Hi there,

I have searched this subforum, but found no answer yet. Sorry, if this has been asked before.

I have a new Intel Core 2 Duo EN6600 which runs fast as lightning. My GFX-Card is a rather small-prized ASUS 7600GS, but it's enough to run LFS with nice graphics at a limit of 60fps, which is all my old TFT can display.

Now I heard the rumor, that limiting the FPS in LFS will also limit the frequency at which LFS processes inputs (from my steering wheel).

If this is true, I think it could be a big disadvantage for me in races.

And what if the framerate drops lower than 20 (for example, that was the lowest framerate on my old PC). Will this result in my car bouncing left and right, due to a "lag" of input signals?

I allways thought, LFS does the physics calculations at 100Hz, no matter what FPS I have.

So what about this rumor? Is it true?

I feel perfectly comfortable playing with my limit 60fps and never noticed any problems.

BTW: What's the optimum minimum sleep setting? The lowest as possible? I have 3ms right now.

Thanks for your replys!

Regards,

HorsePower

EDIT: What if I turn limit FPS off, but VSync on? Has this also the effect of slowing down input processing?

Vsync will reduce your FPS to the refresh rate set on your monitor.

IMO Vsynch should always be off unless you get real bad texture tearing.

never heard anything about limited FPS limiting the physics calcs though.

Dan,

There is no disadvantage in using vsync, the physics engine rate is not linked to the graphics engine - I forget how many Hz is speculated that the physics engine runs at.

One could debate that visually there might be a slight advantage of sorts since the framerate is consistant throughout the session instead of flunctuating, much as using the limit FPS option by itself... but it just might be more psychological than anything else. (unless we're talking under 30fps)

EDIT:
The engine runs at "100Hz with 20 uninterruptable sub-updates", according to this wiki entry:
http://wiki.lfs.4players.de/index.php/About_LFS

The main physics loop runs at 100Hz, that includes player inputs, collision detection, etc. In each loop the tyres physics have 20 sub-updates, so you could say the tyres effectively run at 2000Hz.

When my framerate drops really low the game WILL become a bit sluggish. The wheel will have poor response, the pedals aren't affected too much, but the car is a whole lot harder to drive and is very prone to making you spin out.

I've had way too many situations where my FPS drops to an incredibly low amount and I just cannot make it through in one piece (sometimes I do and man is that pure luck).... but like for example going through the SO Classic chicane where there is lag and pileups, my FPS could be struggling and I see a gap I can fit through in my tiny UF1000 and it is just so hard to get the car where I want it to go because I have so much video lag .

I am not sure about the physics calculations, I am pretty sure you really just get poor framerate, and things start to skip and bog down. I do believe that with each "studder" your inputs are frozen for a short while...because that would only explain why the steering would get stuck in one position, or the pedals as well.

Maybe the framerate drops WHEN the game becomes sluggish instead of the other way around?

Meaning, are you sure it's the framerate constraining the physics engine and not the other way around, due to a weak CPU for example, in your case?

Thanks for the answers so far.

I think, when the computer is slow in general, such that the fps will drop down to the bottom, it clearly will affect the input processing (since the machine is just overstrained (right word?) ). Dynamic detail reduction helped me on my old machine.

I noticed that on my new PC, VSync really makes it better (visually)

In the german version of the LFS manual (there's no such comment in the english version), there's said

Quote :

FPS limitieren: Limitiert die Framerate im Spiel auf einen bestimmten Wert. Bei schnellen Rechnern sollte sie auf 100 FPS limitiert werden, da die Physikengine auch nur mit 100 HZ (entspricht 100 FPS) arbeitet. Eine höhere Framerate frisst also nur Rechenpower, bringt aber nichts, da sich die einzelnen Bilder nicht voneinander unterscheiden.

Which in negation could mean, that low FPS leads to low input processing and physics calculations. I don't believe that to be honest.

I really would like to hear the devs comment on that (can you here me, devs? ).

At the end of the day(correct me if i'm wrong)if the wheels run @ 2000Hz and you say the gfx engine runs at about 100Hz.These two factors are running while your fps are variable , and seeing as the only method of control is viually , your gfx engine/control input frequency may as well be that of your fps .yes/no
ie. your gfx/control engine may as well be variable even if it's constant...

I don't know. That's why I'm asking here.

Let me put it together again:

Physics @ 100Hz (Q: Does this depend on the FPS?)
Tyres @ 20 x Physics (= 2000Hz, but varying, if physics calculation rate varies).
FPS @ Whatever I want / my computer is able to do.


If the answer to the question in bold letters is "YES", then my next question would just be:

Does it depend only on the hardware-limit of the FPS (i.e. what my computer is able to do), or on the software-limit (which I put in by activating VSync or specifying a fps-limit). If software-limit, then is there a difference between VSync and fps-limit?

I really would like to hear more opinions. Thx alot!

AFAIK - Physics are ALWAYS 100Hz, regardless of whether your framerate is 1 or 1000

Quote from Jakg :

AFAIK - Physics are ALWAYS 100Hz, regardless of whether your framerate is 1 or 1000

I agree but when the fps are low everything else goes out the window'

last week i used a 64mb graphics card i was able to drift and get around 1.30 reversed blackwood, good enough for me. this is ranging from around 40-50fps my graphics car broke and had to fit my old 16mb graphics card now i get around 30fps on a good day but i am struggling to get 1.35 on the same track and i cant drift at all. the steering does turn around half a second later and when your sliding and then the car straightens up again i have no chance in holding the car in a straight line.

is your power supply unit up to the job of powering the graphics card processor and what ever you have in the usb socket/s?

Hey, I didn't say I have a problem. Everything runs fine. Concerning the gameplay-feeling and my pb's I even don't recognize any difference between my new and excellent running system (fps limited @ 60, but surely higher fps are possible) and my old AMD 2000+ with GeForce4 Ti4400 (fps around 20-50 with low gfx settings).

This is meant to be a more fundamental question.

But I'm wondering how you are able to play with a 16MB gfx card at all? This sounds weird to me. Even 64MB is pretty low. So I suppose your whole system is running at the limit and that indeed may affect the input processing of LFS.

amd athlon xp 64 bit 3700+ san diego processor does the job just nicely but the input lag is bad. with all of my computer going to the graphics because the 16mb card is doing j@ck sh!t other than sending a few colours to the monitor.

not a problem really but i do need a better graphics card

graphics settings are set quite high actually other than the mip bias i put that on 0.00

I think the problem with low frame rates isn't that the physics engine is slowing down but that you are receiving visual feedback with too much of a delay. That is, the state of the simulation on the screen is different to what is actually happening in the internal physics loop. This means that you could actually be making the wrong inputs as you're reacting too late.

^ Yup, I agree.

I don't think the physics go haywire, but rather the most important input source you have. When fps get low, the delay between what happens in the physics and what gets displayed grows bigger.

But then again, we don't really know any technical details of how Scawen programmed the physics engine, so everything's just wild guessing anyway.

Yes, I would say the actual physics are unaffected by framerate, but it is confusing because we're told that the physics limit the framerate.

e.g 100fps vs. 1fps: lots of cars close to your car, a lot of calculations to be made. The 100fps pc will show you 100steps from point A to point B within 1 second correct? The 1fps pc will only show you where everything ends up after that one second, but if the physics are unaffected by the framerate, then it will all end up in the right place, and that would only happen because it made the 100 steps along the way.

So why do the physics limit the framerate and why, if the physics are so cpu dependant, do the graphics seem to rely on the cpu so heavily too?

Quote from AndroidXP :

I don't think the physics go haywire, but rather the most important input source you have. When fps get low, the delay between what happens in the physics and what gets displayed grows bigger.

Yeah, kind of like closing your eyes briefly every so often when driving in real life... your inputs are still being processed but you're not quite getting all the info you need. That's how I see it.

This is Michael's guide on FPS in LFS:

FPS below 40: If it's really sucking, it would compare to racing your nice Subaru STi with no seat. Basically a waste of time. Towards the upper end of this bracket it's like racing with a crappy seat with no lateral support and no seatbelts. "You are not going to compete with the hotshots with no seatbelt and a shitty seat!"

FPS 40 - 60: Now you're doing alright. You have your nice seat with lovely bolsters and seatbelt and you are able to feel what the car's doing and control it pretty well. Maybe you also have one of those g-lock things to keep the lapbelt tight and hold you in place a bit better. Things are good, and any disadvantage isn't so bad that you're going to be off the pace just because of this one factor. "If you've got the minerals, you'll be fine."

Constant FPS of [insert desired number here]: Your setup is the shiznit. You have a racing seat and 6-point harness and your car starts singing that lyric "when I move you move, just like that". You feel everything the car does and this helps you squeeze the maximum out of it given your current ability level. "The only thing holding you back is your lack of talent, boyyyyyyyy."

Quote from sinbad :

So why do the physics limit the framerate and why, if the physics are so cpu dependant, do the graphics seem to rely on the cpu so heavily too?

Well, I wouldn't call it heavy relying, but of course you also need CPU power for doing graphics stuff. And in LFS the priority is clearly on physics, so when physics take up much CPU time, the graphics get the cut and have to wait till the CPU continues processing the graphics data.

On my current PC, with anti-alaising on (it's a must) I get an average of 40fps. I only ever notice 'low fps' when it gets to 20 or less. Anything more than 20 is fine (for short periods), and anything over 40 for me is indistinguishable.

I would like, however, the CPU power to turn on more AA/AF, and a guaranteed 40fps minimum at any point, at ay time, which is why I've just ordered some new bits for the PC

AA and AF will be controlled/limited by your GPU rather than your CPU.

As for FPS, I would personally say 60fps is a good minmum, I find it quite easy to distinguish between 30fps and 60, 60 is just so much smoother, although my system easily runs 120fps with all detail at full and 4x AA and 16x AF, I have to limit my FPS to 90 otherwise I get small stutters.

I would say that LFS works on the basis that the physics calculations are done first mainly by the CPU, and given priority, while whatever is left over graphically is done by the GPU, which is why physics have an effect of FPS, if your system doesnt have enough "left over" after the physics have done there bit then you will suffer, likewise, it you don't have a decent GPU to handle the graphics so your CPU doesnt have to you will suffer, it is probably quite important therefore to have a decent GPU.

I wonder exactly how much overhead the physics calcs actually have?.

Dan,

@tristan:
Well, anything below 30 is awful for me, because the actual visual stuttering/laggyness gets distracting. I don't mind if it dips to 30 or so at times in crowded situations mostly at the race start, but I'm quite happy with it staying atleast 50+ most of the time.

Also I can quite confidently say that I notice the difference between 30 and 60 fps, and the common "urban legend" that a human can't notice more is pretty much BS. Maybe at 25 a picture starts to look "fluent", but that doesn't mean you cannot notice a difference. The best example for this is: how does it come I instantly get a queasy feeling when seeing a 60Hz (= 60 frames per second) monitor? I also notice the ever so slight blinking of it at everything around the focal point of my eyes. That also demonstrates how eyes do not work like a fixed framerate videocamera. At the focal point you kinda have highest resolution but slowest updaterate, while at the corner of the eye you sacrifice alot of resolution/detail for faster processing.

Anyway, the last thing you need for AA/AF is CPU power. Afaik AA/AF is something that is done 100% by the graphics card, because it doesn't actually need any new vertex (polygon) data from the CPU, but is just visual postprocessing.

I am waiting for the "well the human eye can't detect anything over 24fps" bullcrap LMAO.

Dan,

Quote from AndroidXP :

@tristan:
Well, anything below 30 is awful for me, because the actual visual stuttering/laggyness gets distracting. I don't mind if it dips to 30 or so at times in crowded situations mostly at the race start, but I'm quite happy with it staying atleast 50+ most of the time.

Also I can quite confidently say that I notice the difference between 30 and 60 fps, and the common "urban legend" that a human can't notice more is pretty much BS. Maybe at 25 a picture starts to look "fluent", but that doesn't mean you cannot notice a difference. The best example for this is: how does it come I instantly get a queasy feeling when seeing a 60Hz (= 60 frames per second) monitor? I also notice the ever so slight blinking of it at everything around the focal point of my eyes. That also demonstrates how eyes do not work like a fixed framerate videocamera. At the focal point you kinda have highest resolution but slowest updaterate, while at the corner of the eye you sacrifice alot of resolution/detail for faster processing.

Anyway, the last thing you need for AA/AF is CPU power. Afaik AA/AF is something that is done 100% by the graphics card, because it doesn't actually need any new vertex (polygon) data from the CPU, but is just visual postprocessing.

I totally agree on this. This "Urban legend" [lol] as you call it and what i have heared from other persons is totally mischief. Anyone who says there is no noticeable change between 30- 60 fps or 20- 40 or whatever probably never played games like quake, CS - you name it. Games where every single frame is important for the handling & feeling. I would say the best framerates are around the refresh rate of the monitor or way above. That should be at least (absolute minimum) 75 to 120+ fps. The average value should be with full grid or alone at least 40-60 fps. Everything below is a joke and will give you psychological damage at longer play periods . As for the fps limiter, with my 7800gtx i could go above 100fps, but not at every situation. With a full grid i have around 50-90 fps so i set the limiter to 100 max and added AA which gives me the best result, visual & overall.