Bullet soft body method

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strangelet
Posts: 3
Joined: Sun Mar 25, 2012 12:54 pm

Bullet soft body method

Post by strangelet » Sun Mar 25, 2012 1:09 pm

Hello,

could pls someone post here an article, which describes best the method used in Bullet's soft body dynamics?
Thanks in advance.

Loic
Posts: 2
Joined: Sat Mar 31, 2012 5:07 pm

Re: Bullet soft body method

Post by Loic » Tue Apr 17, 2012 12:11 pm

Hello strangelet,

The soft body model is based on mass-spring system.

This paper may be helpfull: http://sites.google.com/site/chiwa737/d ... lation.pdf

Marco13
Posts: 1
Joined: Wed Jun 27, 2012 6:31 pm
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Re: Bullet soft body method

Post by Marco13 » Wed Jun 27, 2012 6:40 pm

Hello

Are there any more detailed papers about the methods and optimizations that are used in Bullet? The Siggraph 2010 BOF presentation, "Rendering The Breeze" (http://www.khronos.org/assets/uploads/d ... -Jul10.pdf , 4.1 MB PDF file), describes one of the methods that seem to be implemented in Bullet. As far as I could see from the source code, the computation of the "independent subsets of links through graph coloring" is implemented in the OpenCL soft body solver. Is this method described in another paper/publication? Are there any further optimizations to this? E.g. concerning the cache efficiency of the resulting structures, which is occasionally mentioned in the source code, but seems not to be treated explicitly.

Thanks in advance
Marco

strangelet
Posts: 3
Joined: Sun Mar 25, 2012 12:54 pm

Re: Bullet soft body method

Post by strangelet » Wed May 15, 2013 2:44 pm

After inspecting the code and searching on the web I think that Bullet is based on heuristic position based dynamics, which is described here: http://www.matthiasmueller.info/publica ... sedDyn.pdf
not mass spring model.
I think that Bullet uses only position constraint between nodes and iterative correction of that constraint (equations 10 and 11 in added paper), which is implemented in btSoftBody::PSolve_Links method
am I wrong?

benlansdell
Posts: 1
Joined: Sun Jan 10, 2016 6:25 am

Re: Bullet soft body method

Post by benlansdell » Sun Jan 10, 2016 6:28 am

A bit late replying, but I couldn't find this mentioned explicitly elsewhere on the web. So, yes, I'd like to second strangelet's answer. This paper: http://image.diku.dk/kenny/download/kel ... e.ea10.pdf
states position based dynamics are used in Bullet.

mobeen
Posts: 122
Joined: Thu May 05, 2011 11:47 am

Re: Bullet soft body method

Post by mobeen » Mon Feb 15, 2016 7:32 am

Bullet is based on method detailed in Advanced Character Physics by Thomas Jakobsen which was later known as Position based Dynamics by Mathias Mueller.
The soft body (and cloth/rope) simulation in the open source Bullet physics library is using position based dynamics, as described by Thomas Jakobsen ( http://www.gamasutra.com/resource_guide ... n_01.shtml) and your paper link by Matthias Mueller.
See http://bullet.googlecode.com for the C++ source code.
Source: stackoverflow reply by Erwin Coumans (author of Bullet Physics)
URL: http://stackoverflow.com/questions/5517 ... er/6905067

trebalmen
Posts: 3
Joined: Sat Apr 22, 2017 10:48 am

Re: Bullet soft body method

Post by trebalmen » Sat Apr 22, 2017 10:50 am

Loic wrote:Hello strangelet,

The soft body model is based on mass-spring system.

This paper may be helpfull: http://sites.google.com/site/chiwa737/d ... lation.pdf
Thanks it is indeed very helpful!

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