Blur Buster's G-SYNC 101 Series Discussion

[KKNDT]

Which scanout diagram is correct while using GSYNC + VSYNC OFF when frame rate is higher than refresh rate?
Refresh cycle : Frame time ~= 3:2

A: similar with pure NO SYNC
B: Part of the current frame (eg. frame 2) will be abandened, the next refresh cycle (cycle 2)starts synchronously with delivery of frame 3 (yellow).

1.png (10.61 KiB) Viewed 352 times

[Chief Blur Buster]

This thread is not ideally for display engineering style questions. Those should be posted in Area 51, and not in this GSYNC 101 tweaking HOWTO. This discussion may later (in the next few hours) be moved to Area51 once you've read the reply.

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Advanced Reading for Advanced Users

Scanout diagram A

However, scanout diagram A needs to contains some thin slices of minimum-possible VBI blanking interval, so corrected diagram A for both VSYNC OFF as well as GSYNC+VSYNC OFF for the situation of continuous "frame-time < refresh-time" (framerate permanently above hz):



The relevant Blur Busters themed scanout diagram is:



The same situation happens with 360fps during 120Hz GSYNC+VSYNC OFF and 120Hz FreeSync+VSYNC OFF. There are implementation differences behind the scenes for GSYNC/FreeSync but the scanout behaviour (because that's where matters from a human vision & latency perspective: displays painting the refresh top-to-bottom, so top edge of a refresh cycles have photons hitting eyes first) is the same; a new refresh cycle cannot be started until right after the minimum-specified VBI size. For FreeSync, the minimum VBI size is dependant on the EDID/DisplayID advertised by the monitor or the custom resolution configured as the current Vertical Total. FreeSync/HDMI VRR/VESA AdaptiveSync -- all interoperably enlarges/reduces the Back Porch (embedded in the Vertical Total number) changing every single refresh cycle to dynamically space the refresh cycles apart, but can be never be below the minimum allowed number.

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[jorimt]

G-SYNC 101 series part 15, "G-SYNC 101: Closing FAQ" posted:
https://www.blurbusters.com/gsync/gsync ... ttings/15/

[MonarchX]

Is there any harm in enabling G-Sync and keeping it enabled for both Fullscreen AND Borderless Mode? I use FSE 99% of the time, but some Unity-engine-based games do not even support FSE and use only Borderless mode. I think the most recent Unity builds do offer FSE, but Pillars of Eternity and 1 and 2, for example, don't support FSE

Microsoft says that D3D12 does not even have FSE and keeps pushing for Borderless mode, which is bothersome because it reduces FPS and can cause stutters... More info on that can be found in educational video from MS here - https://www.youtube.com/watch?v=E3wTajGZOsA .

[jorimt]

There is no harm for games; the sole difference between the two G-SYNC modes, is that one is only active in FSE, and the other is active across FSE, borderless, and windowed mode.

G-SYNC "Enable for windowed and full screen mode" does apply to some non-game apps, however, so you can get the occasional/rare nuisance of certain program windows dropping/fluctuating Hz on the desktop unnecessarily when active/focused on.

[Chief Blur Buster]

Even among FSE (Full Screen Exclusive) I've seen some wonkiness occuring for some reason.

With the new Windows 10 gaming mode, some windowed applications start behaving as if they're in FSE when they go borderless windowed. There are subtle differences but tearing suddenly appears (VSYNC OFF) or suddenly goes in VRR mode (even when windowed VRR is disabled).

This even happens in applications with no true FSE support (Full Screen Exclusive).

In many situations, this is often desirable (except in situations when it is not).

Even the Chrome web browser behaves this way. When I disable GSYNC and configure NVIDIA Control Panel to use VSYNC OFF for full screen mode -- then I can see tearing in TestUFO animations when I run chrome.exe with the --disable-frame-rate-limit and then I do Full Screen on the browser window via the TestUFO full screen button. Framerates are ultrahigh though, like 1000fps or 2000fps! It's like I forced Chrome into a FSE mode everytime the window is maximized (F11 fullscreen mode). Basically I've forced an FSE-equivalent onto a non-FSE app like the Chrome web browser.