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Physics For Game Developers
Programmers who want to get serious about game physics will love David M. Bourg's Physics for Game Developers. As I've said, the subject is inherently very difficult, and the book assumes that you are already familiar with vector and matrix arithmetic up to college level, integration and differentiation, and at least you hazily recall your mechanics/physics lessons from school. You also won't be afraid to wade through Bourg's carefully documented derivations of formulae for various physical effects, and his well-commented source code.
The book starts off by recapping the basic concepts of mass, centre of gravity, moment of inertia and inertia tensors. Bourg assumes that you have a working grasp of these subjects, and I admit that I had to go back to some of my A-level mechanics text books. He then goes straight into kinematics, where he uses standard (but forgotten!) integration techniques to calculate velocities from accelerations and positions from velocities. His examples are excellent, although a few exercises wouldn't have gone amiss. The chapter on forces covers a great many different types of forces such as springs and buoyancy, but curiously omits the important subject of contact forces (the normal force that a table, for instance, exerts on your computer monitor to stop it falling through the floor). In fact contact forces don't appear until much later in the book. Particles, rigid bodies and impulses (forces from collisions) are introduced in chapters 4 and 5.
At this point I have to say I was a little bit confused. What did this have to do with game programming? Everyone knows that games spend most of their time running round a single big "main loop," working out the forces on each object, looking for collisions and working out which keys the user is pressing. It doesn't seem imaginable that a game programmer could completely solve all the equations of motion by pure integration at the beginning of the game, and then just run the positions of the players through the graphics engine like a movie!
I already knew a little about this from what I'd found from the web, but what most games actually do is calculate all the forces on all the objects (players, scenery, etc.) in the game, and then integrate them at each step. Some of these forces will be generated by human players pressing keys on the keyboard or wiggling the joystick, and that's how the objects end up moving. Pure integration isn't usually possible, so the physics engine performs numerical integration - a kind of fast approximation to the pure "closed form" solution. Numerical integration is itself a tricky subject, but it's the meat-and-veg of good game programming. Surprisingly, numerical integration and a realistic main loop doesn't appear until chapter 11 (172 pages into the book). I skipped straight to this section, and I suggest you do so too...
The chapter on numerical integration is excellent and contains the first realistic gaming (or at least simulation) code. Many games I've examined use simple numerical integration, like this:
// At each step ... A = acceleration, dt = time step
Vx += Ax * dt;
Vy += Ay * dt;
Sx += Vx * dt;
Sy += Vy * dt;
Unfortunately this method (Euler's method) is very inaccurate and unstable: if you tried to simulate planets orbiting around a sun using this method, they'd soon fly off into outer space unrealistically. Bourg gives an excellent introduction to better methods such as the "improved Euler" method and the popular Runge-Kutta method, and he covers them in a context which will make it clear how to use these methods in your own programs.
The book reaches a crescendo with three fully developed simulations: two hovercraft which you can drive around and jolt into each other like bumper cars -- they spin around realistically; a flight simulator; and a 3D car which can be crashed into blocks that bounce around. Again the source code is meticulously commented and generally well written. My only two reservations about the code are: It would be nice if Bourg had chosen to use OpenGL instead of Direct3D so that those of us without regular access to Windows could actually compile and run the examples. The book would make an ideal companion to the OpenGL Red Book. And coming firmly from the Windows camp, Bourg's examples are full of all the horrors of Win32 APIs and Hungarian Notation. But maybe that's just my personal preference :-)
So in summary: The Bad Points:
- Measurement systems: Bourg moves uneasily between the English/US system and the European SI units. So we get examples which combine ft/s, meters, slugs and kilograms, uneasily converting between the two. He should have chosen one system and stuck with it.
- A common complaint about computer books: I've just spent 25 quid on a book which will sit open on my desk for months. Is it too much to ask that it be ring bound?
- Some subjects are not explained in enough depth. Particularly: moments, contact forces, impulse methods. Bourg should probably have written a chapter or three on collision detection.
- The chapters are presented in a very strange order. Move chapters 6-10 until later, or introduce numerical integration earlier.
- A few of the illustrations are inaccurate.
and The Good Points:
- Considerably better than the usual round of maths/physics text books which make up this field. In fact, this is really one of only about 2 or 3 significant books in this area which are pitched for game developers as opposed to mathematicians, and it's certainly the best.
- The areas which are covered are done well, in significant depth, with a good bibliography where you can find out more.
- The commentary on the difficult equations is good, and Bourg resists the temptation to derive many of the formulae he presents, instead referring interested readers to other references.
- Code is well documented and explained.
And now I suppose I have no excuse not to resurrect XRacer :-)
You can purchase Physics for Game Developers at Fatbrain
me'sa confused - i likes to play pretty games tho sho nuf!
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i've played a lot of games, and gone 'wow' at some of the eye candy, but if you've played baldur's gate for PS2 you know that the coolest thing that has ever been coded for a game is the WATER for this game. you leave a wake behind you when you walk through it, you splash when you jump in, and ripples interact and reflect from the shore. maybe the physics aren't 'perfect' or whatever, but the realism of the water was enough to really 'immerse' myself into the game.
-sam
burn the computers. go back to the abacus.
Somestimes games are actually more fun if they defy the laws of physics. Such as being able to jump 20ft in the air (I can only jump about 2ft myself). Don't get me wrong, it has to be somewhat realistic, but any good game will also be a little unrealistic too.
I Heart Sorting Networks
I remember a good old game called "4D Stunts Driving" or something... That had a pretty interesting physic. Often it was sufficient to just bump into another car and you would go up in flames and millions of pieces. Or, if you reached high enough speed in the jumps, you could get such an angle, you would fly right into the athmosphere, and if you changed the camera POV, you could maybe see the car as a few pixels high in the sky. I think that, though, is part of the charm with this game. That, and the music :)
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So pair up a couple of guys. One to worry about the artistic design, and another to worry about realistic physics.
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Some people aren't into super realistic physics. Some don't want to read a 300 page manual for a flight sim and spend weeks figuring out the flight model. They would rather just grab a joystick and start playing like in Wing Commander.
Its called "Physics for Scientists and Engineers".
Lets face it, the best physics is REAL physics.
If you want your game to have good physics, then slap a good physics engine (based on real formulae) into it!
Good quote, too many chars. Seriously, the slashdot 120 char limit sucks!
IMHO the game has good physics, if you don't count the car handling himself (who sucks, really)
I really doubt that your method of numeric integration is going to be that critical an influence on the quality of game play. In fact I think that you ability to simulate physics without really doing the math would be more important. I doubt anyone is going to be timing a car's drop off of a cliff in Carmegeddon to determine what gravitational constant is used in the game.
I think it is more important to include as many effects as you can: gravity, linear momentum, angular momentum, elastic/inelastic collisions, friction (surface and wind), than it is to model the effects perfectly.
In fact one could argue that it is to the game designer's benefit to use an innaccurate and exaggerated physics model. Most real world collisons with the guard rail on a race course are relatively unspectacular (by design) - but that would be oh so boring in a racing game now wouldn't it?
-josh
OTTOH, I'll either need or just make up constants for elasticity, friction, etc., which I used to do to accomdate display restrictions, like on a VT52 or a 600x400 screen. Adapting real math often produces bizarre simulated behavior on the small screen, so fudging is often called for.
A feeling of having made the same mistake before: Deja Foobar
Better check out the Cartoon Laws of Physics. It always amazed me how Chuck Jones and Max Fleischer had such an instinctive, albeit exaggerated, understanding of the laws of physics in their cartoons. You can't be a good animator (or game designer) without understanding of the Cartoon Laws of Physics.
The PC versions of the Carmageddon games (the console versions came out later) have superb physics. It's fun just to explore the course in search of ramps and hills to jump off of. If I remember the game notes correctly, the development team for the first game included someone with a Phd in physics. Heck, the engine for the second game even allowed for magnetism, but the feature never got enabled in the released version (there was a big electromagnet on a crane in the junkyard that you would have been able to drive under and get stuck to - the video that the dev team released looked fantastic). But at any rate, I must agree with the fact that good physics can make or break a game.
Is it just me, or does that describe Pong perfectly?
Note: Greatest game of all time referes to the classic version, 2 controls, 1 console, 1 tv, 1 wasted childhood.
Wax-Museum Fire Results In Hundreds Of New Danny DeVito Statues
It was actually pretty interesting to see how this aricle mentions that numerical integration is done in computer games by means of Eulers method. But: Good old Euler is slow and inaccurate!
... + y(n))
Simpsons method is more accurate method to integrate, since it creates a exponential polynome that more accurately represents the function. The method follows:
S(n) = dX/3(y(0)+4y(1)+2y(2)+4y(3)+
Use this in your gameengine the next time, and impress!
This beleif is why CompUSA is filled with games that suck. This is because, quite simply, the most difficult aspect of writing a good 3D game is NOT coding, it's coming up with a good idea and having good artists and map makers so that the game is worth playing in the first place. This is why the PSX and Game Boys are still popular, even though they have "primitive" graphics.
The game may be three years old, with (originally) dodgy graphics, but it had the best car physics engine of any PC driving game. You could actually get a feeling for what the car was doing, how it was sliding etc, and in a '67 F1 car, which slides a lot, that was a big help.
It's still one of the most popular games in the driving sim community, with new mods and graphics appearing almost daily, but in the end it's the physics that draws people in. Yah it's hard to drive, but it should be hard to drive, and once you learn it, you'll never look back.
..although i picked the cheapest form of delivery so it won't be here for a bit more time...
i read thru the sample chapter [here] it's all about particle physics. i was quite impressive, i enjoy the *conversational* style that most o'reilly books have.
i implemented all of the examples in java using java3d.
i hope the book meets my expectations....
Maybe this book has an answer to a question that's been on my back burner for a while, and for which I've been unable to find a good answer for while surfing.
;)
Suppose you have a device that records lateral acceleration, longnitudnal acceleration, and forward velocity, with 100 samples per second, and stores them in a text file, one sample per line, one value per column.
Given the file parsing routine is a gimme and thus provided the values for elapsed_time, LatG, LongG, and FwdV, produce a function that will return the current X and Y co-ordinates of the vehicle, so that its ground track can be represented in a diagram.
Anybody got any good sources of information (or better yet, an existing library) for how to do this?
No, this is not an exam question.
DG
Want to learn about race cars? Read my Book
...when you can turn on the "Winds of Space"
--Steven Levy fans will understand...
I agree, in some games, realistic physics can make a big difference. I remember when I first played Super Mario Bros. 1 on the NES, seeing how the fireball bounces along in a straight line until it gets to a hole, and actually falls down, I was rather impressed. (Small things, small minds, whatever. I liked it.)
However, in modern 3D-type games, it's important to pick and choose where you spend your time coding in the physics. In a racing game, it's a lot more important to spend time making sure the cars handle correctly than how realistically the trees sway in the background.
Unfortunately, there just isn't the time to make everything about the game perfect, and it's sad to see when a program has missed it's spot because of delays in implementing useless features.
I'm not a game programmer, but my current project is a simulation with lots of trajectories, global coordinates, points of view, and interactions. This sounds like the perfect reference for what I've been doing. It's going on the xmas list. I only wish the reviewer had told us what language the examples are in.
Light cup, beer drink, thin so chain, neck turtle fat, man I won't say it again
I want a FPS that lets you blow holes in walls, accurately representing physical damage from weapons. Imagine Counter-Strike with realistic bullet physics: ricochets, windage, and weapon recoil that isn't predefined.
Hacking physics though, now that's a job and a half: figuring out a quick and dirty method of approximating the complexities of the real-world, and still have it look natural, making it look like a real environment filled with objects that have familiar properties and behaviours. And then blowing them up, REAL GOOD.
Wasn't Dick Jones shot out a window by RoboCop?
Damn, that guy's tough if he's still able to write book reviews.
Is it only me, or Halo (on Xbox) has some of the worst physics engine I've EVER seen? (did you try driving the "jeep"? This thing handles like crap).
Well, while it covers an important topic which many look over, I don't think that it's going to teach me anything new.
If you are at the stage where you are game programming, I would hope that you know the basics of Newtonian Physics. If you don't, then you didn't really do anything in college, or on your own (whichever way you were educated). In reality, you should have basic understanding of how things work, and be able to code this as well.
You shouldn't be forced to read a book that tells you how to create physics models in your game world. I am hoping that this book does more than just implement the basic acceleration formulae.
"Time is long and life is short, so begin to live while you still can." -EV
The game had wonderful physics, just not *realistic* physics. The wildly over the top game would've suffered quite a bit if it was limited by 'the real world'.
I believe one of the most accurate numerical integration methods is the famous LSODE (Livermore Solver for Ordinary Differential Equations), an implementation of which is available at http://www.netlib.org/odepack/.
Another one is VODE, which is based on LSODE. http://citeseer.nj.nec.com/1230.html. I think both are more accurate than Runge-Kutta.
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Dead reckoning like this produces bad results. Unless you have a laser gyro or something crazy. Any loss in angle measurement is going to compound fast (unless you take angles in some constant way, like via gps - in which case why are you dead reckoning). What sort of project are you doing? I'd make sure you don't have some other way of finding position.
Let's not stir that bag of worms...
Tribe 2 has the best game physics ever in my opinion. It's a shame that there arne't people playing it anymore. The only reason it went down the tubes is because there aren't enough non-mod servers. Just about every server runs some variant on the game. As soon as I get a new computer I'm setting up a non-mod Tribes 2 server and me and my friends will rock the house again.
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There was a good article a while back in one of the mags (Scientific American?) i get about a team putting even more physics into games. If you shoot someone in the shoulder, they spin a bit etc. They were trying to make bullet hits look more real (as in reaction not gore). Anyone have a link?
As fascinating as the book sounds, individual developers or teams that are writing (and debugging, and debugging, and debugging) code to calculate the acceleration of a mass on a curved path are not using their time productively.
These functions are based on laws of physics, and should be the last thing to be reinvented.
Game development as a whole will be of a far higher quality when games don't have to be developed one molecule at a time.
On the other hand, the inherent problem with domain-specific software is that those who know how to program the software are the ones who don't understand the domain. Computer programmers can't be expected to study everything in the case that they might someday be called upon to code a gene sequencing program or a complex financial application or psychological model. This tends to result in bad software written by people with no training and little experience in software development.
Don't get me wrong--I don't mean to be elitest here, but in the few times that I've had to work on domain-specific programs written by domain-specific people, I've found that the existing code was very difficult to maintain.
I remember reading an article with a game developer a while back, who pointed out that the key for physics in a game wasn't realism, but consistancy.
He was developing a racing game, and says in order to make the game more fun, he had to sink the center of gravity for all of the cars several feet below the pavement, so that the cars wouldn't tip over when making hi speed turns.
As long as all the cars behaved the same way, it didn't matter that you were "cheating".
When playing your game, the user is entering your world, and learns a new set of rules. As long as you present your set of rules as consitant, it doesn't matter if they don't correspond with how things behave in "real" life.
Captain_Frisk - wannabe game designer.
http://www.d6.com/users/checker/dynamics.htm
provides an excellent, and free alternative to purchasing a weighty tome on the subject. Chris covers the details of rigid body mechanics in a thorough, but light manner.
I went to a physics lecture at GDC, the most memorable part of which was Chris saying:
"Here's how it's going to go... you're going to write your first rigid body dynamics simulator. You're going to simulate a cube dropping onto a plane. You'll run the program, the cube will drop, hit the plane... and disappear."
So, so true.
Games do not need good physics, they need to be fun. Anyone remeber playing Super Mario endlessly? Remember all the jumping forward and pulling yourself back in the air? That game would be damn boring if you couldn't reach half the powerups because it had real physics.
Excepting the possibility that the N64 version is completely different from the PC version, you are completely clueless. Carmageddon, of ALL the games you could have chosen, was a pioneer in game physics. It was the very first game that I played that had a real rigid-body simulator built into the engine.
Say what you will about the gameplay, or the physical settings (gravity was too low), but you can't say it had sucky physics. The cars and environmental objects interacted in an incredibly realistic manner. It was miles ahead of Re-Volt in that department.
I don't know that I really agree with the idea that physics need to be wildly realistic in the 'games' that I play. Honestly, I don't want to know what kind of recoil the rocket launcher in Half-Life would inflict on my character. I'm happier just watching the rocket track nice and straight towards my target instead of attempting to pick myself up off of the ground where I slid to a stop from the highly realistic recoil.
On the other hand, when I play a 'simulation' the physics are quite important. The best physics I've found in a sim are in a 3-year-old game: Grand Prix Legends. You're racing 1967-era Formula One cars, which means skinny tires, no downforce, high powered...which is a combination for difficult driving. But the physics engine is spectacular: you touch the gas when in neutral, you can feel the torque twist the body of the car; each wheel has its own model; touch the gas a bit to hard in a corner and be prepared to swap ends of the car, etc., etc.
The graphics are what you'd expect for a 3 year old game, but a dedicated community has sprung up to support the sim with everything from replay analysers, new tracks and graphics, and even a movie maker!
It seems that if you make a sim with good enough physics behind it, the fans of it can create new 'eye candy' to keep the sim looking good. But if you have crappy gameplay (see: Andretti Racing) and good graphics, the game will quickly be relegated to the bargin bin when something prettier comes along.
-Mark
I'll bet that in at least 90% of the games out there realistic physics would completely ruin the whole fun. What is the point of interacting with a fake environment when the environment reacts the exact same way real life reacts? Racing games are a good example. People want cares to handle well, generally. They don't want realism, in real life operating cars at high speeds is a lot more difficult than most games.
And in *any* game where people jump, realistic jumping becomes completely pointless. People want to be superhuman. Imagine quake with realistic physics....
Realism is not the high mark of games in all aspects, that is the whole point of games, to escape reality...
XML is like violence. If it doesn't solve the problem, use more.
Has anyone else seen the quake II secret level that has less gravity. Jumping, the remains of oponents, those bouncing gernades.. everything was like it was on the moon.. Lots of fun..
Now thats physics
my pool-teammate's buddy from ireland (sister's former roomate) works w/ a company (in ireland) that produces physics engines for applications. well I guess it is really one physics engine that they license out to anybody who wants it. obviously game co's are interested but engineering and modelling progs use it too. sorry but I don't remember the name.
Try Red Faction. You can blow holes in the ceiling, floor, walls...the game actually depends on you doing this to advance through the levels.
Really fun in deathmatch mode since you can blow a hole in the wall and hide in it.
Return to Castle Wolfenstein has great physics, as all QuakeIII and such gamers know. But I find the grenade toss of the game somewhat limp. Last night, under heavy fire while a teammate tried to get the M60 firing. I tossed a grenade into a alcove to keep incoming Nazis from cutting us both down. Oops!?! My grenade hit the wall right beside me (but, but, I'm beside the wall!?!? How could I possibly have ... KA-POW!
;-D
Game physics. Priceless.
its a fallacy to believe
realistic physics realistic gameplay fun game
some 'old' games are still interesting today and hence being played for no other reason then that their physics system is fundamentally flawed (e.g. the original Quake or QuakeWorld; released over 5 years ago). learning how to exploit these flaws efficiently is what makes those games fun today, with new 'defects' being discovered on a weekly base.
make a game with perfectly realistc physics and it will be perfectly boring; why not do the real thing instead?
In my opinion, the most difficult aspect of writing a good 3D game is coding complex physics
IMNSHO, getting good human motion is the hardest. Sure, EA does great motion capture for their sports sims, but where else do you see this in the industry? Download the Wolfenstien single player demo and see how stiff the models look (especially in the intro).
I think getting realistic physics is important, but, since most of it can be reduced to math anyway, GHz machines and loads of memory, combined with good programming, should be able to get it right. Making motion look good is far more important to my enjoying the game, and much more difficult.
On a side note....
Has anyone else noticed how this seems to be what sets WETA's effect in LOTR apart from the rest? Instead of generating a digital army, they film a bunch of guys walking in armor, then copy/paste/randomize to make a realistic hoard of warriors.
The cave troll, while the rendering was supurb, was entirly motion-captured. They had some actor plodding around with a big stick and ping-pong balls taped to his joints. They seem to understand that they can make everything look perfect in a still image, but the motion will still look fake.
I'd rather have someone respond than be modded up.
The VV algorithm has a lot of advantages: it's simple, stable provided dt is small enough, and unlike straight Verlet is self-starting given an initial velocity set.
Eric
"Seven Deadly Sins? I thought it was a to-do list!"
Some of my all time favorite games are great because they move 'right'. Can you imagine playing Spindizzy or Marble Madness with crap physics? I can, on a dire MM ripoff. It was frankly painful. The unexpected coolness that can result from engines that do things properly is very nice - although they cheated on the amount of kickback to do it, rocket jumping would never exist if they hadn't used impulses and momentum to control movement rather than old style 'move forward if the player pushes forward' arcade method.
"I Know You Are But What Am I?"
What I'd like to play (or code myself when I get out of college) is a fighting game that incorporates a lot of physics:
Instead of a hit just causing the victim to go into a canned fall down sequence, the force imparted by the blow would be computed and the proper response of the impacted body would result in a unique reaction for blows landed on different parts of the body with different ammounts of force.
In addition to reaction to hits, all the moves should be based on biokinematics rather than canned sequences- the fighter would not execute perfect flying whatevers every time, but some phsyics model would cause them to attempt the move and the result would vary by the conditsions it was executed under.
More physics in any kind of game makes for much more interesting and varied play, if the alternatives is just as many sequences as the designers bothered to record.
Carmageddon didn't have sucky physics, it had goofy cartoony physics. I mean seriously, asking for realistic physics in a game about rocketing through a city at 200 mph running down pedestrians and picking up powerups is just plain silly.
-Rob
Whenever a game is produced it is decided how much physics will go into the game, this is dictated by a lot of factors, some of which are (in no particular order):
1) Possible cost. (Do you buy a prebuilt physics engine? Or spend developer time on it?)
2) How realistic does the game need to be?
3) How realistic can you make the game? With given platform constraints.
It won't be long before people begin to notice not just the graphics/game engine (Such as the famous Q2 and Q3 engines) but also who's physics/mechanics engines are being used...
Background:
I've got a degree (BSc Hons) in Physics, I work at a games development house as a programmer.
Actually, the game is not working out the forces of each object. This is why most objects in 3d fps games are static. Beyond basic collision detection, there is no interaction with the objects. If there are interactive objects in your game, the math involved in calculating the physics of a 3d pack of cigarettes or a 3d can of cola would not only take an enormous ammount of coding to bring to light, but also put undo load on the CPU.
When we worked on Ghost Recon, one of the big problems with physics involved calculating the way the trees swayed in the wind(believe it or not). Part of the solution involved going from multiple wind directions to a single one. The users wouldn't notice it. Heck, we could have made the trees static, thus relieving the system of about 40% of it's performance hit, but we wanted some level of realism in the background and atmosphere.
Perhaps a game would be really successful if it had totally screwed up physics, but screwed up in cool ways, like paths that can twist around so you're upside-down but still gravity pulls you toward the path. Add flashy surreal graphics, and you've got something I'd like to play.
The ability to jump 20 feet into the air has nothing to do with whether or not you're using a realistic physics model, just how much acceleration from gravity is present and how hard you jump.
Things don't need to be exactly as they are here on earth, but having 'no physics' I don't think would be very much fun.
autopr0n is like, down and stuff.
Is that it gives you all the important physics equations that I learned throughout freshman and sophomore years of college all in one place. They equations are easy to find (though the variables used aren't the traditional ones in physics).
The book is a good reference to have. To me this would be good to have because I already "learned" all of this, but like most don't remember all of it. Having all these equations right in front of you will enable you to remember everything swiftly and apply what you need to.
Like most O'Reilly books, this is a good reference to have, and I think it should be bought by people that already know most of the basic physics stuff.
"Time is long and life is short, so begin to live while you still can." -EV
Half life is based on a heavily modified quake 1 engine with some quake2 code thrown in for good mesure.
autopr0n is like, down and stuff.
Quote: "A common complaint about computer books: I've just spent 25 quid on a book which will sit open on my desk for months. Is it too much to ask that it be ring bound?"
The book is not ring bound because it costs 25 quid (= British Pounds).
'Twould be far too easy to stick it through a photocopier or scanner if it were.
Not confused enough? http://translate.google.com/translate?u=www.slashdot.jp&hl=en&ie=UTF8&sl=ja&tl=en
Aside from the obvious compromises that must be made to achieve decent framerates, I think playability requires design decisions that are more complex than just realistic vs oversimplified physics.
The challenge in game design is figuring out how you want it to feel, then determining what kind of physics model best achieves that.
Take a game like Gran Turismo 3... the greatness comes from an extremely realistic physics model. But that same principle shouldn't be applied to all games. Grand Theft Auto 3 is an equally great game that uses oversimplified physics to make the game flow better.
I think one of the greatest games is Halo, which for those of you who haven't played is a FPS with vehicles. The physics aren't overly realistic. Inverse kinematics are used to give a sense of realism, but gravity, traction and flight are decidedly unrealistic in the interests of playability.
Halo also has fantastic controls which illustrates another good point, which is that physics are just the tip of the iceberg on playability. More important are the ergonomics of the controls. One other thing that's also more important than physics in my mind is environment robustness. There needs to be a critical mass of weapons/enemies/missions/goals/secrets to keep things interesting.
Yes, you can have a world where the physics don't behave as our world. However, you still need to be somewhat consistent. Imagine a game based off the Coyote and Roadrunner (I really don' know if a recent one exists,)
Your rules would be much different.
First person game... you can run over empty space as long as you don't look down, or hadn't been there before.
Once you start falling, your legs generally go down a lot faster than the rest of you body until it catches up, and you quickly assume a very fast constant speed.
Tunnels can be painted, but only used by the one who didn't paint them.
Extremely laughable motors can give extraordinary kicks, and small balloons can carry enormous amounts of mass.
Now, as long as these rules are consistent, you can have a very fun game. Note that things should still arc (hence some rules of our world physics are still there), but things like static friction aren't as significant until they need to produce a lot of heat.
While this book is important to know how to code rules of physics, more importantly, a consistent or at least consistently inconsistent rule set makes a game great fun.
I demand a million helicopters and a DOLLAR!
which still uses dead reckoning to guess where the ship is in the middle of the ocean.
I'm still waiting for Physics for Cartoon Developers: just how long should a character remain suspended after realizing he's in mid-air? We'll need pure math computation methods for ordinary cartoons and numerical methods for interactive cartoon games.
What do you mean they cut the power? How can they cut the power, man? They're animals!
This is a refresher course in high school physics, sometimes freshman college physics, but the author does not have any kind of perspective on game development. It's easy to pick up a book about physics and implement what's in there. The equations are well known. But that kind of implementation is much, much, too hardcore for game use, where you need to devote 15% of each frame to physics calculations.
The trick is coming up with a way to seem like you're doing much more than you really can. The book gives little help there, as trickery and non-traditional techniques can buy you a lot more than just implementing standard mechanics.
I have a quaternion question thats been buggerin me.
A 4x4 rotation matrix describes an arbitrary rotation about an arbitrary axis. But some combinations of rotations cannot be represented by a single rotation about an axis. For example, rotate the Earth 90deg about an equitorial axis, then rotate 90deg around the N-S poles axis. The final orientation can't be done in a single rot about a single axis.
My question is: Can quaternions handle this? With a single 4 parameter quaternion, can I describe this combined rotation?
This book is not aimed at the gamer, it's aimed at the game developer.
You want to jump right in and play a game? Then you'll find it easiest if it has fully realistic physics, as that's what you are used to.
ac.uk
95% of all the problems I did in physics started out with: "Assuming you're in a vacuum"....
Then you simply used..
d(t) = 1/2at^2 + vt + d0
But with wind resistence, acceleration is inverse logorythmic proportional to wind resisteance (which is proportional to velocity), so (A) is not a constant, or at least you need to make the above a much more complicated differential equation.
Not to mention when g = a (gravity)... In a vacuum you'd fall so fast, but maybe you're on a different planet where the atmosphere is much thicker and (g) granvity oh so much smaller. Instead of reaching a maximum falling velocitry of 200MPH, maybe it's only 30MPH.
Conservation of energy should be observed for sure, but friction, and wind resistence make projectile flight mapping much more inexact without a beowulf cluster of crays and some bang-up fluid dynamics simulation.
Let's not even touch relativity. If you're writing a space shoot em up, and you kick in your thrusters and approach (c) the speed of light, do your enemies get shorter? Does the universe begin to collapse.. And oh yeah, w.t.f. is hyper-space? A black hole super-nova?
Do we grow beards while playing? It's been proven on fighter pilot's atomic clocks that they travel in time (albeit on the order of millionths of seconds).
I am a flight-sim junkie, and a former military pilot (before anybody asks, I am NPQ, not physically qualified to fly anymore). I have owned maybe two dozen different flight simulator programs over the past fifteen years.
My favourite for a long time has been Austin Meyer's X-Plane. X-Plane uses an engineering process called "blade element theory" to approximate the true behaviour of an aircraft in flight. And it does this fairly well; I think X-Plane does the best job of any of the PC-based sims at mimicing the actual feel of the aircraft.
X-Plane doesn't have the "eye candy" of MSFS-2002 or any of the Flight Unlimited series, but as far as accurately modeling flight physics, X-Plane is head and shoulders above the competetion.
hi, this look like relative topic to what i am doing, also, i know i have faced that i had to remember all the college physics.... on the other note, i am creating a small 3d-game for my self which involves a lot of rewriting the things that are done... like i would like to use a open GL 3d-engine with the distributed computation, but the problem is i need to find the open sourced one with right to use it freely.... any help would be appreciated...
Who controls the information, controls the world...
Runge-Kutta is a complex method for quickly and accurately solving differential equations by numerical means. It is used instead of simple Euler iteration because it is equivalent in speed and gives much more accurate results. It works by adjusting the timestep dynamically to skip over regions where the system is changing slowly, and to integrate more carefully when the system is changing quickly.
This is all well and good when you are trying to do something important, like simulating heat flow within in a heatsink. But for simulating the orbits of planets around a star, for example? What a waste of time! The orbit is elliptical, so just simulate a freaking ellipse!
What about space missiles? Do you need Euler integration? No! There is a closed-form solution to the linear acceleration problem -- it's a quadratic. This procedure does not give low error. It gives zero error.
I read this guy's articles several months ago. I thought he was off his rocker then, and I still think so now.
Check out Red Faction. It has a feature called GEO-MOD that allows you to do just this. It has similar game play to Half-Life. IMHO, it has gotten far too little attention by gamers. The one annoying thing now, is that cheating is rabid on multiplayer games, allowing peple to tly and shoot 60 rail shots per second...
I turned off my moderator points awhile ago, but I agree. Gamasutra is a very professional site for game developers that has resources that any independent game programmer could really use. Especially new game programmers. They have many in-depth articles on physics and realism.
So there I am trying to solve a ballistics problem for a game. I need to drop artillery shells on target, based on launch speed, required horizontal distance and gravity, but not, thankfully, air resistance or other accelerations. We need this to work right, but more than that, we need it to work quickly for an imminent product demo, so a co-worker is thrown at it as well. He has his Halliday and Resnick Fundamentals of Physics Extended Third Edition, and a couple of years of college maths.
So we get to work. I do a quick napkin calculate and can solve for the range based on the speed, angle and gravity, but I can't figure out how to solve the equation for the angle. It's fairly easy, but I'm an absolute duffer at maths (it nearly dropped me out of college). My coworker has started right, trying to solve it for the angle.
Five minutes later, I'm done, and I mean done. I'm dropping shells within spitting distance of the target. "Oh, you solved it then?" asks co-worker. Heh, not exactly. I'm pumping angles into my napkin equation and doing a bsearch until I get a distance that looks close enough.
Coworker is outraged! It's inefficient, he claims, which is technically true, but it's a few iterations happening every few seconds at most, which isn't even worth our time profiling. It's not perfect, which is also true. But our engine is using cheap and nasty "X += dX * dt" anyway, so even a perfect calculation wouldn't be accurate.
My points: it's hitting the target. We hit the time target. It's a game.
Sure, physics has a place, and it's aesthetically appealing, but as long as you get the results that you need, the method isn't important. The games that you think have great physics? Probably fudged nine ways from Sunday to make them feel great.
If you were blocking sigs, you wouldn't have to read this.
I've found in my limited (hobby only) game programming experience that real physics make for boring run 'n' jump games, but they make for wonderful projectile games. Think ballistics (Scorched Earth, Quake, etc...).
Another pet peeve i have is that a lot of these sort of things never really mention one killer point. When computing whatever delta t for updating a scene, it is best to use a moving average of the last n frames (i use 32, kept in a rotating ring buffer), because that keeps an unusually long or short frame from fucking up any calcultions.
---
Play Six Pack Man. I
Actually, some of the people I work with have been doing research on trying to simulate cartoon physics, it's VERY difficult! It's basically research into getting game characters to stretch or compact realistically when accelerating or colliding with walls/floors. In terms of "real" physics, this is close to soft-body dynamics, which is MUCH harder than the rigid-body dynamics presented in this book...
Dan
Kalman Filter
I'd like to see some mesh deformation when a grenade gets tossed into a room. But more than just deformations I suppose. Walls should be able to collapse, etc. Am I dreaming? I don't think so. This technology should be available in a couple years at best. In fact, I don't think anyone knows how to do it well yet, and that's why it doesn't exist (afaik) - because processors are fast enough to handle this sort of thing I imagine. I'm not saying I need perfect simulation, far from that.
Just because this book tells you how to program more realistic models, does NOT mean they have to be realistic. For example, you can set gravity to 9.8m/s^2, or hell set it to 4.9m/s^2 and have it be the moon. Or if you JUST want higher jumps, increase the force you apply when jumping.
The important thing this book (I assume) lets you do is generate better MODELS. These models can be parameterized on all sorts of things. The outcome doesn't have to be more realistic, but the interactions will be more consistent and reliable. In this way, the interactions of the forces (even if gravity is half or what it is normally) can still be realistic.
"Of all days, the day on which one has not laughed is the most surely the one wasted." -Sebastian Roch Nicol
Many of these methods are numerical in nature and lend themselves to computer calculations. Taylor series, perterbation theory, iteration methods, hell ALL of statistical physics is this way.
I think that the programmers can go past the "quick and dirty" methods and with just a bit more effort come up with wonderful physics models, and it looks like this book is trying to do just that.
For those of you interested in the physics of motion (mechanics), I would suggest you pick up the books "Vector Mechanics for Engineers" by Prof. Beer and Prof. Johnston. It is easily the best book for mechanics I have personally read. And it is modular in the sense you can skip some chapters if they're not interesting without going "DUH" while reading the later ones. Although it says 'For engineers,' the books are understandable even if you haven't got too much math experience. If you're scared of vectors, they also have a "Mechanics for Engineers."
-Shaunak.
Here's a link to the website./ index.mhtml
http://www.mhhe.com/engcs/engmech/beerjohnston/vm
-Shaunak.
I'm reminded of folks in high school who would get hot under the collar arguing that the Arduin rules for magic and hit points were more realistic than the D&D versions, or the realism of different types of dragons . . .
hawk
Try Infiltration, at http://www.planetunreal.com/infiltration
Oddly enough, it is a community driven project, and anyone with demonstrated programming skills is free to offer contributions.
Bullet holes based on surface type and round caliber are slated for the version release in January, but a current partial list of features includes a breathing system (must hold your breath for greater accuracy), leaning, lying down, inertial running system, no crosshairs (you aim with the iron sights on the weapon), weapon physics (kickback, sounds, take-down power, etc.) taken directly from the actual weapons and ballistics data.
It's a lot like Counter Strike, minus the ridiculous video game aspects. It's a mod focused on realism where nearly every design issue is resolved around the question, "What would be more realistic?"
hawk
I think I just figured out why my ground tracks are such a bloody mess.
The acceleration values I have are taken _with respect to the vehicle's axis_ not the world co-ordinates' axis.
So I somehow have to translate the co-ordinate systems before I can apply the acceleration to the vehicle....
Any ideas on how to do that?
.
Want to learn about race cars? Read my Book
The only one worth playing is TM2.
The anonymous coward above is correct - a Kalman filter will help smooth out some errors.
That said, I'd invest in a fancy pants GPS or two. Or a black box sort of solution. If you do need Kalman filtering - I suggest downloading a library to handle the mess.
Let's not stir that bag of worms...
The main problem with realistic physics in video games is that it really isn't possible to do it.
What's that you say? But this whole post is about how you can do it? Nope sorry, but I don't know of any games today that really model what is going on in terms of 3D solid mechanics. Once one body interacts with another the calculations get staggering complex. Likewise do you really think that the flight sim calculates the flow around the aircraft to get it to behave right? Of course not.
What most games actually do is model everything as a point mass and then add a handful of other parameters to take into account solid body rotations. Collisions and other more complex events are handled with simple rules of thumb. Or in other words they are fudged. Provided they are fudged well it doesn't really matter. This is what many simulation games do (like Terminus). If you are very lucky they may actually calculate the stall of an aircraft using bernoulli's principle at a few key points. However it far easier to supply a stall angle and stick with that.
So when we talk about "game physics" keep in mind that some of the best game physics of all is completely fictitious. It just has to look and feel right, it doesn't have to be right especially when being right would take way to much processor power.
So far I've gotten all my Karma from telling people they are wrong... :)
one of the best on the subject, apparently in the minds of others as well, is Andre LaMothe's The Black Art of 3D Game Programming. It covers vector mathematics and matrix multiplication in a fairly accessible way, and more importantly goes through the optimization necessary to turn conceptually correct algorithms into something that will churn out FPS.
_______________________________________________
...vividly encapsulates that post-Watergate/pre-punk/coked-up moment when you could trust no one, least of all yourself.
A very simple (*) way to model downforce is to drop the centre of gravity of the model so that it is below the ground. Other variables such as tire grip also have to be changed as well but these are generally constants.
(*) Downforce changes with vehicle speed so this is a very simple model.
wot no sig
Realistic physics in games will never catch on. Lara Croft would keep falling over forwards.
11.0010010000111111011010101000100010000101101000
This appears to be more of a review so it's not as bad but this story covered the same book.
Come on editors
As someone else pointed out, there's a straightforward way to approach game physics, based on what you learn in a first-year dynamics course, and it won't work. Free flight is easy. Contacts and collisions are hard.
Detecting contacts between objects is complicated, but well-understood. There are several free collision-detection engines available, and many research papers. The time bounds are quite good; only slightly worse than O(N) with the better algorithms. Writing a collision detection system is a big job, but the theory is tractible.
Taking appropriate action when you detect a contact is the hard part of the problem. Bouncing balls are easy. Multiple irregular objects with multiple contacts, slipping and sliding, are hard. Most current games simplify their collision geometry down to cubes or spheres and botch the hard cases ("But my sword went right through him and he didn't even notice!") The latest generation of games is just starting to get contact right. In another year, correct contact handling will be a "must-have" for commercial games.
If you simulate contacts between objects with a spring and a damper, you run into numerical stiffness during integration. Soft objects at slow speeds will bounce fine. In a hard collision, the forces become huge for short periods. The simple integration algorithms will result in huge errors, and the objects will go flying off into space.
If you simulate contacts between objects as impulses (an impulse is an infinite force applied for zero time, but with a finite energy transfer), two objects bouncing off each other will work great. More than one contact per object doesn't work too well. Resting contact doesn't work; objects may fall through each other. And everything bounces like it's a pool ball, because all collisions take zero time.
If you try to do everything with constraints, resting contact works. But combinations of sliding and resting contact result in wierd corner cases that are hard to get right. Trying to solve contact, rather than simulate it, leads to static indeterminacy. (Think of a table with four legs, slightly different in length. How the table behaves is very sensitive to small changes in leg length. Numerical solutions of multipoint contact problems become similarly sensitive). This is the approach Baraff preaches at SIGGRAPH, but few others have been able to implement it.
After a few years on the problem, I developed Falling Bodies, which successfully solves this problem well enough to simulate a human figure falling down a circular staircase. It can be done. I hammered through the spring-damper problem by using unusual and robust integration techniques. This is computationally expensive, but sound.
If you're developing a commercial game, and need working physics, go with the Havok engine. They have a rigid body engine, a soft-body system, and a specialized vehicle simulation engine. (Yes, vehicle physics in games typically has fake components. In most racing games, the tires are impossibly good and the vehicle CG is impossibly low. But you need a real physics engine to fake it properly.) It's not cheap, but you're not going to solve this problem in a few months. Major developers have blown years on this problem and failed. Trespasser, from Dreamworks, went down the drain that way.
ciriclum includes statics, dynamics, and mech. of materials. The first two are basically the physics of rigid things and the latter goes into how things squish. Statics and Dynamics are offered at many community colleges and I would highly recommend them for programmers who want to a better understanding of how F=m*a applies to the world.
Simple people talk of people, better people talk of events, great people talk of ideas.
Actually, a PC/PS2 game called Red Faction featured something it called "Geo-Mod" technology, which was basically real-time boolean subtraction to simulate holes in walls, etc.
It wasn't as interesting as it could have been, from a game-play perspective. The problem is that we game developers are used to making environments *very* static -- often based on BSP-trees and such. This saves the engineers a lot of headaches, but guarantees rock-solid, unchanging environments.
What you're talking about, with full structural physics and everything... it's going to be a while. I'd love to see an area where, if you destroy enough pillars/supports, the floor above you comes crashing down. Unfortunately, that's a sh|tload of math, and the environment would have to be created in such a way that it doesn't close off any critical paths when collapsed, etc etc etc.
It's a tough problem. But consider this: We're just now starting to get shadows that move when you move lights around! (That's what Carmack's working on right now...)
That was really funny game! The physical model was horrible, so much, than when you crashed into another car and went flying at amazing speeds, you did fly in a parabolic trayectory (as newton says), but it had a positive gradient, not negative, as in the real world!!!
This is a very interesting point -- I imagine that a lot of modern game development has to do with squeezing as much as possible out of each frame....and for the same reasons that 3D graphics programming is more than just "calculate primative, raterize, clip scene, etc." but actually uses well-designed algorithms to make this process more efficient.
Do you have any links/books/info on the "trickery and non-traditional techniques" that game developers might use?
--Noah
Ferrari and other exotic car rentals in New York
I picked up this book just last night at Borders... flipped through it, and thought it was really interesting. I'm not particularly interested in programming games, but I am interested in doing simulations. Can anyone recommend any other books that would get one into this?
Libertarianism is rich wolves and poor sheep playing gambler's ruin for dinner.
In order to willingly take 'programmatic' licence with kinematics, you have to know it. Just like a poet needs to know the language very well before he can successfully use poetic licence.
I agree. Infact any eningeering degree will cover what you need to know. A computer science degree probably won't, but thats what computer engineering degrees are for.
Yes but every time I try to see it your way, I get a headache.
As it turns out, the book cites several gamasutra articles as references.
Libertarianism is rich wolves and poor sheep playing gambler's ruin for dinner.
Guess what: quantum mechanics is also approximation in nonrelativistic limit. Only 1 electron (Dirac) problem was solved so far without any approximation (with latest model of universe)
Unfortunately this method (Euler's method) is very inaccurate and unstable
This is only true if you're simulating a standalone system (like the orbiting planet example). In real games, the player is constantly pressing the controller, collisions are occurring, and the "AI" is making decisions. Stepwise integration makes perfect sense in that case. Calling it "inaccurate and unstable" shows a lack of game development experience.
Just read Feynman's lectures on physics...the best.
yes, Revolt for N64 had good physics but...
It was _unplayable_ because of the terrible framerate.
I just wish it would have had a decent framerate like on dreamcast.
I find the title with "physics" a bit pretentious when it is only an introduction to mechanics and a few methods of numerical analysis. ...)
To cover the subject would require for instance: -Optical effects (refraction, interferences and moires )
-fluid dynamics (for smoke, fire, waterflows...)
-condensed matter ( relations between thermal, electrical and optical properties of matter, cristal/amorphous, phase transitions) for calculating textures.
-electromagnetics (realistic fade of a radio signal, for instance in a first person shooter)
-acoustics (delay effects with distance, effect of fog and other materials on phase/frequency, doppler shifts
and this could go on and on.
Some things are expensive, but some are probably not and would give an extra presence to the games that would be worth lots of brute-force (frames per second, polygons, or other usual rendering issues)
I wonder why I didn't have a better subject line. Hm. Anyway, you're right, the cars could be flying in weird trajectories, it made the game very funny, very playable!
Will work for bandwidth
Carmageddon is an addictive game not due to the physically simulated space but due to the simple fact of being able to crash someone's eye balls after you run them over with your truck over and over and over and over and over again! (the sound of crashing bones is what makes that game addictive)
You can't handle the truth.
Where is the world going? The orbit simulation is probably the most complex problem for integration ordinary differential equations. 3-(or more)-body problem does not have closed form solution and can have attractors with fractal dimenstions. This kind of problems are very difficult to integrate numerically. 16-th and higher order methods (opposed to usual 4-th order runge-kutta) are most common. On the other hand, "simulating heat flow within in a heatsink" is usually done with no more than 4-th order schemes and 2-nd order are most common. (Partial differrential equations have other problems, of course)
;)
Good luck with your degree...
Getting the physics model right is something very important. However, to go along with this would be a nice model of the materials involved in the game. Wodd colored textures should give, dent, and mold like wood. Skin whould flake, scrape, and change color when abraised, etc. Steel should ...well, you get the idea.
Not quite sure how to take your comment on my degree :) I'm also getting a degree in CS so it's a lot of juggling to be doing. I'm putting the priority on CS.
Most often then not, the game is tweaked by a producer with an app that has a few sliders that allows him to change anything from gravity, to acceleration, to, well... you name it. Think about it - when was the last time you had fum driving an normal car? No way man! You want mega jumps, you want to turn on a dime... etc etc etc.
I'd really really love to hear about the physics of FINAL FANTASY.
Let's see --
Cloud 70Kg.
Big badass sword 40Kg.
Height of jump 30 meters.
I've dabbled a bit in 3d graphics and physics, though I'm not a professional developer or physicist, just a student. But I have read some good books that were really useful for physics programming, and 3D programming in general. I recommend reading a good textbook on linear algebra with matrices or sitting in on a course. There are a lot physics uses for matrices, and you can write a pretty good 3D engine based on them. My recommendations for reading:
Cutting-Edge 3D Game Programming with C++, by John DeGoes. Publisher: Coriolis Group Books, 1996.
This book, although probably not cutting edge any more, is a good introduction to 3D programming (polygons, lighting, shading, optimization, physics, a little bit on AI, etc). The code is written in c++ and the examples in the book require Borland C++'s power pack (these were written before DirectX, OpenGL etc. were widely used, probably because not many people had exclusive 3D hardware back then). Although today it's probably too much of a waste of time to code your own 3D engine, as there are a lot of good code libraries out there that work just as good, reading this book walks you step by step through the development of a 3D engine, so you can get a good understanding of how things work.
Introduction to Linear Algebra, by Johnson, Riess, Arnold. Fifth Ed. Publisher: Addison-Wesley.
This was my college textbook for matrix algebra. I still refer to it, there are a lot of really useful applications for matrices in physics, and computer graphics, especially when you have to deal with huge systems of equations--matrix algebra solves these problems pretty easily. This book isn't too dry imho, probably just because I'm a geek though.
4-bit adder: A snake made of 1's and 0's
This is a subject on which I am as close to a world expert as it's possible to get. If you are familiar with MMOG development, you may have heard of MUD-Dev. If you do a search for my name and "physmud" you'll turn up hundreds of articles on the simulation of physics in a game engine. I used to simulate multi-day trajectories of orbital and ballistic bodies for SDI purposes for a living. I know just about all there is to know about this kind of modeling, and where you can take a shortcut, how to do a numerical approximation in n or nlogn steps when possible, what the inaccuracies introduced by each approximation would be... sometimes, I know how to do an exact solution to a transformation in a far smaller amount of time, using a jacobian transformation on complex geometries with an angular integration... but the reason I know this is, I learned on the job, and I took a degree (plus a bit) in physics, and I read all the books I could find. So, it is with regret that I say this book was not terribly good. I've seen better in a text entitled "An Introduction to Computer Simulation Methods, Applications to Physical Systems", a not too well written textbook with source in BASIC, but at least featuring a fair breakdown in the nature of algorithms, numerical integration, efficiency and accuracy, etc. A much better choice, IMO, would be "Numerical Recipies in C", though it's a little more advanced... "Numerical Methods for Physics" is hard to find, but very good. "Numerical Methods for Scientists and Engineers" is not the same book, and while very good for numerical analysis, it isn't an ideal book for learning simulation techniques. If you're interested in related fields, try looking on Amazon under Books/Subjects/Science/Mathematics/Applied/Compute r Mathematics. There's stuff on 3D graphics algorithms, signal processing, crypto, genetic algorithms, organic and physical chemistry sims, and more... just be aware that there are a lot of books on using Matlab/Mathematica/Maple/etc.
-- Still waiting for the Nike endorsement
Well... where I work, that's called an "A bug". We can't allow situations where the player can render the game impossible to finish.
Imagine this: You collapse said ceiling, then save your game. Now... you didn't know that this would block your only path out, so it's not really your *fault*. But now that you've saved the game, and you've made it impossible to finish, you'll have to start over (or, more likely, throw the game in the trash).
Along with bad crash bugs, this is the worst sort of game bug.
I'll second this!
This guy is getting a degree in physics, and clames to know something about numerical methods, but doesn't understand the first thing about ballistic trajectories.
Case in point:
"The orbit is elliptical, so just simulate a freaking ellipse!"
Lets just assume for the moment that it is a simple 2 body problem with the mass of the second body being neglible. What is the speed of the object at different points on the ellipse? How long does it take to get from one point to another? You need actual astrodynamics to work that stuff out. I remember a space game simulation (sorry, can't remember the title) that had the object traveling at the same speed over the entire ellipse for a highly elliptical orbit! What a joke.
Now throw in multi-body dynamics, etc. and even your simple ellipse goes out the window.
How is this a troll?
Hrm. Seems my last five comments have each been modded down one point. Fortunetly for me, I could care less.
autopr0n is like, down and stuff.
So now, given the theta angle, we can transform the car-coodinates accelerations into world-coordinates accelerations, and then we process the Verlet algorithm to get positions.
Soooo then... how to determine the theta angle, given that there is no compass on the vehicle?
I don't think I've defined the problem clearly enough:
Imagine you have a car, parked on a flat plane of infinate size. The car is stationary, at the origin, with the nose aligned with the Y axis (so, for the moment, the car axis and the world axis are aligned)
Inside the car is a pair of accelerometers (one along the car's x axis, the other along the car's y axis), and a speedometer (which provides car-y-axis velocity) The car is then driven around in a path, while the accelerometers and speedometer record values at a fixed sample rate.
Given the resulting data stream, and assuming no slip, give the stream of world (x,y) coordinates that correspond to each car (x-accel, y-accel, y-velocity) coordinate.
Seems like we're modt of the way there...
.
Want to learn about race cars? Read my Book
xracer? As far as I recall, after trying it out and even having a look at the source code, there was no physics behind xracer.
.. that the physics-based formulas are just *one* part of a physics engine.
Collision Detection (CD), and more importantly Collision Response (CR) determine the "feel" for your game. You can have the most accurate physics in the world, but if your CD/CR sucks, chances are, you're bringing the game down too.
Check the archives of Game Dev Algorithms if you want more info.
Okay, so what if the player saves the game when his character has 1% health and there is a rocket two meters behind him and speeding directly towards him? The player can't see the rocket that's behind him, so it's not really his *fault*, after all...
Would your company consider this situation a "game bug" too?
Does your company specialize in making games which are impossible to lose?
(If so, I'm pretty impressed--I've never seen anyone who worked at Squaresoft post on /. before :))
Of sorts. As one posted said, "..games are more fun when I can throw physics out the window and jump around in the air."
Yeah, Matrix-like action is still amazingly fun after all this time.
Anyway, I agree with one thought here. Graphics do not matter. But, in reality, they do.
Look at Square. Story? Why, it's our good hero, Cumulonimbus, off to fight the evil (Insert a Biblical-sounding name here), and along the way, his girlfriend (dies/marries him)! The only thing Square has going for it is graphics, nowadays.
Lo and behold, look at all the people who flock to Square's banner because of their flashy graphics.
It's like Top 40 radio. It sucks. I know it sucks, you know it sucks, but the rest of your block thinks Britney Spears actually has musical talent.
Unfortunately, games, like music, like movies, like books, are becoming more 'mainstream' - and that means companies sell to the lowest common denominator, because that section makes up the bulk of the population, thereby netting them the most profit.
I mean, look at Star Wars. First came, "No, Luke, *I* am your father." I can't count the number of times I've seen evil guy = good guy's father because of The Empire Strikes Back. Even in Video Games, it's *there*. Shining in the Darkness and Seiken Densetsu 3 quickly spring to mind, though there's plenty of others.
Lord of the Rings? LCD! LCD! The audience wouldn't understand Bombadil, of course! Arwen? Why, all the feminazis would bitch if we didn't have more than Eowyn kicking ass.
(Note: Not ragging on Jackson here. If I had been handed $300 mil, I'd want to make sure it appealed to as wide an audience as possible. LCD, folks.)
You know what? I was playing Castlevania 2 the other night.
And I found myself wondering, "How in the name of Hell did they fit a game like this onto a Nes cartridge?"
The music in CV2 was excellent (Considering the hardware), and so were the graphics. Yet those weren't the most impressive things.
The single most impressive part of the game was *gameplay*.
Sadly, like the dinosaur, like 8-bit consoles, gameplay as an important feature is now extinct.
You just have to be willing to look for a good clan server to play on. Many have setups where if you cheat you are immediently banned, and it works pretty well. (Went through a short time after punk-buster stopped developing that cheating was horrid, but that has pretty much been fixed) If you want more info, email me, I'm not about to post the game server on slashdot, we really don't want the slashdot effect.
alright guys..calm down ;-) I'm mostly talking about team-based online UT:TO/HL:CS type games. We can generally shoot each other no prob. Ok, sceneario: a wall is blown away and blocks stairs that separate both teams, or a floor gets destroyed. Obviously someone will notice the impass, either 1 team or both teams - a user his tab, votes "restore/remove wall/floor piece", little popup window of the offending piece shows up on other still-living players with a 'yes/no?' option...there. all done. problem semi-fixed. Sure, not a good solution for single player games...
If it is done like most books today, it is simply glued. If color isn't a necessary component of the printing, you could "break" the spine, carefully remove the leaves (I think that is the term) or pages (if it is real cheap), from the book, photocopy them, and ring-bind or spiral bind it yourself.
If it is well bound (ie, with sewing, cloth, hardback, etc), then cut the pages out and photocopy them, then ring-bind it.
Now, I am not one for destroying books in this manner (or any manner - I love books), especially such an expensive one - but if you really need ring-bound books...
Reason is the Path to God - Anon
>Do we need high-order simulation of planetary orbits in a space shooter?
It depends. If you want to stay on the same orbit after 10 loops - yes, you need all accuracy you can get. If you have a crazy gamer who presses keys every millisecond - no, right parts of equations will have bigger effects than any integration errors you can have. Sometimes high-order schemes can produce worse results.
>Not quite sure how to take your comment on my degree
Sorry being nasty. But you need better feeling what is the right method for a problem.
Got Apathy?
First, physics is inherently descriptive and approximate anyway, so if there is a "real" physics, it has yet to be discovered. Physicists are always working with approximations and numerical methods, but it's best to go as far as you can with "exact" solutions and generalities. Then, when you need to start doing numerical work, you have some place to start from. You can't do numerical integration unless you know what to integrate.
Second, the usual 100-level undergrad textbook in physics tells you a lot of things that you probably don't need to know when designing games (like E&M and some quantum mechanics), but also leaves out the more practical aspects of classical mechanics when dealing with less-than-ideal objects. Once you work with the motion of objects that are not spherically symmetric, you need mechanics at the next level, and you need to work with matrices and vectors. This stuff isn't difficult, but it's not in the typical undergrad textbook. And it does require a bit of mathematics, like most things that are worthwhile.
So it sounds to me like this book does have an important niche to fill, combining undergrad classical mechanics, a sampling of junior-level classical mechanics, and some numerical methods to boot.
Personally, I'd like to see a game that let you travel at 0.9 times the speed of light and have it render the distortions of the world correctly
Basically, even if physics are realistically modeled in a game, you can still do stuff in that game that you couldn't (or wouldn't) do in real life.
And I admit that sometimes I do prefer playing arcade style racing games... it all depends on my mood.
Euler's Method is a first-order (rectangular areas)Runge-Kutta method. The Improved Euler's Method (trapezoidal areas) is a 2nd-order Runge-Kutta Method. Runge-Kutta is a class of numerical integration techniques. I think the author is refering to a fourth-order method when he says Runge-Kutta. The higher the order, the better the top of the integration slice fits the integration curve. The trick is to get the best fit for the least amount of computation.
Or maybe, since we're talking about games with realistic physics, give them some way to remove/get around the obstacle, such as being able to climb over it, or blast it with an improvised explosive which would perhaps cost them a lot of their ammo, or dig their way out with a shovel.
Or, there could be limits placed on what can or cannot be destroyed based on the difficulty level the user selects.
My point is that there are plenty of other ways of dealing with these sorts of problems. They may cause a lot of headaches for the coders, but so will realistic physics.
Where I'd personally like to see realistic physics is in space flight simulators. It really iritates me that the majority of them ignore the basic mechanics of movement in the absence of gravity and atmosphere. Given that gravity and atmosphere produce most of the complications in dynamics, it doesn't make much sense to me why they do that, other than that it's cheaper to slap new graphics over an existing flight sim engine than to create a new one that actually works right.
Under capitalism man exploits man. Under communism it's the other way around.
When using real physics in PC golf games, I'm disappointed that the result of the hit is dependant on the user's dexterity with a mouse. A slight deviation from the precise swing path, and the "real" physics causes the ball to hook or slice wildly. For me, this is totally unfair. As a real golfer, I can hit most shots fairly straight, and even a mishit will not result in anything as exaggerated as what a PC golf game can dish up. I'd like gold games to have an option where 50% of all shots finish on the fairway, 50% of all shots are at the optimum distance for the club selected, and 50% of all putts are going to finish within tap-in distance. Until PC golf games can deliver this, I won't bother playing them.
my best example of such a distinction is super smash brothers for n64. the physics are completely unrealistic, as characters can "rejump" in mid-air, send other players blasting off the screen, and other ridiculous things. this is not necessarily bad physics, just programmers taking liberty with the laws of dynamics. it is not confusing and makes game play that much better.
:-).
it is bad physics, however, when i punch someone and instead of that person following the direction of the impulse that should have been imparted by the impact, he travels in the opposite direction. this is just confusing and makes the game annoying at time. still, it's a kick-ass game
that being said, i am done with mechanics for the rest of my undergraduate carrer (which mind you
I have to say I've only played the PC version, but in Carmageddon the physics are very "floaty" and it's that way for a reason!
As Carmageddon is all about massive jumps and stunts and air time (as well as crashes and pedestrians), they made the physics of the game enhance the gameplay aspects they wanted to emphisize.
"There is more worth loving than we have strength to love." - Brian Jay Stanley
I would love to find how to model the physics for a pinball machine.
Bumpers, posts, and the like are easy. The hard part is the flipper, of course.
It's angular movement, and overall the flipper accelerates as it moves up. This acceleration allows the flipper to maintain contact with the ball and push the ball away. The angle the ball leaves the flipper is dependent on when the flipper meets the ball, and the ball position at the time of the flip.
Does anyone have some good pinball physics that could be used? There are more elaborate situations as well, such as balls hitting flippers that are in the process of being lowered (a "drop catch").
Krellan
Dr. Demento On The 'Net!
In my opinion, the most difficult aspect of writing a good 3D game is coding complex physics
And here I was thinking the hardest parts of writing a 3D game were managing oodles of content as fast as possible, creating believable AI that doesn't get instantly panned, creating tools for designers and artists that are not only easy enough to not cause lost time but also complex enough to do everything they require, and generally trying to make a game fun based on an unproven concept (ignoring genre cookie-cutting games).
The most important part of making a game is making it fun. People aren't going to give a rats ass if a game has decent physics if it's a bore to play. Case in point, Trespasser - the most complex physics system seen in a game, and also the biggest flop and butt of game developer jokes for years to come (although that could just be because of Seamus Blackley, but I'm not going to go onto a tangent).
My point is, games are fun first, realistic second. If a game is extremely realistic, it's a simulation. Some may not see the difference, but I'm guaranteed you would after playing an hour of both Railway Tycoon II (Turn-based game based on railroad era) and Microsoft Train Simulation/Trainz (Simulations where you drive a train). The difference here is that one is fun and non-realistic, the other isn't fun to non-trainspotters but is extremely realistic. I'll let you imagine which one makes more money.
Physics never bothered the guys who coded the hooters on the fems in the "Dead or Alive" PS games....
if ya want physics you gotta go download Pontifex from Chronic Logic. That's one good bridge building game!!!!!! Also I recommend Elasto Mania(for a while, until it gets boring and impossible to beat) for it's insane physics.
Finally it got a mention on Slashdot, and above all things, for its outstanding physics engine. If you like realistic racing games, then Re-Volt is for you.
I know this post is mostly pointless.
Karma: \Kar"ma\, n. [Skr.] (Buddhism) One's acts considered as fixing one's lot in the future existence.
Check out http://netdevil.com/jumpgate for realistic Newtonian physics! Makes pilot skill something to work for! fruitito
Notice how symmetrical are the faces of Princess Fiona, Lara Croft and Aki Ross? You can construct a face out of as many polygons or whatever as you like but if they're the same ones on both sides you're not trying.
Plus ça change, plus c'est la même chose.
For me one of the big advantages that this book has over classic physics text books is that it includes C implementations of the formulas, rather than just listing equations.
I find it much easier to understand an equation when I can look at an implementation of it.
Also, has anyone found the 'trajectory of missiles including the effects of fuel burn off' thats mentioned on the back cover?
//this is meant for developers so:
//bad luck
//good luck
//thanks
if (no money available)
{
if (not smart or no time)
{
download_ode_solid_swift_dynamo();
} else
{
read_baraff_mirtich_barenbrug_vandenbergen();
do_magic();
}
}
else
{
buy_commercial_engine();
}
-------------- I don't speak for my boss. My boss can speak himself.
sorry just testing if it happens again
(why did i get a "0" on my last post before any moderation)
On the other hand, when we did ballistics analyses for ICBMs, we used the best approximation methods we could afford.
When I moved to Northfield, I visited Papyrus Software, who were working on extremely accurate head-to-head racing programs to be played by phone connection useing the then-uncommon 9600 baud dialup. They had a room full of 486's tied to a bank of modems. Their big physics modeling problem was that their customers knew how tires warmed up and became "slick", and their players wanted to be able to set up their cars the way the real drivers did. I suspect that most gamer first, then fanatic, players of games requiring any physics are more interested in unrealistic rail rides (ride your board down the Eiffel tower!) than they are interested in realistic physics.