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Say you create a person, monster or robot, with arms, legs, head(s) ... in 3D in a game.

How do you coordinate the body-part movement to achieve the fluidity of real living beings? Is there some theoretical base, or do you just try until it looks good enough?

To put the question in a more precise context, I haven't got some kind of advanced physics engine the would create automatically something physically correct by default.

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You don't need a physics engine to create a realistic living's movements. You need a kinesiology engine. As far as I know, there isn't one commercially available which would be suited for inclusion in games (as opposed to medicine and motion picture special effects shops' software). That said: We usually just wing it, and standard techniques like inverse kinematics and quaternion skinning help. ;) – Martin Sojka Oct 7 '11 at 12:13
Closely related:…. The tech is only commonly used for solider ragdolls because it's too expensive/unreliable for primary animation, although this is changing quickly. – user744 Oct 7 '11 at 19:07

A possible solution to animate 3D body models of human-like actors are the rigging and skeletal animation techniques. Usually, these techniques use an skeletal motion that was captures using a MoCap technique, which basically means that the final result will look super natural because the motion data comes from "real data".

You can have a look at CMU's MoCap database, to see the range of human motions that are available, and see if they suit you.

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I'd contest your claim that mocap is "usually" used in games - it's super expensive both for infrastructure and actors. I'm also not sure that it looks "super natural" compared to fully hand-tweaked animations; mocap still requires plenty of manual labor from artists to really fit a character in a game, and often the broad strokes from a bad actor will be far worse than the same thing hand-animated by a good artist. – user744 Oct 7 '11 at 19:11
I'd say it depends pretty much on the kind of game being develop, but it is defenitely used in a few of them. To give an example, MoCap was used to capture footballers playing football in games like FIFA and PES Plenty of other videos searching in Youtube for 'games and MoCap' – Dan Oct 7 '11 at 22:53
If you think mocap is expensive, you should see the bills for manually doing animations of the same quality =) As for infrastructure you haven't seen the latest systems that even smaller studios can afford to implement in-house, they're a far cry from the old draped stages and ping pong balls taped to everything. – Patrick Hughes Oct 8 '11 at 1:29

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