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RTSS now has new automatic Low-Lag VSYNC ON (raster based)

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Re: RTSS now has new automatic Low-Lag VSYNC ON (raster base

Postby DsKri » 13 Jun 2019, 22:12

You're a legend.

Thanks for replying so quickly this is exactly what I was looking for.

Also I appeciate yourself and others such as @RealNC for being so patient in explaining the same things for the umpteenth time.
The TL;DR states the same as many posts elude to and with a little more careful reading I could probably have dug out the answers myself, so I'm very thankful for you running through that again.
And to for being unrelentingly willing to provide innovations and support. It goes such a long way! :mrgreen:
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Re: RTSS now has new automatic Low-Lag VSYNC ON (raster base

Postby EeK » 19 Jun 2019, 02:59

Hi, everyone, I'm new to these forums, but not to low-lag gaming without tearing.

I was just wondering if the how-to posted by @Chief Blur Buster here is still up-to-date, or if there's a more recent write-up somewhere else.

Also, I use a 4K TV (LG OLED C8) as a monitor, and for 3840x210 resolutions, Scanline Sync is set to -140. Does that sound right to you guys? I mostly see people mentioning their settings for 1080p displays.

Finally, Chief Blur Buster mentioned in a post that you can use SS in conjunction with Fast Sync (my GPU is a 1080 Ti), for games that are too demanding. If I do that, do I have to limit the framerate to my TV's refresh rate in RTSS (like the "traditional" low-lag method), or should I leave it uncapped, just like for SS with VSync off?

Thanks in advance, I really appreciate the work you do here.
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Re: RTSS now has new automatic Low-Lag VSYNC ON (raster base

Postby Chief Blur Buster » 20 Jun 2019, 10:09

Scanline Sync is defacto framerate limiting.

Simple TL;DR: Scanline Sync in its usual mode, will limit framerate to matching refresh rate.

Technical TL;DR: It's essentially a beamraced pageflip mode at the raster scan line position you want (adjustable tearline location), once or twice every refresh cycle. This minimizes framebuffer backpressure as much as possible, by bypassing all the VSYNC ON framebuffering logic built into graphics drivers. Essentially Scanline Sync creates a new sync mode using the VSYNC OFF mode that looks like VSYNC ON in appearance (and self-capping like VSYNC ON) if the game's frametimes rarely reach a full refresh cycle.

Now, although Scanline Sync is normally used with VSYNC OFF, it will self-cap to Hz with all other sync modes (including Fast Sync too). Layering two sync modes is tricky, so make sure that you do the tearline pre-calibration before you use it.

For games whose framerate rarely reaches refresh rate, the use of S-Sync has little to no benefits.
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Re: RTSS now has new automatic Low-Lag VSYNC ON (raster base

Postby EeK » 20 Jun 2019, 18:08

Chief Blur Buster wrote:Scanline Sync is defacto framerate limiting.

Simple TL;DR: Scanline Sync in its usual mode, will limit framerate to matching refresh rate.


Hey, Chief, thanks for replying.

I didn't understand most of the technical explanation, but the simple one was easy enough for me to follow, so I appreciate it. :lol:

I've been playing Bloodstained: Ritual of the Night, a game that's very easy on the GPU. In 4K, I can get upwards of 400 FPS (uncapped) on my 1080 Ti, running with the highest settings. So, obviously, I decided to test some even higher resolutions, using DSR.

Up until 5760x3240 (2.25x), I can use Scanline Sync without any issues, as the framerate constantly stays above my display's refresh rate of 60 Hz. 6651x37741 (3.00x) doesn't show up in-game, so the next step is 7680x4320 (4.00x), which is essentially 8K.

With the framerate uncapped, I see an occasional drop to 58 or 59 FPS. I figured I could still use S-Sync with that kind of performance, but as soon as there's a dip, no matter how small, the framerate is halved to 30 FPS - and remains halved for the duration of gameplay.

Is that normal? That's with V-Sync off, btw.
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Re: RTSS now has new automatic Low-Lag VSYNC ON (raster base

Postby RealNC » 21 Jun 2019, 04:01

EeK wrote:With the framerate uncapped, I see an occasional drop to 58 or 59 FPS. I figured I could still use S-Sync with that kind of performance, but as soon as there's a dip, no matter how small, the framerate is halved to 30 FPS - and remains halved for the duration of gameplay.

Is that normal? That's with V-Sync off, btw.

Yes, that's normal. If the current vblank is missed, meaning the frame took longer than 16.67ms ,it needs to wait for the next vblank, which will come 16.7ms later. So the frame interval becomes 33.3ms, which of course is 30FPS.

The "vblank" is the vertical interval of the display signal. It is the time between the end of the final pixel line and the beginning of the next first pixel line. Scanline sync waits for that before displaying a frame, because anything that happens within the vblank is invisible. Meaning tearing becomes invisible.
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Re: RTSS now has new automatic Low-Lag VSYNC ON (raster base

Postby EeK » 21 Jun 2019, 15:56

RealNC wrote:
EeK wrote:With the framerate uncapped, I see an occasional drop to 58 or 59 FPS. I figured I could still use S-Sync with that kind of performance, but as soon as there's a dip, no matter how small, the framerate is halved to 30 FPS - and remains halved for the duration of gameplay.

Is that normal? That's with V-Sync off, btw.

Yes, that's normal. If the current vblank is missed, meaning the frame took longer than 16.67ms ,it needs to wait for the next vblank, which will come 16.7ms later. So the frame interval becomes 33.3ms, which of course is 30FPS.

The "vblank" is the vertical interval of the display signal. It is the time between the end of the final pixel line and the beginning of the next first pixel line. Scanline sync waits for that before displaying a frame, because anything that happens within the vblank is invisible. Meaning tearing becomes invisible.


That makes sense, thanks for the information. Also, good to see you around these parts, you've helped me before on the Guru3D forums, haha.

Still on the subject of Bloodstained, the game received an update and now I can't seem to get S-Sync to work on any resolutions other than native. 8K makes the game slow to a crawl and run at around 15-20 FPS. And even with slightly lower resolutions, like 5760x3240 and 5120x2880 (which used to work fine and run smoothly with S-Syn at 60 FPS), the framerate also becomes a stuttery mess and dips to 50 FPS and below, down to 15-20, just like in 8K.

Fast Sync in combination with S-Sync and any resolution renders the game unplayable (15-20 FPS range). Its engine is Unreal Engine 4. Any ideas as to what's going on?
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Re: RTSS now has new automatic Low-Lag VSYNC ON (raster base

Postby Chief Blur Buster » 21 Jun 2019, 18:50

It's possible some games have custom swap chains that has nasty interactions with external frame rate capping of any kind, so that can be a problem with some games. This can also be caused by game updates and other things.

But it can also be a Scanline Sync misconfiguration. Launch a known "Scanline Sync" friendly game first, before trying to tweak the problematic game.
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Re: RTSS now has new automatic Low-Lag VSYNC ON (raster base

Postby BrokeChemGrad » 10 Jul 2019, 19:10

so question, ive fiddled with the scanline numbers and i havent seen any scanlines appear in any of my games. i've tried Apex Legends and Mordhau. are you using V totals when looking for a good scanline? like say its a 1080p monitor but you have V total set to 1500. theres over 400 invisible right?
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Re: RTSS now has new automatic Low-Lag VSYNC ON (raster base

Postby Chief Blur Buster » 10 Jul 2019, 19:17

Use VSYNC OFF and keyboard strafing to find the stationary tearline (the scanline). If you cant see it, enable your tearing before you enable RTSS.

1. Temporarily turn off RTSS, and fix your VSYNC OFF and get tearing intentionally
2. Lower your refresh rate, game detail, and settings until your minimum framerate does not go below refreshrate.
3. Now begin tweaking RTSS Scanline Sync to make the tearline stationary (look for it while strafing), and tweak RTSS to "steer" it off the top edge of your screen. (Use the howto earlier in this thread)

Now you got a low-lag tearingless VSYNC OFF that is effectively VSYNC ON with absolute minimum framebuffer depth possible.

For you programmes -- it is a classic 8bit era programming trick to lower 3D render pipeline latency on ultrafast games -- essentially raster-interrupt-style beamracing the tearline location.
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Re: RTSS now has new automatic Low-Lag VSYNC ON (raster base

Postby Chief Blur Buster » 17 Jul 2019, 17:13

Some helpful information:

RTSS Scanline Sync is extremely difficult with modern games.

1. Your MUST have a framerate range above your refresh rate
2. You should use VSYNC OFF (easiest) with Scanline Sync.
3. You may need to limit RTSS Scanline Sync to older games

Reduce Your Refresh Rate To Cover Your Frametime Spikes
Your refresh rate for RTSS Scanline Sync must be below your 0.1% frametime!

1. Run uncapped VSYNC OFF
2. Measure your frametimes using RTSS
3. Find your worst 0.1% frametime spike (e.g. 10ms)
4. Now divide 1000 by the milliseconds of your biggest frame time spike (e.g. 1000/10ms = use ~100Hz)
5. Reduce your refresh rate to that number. A 10ms frametime spike means you should reduce your refresh rate to ~100Hz.

Reducing your frametime spikes to permit higher refresh rates

1. Reduce game detail
2. Upgrade GPU
3. Stick to older games for RTSS Scanline Sync
4. Some games will give you unavoidable framerate spikes

RTSS Scanline Sync only looks+feels amazing if you keep your entire framerate range above Hz

If you are unable to do this, prefer not to reduce refresh rate, or the compromises outweigh the benefits (refresh rate too low), then please consider using alternative methods such as HOWTO: Low-Lag VSYNC ON

Prioritizing on visuals and consistent glassfloor latency (even if a bit higher than a lower-but-varying lag):
When combined with Scanline Sync, there are situations where reduced refresh rates can look massively better with strobed operation (e.g. ULMB), since perfect 100fps@100Hz ULMB looks CRT quality, while 110fps@120Hz looks jittery/stuttery/harsh/ugly strobing. Oh and if you use motion blur reduction such as ULMB, please don't forget to raise mouse DPI (1600dpi+) and lower in-game sensitivity since ULMB benefits from high-DPI. HOWTO: Using ULMB Beautifully or Competitively.

Hopefully your ~0.1% or ~0.5% frametime spikes permit you to stay at 144Hz or higher, but RTSS Scanline Sync is much easier with older games like Quake, CS:GO, emulators, 60fps-limited console ports, and other games that are more amenable to avoiding frametime spikes that prevent RTSS Scanline Sync from looking amazing.

Rare frametime spike are okay, just try to minimize them
It's okay for your sub-0.1% or sub-0.5% frametime spikes to be worse (the stutter+tearing briefly appear 1 in 1000 frames for 0.1% spikes, and the stutter+tearing appear 5 out of 1000 frames for 0.5% spikes). Regardless, you must have more than 99% of your frame-rate / frame-time range above your refresh-rate / refresh-cycle-time, if you want RTSS Scanline Sync to look beautiful

For more reading, see threads
- RTSS now has new automatic Low-Lag VSYNC ON (raster based)
(easiest)

For advanced readers wanting to get into more advanced RTSS Scanline Sync as a Quick Frame Transport mode
- Optional: Large vertical totals for low input lag
- Optional: Using RTSS Scanline Sync to create Quick Frame Transport.
(harder)
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