mathematically calculate the exact number of microseconds for a specific scanout position. (Nintendo Zapper lightgun depends on microsecond-accurate relative timing too; given CRTs scan out -- to determine position of light gun aim relative to screen). VSYNC OFF can be a big latency saver (many milliseconds) or only an insignificant latency saver (mere microseconds, in the case of wanting to eliminate tearlines that hover only at the bottom edge of the screen)
Sure, Yes. VSYNC OFF is competitively important without GSYNC
But, No. VSYNC OFF during GSYNC is quite unnecessary if your tearlines hang
only near the bottom edge of the screen.
If tearlines appear ONLY at bottom edge of the screen, turning VSYNC ON adds far less than a tenth of a millisecond of extra lag. That's mere microseconds! The fetish of VSYNC OFF + GSYNC for "my tearlines only show at bottom edge" scenario, is almost always a mountain out of a molehill, because tearline position at the bottom edge of the screen is only microseconds away from VSYNC ON.
In other words, "170fps cap during 180Hz GSYNC + VSYNC ON" will generally be competitively better than "150fps cap during 180Hz GSYNC + VSYNC OFF"
if your tearlines only hover near the bottom edge. Significantly more frames per second (15% more fps) is preferable over adding a few microseconds of input lag. Even a tiny 10Mhz (0.01Ghz) overclock has a bigger effect on input lag than that. Even running the gaming monitor in a warm room than a cold room (Colder room = slower LCD pixel response = Slower GtG = more microseconds of lag) has a bigger effect on input lag savings than using VSYNC ON to remove bottom-hugger tearlines!
TL;DR: If your tearlines ONLY hang near the bottom, just simply use default GSYNC (with VSYNC ON at max Hz) and a higher framerate cap. The advantages of a higher framerate will far more than competitively compensate for the extra microseconds of input lag for bottom-edge-hugging VSYNC OFF tearlines.