[ODE] pressure soft body

Patrick Enoch Hendrix_ at gmx.net
Tue Apr 17 10:57:13 MST 2007


the link is:   http://www.smorfland.uni.wroc.pl/~toczka/2ndtype/ 
None of your applets works here (Windows-firefox || macosx-safari).


what do you mean with "3d-softbody" - including collisions? how  
complete is your engine already? (would be probably answered on your  


about integration into ODE:
- i dont know if the collider can handle "expanding/contracting"  
objects - the AABB might change while the body is at rest! - TODO
- the collider must handle concave bodies, in case a rigid object  
hits the soft object. - AFAIK DONE

you probably use implicit integration? (or explicit with a *very  
small* timestep). there is a SOR and a CG solver already in ODE, that  
could be raped for that purpose. it is able to solve (constant-)  
linearized box-constrained problems. though i dont see a problem for  
a non-constant matrix. the CG would have to restart a couple of  
times, SOR should handle that w/o probs.


cloth would be a nice addition. i have played with simcloth3 which  
gives good results but not perfect. problem is, there is no "front"  
of the cloth. using double-sided polygons didnt really resolve my  
problems. i had mainly problems with cloth-cloth intersections that  
did not get resolved - even with very small timesteps or increased  
penalty forces. (how) did you solve that?


I thought a lot about coupling simcloth3 (implicit) with ODE  
(explicit). but with no real solution.
a primitive solution would ping-pong the two simulations into a  
steady state, which is then the next timestep. that is, integrate  
from t_0 to t_1 until both engines are satisfied (in terms of  
collisions, body-volume, constraints). in simcloth, collisions at t_1  
are used in order to implicitly integrate from t_0 to t_1.


Please find the attached "quickstep.cpp" with a working CG solver.  
You need to replace some stuff in your files.

Looking forward to your applets!
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