game timer is actually a frame counter

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I shortly wrote about this issue already 6 month ago:
http://harddrop.com/forums/index.php?s=&showtopic=2035&view=findpost&p=18342
http://harddrop.com/forums/index.php?s=&showtopic=2035&view=findpost&p=18411

Basically as you all know the timer ingame counts the frames and not the actual 
time and assumes that the game runs at 60 fps.
Altho I see that a timing based on frames (and probably input cycles?) is not a 
bad idea by default (if we can assume a capable machine running the game), I 
think this needs to be fixed. Especially when we plan to have some sort of 
competitive 40L online leaderboards.
I'm not suggesting to put in some wild anti-cheating efforts, so that ppl can't 
fake their 40L scores online, they always will probably, if they really want 
to. Since this problem can occur for many reasons tho, since it is essentially 
an engine problem, I think it is worth to be fixed.

The reason why I came accross this issue again, was purely by accident. I 
opened up a second nullpo instance, to watch an older replay, while I didn't 
want to disconnect the other instance from the netplay server. I watched the 
replay and noticed that it was somehow really slow. That's when I noticed both 
instances were running at exactly 30 fps, instead of 60. This means you can 
considerably slowdown the game clock (on purpose or not), even without the use 
of any external programs - beating nullpo with nullpo itself so to say.
So I just opened another 2 instances (total of 4), and played one single 40L 
game on the HD server. => 23.98 - you can download the replay, it looks 
perfectly fine @ 60 fps, but was actually played at 15 fps, very casually, with 
many missdrops etc.

What steps will reproduce the problem?
1. Open more than one nullpo instance.
2. Observe that the actual framerate of all windows is: 60 fps / #instances
3. Play a 40L game (online or not) - record uploads fine, replay doesnt show 
any hints of lowered frame-rate / slower game clock.

Original issue reported on code.google.com by bob.ins...@gmail.com on 31 Oct 2010 at 8:34

Attachments:

• netreplay.rep

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I'm sure some of my gamerate/TAS detection code is still in there. We can use 
that. (Basically, it would mark a game as a TAS when it was played below 95% 
normal rate on average.)

Original comment by Zirc...@gmail.com on 1 Nov 2010 at 4:02

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That also sounds good.
I'd suggest a simple integrity check regarding the actual real-time of a game, 
without getting into high precision timers and stuff like that. Just take a 
normal time stamp at the start and end of the game (with simple precision of 
some 10ths of ms, e.g. of the OS scheduler) and check if the actual time played 
differs too much from the calculated game time (meassured with frames), e.g. by 
more than 100ms.
This should be enough to detect most games, which would produce invalid 
high-scores by playing at a low frame rate.

Original comment by bob.ins...@gmail.com on 6 Nov 2010 at 3:19

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That's basically what my TAS detection does. 100ms isn't a very wide margin 
though, I've had replays save at 98% rate (which is very much larger than 100ms 
difference) so something that small would probably not be very good.

Original comment by Zirc...@gmail.com on 8 Nov 2010 at 8:16

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hm interesting to know - if you say > 100ms is not very uncommon, the current 
timer is imo not usable for timed highscores on a real leaderboard then.
I mean if someone easily can get a time that is .1 sec better (and won't even 
feel much/any lag, cause the framerate is still about 60Hz), just by running 
the game on a slower computer, that should not be allowed, por at least not 
regarded as a valid record, e.g. for 40L.

Original comment by bob.ins...@gmail.com on 8 Nov 2010 at 9:51

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This gives me an idea: Record the system ticks at start, and record the system 
ticks at every 60th frame. During replay playback, add a second FPS counter 
above the usual one to display what FPS the replay was recorded at, by taking 
60/(timestamp[t]-timestamp[t-1]) and updating it every 60th frame.

This would allow you to see just where the replay was slowed down, since a 
constant 57 FPS is a different story than playing the first 90% at 60FPS and 
the final 10% at 30FPS, but both would have an average rate of 95%.

Original comment by Poochy.EXE on 9 Nov 2010 at 1:48

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@5: I like that idea a lot. This would make potential new high-score replays 
really easy to verify.

The problem with games that are unintentionally played at a slightly lower 
frame rate still exists tho, and should be addressed. A short example with 
numbers:

Let's say the new legit 40L record on the leaderboard is exactly 25.000 sec (= 
1500 frames) and was played on a normal machine, which can easily handle 60 fps 
at all times. Now someone plays on a netbook for example, and pretty steadily 
averages the mentioned 57 fps, this means his game still runs about as smoothly 
as anybody elses. A game is played on that computer only using 1490 frames, 
i.e. 24.833 sec in game-engine time! With a rate of 57 fps this game actually 
took 26.140 sec tho, which surely shouldn't be regarded as a new 40L record.

Original comment by bob.ins...@gmail.com on 9 Nov 2010 at 2:30

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also, what I forgot to mention: this is of course not only an issue for online 
leader-boards and their integrity (as I said, if people want to find a way to 
insert faked scores, they probably always will), but also for everybodys own 
personal high-scores played in offline mode.
Looking at the above example, even tho I'm not a fast player at all, how can I 
trust my new personal best / record, if I'm not playing on a machine, where I 
can guarantee that I have 60 fps 100% of the time? Since we're easily talking 
of margins > 100ms or even whole seconds here.

Original comment by bob.ins...@gmail.com on 9 Nov 2010 at 2:38

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Just wanted to check if there are any plans to address this issue somehow in 
the near future, just discussed this with paradox again.

Detecting slowdowns/speedups with the new percentage display is fine, but 
doesnt really fix the issue that the clock is off and your own timed records 
can't really be trusted.
I tried a couple different fps limiter settings on config page 3, but still get 
103-105% etc.

Fixing this is probably not something for 7.5, but I think changing the way 
timing is handled (not fps based) should be addressed sometime.

Original comment by bob.ins...@gmail.com on 4 Jan 2011 at 5:12

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nullpomino should skip frames instead of slowing down, this will fix most of 
issues.

TAS detection / game rate you talking about is really pointless, because if 
somebody want to cheat, he will most likely slow down real time clock with 
cheat engine.

Original comment by w.kowa...@gmail.com on 4 Jan 2011 at 10:47

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I made two meassurements, recording the sound for 40L games, to measure the 
approximate real-time of these game, while having a 100% stable system during 
the recording. (in contrast to video mostly)
I took the time of the audio recording as a lower boundary, meaning the game 
must have lasted at least that long. Starting from the beginning of the first 
preview piece sound (after the two beeps), and ending with the beginning of the 
last line clear "crash" sound, ofc using no line clear delay.

The settings (page 3) I used were:
(I) vsync: on, sleep timing: render, dynamic adjust: off, perfect mode: on, 
perfect yield: off
(II) vsync: on, sleep timing: render, dynamic adjust: on, perfect mode: on, 
perfect yield: off
All on slick. Judging from the descriptions these options should be the 2 
candidates for the mose accurate fps limiting, granting a capable machine 
running the game.

Results:
(I) showed a time that was 0.10s faster (~ 6 frames) than the realtime of the 
sound recording. (the rate/% display showed 103% btw, which makes no sense in 
this case, because the game didn't ran faster but actually slower apparently, 
judging by the ingame time)
(II) showed a time that was 0.08s faster (~ 5 frames) than the realtime

System specs:
3GHz Phenom II Quadcore, 4 GB RAM, ATI 4870

We just discussed this issue on IRC a bit.
Wojtek proposed the implementation of a frame skipping mechanism, to improve 
accuracy of the timer. (just saw that he posted about it himself) While I agree 
that his is a good idea and probably a fix for low-end machines that can be 
implemented without creating too much headache for adjusting the rest of the 
code relying on the timing engine of the game (such as replays, etc), I don't 
think it will address the problem that currently exists for mid- to high-end 
machines, which are capable of rendering a lot more fps, and thus would never 
skip a frame in the first place.
We can see from the results above that these machines, which should be expected 
to give the player accurate timings for his records, cause they are fully 
capable of running the game as good as they can, still cause inaccuracies in 
the range of 0.10 seconds or maybe more.

We also discussed the issue of replays a bit and the problems that exist with 
it, if they wouldn't be recorded or played at 60fps.

Since it would not change the behaviour of how replays are played at all (just 
do this the same way), I propose the addition of high precision/resolution 
timers (as they are commonly used for game development) to get improved game 
times, which can be accurate with a precision of at least 1ms on a normal pc 
system. I used them in C++ for both windows and linux before, never in java 
though, but I do know they exist there. (maybe System.nanoTime() is good?)
I can't vouch for their precision in the area we would need, but I think they 
should be more than fine, because we are just talking about an end-time we show 
down to 10ms increments, which is easily achievable for any real-time 
measuring, even when done on a pc system (which is not designed for this task 
at all actually), if it does not go through the os scheduler ofc.

I think it is worth to look into this option to provide more accurate timings 
and therefore records in the long run. Regarding the issue of replays, I would 
play them just as it is done now, meaning if it is recorded at lower fps, and 
watched on a more powerful system, it just runs faster. If timestamps would be 
saved with every frame or just key frames for that matter, it would be possible 
to display a more or less correct clock on the side, not in a sense that the 
clock would run right on the more powerful system that watches the replay, but 
actually giving the timings that occured when the replay was recorded, which in 
my opinion is what matters here. There is definitely no need to try to adjust 
playback of the replay that it somehow would match the original speed, how it 
was recorded, which is most likely way too much effort for no real gain here.

I can't evaluate how much issues this cahnge would create for other parts of 
the game that rely on the timing engine, but it could be kept minimal when it 
would be implemented by just getting the clock/time data from a high reolution 
timer and keeping the rest as is.

Original comment by bob.ins...@gmail.com on 4 Jan 2011 at 11:24