Is there Input Lag with FPS Smoothing?

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ironhorse
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Is there Input Lag with FPS Smoothing?

Post by ironhorse » 08 Aug 2014, 14:59

I cannot find any technical details or documentation on how frame rate smoothing is being done by some game developers such as PS2:
https://forums.station.sony.com/ps2/ind ... ng.155313/

They aren't just capping FPS, (it's done internally at least!) but also somehow lessening the frame time variance between frames.. I am unsure if they are throwing these high FPS frames away, buffering them first then lowering them somehow, or just using sorcery.

So my question is : Will whatever method that is being used to employ "FPS Smoothing" incur input delay? If so, how much exactly?

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Re: Is there Input Lag with FPS Smoothing?

Post by Chief Blur Buster » 11 Aug 2014, 04:32

VSYNC ON is typically the common method of framerate smoothing, and it does add input lag. Running at 30fps @ 60Hz can create much more consistent motion than wildly-fluctuating framerates. 60fps @ 60Hz is much better, but isn't common on older PlayStations until the PS4 came along (and even so, not all games).

Historically for 3D rendering, many kinds of FPS smoothing can incur input delay. Sometimes it is a tradeoff between fluidity and latency (e.g. VSYNC OFF versus VSYNC ON).
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Re: Is there Input Lag with FPS Smoothing?

Post by RealNC » 11 Aug 2014, 15:09

Framerate smoothing does add latency. No way around it, since it's based on rendering frames ahead of time and presenting them at a fixed interval rather than immediately. Every time you introduce a delay before showing a frame you already rendered, that's input lag.

The amount of lag you get depends on the amount of frames that are being rendered prior to showing them.
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Re: Is there Input Lag with FPS Smoothing?

Post by Chief Blur Buster » 11 Aug 2014, 18:20

RealNC wrote:Framerate smoothing does add latency. No way around it
Except with GSYNC, but that's a very different method of refreshing a display, and can't be done by a game developer. It's a monitor technology that is doing this.

It makes fluctuating framerate really smooth looking, by allowing the display refresh to be at non-discrete intervals -- monitor refresh cycles stay in sync with framerate even with erratic framerates -- as explained at www.blurbusters.com/gsync/preview
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Re: Is there Input Lag with FPS Smoothing?

Post by ironhorse » 16 Aug 2014, 02:31

Chief Blur Buster wrote:VSYNC ON is typically the common method of framerate smoothing, and it does add input lag. Running at 30fps @ 60Hz can create much more consistent motion than wildly-fluctuating framerates. 60fps @ 60Hz is much better, but isn't common on older PlayStations until the PS4 came along (and even so, not all games).

Historically for 3D rendering, many kinds of FPS smoothing can incur input delay. Sometimes it is a tradeoff between fluidity and latency (e.g. VSYNC OFF versus VSYNC ON).
Ah, but see these devs aren't employing VSYNC - they say as much..

This seems like a relatively new method to me. That's what has got me thinking.. this is is more akin to the game engine internally capping frames, which you say incurs no input delay. (or at least compared to external methods)

Meaning this isn't like VSYNC or "Maximum Pre-rendered Frames"... (unless there's a delay associated with the way they are capping these frames, internally)

I suppose a more simple way of asking is: If you throw away frames OR dynamically and internally frame cap so that it mimics throwing away wildly varying frames, all in the name of smoothing out the fps for whatever amount you may be achieving.... will it incur delay?
If so, why? How is it any different than a game engine level internal fps cap and is there a measurable (in ms) difference between the two?

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Re: Is there Input Lag with FPS Smoothing?

Post by RealNC » 16 Aug 2014, 08:14

Framerate smoothing and capping are two different things. Capping doesn't introduce big delays (there's still a small delay, since waiting is still involved, but the game can be smart about it.)

If you cap the framerate to 30FPS in order to "smooth" it out, then that's not framerate smoothing. That's just capping.

Smoothing on the other hand, doesn't necessarily cap the framerate (though it can and usually does.) It's different to a simple cap in that it keeps some frames in reserve when rendering takes too long and presents them in those cases so that there won't be a stutter.

Doing this at 30FPS would feel atrocious, btw. Framerate smoothing needs 60FPS+ to be useful. But I guess they might still do it at 30FPS on consoles, since no one cares about latency there. Most console games feel like they have half a second of input lag, but people still play them.
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Re: Is there Input Lag with FPS Smoothing?

Post by trey31 » 16 Aug 2014, 10:23

RealNC wrote:Most console games feel like they have half a second of input lag, but people still play them.
I originally played Dead Space on PS3 and despite at least an hour of trying, I never got past the asteroid defense turret part in Chapter 4 Obliteration Imminent. Apparently I wasn't alone, as there are absolutely tons of posts about it on the intrawebs. I gave up on the game entirely. Then I bought the game for PC during a Steam sale (or Amazon Digital sale) and with a cheap wireless "gaming" mouse (and 1080p @ 120Hz vs 720p @ 30Hz) easily passed that section on the first try (on Medium difficulty) and hull integrity only dropped to 67% (it starts at 85% and when it drops to 0% you die and have to start over). Now I can get passed it without it dropping below 80%, which is funny because after an hour of frustration with a PS3 controller and 30fps with massive amounts of input lag I couldn't get passed it at all.

What was an intense and frustrating experience when dealing with console input lag, became easy to the point of being monotonous when input lag was no longer a significant factor.

Consoles stink, even the "new" ones.

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