How would you model a person or other hierarchial model accurately? Ideally I''d have no inbuilt constraints on joints but it would all be modelled with forces and collisions between body parts. However I''m told that''s difficult almost to the point of impossibility to properly use physics. So what would I do to make something that''s accurate enough not to be noticeably different? So I can put in masses, forces from real situations and get tolerably similar results. Like somebody sweeps out your legs and you collapse in a sprawling heap. Cheers guys.

A very challenging problem indeed! There was a presentation at GDC last year I think, or the year before, that talked about some of that. Check out www.gdconf.com for the programming track archives. And Jeff Lander had a couple or more articles in Game Developer Magazine a while back, check out www.gamasutra.com features.

Also, Frontier Developments in the UK has a technology called R-TAG, which is very cool. Its something like "artist-controlled physics" for characters. They have a downloadable demo of some simulated dogs walking around on terrain and looking around. They''re actually using it in a secret game for, I think, PS/2. It was shown in a session a GDC last year. Check them out here, and be sure to download their

www.frontier.co.uk/

That will at least give you some reading material! This is a topic that I''m very interested in, but its not at the top of my priority list to look into in detail.

Graham Rhodes
Senior Scientist
Applied Research Associates, Inc.

I should also add that havok.com and mathengine.com have physics engines that support physically-based character animation. They have, for example, "rag-doll" physics for characters which is just simulating a body that goes limp when hit by, say, a bullet, or when an unconscious character falls down stairs. Their solutions look moderately realistic in these situations. Definitely not perfect, but usable.

MathEngine did have a cool thing at one point in Karma, where they could blend between a fully animated character and physics-based effects, so the character would partially react to a physical hit.

To do it completely right, and have everything look natural is quite a hefty challenge, but there certainly are some compelling solutions out there that can work well in some situations. I think they''ll only get better.

Graham Rhodes
Senior Scientist
Applied Research Associates, Inc.

Do any of them have algorithms or tuts rather than source code - I think oncew I got started it won''t be TOO bad, but my mechanics is stuck at A-level/1st year uni level, which deals only with very simple systems, especially WRT collisions ie single particles.

I don't know how useful they'll be, but I found (A) this and (B) this.

Edited by - TerranFury on March 12, 2002 10:03:29 PM