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GDC - Physics in Half-Life 2

Posted by ryuzaki0 on from the super-gravity-gun-ftw dept.

Jay Stelly is a senior engineer at Valve, and on the last day of the conference he kicked off the morning with a discussion on Physics in Half-Life 2 (HL2). The physics simulation, and inventive physics-related puzzles used throughout the game, were complicated elements to implement. He discusses the problems they faced, relates some of the humorous demos they used to flesh out their ideas, and laid out the ways that good engineering can make design that much better. In 1999, world physics was a new technology that hadn't been integrated into the genre before. That meant that the solutions were not very well understood. There was an obvious visual payoff, with problems both from a technical and design perspective. Just the same, it was an opportunity to integrate gameplay. At the time, everyone was talking about physics, but there was no discussion of incorporating that technology into gameplay.

Their high-level strategy was to invest in gameplay. They decided not to start with a simulator, and to not add features to simulation (until it became necessary). They set out to make HL2 stand apart with the depth and quality of gameplay, as opposed to just 'cool simulation'. This would require a lot of engineering work on tools and design.

A timeline for HL2 Physics:

  • They looked into physics demos.
  • Demos generated ideas.
  • Looked into licensed physics simulators.
  • Internalized physics into their design ideas.
  • Built a bunch of prototypes and tools.
  • Gameplay mechanics experiments.
  • Solved technical issues.
  • Focused design and tech.
  • Solved more problems on the technical side.
  • Incremented to deliver a stable system (with valuable features at each deliverable goal).
  • A long polish stage before shipping the game.
Some physics prototypes:
  • Zombie basketball -Satchel charge, trying to explode zombies into nets.
  • Watermelon skeet shooting - Watermelons loaded up into an ejector, tossed into the air to be shot.
  • Glue Gun - Trying out 'building things' within the game. A gun that placed glue on objects, glue attracted itself to make constructs.
  • Danger Ted playset - Glue a model of a designer to a car, glue propane canisters to the car, launch the designer strapped to the car into the air.
  • Toilet Crossing - Build a zipline construct with junk to cross a chasm, extra points if you rode on the toilet during the experience.
New technology can be intimidating; To fully understand this, they needed to create their own point of reference. Led to really cool things like Garry's Mod.

So, how can they make the gameplay more focused? What ideas are good? How many ideas do they need? How can they measure the difficulty of the gameplay? And, of course, how are the prototypes going to be turned into shippable gameplay?

They reduced design to 'training and testing'. Game design is a set of player experiences that trains the player, allows them to demonstrate a learned skill, and is presented with style. With this criteria, they had an easy way to judge ideas for merit.

Design is also engineering. Defining success, identifying constraints, generating ideas, analyzing solutions, building prototypes, testing results, measuring success, and then re-examining your constraints. Distill out the elements of game design, be creative, but you want a way to analyze your solutions and measure your progress.

This allows you to reverse engineer your experiences. I want them to do 'X'. Okay, what do they need to know before they can do X? Training skills in isolation allows the player to be prepared for future gameplay elements. When something went badly in playtesting, they could look back and see if they'd prepared the player adequately for the experience. If something isn't eventually used, or isn't working, it becomes obvious and can be cut.

Training can have obstacles, though. If the player is in combat or in peril, they're probably not learning. To improve the training experience, you make it clear it's okay to experiment. Sell forced choices tot he player with style. Suggest experiments with the the gameworld. Story should not be an obstacle to training, it should enhance the experience. It's also not distracting like combat. Players can play attention to both. (He uses the example of the sawblades in Ravenholme to chop Zombies in half.) Player value as a metric for skills and knowledge. Each piece of skill must have value, or it gets cut from the game. There is a limit to the total number of things you can teach in a game. You want to cull skills down to the fewest required. Having skills interact makes them both more valuable. Requiring skill from a player makes the skill more valuable to the player. These relationships form a sort of economy, which they refer to as 'design economy'. Allowed a framework for discussion about the process.

Of course, every design has constraints. Objects have to be breakable, with the quintessential crowbar. Physics have to interact with the core combat gameplay. Collisions should cause damage, objects should be used as cover. Physics need to extend the core puzzle gameplay.

Integrating physics turned out to be kind of difficult. Physics are kind of intuitive, but it doesn't "just work". Most designers don't completely understand the technology. Taking the design to the fullest required understanding the simulation. Game logic may place impossible requirements on the simulation. Some elements have to be one part physics and one part game design, fudging the edges.

So, they took on the design interface for the physics. They need to teach the designers about the system (decomposing machines into physics blocks). They needed to become proficient with unfamiliar units and tuning parameters, dealing with a complex set of variables that imply calculations. So, to deal with this they delivered technology incrementally (ramping up the learning curve). They needed a physics expert to support designers.

Some other problems came up, especially in the early days. Many physics engines interact with the game in discrete steps of time. Changes to the state of the system are often queued. Game rules are often discontinuities in state. They also needed to reserve space for 'inventory items' (grenades, etc.) Motion planning is a problem as well (will I hit anything when I go over there?). Collision detection without physics was a required - especially for AI. They ended up building a collision speculator for themselves so the AI would behave intelligently.

This then becomes an over-determined systems, with simulation variables, design variables, and design criteria. The 'Superman problem' - Beating people to death with tin cans. They fixed this by making the mass of gravity gun held items very low, so that you couldn't destroy a car with scrap metal.

Simulation failure also was a problem. Objects get stuck in each other, they don't settle, something that is valid for physics becomes invalid for the design. Simulator 'explosion', game design constraints that can't be satisfied, and creating objects in solid space. Plan for the simulator to fail, and be flexible with your expectations. realize you're going to need to fudge.

To sum up: Engineer to solve gameplay mechanics. Use analysis and design economy to intentionally improve the design. Tech problems remain with phsyics. Some can be solved with design, put plan on investing in the technology. Plan for failure cases and be sure to ask "is this failing as a result of bad design?"

93 comments

  1. I ranted about this by Shadow+Wrought · · Score: 4, Insightful

    In my Jounral already, but how is it that just about every write-up from the GDC is long and expansive except for the Iwata's keynote? Am I alone in thinking that that was far more important to the gaming industry than what the producer of Battlestar Galactica had to say?

    --
    If brevity is the soul of wit, then how does one explain Twitter?
    1. Re:I ranted about this by jdgeorge · · Score: 4, Funny

      Am I alone in thinking that that was far more important to the gaming industry than what the producer of Battlestar Galactica had to say?

      No, but you are alone in thinking that someone might read your Slashdot journal (which I imagine is very interesting, insightful, informative, funny, and unread.)

    2. Re:I ranted about this by Shadow+Wrought · · Score: 1
      (which I imagine is very interesting, insightful, informative, funny, and unread.)

      Or at least two of them ;-) Mianly I was lazy and didn't want to spend a lot of time posting something that I had already written, but on the off chance that someone cared, well, maybe they'd share their lottery winnings with me, too. Same odds and all that.

      --
      If brevity is the soul of wit, then how does one explain Twitter?
  2. HL2 Physics by ShakaUVM · · Score: 0, Troll

    Oh lord, Half-Life 2.

    The entire game was a giant demo for the Havok engine. It's a poster child for letting your technology drive game design, when it should be done the other way. Bad Valve. No cookie!

    I'm curious what they spent four years on when they licensed the Havok engine only a year before release.

    1. Re:HL2 Physics by Amouth · · Score: 0, Flamebait

      "I'm curious what they spent four years on when they licensed the Havok engine only a year before release."

      absoulty nothing.. nothing at all except advertizing.

      and personaly i thought the game sucked compared to Doom 3 (just shows the more time you put into something the better it is)

      (duke nukem forever is going to be killer :)

      --
      '...if only "Jumping to a Conclusion" was an event in the Olympics.'
    2. Re:HL2 Physics by kannibal_klown · · Score: 1

      Personally I wasn't a big Doom 3 fan. Yes, my rig could more than handle it. And a couple of times towards the beginning I got the piss scared out of me. But after that it was pretty humdrum.

    3. Re:HL2 Physics by Anonymous Coward · · Score: 4, Insightful

      To put it simply, Half-Life 2 is a moderately well rendered city, that feels vaguely real. Doom 3 is ten thousand miles of beautifully rendered corridor.

    4. Re:HL2 Physics by Jorkapp · · Score: 2, Insightful

      I would assume the years leading up to the licensing of the Havoc engine were spent on developing other aspects of the game.

      * Audio work does not require the game engine.
      * Modelling the objects and maps does not require the game engine per-se.
      * Aspects of the engine can be coded without the physics engine - AI, weapons, Player->NPC interaction, etc
      * Other things were going on behind the scenes at Valve besides HL2 - Steam, Creating DOD:S, CS:S, HL:S, etc

      Of course, we can't deny that they probably took a day or two here or there just to duke it out in an office Counter-Strike tournament.

      --
      Frink: Nice try floyd, but you were designed for scrubbing, and scrubbing is what you shall do.
    5. Re:HL2 Physics by elmegil · · Score: 1
      It's a poster child for letting your technology drive game design, when it should be done the other way.

      I guess I played a different version of Half Life.

      --
      7 November 2006: The day Americans realized corruption and incompetence weren't addressing 11 September 2001
    6. Re:HL2 Physics by 2008 · · Score: 2, Funny

      I guess I played a different version of Half Life.

      You did. He was talking about Half Life 2.

      --
      I quit!
    7. Re:HL2 Physics by Jasper__unique_dammi · · Score: 0

      I loved that game, the physics element was a huge part of that, immersive apocaliptic feel. Kindah appropriate too, the main character and his friends are physisists..

    8. Re:HL2 Physics by ShakaUVM · · Score: 1

      The maps are all build around physics puzzles. You have to pile up junk, or push junk off ledges, or remove junk blocking a ramp, which then lets you jump over a gate, the long fenced corridors of Ravenholme seems entirely designed around cutting zombies in half with the gravity gun.

      And yeah, the gravity gun being a weapon that wouldn't exist without Havok physics.

      And, ok, sure. They probably could have done the dialogue without the Havok engine. =)

    9. Re:HL2 Physics by ShakaUVM · · Score: 1

      I liked Doom3 better... I guess.

      Like you, the first 10 times you get scared by monsters popping out of the darkness scares you. After that, you start becoming resigned to the fact that the game spawns creatures in areas you've already cleared, making the tactical aspects of the game frustrating.

      When I play a FPS, I clear an area, move into that area, and from cover clear the next area, and so forth. Which is worthless when the game just arbitrarily spawns monsters behind you.

    10. Re:HL2 Physics by Anonymous Coward · · Score: 0

      assuming most readers have enough brain matter

      Well, duh. The game does involve zombies.

    11. Re:HL2 Physics by 2008 · · Score: 1

      Yeah, that was the joke.

      It's 5am, so sue me.

      --
      I quit!
    12. Re:HL2 Physics by Fallingcow · · Score: 1

      Doom 3 tried to merge elements of Doom 1's nonsensical-but-fun action-horror and System Shock II's story-instensive, suspenseful survival horror. The result was something that was neither fun nor interesting, nor did it contain a good or and well-developed story.

      My favorite part is the beginning, up to about 15 minutes' of play past when everything gets zombified. The rest was mind-numbingly dull. Hell was OK, I guess.

      Half Life II, which I never expected to be remotely scary, managed to have more and better scares than Doom 3. What a sad state of affairs.

    13. Re:HL2 Physics by shmlco · · Score: 1

      Huh. As if in the real world the enemy doesn't try to sneak up behind you, or send scouts and soldiers into areas you've just vacated. I think if you ask the guys in Iraq they'd all agree that an area once cleared should stay cleared. Would make things much easier.

      --
      Any sect, cult, or religion will legislate its creed into law if it acquires the political power to do so.
    14. Re:HL2 Physics by Amouth · · Score: 1

      the thing that got me was the sound i have a realy nice sound system.. and the EAX was amazing and god the screams that seemed to be coming from the other room of my house scared the shit out of me.. it made me shiver many times.. (i don't play it at night)

      i have played it on a freinds computer with normal suround sound.. it isn't the same..

      only with quality audio do you realy get that i am scared as shit feeling

      --
      '...if only "Jumping to a Conclusion" was an event in the Olympics.'
    15. Re:HL2 Physics by Anonymous Coward · · Score: 0

      Doom 3 really was boring in a way Half-Life 2 couldn't manage, and Half-Life 2 had its moments with the first half of the game being basically boat and buggy levels, with some Unreal 2 "DEFEND THE AREA FROM INCOMING ATTACK!" mixed in for good measure. Half-Life 2, despite being little more than a tech demo for the gravity gun, was just way more fun than Doom 3, on top of looking better because of a better artistic theme and less darkness. FEAR is better than both of them, of course. It even eats computers better than both of them.

    16. Re:HL2 Physics by Fallingcow · · Score: 4, Interesting

      I don't mind the occasional monster popping up behind me. Especially if I notice some sort of entrance that it made to get there, I.E. crushing a vent cover, or smashing through a locked door, or whatever. I can even tolerate teleporting enemies.

      The worst part, and what really killed any suspension of disbelief, were the "monster closets". Rooms whose doors look just like a wall, but which open up when you walk by, revealing a tiny room filled completely with as many monsters as it can hold (in the original Doom games, this was sometimes a dozen monsters. In Doom 3 it was usually one or two.) Not just closets, either--these are rooms that could not possibly serve a purpose, other than to hide things to pop out and scare you. It's like they're trying to remind the player that it's just a game.

      Also, every out-of-the-way spot in a room contained a monster. ALWAYS. Walk in to a new area, no enemies. Huh. Oh, there are two pillars on the other side. Two zombies behind them, guaranteed. Might as well fire somethign with an area effect at the walls behind them, and get this room over with, even though I havn't "triggered" them yet. Done, next room, same fucking thing. BORING.

      Just enough to throw any sense of suspense or anticipation right out the window, but not enough to give me any of the fun 100-on-1 scenarios that made the original Doom so much fun.

    17. Re:HL2 Physics by Anonymous Coward · · Score: 0

      With the lights switched off.

    18. Re:HL2 Physics by Hydryad · · Score: 0

      You know what really makes Doom 3 scary is just having a low fps. I noticed that it suddenly became a lot more boring when I got a decent computer that could pull 60fps on it. Maybe it is just me, but that is what I contribute a lot of the edginess to.

      --
      No sig for you, two weeks!
    19. Re:HL2 Physics by Anonymous Coward · · Score: 0

      Something tells me that your knowledge of modern game design was shaped by, and limited to, your eighth-grade class field trip to a woodworking factory that made pool tables.

      All of the tasks you mention most certainly do require a working game engine in near-final form. Designers can't prototype on paper these days, you know.

    20. Re:HL2 Physics by friedmud · · Score: 1

      I actually had this exact same experience... I'm glad I'm not the only one!

      It seems that with the low framerate I had to kind of "creep" through the game... which, I think, is what they really wanted you to do.

      With the high framerate (pretty much replaced most of my computer) I felt free to kind of "run-and-gun" and it lost a lot of the suspense factor.

      Friedmud

    21. Re:HL2 Physics by Mac+Degger · · Score: 1

      That's cool if it's done right, like in F.E.A.R., where the enemy actually does flank you (and you can plan accordingly). It's not ok when it's done in an arbitrary fashion like D3, where the monsters appear out of nowhere, for no reason. That just provokes feelings of unfairness (as opposed to 'damn, that was my own fault!') and breaks immersion...which is not a good thing in games.

      --
      -- Waht? Tehr's a preveiw buottn?
    22. Re:HL2 Physics by ScrewMaster · · Score: 1

      At least the flashlight is atomic-powered and doesn't need batteries.

      --
      The higher the technology, the sharper that two-edged sword.
    23. Re:HL2 Physics by kannibal_klown · · Score: 1
      Huh. As if in the real world the enemy doesn't try to sneak up behind you, or send scouts and soldiers into areas you've just vacated. I think if you ask the guys in Iraq they'd all agree that an area once cleared should stay cleared. Would make things much easier.

      Yeh but I doubt in realy life you'll clear out a supply closet, walk 5 meters, and turn around to see 10 more living guys appeared in the supply closet out of nowhere and are readdy to mess you up something fierce.

      I'm sure the occasional room might have a trap door or something but I doubt that happens often.
  3. Drunken GDC folks singing karaoke by t0qer · · Score: 0

    Sort of off topic, but we had a *HUGE* turnout of GDC folks at my bar last night. Had a nice chat with the art director for zipper interactive, few other folks. Replay video from last night will be playing till 5pm today, then again on sunday.

    Winamp compatible stream here

    --toq

  4. I was there... by djohnsto · · Score: 2, Interesting

    To be honest, Nintendo's keynote was light on any real info. He spent more than half of the keynote going over how the game Brain Age for the DS came about, how they convinced stores to carry it, and had a live demo / showdown of the game with some "friends". The most popular part of this was when he announced that everyone in attendance would be getting a copy of the game (which turned out to be a demo).

    He then talked about Metroid Prime: Hunters, and again had a live deathmatch between some of the developers. He wrapped up the DS segment with a preview of Zelda: Phantom Hourglass (which looks a combination of Link to the Past + Wind Waker).

    Finally, he spent a (small) bit of time talking about the Revolution and the Sega / TurboGfx agreements.

    His whole keynote stressed that pushing tech for tech's sake wasn't sustainable and that true innovation needed to happen. Nintendo is innovating with their DS, with games like Brain Age, and with the Revolution (controller, content agreements, etc.). All real information + hands-on games will be available at E3.

    So, unless you really care about the life of Brain Age, you aren't missing much. :-)

    --
    Dan
    1. Re:I was there... by Shadow+Wrought · · Score: 1

      Well its nice to know we didn't miss much, but a simple line to the effect that nothing much was said would have been, IMHO, much preferred to making it look like Iwata's speech was simply glossed over.

      --
      If brevity is the soul of wit, then how does one explain Twitter?
  5. Re:I trolled about this by Anonymous Coward · · Score: 0

    THANK YOU.

    I'm so sick of people saying, "As I wrote in my journal the other day," "As I've been saying for so long," "If you're familiar with my previous posts," etc. I don't care and I doubt anyone else does.

    To head off some stupid criticism, I'm only posting this as an AC because I'm too lazy to make an account and, no, I do not want to move to digg.

  6. What the... by voxel · · Score: 0

    What the heck are you talking about, no cookie? I think they got about 100 million cookies right after launch... That is if one cookie costs one USD.

    --
    Modesty is one of life's greatest attributes
    1. Re:What the... by ShakaUVM · · Score: 1

      They didn't get sent a free cookie from me.

    2. Re:What the... by voxel · · Score: 1

      I gave them about 50 cookies, and it was well worth it, best game I ever played. One of the, if not the only game I've ever finished.

      My wife enjoyed it more than I did, she would beg me to play just so she could watch. She said it was like an interactive movie for her, where she could "help me" try to figure things out.

      --
      Modesty is one of life's greatest attributes
  7. Failing the leaning tower test by omarius · · Score: 3, Interesting

    I was somewhat disappointed that the physics in HL2 fails realism testing in at least one respect; on the "bridge" level, I had the idea to run a little experiment: I jumped off the bridge, and then used the "toss" fire for a grenade to see if the grenade and "I" would fall at the same rate. That grenade shot up in the air like a balloon, relative to my descent. I wanted SPLAT-->BANG! and all I got was SPLAT. What's up with that? :)

    1. Re:Failing the leaning tower test by Fallingcow · · Score: 1

      Maybe they just give items weight and calculate fall rates based on that, rather than giving them both weight and some number to define the level of air resistance that they encounter when falling.

      A five-pound chunk of styrofoam should shoot up above you if you release it while falling. A 5-pound grenade should not.

    2. Re:Failing the leaning tower test by Dr.+Eggman · · Score: 1

      I tried the same thing, but toss still puts force behind the grenade, it doesn't just let it go. grap a small object like the bucket in the small shack half way through the bridge and repeat. The secondary fire key (or primary, I forget which) will just drop the object. I forget what happens...

      --
      Demented But Determined.
    3. Re:Failing the leaning tower test by syphoon · · Score: 4, Interesting

      I can't speak for other objects, but I do recall reading that they deliberately lessened the gravity for grenades to let them arc higher for a better visual effect.

    4. Re:Failing the leaning tower test by Mr_eX9 · · Score: 1

      The game doesn't take place in a vacuum.

      Air resistance, anyone?

    5. Re:Failing the leaning tower test by Anonymous Coward · · Score: 0

      Except grenades are denser than people, so it should actually fall faster, not slower. Thanks for playing, though!

    6. Re:Failing the leaning tower test by uhmmmm · · Score: 2, Informative

      The grenade would fall faster than the person, but not because of density - density doesn't play into it. It's because of less air resistance, which may have a little to do with the density, but a lot more to do with the shape.

    7. Re:Failing the leaning tower test by EnderWigginsXenocide · · Score: 1

      You:
      The grenade would fall faster than the person, but not because of density - density doesn't play into it. It's because of less air resistance, which may have a little to do with the density, but a lot more to do with the shape.

      Reply:

      A grenade made of aerojel will fall much slower than one made of steel with an explosive core. Sure, shape is a factor. So is density. Gravity dosen't give a squat about density. Unfortunately the ability of a projectile to penetrate a fluid (like air) does depend greatly upon density (as well as shape.) This is why heavy bullets have a greater balistic coefeccient than lighter bullets of the same shape. They have more mass, therefore more interta, and will tend to penetrate a fluid with less loss of energy than a less dense bullet.

      But, as far as the game goes . . . unless the player is considerably denser than the grenade there is a problem with the realism of the physics engine (assuming that when one "drops" a grenade it's not actualy THROWN [IE: given a velocity vector that is diffrent from the player who "drops" the grenade])

      --
      Blessed are the pessimists, for they have made backups. -- 0 1 My two bits
    8. Re:Failing the leaning tower test by Anonymous Coward · · Score: 0

      Gravity for characters in games is often significantly higher than real-world gravity. I work as a game designer and part of my duties is tuning the handling for a particularly acrobatic character. To get a feel that is natural and "real" to the player, the character's gravity needs to be at least 2 times that of the real world. Otherwise, the player feels like their character is floating whenever they leave the ground.

  8. Things like this... by TheNoxx · · Score: 2, Interesting

    Make me wish, if only a little bit, that I'd gone into programming instead of art/3d modelling/graphic work/etc.

    Oh, what a good game programmer could do with an easily scriptable physics engine. Imagine WoW when the spells have effects on the physics, or interact with each other based on their level and element and alignment... I dream of a combination of Mage: the Ascension and Dungeons & Dragons... tell me I'm not the only one.

    --
    Ex nihilo nihil fit.
    1. Re:Things like this... by Dr.+Eggman · · Score: 1

      Your not:

      http://physx.ageia.com/titles.html

      "Warhammer MMORPG"

      Its got the MMORPG part, but if you want the magical part you want:

      http://www.mightandmagic.com/us/darkmessiah/teaser /

      FPSRPG Might and Magic game powered by an enhanced version of source, anyone?

      --
      Demented But Determined.
    2. Re:Things like this... by aarku · · Score: 1

      An engine like this? http://www.unity3d.com

    3. Re:Things like this... by rasmusneckelmann · · Score: 1
      Imagine WoW when the spells have effects on the physics, or interact with each other based on their level and element and alignment
      There's a reason why the "physics" of WoW, and MMORPGs in general, are very simplistic; synchronizing complex HL2-class (full rigid-body simulation) between several computers in an ordinary multiplayer game is NOT simple... Now try to do it in a game like WoW, where thousands of clients need to have their physics synchronized. It's a daunting task to say the least. The thing to note about WoW, is that the game is designed in such a way that client synchronization isn't strictly important; it's playable even when client latencies differ with several hundreds of milliseconds. The only "physics" of WoW is that of the position of the players which can be handled easily on the client-side, and checked easily from the server. If HL2-class physics where applied to WoW, then it would no longer be enough to see the player as a single body, but suddenly he would be consisting of a head, upper arms, lower arms, hands, upper legs, backs, and so on. Try multiplying the bandwidth required with 20. (and that's not considering all the physical bodies of the world that would be cool to interact with). Another thing is that MMORPGs (at least those I know of) are very static in nature - I have a hard time imagining how physics could be integrated into existing gameplay "archetypes". To summerize: I'd say it is close to impossible with today's hardware and consumer internet connections. But yeah, personally I think it would be very cool with such a game :)
    4. Re:Things like this... by brainwash · · Score: 1

      That not necessarily true. A script can be applied both localy and remotely and the communication overhead is still minimum. For example, you could send a 'chest thump' as a script or you can send the positions for all the body parts individually. In the first case you have a processing overhead that is handled at the client (receiving) side, but since the engine is already there it might be invisible to the user. In the second case you have a communication overhead which might make your game latency-dependent.
      If you were a developer you would make sure that the physics API is applicable through network protocols, that's what makes an API transparent and/or easy to use.
      Positional updating is used where you can afford loss of packets - see racing games for example.

  9. Re:Hmmm, interesting by JimmehAH · · Score: 1

    If you own Half-Life 2 then you can download the SDK. It comes with quite a few example maps and also the code for the game logic.
    There's lots more information at the developer wiki.

    You can also get a free version of the modeling/animating software they used, which is called XSI.
    http://www.softimage.com/community/xsi_mod_tool/de fault.aspx

  10. Motion and path simulation by AK__64 · · Score: 1
    FTFA:
    Motion planning is a problem as well (will I hit anything when I go over there?).
    Getting around tended to be more difficult than I'd like to see in a FPS. Part of it was overambition in striving for a truly 3D physical environment, replete with small ventilation ducts and bizarrely slanted ceilings, but I rather frequently found that I needed to jump to get over a 1" ledge or duck to get under a certain threshold, and sometimes both, sadly.
    Hopefully this is still a work in process in game physics and we see marked improvement as time goes on. Also object weights tended to be too light IMO. I really felt that objects' fall rates and throw trajectories reflected not enough weight.
    Other than that, I really enjoyed what I felt was a truly innovative method of problem-solving. Way better than those old jump puzzles. +5 to Valve for the gravity gun. I want one!
    1. Re:Motion and path simulation by rentedflowers · · Score: 2, Insightful

      Also object weights tended to be too light IMO. I really felt that objects' fall rates and throw trajectories reflected not enough weight.

      You realize the fall rates are largely independent of the weight, right Gallileo?

    2. Re:Motion and path simulation by Animats · · Score: 2, Interesting
      Also object weights tended to be too light IMO. I really felt that objects' fall rates and throw trajectories reflected not enough weight.

      If motion in free flight looks wrong, that's probably intentional.

      But if big objects bounce as if they're very light, that's a fundamental limitation of impulse-constraint physics engines. All bounces occur instantaneously in such systems. (That's what an "impulse" means; an infinite force applied for zero time with finite energy, leading to an instantaneous change in velocity.) So big objects don't appear to have "weight". We call this the "boink" problem.

      We solved that problem in 1996-1997, but it takes more compute power to do it right, so most physics engines take the cheap approach. This is the main reason physics in games consistently looks unrealistic.

      When our ragdolls fall down, it looks like they're hurting. (Then again, do you want that level of realism in death scenes?)

    3. Re:Motion and path simulation by Paradise+Pete · · Score: 1
      When our ragdolls fall down, it looks like they're hurting.

      "main: no suitable decoder module for fourcc `IV50'. VLC probably does not support this sound or video format."

    4. Re:Motion and path simulation by Hortensia+Patel · · Score: 1

      Interesting. So (speaking as a physics illiterate), what is it that's not being modelled by impulse-constraint engines? Compression?

      I've seen this in movie CGI as well as games, so it can't be just down to realtime computational constraints. Most recently in Serenity (the docking clamp on Beaumonde and the final crash sequence both made the ship look far too light).

    5. Re:Motion and path simulation by Animats · · Score: 1
      Most recently in Serenity (the docking clamp on Beaumonde and the final crash sequence both made the ship look far too light.)

      Yes, and you can also see a helicopter bounce badly in Charley's Angels.

      Interesting. So (speaking as a physics illiterate), what is it that's not being modelled by impulse-constraint engines? Compression?

      Yes. If you do strict rigid-body physics, bounces take zero time. That's not realistic. There's always some compression. To look right, some compression needs to be simulated. Deforming the visual geometry is optional (we didn't do that in 1997, but one would today, since the GPU can do most of that work), but some degree of springyness in collision simulation is essential.

      This is even more important when you try to simulate sliding contact. Impulse-constraint sliding contact has fundamental problems, like static indeterminacy.

      We used to sell a physics plug-in for Softimage, but figured that about twenty copies would service all of Hollywood. We sold about that many. That's not a viable business. Then Softimage tanked. (Microsoft sold them to Avid, which really wanted Softimage's 2D "Digital Studio" system to prevent them from underpricing Avid's 2D compositing market. Avid had no clue what to do with 3D, and eventually spun off the 3D operation. By then, Softimage's 3D line was no longer dominant in high-end animation.)

      So we licensed the technology to a well-known middleware company. But then the PS2, with no double precision floating point, took over. Our approach requires double precision to correctly handle the huge forces that appear when heavy objects hit. So most game code has to use an impulse-constraint method, which works OK with 32-bit floats.

      Financially, we did fine, but not many people are using our approach. Yet.

    6. Re:Motion and path simulation by Mac+Degger · · Score: 1

      Couldn't you just hack in the deformation by adding a slight time delay to the bounce? Kind of an 'on contact, wait so-many-ticks-dependant-on-object, then resume bounce' with a different delay per object. I know it doesn't simulate reality per-se, but it seems that it would a computationaly-cheap hack to enhance realism. Or is something like that too obviously not real?

      --
      -- Waht? Tehr's a preveiw buottn?
  11. Valve created no 'Physics' in HL2 by Anubis333 · · Score: 0

    Valve licensed a Popular physics engine right off the shelf. Many companies do write their own Physics engine from scratch, but Valve didn't, so I find it funny they talked about this, shouldn't Havok have spoken instead?

    1. Re:Valve created no 'Physics' in HL2 by Dr.+Eggman · · Score: 2, Informative

      Read you own link, it says Havok worked with Valve for 3 years to bring about Havok 2. Kind of similar to how Half-Life's engine was built off a licensed Quake engine, no?

      --
      Demented But Determined.
    2. Re:Valve created no 'Physics' in HL2 by SnT2k · · Score: 1

      It's not the Havok physics engine itself that made HL2 stand above the rest. In fact, a dozen more companies license this ridiculously expensive engine. However, it is how they utilize the engine that made them stand out. Many games limit the implementation of the physics engine to how the character will jump, how will the grenade fly, how will the particles of an explosion go and how will the car fly when an explosive is placed under it - of course there are more areas but they are generally limited. HL2 on the other hand, made things a little bit more realistic by implementing the physics engine on every object possible (the environment) and a little bit wackier by implementing a gravity gun.

    3. Re:Valve created no 'Physics' in HL2 by Anubis333 · · Score: 1

      Being part of the testing process of Physics engine someone else is making is not the same as creating one... sorry.

    4. Re:Valve created no 'Physics' in HL2 by Anonymous Coward · · Score: 0

      Havok aren't the ones that designed a fun game based around the engine. He's talking about how they implemented the engine into the gameplay, not just the specifics of the engine itself. Did you even read the article?

  12. Physics by Anonymous Coward · · Score: 0

    I loved HL2 physics in single player but I can't stand it in multiplayer. Multiplayer games really need to use old HL1 and Quake1 style physics (with air control, but not neccessarily bhopping) to be fun, IMO. I can't stand playing all these new realistic games in multiplayer--I feel like I have no control. Not being able to turn in the air and having movement that is more real may make the game more realistic but it doesn't make it more fun.

  13. Re:Hmmm, interesting by Chabo · · Score: 1

    Someone did for them. ;)

    I know, I'm mean.

    --
    Convert FLACs to a portable format with FlacSquisher
  14. Re:I trolled about this by Shadow+Wrought · · Score: 1
    To head off some stupid criticism, I'm only posting this as an AC because I'm too lazy to make an account

    Even though it takes the same amount of time to do as to post? It's certainly your right to criticize, but if you're not willing to even become part of the community you're critizing, then I can certianly understand why your criticism is consistently criticized.

    Plus, if you make an account, you can spend that extra 5 seconds foeing me and never having to see me again. ;-)

    --
    If brevity is the soul of wit, then how does one explain Twitter?
  15. HL2 physics is priceless... by __aaclcg7560 · · Score: 1

    I loved the physics in HL2. My favorite part of the game was shooting down this flying thing (I don't think it was a helicoptor) in the middle of a mud flat. I fired off the last shoot to put the thing out of commission right above me and I enjoyed the moment of a victory of seeing it come back down. Until I realized that the damn thing was going to crash on me! Fortunately, I was able to get out of the way. That was a fine moment when I realized I nearly lost the game because I was rubbernecking the kill.

    1. Re:HL2 physics is priceless... by fujiman · · Score: 1
      The "physics" you just described was a scripted event. It plays out the same way every time. Go and check.

      Oh, and BTW, I loved the scripted events is HL1, too!

    2. Re:HL2 physics is priceless... by Anonymous Coward · · Score: 0

      Wow! They must have vested thousands of valuable man hours into creating the wonder of modern mathematics and computer science that is "PrerenderedModelFallsOnTheGround.cpp".

      Physics at its finest, right there.

    3. Re:HL2 physics is priceless... by __aaclcg7560 · · Score: 1

      Seem like yesterday that I was admiring the physics for "Lunar Lander". It's been a long road from the early 80's. :P

  16. Spirit of HL1 by Jainith · · Score: 1
    # Zombie basketball -Satchel charge, trying to explode zombies into nets.
    # Watermelon skeet shooting - Watermelons loaded up into an ejector, tossed into the air to be shot.

    These remind me of a map I made years ago for the HL1 community project called 'The Spirit of Half-Life'. The map had a number of different 'sport' type activities, including a basketball and skeetshooting games using snarks. Heck I even made it keep score correctly...Ahhh those were the days...

  17. You can't own it by Anonymous Coward · · Score: 2, Insightful

    You can't own Half Life 2.

    You can only rent it, using Steam to grant you permission to play it.

    Steam sucks.

    1. Re:You can't own it by Anonymous Coward · · Score: 0

      Thanks for contributing so much to the topic at hand. Why the hell is this modded as insightful and not offtopic?

    2. Re:You can't own it by Anonymous Coward · · Score: 0

      Because people that dislike the direction Half-Life 2 took with regard to game ownership and distrust of the end user. No matter how interesting the gameplay and technology is in HL2, I (and likely many others) will not buy the game due to its use of Steam as excessive copyright protection to the point of judging the game owners guilty until proven innocent.

      This is not a game to be praised. This is a game that has shown exactly how far companies will go to inconvenience legitimate, paying customers.

      From what I hear, pirates still made the game work just fine, by the way.

    3. Re:You can't own it by jettoki · · Score: 1

      This is not a game to be praised. This is a game that has shown exactly how far companies will go to inconvenience legitimate, paying customers. From what I hear, pirates still made the game work just fine, by the way.

      I sincerely doubt you are a "legitimate, paying customer," so it really doesn't matter. I refuse to buy games with StarForce attached, because it's genuine malware that treats the customer like a criminal. In contrast, I've found Steam to be incredibly convenient for content delivery -- I don't even have to have my CDs to install the game. In fact, I really dig Steam, because it guarantees small developers a greater percentage profit than conventional distribution methods.

      So save your high and mighty derision for a game that you've actually bought and given a chance, okay?

      As for the physics in Half-Life 2, they're phenomenal IMO. In retrospect, I'm glad the game was delayed for so long, if perfecting physics integration was this complex of a process.

  18. Kid Physics by Anonymous Coward · · Score: 0

    "I guess I played a different version of Half Life."

    Poster Child 2: I'm going to tell mommy!

  19. Magic by Kaenneth · · Score: 3, Funny

    Any sufficently advanced physics engine is indistinguisible from scripted events.

  20. It's even in Q3 by Troglodyt · · Score: 1

    It's funny, because this feature is in Quake III.
    Projectiles will spawn with the same speed and direction you have when firing them.
    It's not on by default though, and I don't think people enable it because it seriously messes up aiming with the rocket launcher.

  21. Re:Shell game. by Ash-Fox · · Score: 1

    Yup, you should see my windows login screen, all the logins are the names of games I have.

    --
    Change is certain; progress is not obligatory.
  22. Maybe by SanityInAnarchy · · Score: 1

    Your HEV suit is denser than the grenade?

    --
    Don't thank God, thank a doctor!
  23. Not so much. by SanityInAnarchy · · Score: 1

    If memory serves, yes it's scripted that it'll fall and explode the way it does, but the place it falls and the way it settles is done in realtime.

    --
    Don't thank God, thank a doctor!
  24. Rube Goldberg© device by AniamL · · Score: 1

    I'm trying to construct a Rube Goldberg device (see http://www.rubegoldberg.com/html/gallery.htm) in Hammer, which is Half-Life's level designer, but I'm running into one major problem. The HL2 physics engine does whatever the heck it wants! I'll load up a map, and the entire device will work fine, but then I'll load up the SAME map again and, for example, all the dominoes will immediately fall over, as though hit by a sudden gust of wind! Even more oddly, objects affected by a trigger will respond variably. A barrel, suspended in midair, that is dropped via a remote trigger, will land with a different orientation each time the trigger is activated! This indeterminateness makes it nearly impossible to create an extensive physics project in Hammer. Garry's Mod, interestingly, seems to be more reliable, but it takes away some of the satisfaction (it's basically like using a wizard).

    If anyone has any idea how to fix this problem, or even any more knowledge of the situation, -please- let me know.

    1. Re:Rube Goldberg© device by dgp · · Score: 1

      have you seen this movie of an HL2 rube goldberg machine?

    2. Re:Rube Goldberg© device by AniamL · · Score: 1

      Yes, I have. It's actually where I got the idea. There's plenty of videos out there, including a few Garry's Mod contests. But it still sheds no light on how to combat the absurdly random physics engine.

  25. My only complaints about halflife 2 ... by AngelofDeath-02 · · Score: 1

    My only complaints about half life 2 are the total time spent playing, and the forced puzzel solving. There was one point in the game where I was not allowed to progress due to an invisible wall until I solved the puzzel the "proper" way (as in blow up a storage bin and race up a ramp, vs jumping over the baricades and racing up a ramp.)

    If you're going to have an environment where physics are supposed to play into the game, you shouldn't prevent the level completion with invisable walls. If they get there they got there!

    I'm infinately more sore about the second detail ;P I enjoyed the game otherwise, short or not.

    --
    No, I am not an English major. My posts are subject to typos and incorrect grammar. Do not expect perfection.
  26. New technology? by 0123456 · · Score: 1

    "In 1999, world physics was a new technology that hadn't been integrated into the genre before."

    That's odd, given that Trespasser was released in 1998.

    http://en.wikipedia.org/wiki/Trespasser_(game)

    Sadly, about all it was used for was naff box-stacking puzzles, with an interface that made stacking boxes extremely hard.

  27. A doom review by Anonymous Coward · · Score: 0

    In related news, my blog recently reviewed Doom. I have to say the graphics are terrible, what did ID think they were doing releasing a game made in the 1980's in the middle of the 00's?

    Is it just me or did it take them like 3-4 years before this came out on the HL2 physics engine? Also, FTA it looks like a couple friends got together and played with Gary's Mod (allows you to play with the physics engine and the HL2 objects) for a few hours. Whoop-de-freaking-do.

  28. got modded over-rated by Jasper__unique_dammi · · Score: 1

    Ok I am offtopic here (but at little pain for community) I got modded over-rated, how? I haven't even been modded before i got modded overrated. It would suck if i got modded just because my opinion of halflife2 is too high, and the other guy didnt agree.
    Mod-points aren't meant for giving your opinion, replying is for that, mod points are just for trying to get the "better" posts to stand out more.
    in the faq
    Btw I admit this post wasn't so great, but choose the reason for modding me down better!

  29. Chaos by Anonymous Coward · · Score: 0

    It's called chaos. Just like real life.
    Make sure you have all physics properties set to Zero variance. Variance makes things realistic, but when you want an EXACT behavior every time, well, you want to eliminate that variance. Don't blame the engine. It's just doing what happens in real life.

    1. Re:Chaos by alienmole · · Score: 1
      Don't blame the engine. It's just doing what happens in real life.
      No, it's not. Not even close. It's just making a primitive attempt to imitate what happens in real life, and not always succeeding.
  30. Atomic-powered torch by FoamingToad · · Score: 1

    Yeah - it made me wonder what possible advantages were seen in the actual corridor lighting which was less reliable than the torches. How come UAC didn't duct-tape torches to the walls every couple of meters? Would have been better uptime.