How Scanline Sync actually works?

[CoolJosh3k]

In my mind, it is trying to predict how long rendering the next frame will take, then delays starting the task.

 

I am rather curious as to how RTSS can reduce latency by so much, compared with alternatives like just VSync

 

I would expect that for a scenario with 1% lows of 120FPS+, that enforcing a frame cap of 120FPS would actually have higher latency than Scanline Sync 120Hz.

 

Can anyone with the technical knowledge on this chime in, or perhaps just anyone who is also curious?

[Bombastinator]

I suggest wikipaedia for that one.  I think you are using the wrong words. 

[CoolJosh3k]

4 hours ago, Bombastinator said:

I suggest wikipaedia for that one.  I think you are using the wrong words. 

Scanline Sync is an RTSS (RivaTuner) feature.

 

Wikipedia is also not usually all too technical from what I have read. 

[Bombastinator]

2 hours ago, CoolJosh3k said:

Scanline Sync is an RTSS (RivaTuner) feature.

 

Wikipedia is also not usually all too technical from what I have read. 

Depends on the entry.  Generally the longer the entry the deeper it goes.

[Doobeedoo]

In short in moves scanline near edge of monitor and such so it's not as noticeable. Vsync is garbage especially with input lag it has. Would never use it really.

 

Check more here

https://forums.blurbusters.com/viewtopic.php?t=4916

[Stahlmann]

From just reading a bit of the blur busters article i have 1 question: Why bother? Turn on G-Sync or FreeSync and enjoy a tear-free experience without any noticeably higher input lag, and especially without any need for calibration or configuration.

[BuzzingBee]

Scanline sync basically still has tearing like turning off V-sync but is adjusted to tear at precise horizontal position and can be moved off-screen. V-sync has to wait for frame to shown which adds lag.

 

As for whether you should use it? No, unless it's for really niche use. I've tried it with 6800XT and B9 because for some reason 9 series don't support Freesync. It was a time waster to get it working and even when it does, I had to cap at 60 fps instead of potentially 80-90 which would look way nicer. And it's not perfect, any spike coming from CPU or GPU the tear would appear for a second or two. I would rather get Freesync display at this point.

[Andrewtst]

First time know got scanline sync.

 

Unless your monitor and GPU not support G-sync compatible or Freesync. Else I don't see this scanline sync is worth to use as from the information link above showing too many compromise required.

 

If your monitor not support G-sync compatible or Freesync, it is better just get a new monitor IMO.

[CoolJosh3k]

13 hours ago, Doobeedoo said:

In short in moves scanline near edge of monitor and such so it's not as noticeable. Vsync is garbage especially with input lag it has. Would never use it really.

 

Check more here

https://forums.blurbusters.com/viewtopic.php?t=4916

Thanks, but that is just a how to and does not cover how it works in detail

[CoolJosh3k]

12 hours ago, Stahlmann said:

From just reading a bit of the blur busters article i have 1 question: Why bother? Turn on G-Sync or FreeSync and enjoy a tear-free experience without any noticeably higher input lag, and especially without any need for calibration or configuration.

Your confusing 2 different technologies.

 

G-sync lowers your refresh rate to match your low FPS.

Scanline Sync lowers your FPS to match your refresh rate.

[CoolJosh3k]

6 hours ago, BuzzingBee said:

Scanline sync basically still has tearing like turning off V-sync but is adjusted to tear at precise horizontal position and can be moved off-screen. V-sync has to wait for frame to shown which adds lag.

 

As for whether you should use it? No, unless it's for really niche use. I've tried it with 6800XT and B9 because for some reason 9 series don't support Freesync. It was a time waster to get it working and even when it does, I had to cap at 60 fps instead of potentially 80-90 which would look way nicer. And it's not perfect, any spike coming from CPU or GPU the tear would appear for a second or two. I would rather get Freesync display at this point.

Indeed, but I am curious to how it moves the tearline and what is actually happening to the timing of rendered frames.

[CoolJosh3k]

2 hours ago, Andrewtst said:

First time know got scanline sync.

 

Unless your monitor and GPU not support G-sync compatible or Freesync. Else I don't see this scanline sync is worth to use as from the information link above showing too many compromise required.

 

If your monitor not support G-sync compatible or Freesync, it is better just get a new monitor IMO.

You’re confusing 2 different technologies.

 

G-sync lowers your refresh rate to match your low FPS.

Scanline Sync lowers your FPS to match your refresh rate.

[Bombastinator]

6 minutes ago, CoolJosh3k said:

 

You’re confusing 2 different technologies.

 

G-sync lowers your refresh rate to match your low FPS.

Scanline Sync lowers your FPS to match your refresh rate.

Was trying to figure out how to put that in a way that made sense.

[Andrewtst]

Just now, CoolJosh3k said:

 

You’re confusing 2 different technologies.

 

G-sync lowers your refresh rate to match your low FPS.

Scanline Sync lowers your FPS to match your refresh rate.

Sorry for that.

 

May I now what is the benefits using scanline sync as I find it is so troublesome to use and most games already can limit the games fps.

 

Also for monitor with 240hz is very hard to reach 240fps where no longer an issue.

[Stahlmann]

2 hours ago, CoolJosh3k said:

Your confusing 2 different technologies.

 

G-sync lowers your refresh rate to match your low FPS.

Scanline Sync lowers your FPS to match your refresh rate.

So why don't just lock the FPS to your refresh rate? There's a simple setting for that in both AMD and Nvidia's drivers.

[CoolJosh3k]

6 hours ago, Andrewtst said:

Sorry for that.

 

May I now what is the benefits using scanline sync as I find it is so troublesome to use and most games already can limit the games fps.

 

Also for monitor with 240hz is very hard to reach 240fps where no longer an issue.

The most obvious is eliminating a the tear appearing on screen, where the top and bottom are mismatched. It also will get rid of a difference in timing between frames (the part I personally care about).

As a side benefit, your system take less energy to run, puts out less heat and will run quieter.

However, it comes at the cost of some latency and is going to work properly if you have like 99.9% of your frames being rendered in time.

[CoolJosh3k]

4 hours ago, Stahlmann said:

So why don't just lock the FPS to your refresh rate? There's a simple setting for that in both AMD and Nvidia's drivers.

It is complicated and I actually want to know specifically how RTSS’s sync method works.

 

A simple frame rate cap is just that. Those sync technologies, like the basic (and terrible) Vsync, instead stop working on rendering a new frame until your monitor is ready for another.

 

Worst case: it’ll see the monitor needing a new frame in 8.33ms (for example) and start working on the next render asap. It may well finish in just 4ms and when the monitor is ready after 8.33ms, the image it’ll display is already 4.33ms old.

Best case: we somehow figure out it’ll take 4ms to complete a frame render and so do nothing for 4.33ms and then start the workload. Render would be completed just in time, leaving 0ms of delay.

 

Locking the frame rate would be inserting an arbitrary delay between starting each render. It is also imperfect and not synced exactly to the right timing.

 

My question is how exactly Scanline Sync can get such a low latency.

[BuzzingBee]

7 hours ago, CoolJosh3k said:

Indeed, but I am curious to how it moves the tearline and what is actually happening to the timing of rendered frames.

Tearline can be moved by pressing hotkey manually but varies from one game to another.

Can't say about how scanline sync really works as I'm no expert in that field, I am casual player who just want tear-free experience. Maybe try asking on different forum like blurbusters.

[Doobeedoo]

12 hours ago, CoolJosh3k said:

Thanks, but that is just a how to and does not cover how it works in detail

Well it allows you to choose specific scan line, basically setting it like off middle of display where you mostly look and notice it, to bottom like so. Really it's like a buffer showing the some what close to latest near done frame per say, so you don't see mid screen tear or multiple. Difference is that it doesn't work with fluctuating frames like hardware based VRR does, so it doesn't sync the refresh rate to the rendering of the frames. It adds a frame or so delay vs not having at same framerate. Need powerful GPU.

[CoolJosh3k]

That is the thing. Once you set the tearline position it stay there. It doesn’t move at all like it would with a frame rate cap.

Somehow they do this in a really clever, but complicated way that results in still having a really low input lag.

 

Sounds like I will indeed have to ask over on blur busters. I plan to share the answer her if I get one. Sadly it is not possible without the old method of creating a blur busters specific account

[Gemini Saga]

On 9/13/2022 at 2:53 AM, Stahlmann said:

So why don't just lock the FPS to your refresh rate? There's a simple setting for that in both AMD and Nvidia's drivers.

It's because this increases input lag. In the study below it was demonstrated that Vsync is what increases input lag the most, followed by frame rate cap. 

A Measurement Study of Vertical Synchronization Configurations in PC Video Games. (wustl.edu)