[done]Nvidia’s FleX Technology Used In Killing Floor 2

[xyriin]

If I have a 144Hz panel, and my game drops down to 20fps/Hz.... how is screen tearing even an issue at that point? My understanding is that tearing is a problem when the fps of the game exceeds that of the panel, not the other way around.
And if you do use Vsync at that point, are you actually waiting for frames when your monitor is refreshing ~7 times for every new frame to display?

Yes and no on tearing. The tearing effect can occur anytime the FPS isn't at a perfect ratio with the panel refresh rate. So if your panel is at 144hz and your FPS is at 9, 18, 36, 72, 144, or 288 for example you're in a perfect ratio meaning every time the panel refreshes it's doing so in alignment with fresh output from the video card. A 'tear' happens when the video card is drawing a screen but isn't finished and the panel decides it's time to refresh anyway so you get two screens smashed together or a 'tear'. If you have a static display you'd never see this, but obviously the faster the action is on screen the more noticeable the 'tear' is.

Vsync was the old solution to this problem. It essentially capped the FPS to the max panel refresh rate so that any FPS greater than or equal to the refresh rate would be at a perfect ratio (1:1 in the case of Vsync). Vsync also tried to help lower FPS with the use of a buffer. Essentially the screen would draw to the buffer and when the panel was ready to refresh it would have the last complete screen from the buffer. This eliminates tearing but instead you get stuttering. Let's say you're in Vsync mode and panel is refreshing at 60hz. If your FPS drops to say 50 FPS then on the first draw attempt you don't get a full screen so panel refreshes your old screen. Next frame you finish drawing a screen and start on the next one, panel picks up the completed frame and buffer and displays it. The first problem is that there is lag due to the buffer, and gamers hate lag which is why they never use Vsync for a competitive game. Second problem is that it's possible to duplicate the same frame and/or skip frames depending on how your frame rate changes and how much is stored in the buffer before the refresh. This duplicate or skipped frame effect is called stuttering.

FreeSync/G-Sync solve the buffer lag, tearing issues, and stuttering issues by instead driving the panel at the FPS of the video card resulting in a perfect ratio of 1:1. However below around 40hz LCD technology suffers from a problem called ghosting. If you attempt to refresh the panel below 40hz you get ghosting.

FreeSync's work around to this problem is to default to normal panel mode (either Vsync on or off which can cause stuttering or tearing).

G-Sync's work around to this problem is to drive the panel at a perfect ratio of the FPS. So if your FPS drops to 30 for example, it drives the panel at 60hz so that you don't get ghosting but each refresh lines up with a new screen (no stuttering or tearing).