View Full Version : centripetal force and jk2's movement

02-07-2002, 11:43 PM
After playing EF, I found a overally pleasant game, although the largest thing that I disliked at the start was the lack of centripetal force, and if its possible, I'd like to hear from one of the Raven developers on whether movement will resemble JK or EF more. If you're unable to comment on this topic Raven, no problem. :)

I suppose I'll clarify what centripetal force has to do JK with one of the JKii.net's forum users, Lucky:

Centripital force
This was a huge aspect of JK. It took a lot of skill to run fast in that game, and everyone moved at different speeds according to their style.

Just about no other game has that centripetal force factor, where u accelerate when you turn.

If you strafe run and apply gentle turns to your path you run significantly faster, if you apply a quick turn you accelerate very fast.

This is the the principle behind the saber style most folks refer to as 'mouse warp', but everyone who knows their salt either does it naturally or has learned to curve their movements just right so that they move at the optimal rate.

It also allows for the 'double jump' applying an extremely quick turn and a jump and using the acceleration from the turn to propel u thru the air at a speed roughly equal to 1 and a half times that of a normal strafe run jump.

Its one of JK's most interesting aspects. Tribes had skiing, ut has dodging, JK has centripetal force which is much more adaptative. I know its prolly not possible to include it in the game at this point, but its worth mentioning just in case the Raven folks hadn't noticed it when they were playing JK.

centripetal force=force exerted tangenital to an object pivoting in a circular motion around a fixed point.

ie, a tether ball, when u hit it, it swings around the poll, if you were to cut the rope it would fly off on a line tangent to the circle it was describing.

This was a factor in JK that most people didn't even realize was present, tho most folks made use of it. Its described in gen_move.cog fairly succinctly.

Basically everything designated as an object in JK was assigned a centripetal force factor and spun accordingly. When you turned fast it exuded force tangent to the circle u described and u accelerated.

This allowed you to move faster by either gradually turning while running in a straight line, or pulling an extremely quick 180 degree turn and rocketing in the opposite direction faster than you could normally go, even with strafe.

It's very subtle, but its really apparent when yer using force speed or trying to jump across the pool in oasis in one splash.

People made very good use of it in sabers and this is why you'll hear 'elite' players making comments about people's speed. ie, "that guy is really slow" or "she's really fast".

Everyone was able to move at different speeds with this very simple physical characteristic.

Strafe running is just a remnant of oldschool 3d shooters, its the same with all of em.

Centripetal force is unique to JK and JK alone. I'd like to see it represented in the movement of JK2 just cause it is so unique and gives folks supreme flexibility in their movement speed. It also allows for interesting 'moves' or tricks like hoping across the pool in oasis in one splash, double jumping in bgj, or running past a mine fast enough that the splash won't catch you.

02-08-2002, 12:22 AM
<font color=cbcbff> I don't mean to be offensive, but that wasn't added into the engine, that was a shortcoming of it. The engine didn't have fast enough physics to detect when you stop and in what direction you went next, especially online. THe terrible effect of this was that for a while, the engine would think you were going in one direction, displaying this on everyone's screen, when in fact you were going the other direction. It allowed you to warp around using a defect of the game to turn an excellent game into a festival of warping based on who can jerk their mouse the fastest and to gain an unfair advantage over those who chose to play the game the way it was meant to be played. Using "mousejerking" is the mark of a coward and a cheater in my opinion, people who can't win playing normally need to make themselves warp around in order to win. I certainly have been hoping as much as anything else about this game that such things are not possible with the faster and much better Q3TA engine as implemented in Jedi Knight II. I'm sorry if you feel otherwise, and I in no way intended this reply as an attack on you. I've just always felt that way and many others share my opinion, especially the players that were also there 5 years ago, at the beginning.

02-08-2002, 12:22 AM
it sounds like a physics class....????!?$?&$% e=mc^2 %$^*#!

02-08-2002, 12:25 AM
Not only that, but technically correct centripetal force would only accelerate your motion if you tighten the curve in which you're travelling. The "centripetal force" in JK is simply something that was an oversight that could be taken advantage of.

02-08-2002, 12:46 AM
<font color=cbcbff> We will call it a "LAY-ZER"....

02-08-2002, 12:49 AM
for 1, it is as you tighten yer turn. You have to keep moving the mouse to accelerate, you run slightly faster if you are running in circular pattern.

also, i wasn't talking about mouse warping specifically, just using that as an extremely obvious example that most folks have experience with, as is evident by obi calling it 'cheating'.

The lack of visibilty is from you outrunning the animation cycle, not from 'terrible physics' in the engine [i think yer describing lag there obi]. JK's keyframes were the only spots you technically 'existed' in, and if you planted them too quickly you started to skip out of existence. Think of stretching an elastic band and being able to see the individual threads where it looked whole before.

However, the 'warping' phenomenon also comes into play when your framerate is reduced. Lots of folks do this and people have started calling it 'tweaking'. Its a prob in any melee situation and unless Raven figured a way to spoof the existance of a person on the server regardless of their framerate, we'll keep having those problems. You see people with crap framerates in q3 all the time. They skip.

The centripetal force thing is indeed an oversight. It's a remnant of the Xwing series, whose engine JK uses. Flying in zero gravity you will experience centripetal force when you turn, or when you go up and down in a circular way. Since you can't go up or down in JK, u only notice it when yer goin left to right.

I didn't realize this until I was trying to explain the thing to someone on the IGDA forums, and I remembered a rundown I read on JK.net a long time ago about the xvt engine. JK is simply that engine with a lot of modifications, and it seems like thats most likely where that bug came from.

Even so, skiing in tribes was a bug the developers worked into the sequel because it added so much to the game. The problem with this bug is that nobody except for the 'elite' [cough egotistical numbnuts that give decent players a bad name /cough] folks realized they were using it. Most people make use of it intuitively after a while whether they get it or not.

I'm sure its too late now anyway. But g'damn didju see that *&#!in wall jump?!


02-08-2002, 03:31 AM
<font color=cbcbff> I'm not entirely sure I totally buy the keyframe theory because when you make the game lose it's keyframe, your model just stands there like a soldier at attention rather than disappear. But either way, it's definitely a shortcoming of the engine. Lag does indeed make it worse, but I've got a good connection and a Geforce 3 64meg and people still warp when they mousejerk, so it's certainly not my framerate that's causing it. Not sure that XvT's engine has anything to do with JK either, but that's really interesting to me if it's true. One thing that is for sure though, warping is incredibly lame. I think it was worse in JK though than in any other game, mostly because of it's peer-to-peer netcode. I actually think it made it possible to generate lag by confusing the engine with your mouse(warping). If not, it sure seemed that way.

And I've never seen a more accurate description of those "l337" people. If you've ever been to Nar on the zone and glanced at the chat, you'll know exactly what I'm talking about. A bunch of 12-year-old kids using a combination of game flaws and toggle-hacks to make themselves feel better than everyone else. And then insulting and degrading everyone that loses to them. I can't stand it. Nar chat. Never will you find a more wretched hive of scum and villiany.

On a side note, that wall jump did look very very cool. I can see it now: warping wall-jumps punctuated with a good acrobatic disappearing act. The humanity...

02-08-2002, 01:05 PM
Using "mousejerking" is the mark of a coward and a cheater in my opinion, people who can't win playing normally need to make themselves warp around in order to win.
I don't approve of 'mousejerking'; primarily because its a stupid tactic and half the time you end up running into their saber.

Secondly, I should clarify what I mean by 'elite'. As I've stated in the Clan Recruiting Forum, I use the term loosely with dedicated competitive players, decent players, hard-core players, etc.

02-08-2002, 01:10 PM
So you're saying that Jedi Knight use a modified X-Wing Vs. TIE Fighter engine??

This is certainly news to me.. I always thought that it was a brand new engine (Sith) at the time. I mean it's true that XvT was released some months before JK, but that doesn't mean they used the same engine (according to gamasutra's postmortem on XvT, it used a modification of the engine used in x-wing).

It would be nice if we could find out the source of that tidbit of data...

02-08-2002, 06:43 PM
it doesn't really matter where it came from (i heard that xvt story as well... somewhere. aren't the file formats the same or something?)

every engine has a different "feel" to it's movenent and physics (even if you can't put your finger on quite what it is) so you can usually tell what engine you are playing on...
it would be nice if JKO had the JK feel... but mainly cos i am getting fed up of every game i play feeling like quake3. ;)

aint gonna happen though... i just hope that the addition of wall walks and flips is gonna amke the game feel different enough.

02-08-2002, 06:59 PM
JK's physics are wicked (I don't mean that in a bad way), you go and try to run all out in direction ^a, make a turn in a circle of a diameter d=1,5m by anangle a=180 and take all your speed v1 with you, converting your speed v1 to it's opposite v1' in real life. If you manage, I'll be deeply impressed heh.

As for warping, that is a flaw in JK's netcode. You can see clearly if you change the tickrate to a very fast rate (by editing the registry since JK doesn't allow you to do a faster tickrate than 100 or something). If you do, warping becomes disabled, even if someone goes all jerky, you still see each of his single little turns and movements.

02-08-2002, 07:11 PM
Originally posted by Raze
JK's physics are wicked (I don't mean that in a bad way), you go and try to run all out in direction ^a, make a turn in a circle of a diameter d=1,5m by anangle a=180 and take all your speed v1 with you, converting your speed v1 to it's opposite v1' in real life. If you manage, I'll be deeply impressed heh.

I get it. Really :)
there is no acceleration (positive or negative, and there should be both)
You should fly away trying to do that turn

So if you derivate (Its said like that in english?) the equation that determines the velocity, you should get 0? I think Im just rambling :D

Weird indeed

02-08-2002, 07:26 PM

Aight, the xvt thing is somthing i read on jk.net a hell of a long time ago. I've been refering to it without looking for it for a while, ill go find it tonight since i have a lil free time.

obi, its not *your* framerate, its *theirs*. They compute where they are and send you the data, if their computer is computing half the points it should, it looks like they're warping. They only exist for each frame they generate on their computers.

Most people have the netcode and the engine code horribly confused. You can't fake out the engine, thats just impossible. Likewise you can't generate lag by running in circles. The 2 things simply aren't related.

If their framerate is low, they don't 'stand still' they actually move relatively faster because the user imput gets qued while the screen is refreshing. This is an entirely different issue that you guys would hate to pick thru, so don't worry bout it.

The tick rate thing is the rate you send packets at, if its low, then it looks like whoever yer playing is stopping and then catching up with themselves constantly. Editing it in yer registry could bring this up quite a bit and increase the stability of yer connection with yer opponent, but ive never seen or heard of this so im not gonna pretend to know. =P

K, gonna go look thru jk.net news till i find it. ill post in a while.


02-09-2002, 03:58 AM
I don't know where you got that bit about gen_move.cog. I'm an experienced cogger, so believe me when I say that it's a very simple script that moves an object from one of it's frames to another, like cutscene cameras in add-on levels. It's also obviously a very early, pre-development script that is unusable and was accidentally included in the game - it uses slightly different declaration syntax.

Nothing to do with movement physics.