   Pluggable Physics Engine
  I think I read that for Half-Life 2, valve didnt write their own physics stuff, instead they bought/lisenced the engine from some other company.I would like someone to explain how this works. Was it just a big library that they bought? It seems to me that physics is a very integral part of a game, and you can''t just stick it in, like you could with say, textures or something. The game has to be designed with physics in mind from the beginning, so how can they use someone elses physics engine? They would have to ''leave room'' for the physics in every game object that they have, so that the physics engine could ''get a hold of them''. Like they would have to have hooks everywhere on all of their objects or something in order for the physics engine to use them.I dont think this is coming out very clearly, but maybe if someone understands what I''m asking they could explain it better BTW, For those who havnt seen the 20+ minute half life demo from like 8 months ago, you should definetly check it out. The physics are tits. 
  http://www.havok.com/It''s a physics SDK, to define it in simple terms. And you''re correct in the assumption that they would have to include "hooks". Register an object''s geometry with the physics sub-system, as well as weight/mass.. things of that sort.Klowner Klowner________________http://dugnet.com/klown ;  Yep, it would be a bit likeSDKCrate myCrate = new SDKCrate(mass,size,position);SDKBarrel myBarrel = new SDKBarrel(mass,diameter,position,...);SDK.UpdateObjects();And that would update gravity and whatnot ;  Ok yea registering each objects weight/mass etc sounds like it makes more sense than what I was thinking. I guess I thought that with all the trouble you would have to go through to attatch all your world''s objects to the physics system, you might as well have written your own. Besides, wasnt HL2 in development for 5 years or something? Its surprising that they didnt write their own physics engine in that time. What have they been doing?! JK the game looks awesome. ;  how will this work once they release the SDK for HL2?  will a full SDK include this physics engine?  now that i think about it, i''m sure no one here has the accurate answers for these questions.  but it''s still food for thought... ;  When they licensed Havok, that gave them access to the source code (which is why Havok now have a problem on their hands - there was Havok source in the leaked HL2 code).They then integrate Havok into their own app, changing the code to fit.   Richard "Superpig" Fine- saving pigs from untimely fates, and when he''s not doing that, runs The Binary Refinery.Enginuity1 | Enginuity2 | Enginuity3 | Enginuity4 | Enginuity5ry. .ibu cy. .y''ybu. .abu ry. dy. "sy. .ubu py. .ebu ry. py. .ibu gy." fy. .ibu ny. .ebu"Don''t document your code; code your documentation." -me"I''m not a complete idiot; parts of me are missing." -}}i{{;  If you are looking for a free physics engine, I would recommend that you take a look at Tokamak. ;  or ODE 