High speed bug in 0.2.8.1 and 0.2.8.0

[Z-Man]

A physics bug found its way into 0.2.8.1, there exists an exploit by which any acceleration possible can be enhanced by a large factor.

Luckily, at the moment, only one player, subliminal.freq, knows it. It's safe to say he discovered it. I'm not going to tell you how it works just now.

As a server admin running a 0.2.8 server, you can do several things about this problem:
1) ignore it. The bug isn't totally un-fun and makes the life of your players more interesting.
2) ban whoever uses it and hope the word doesn't spread too quickly.
3) help test the server version of alpha20060507, it contains a fix for the problem. The more it gets tested, the earlier we can release 0.2.8.2 with the fix.
4) Tweak your server's settings so that the speedup gets less valuable or so high that it is certainly deadly.

Some details to what you need to know for 4:
The speedup one application of the trick gives you is roughly given by
acceleration * 4.5 * DEDICATED_FPS * ping^2
where the acceleration is the cycle's acceleration at the time the trick is applied, which may be positive or negative. It's not just the acceleration from walls, but also the residual acceleration that is applied to a cycle when the player releases the brake.
You probably don't want to touch your physics settings and the player's ping is out of your control, so your main instrument is DEDICATED_FPS. Turning it higher than 1000 probably gives physics accuracy problems elsewhere, and the higher DEDICATED_FPS is set, the more CPU load the server will consume. Lowering it below 20 gives your server additional lag.

An example: The default value of DEDICATED_FPS is 200/s, an average ping is .1s. The speedup from this is
acceleration * (4.5 * 200 * .1^2)s = acceleration * 9 s
in words, you get the speedup you'd normally accumulate in nine seconds in an instant.
Increasing DEDICATED_FPS to 1000 gives an acceleration boost you'd normally accumulate in 45 seconds, I'd say this is a deadly speed in most servers. Note, however, that the player can choose the acceleration by placing himself farther away from walls.
Reducing DEDICATED_FPS to well playable 50, as it is set on CVS Fortress, gives
acceleration * (4.5 * 50 * .1^2)s = acceleration * 2.25 s
Which still is enough to gain a considerable gameplay advantage. If I'd go with 4, I'd reduce DEDICATED_FPS to 25 and maybe go as far as to reduce the acceleration. But of course, CVS Test follows option 3, that's what it is there for.

All developers know how to trigger this trick, so if you want someone to test the deadlyness of your setup, I'm sure you can fetch one of us form IRC.

[Van-hayes]

Luckily, at the moment, only one player, subliminal.freq, knows it. It's safe to say he discovered it. I'm not going to tell you how it works just now.

Well he told everyone in a fortress game how to do it, so at least 10 other people heard how to do it, I'm not sure how many actually knew what he was talking about though.

[ed]

I've had complaints that it's being used frequently in the Wild Fortress which is running 0.2.8.1. But it's an easy excuse to use if you're beaten by another player going faster. It's like the new lag.

I'm trying to persuade the server admin to upgrade. He's sceptical about alpha's.

[Z-Man]

That eliminates option 2.

Ed's admin is right, it's better to be careful with alphas. This one is looking good so far however, no BUG cries for over 24 hours If that continues, it'll be relabeled rc1 soon. We can't accelerate the release process too much, I'm afraid. To full 0.2.8.2, it'll be about two weeks. I'll keep you all informed about bug cries and other known problems in the beta testing forum, so you can determine the point where alpha20060507 is tested enough for you to use.

In the meantime, those who don't want to jump into the cold water would be best advised to stick to option 1, treat it as a neat little trick that is spread from player to player, like color coded names. I've got wax in my own ears on this issue since my servers all run fixed versions; I'm relying on you all to give me hints when the trick should be made know in the server admins only section and when it should be made fully public. If half the players know about it anyway, there is no point in hiding anything.

A special option for CT Fortress would be to modify the map rotation so that more of those maps were speed doesn't give you an advantage, like those with high axis setting, are used.

Sorry for the inconvenience.

[syllabear]

Sorry to bump this out of the blue, but got bored and started trawling old threads, and this really intrigued me.

Any chance anyone remembers what the old bug was?

[Z-Man]

IIRC, it was triggered by doublebinding the brake.

[syllabear]

IIRC, it was triggered by doublebinding the brake.

Aha I think I remember this now, thanks