Search found 78 matches

by Nathanael
Sat Mar 22, 2008 7:11 am
Forum: Research and development discussion about Collision Detection and Physics Simulation
Topic: Soft bodies early preview
Replies: 41
Views: 25214

Re: Soft bodies early preview

what happens if a vertex belonging to a tetrahedron crosses the opposite face(this can easily happen) and so the center will go outside ? will the rest shape converge to an inverted tetrahedron? Keep in mind that i don't use tetrahedrons yet, so what's follow is more guesses than hard evidences. In...
by Nathanael
Sat Mar 22, 2008 3:52 am
Forum: Research and development discussion about Collision Detection and Physics Simulation
Topic: Soft bodies early preview
Replies: 41
Views: 25214

Re: Soft bodies early preview

>Thinking about it, the M matrix is symmetric, there must exist a better (non iterative) way to extract a polar decomposition. if polar >decomposition ever become a bottleneck, i should get back to it.

Never mind, that's wrong.

Nat.
by Nathanael
Sat Mar 22, 2008 3:46 am
Forum: Research and development discussion about Collision Detection and Physics Simulation
Topic: Soft bodies early preview
Replies: 41
Views: 25214

Re: Soft bodies early preview

a rigid frame can be extracted much faster by using a QR approach. see also figure 2 of : http://www-evasion.imag.fr/Publications/2005/NPF05/NPF05.pdf this method is also described in the Physics Based Animation book of Erleben if i remember it correctly. Thanks the the link, i didn't knew about it...
by Nathanael
Sat Mar 22, 2008 2:59 am
Forum: Research and development discussion about Collision Detection and Physics Simulation
Topic: Soft bodies early preview
Replies: 41
Views: 25214

Re: Soft bodies early preview

Here's an update of 'carea', including both methods: - 'com' , that solve the area constraint, but do not minimize displacement. - 'gradient' the solve the area constraint by displacement along constraint gradients. Note: Flipping area is not handled. , Keys: 'c' to allow free COM, '+'/'-' to increa...
by Nathanael
Thu Mar 20, 2008 5:34 pm
Forum: Research and development discussion about Collision Detection and Physics Simulation
Topic: Soft bodies early preview
Replies: 41
Views: 25214

Re: Soft bodies early preview

Dirk Gregorius wrote:Do you have any post-condition you test, such that the volume of the corrected tetrahedron equals the inital volume?
Yes, it does check.

Here's a little visual app to see the triangle case with only my 'solution' for the moment.
by Nathanael
Thu Mar 20, 2008 4:35 pm
Forum: Research and development discussion about Collision Detection and Physics Simulation
Topic: Soft bodies early preview
Replies: 41
Views: 25214

Re: Soft bodies early preview

So you do this the following? c = ( p1 + p2 + p3 + p4 ) / 4 p1 += k * (p1 - c) / |p1 - c| ... This would be an interesting approach. I am not sure if this is physical correct though. The displacements should be in the direction of the gradients to be kind of "workless"". I need to think about this....
by Nathanael
Thu Mar 20, 2008 2:22 pm
Forum: Research and development discussion about Collision Detection and Physics Simulation
Topic: Soft bodies early preview
Replies: 41
Views: 25214

Re: Soft bodies early preview

I edited my post above and added the results for the gradients. How do you get a cubic root? First, I'd like you to understand that I am probably better at coding than at solving equations, and probably better at cooking than at coding... I did drop p1 too, more zeros, better i feel. Then i am solv...
by Nathanael
Thu Mar 20, 2008 2:00 pm
Forum: Research and development discussion about Collision Detection and Physics Simulation
Topic: Soft bodies early preview
Replies: 41
Views: 25214

Re: Soft bodies early preview

How is your solver related to Matthias Muller's work? is it using the same method? Hi Antonio, In fact, a tiny bit of it, but useful indeed, at the end of the step, Muller explicitly evaluate the velocity where Jacobsen implicitly evaluate it. That's not much, but i didn't thought about it before, ...
by Nathanael
Thu Mar 20, 2008 9:20 am
Forum: Research and development discussion about Collision Detection and Physics Simulation
Topic: Soft bodies early preview
Replies: 41
Views: 25214

Re: Soft bodies early preview

Still I would be interested in the volume constraints since it will be fast and simple (if it works). There is a simple open source tool that can create the tetra mesh for you. I just finished deriving the tetrahedral volume constraint for positions, as you said, its simple enough, so I'll give it ...
by Nathanael
Wed Mar 19, 2008 6:35 pm
Forum: Research and development discussion about Collision Detection and Physics Simulation
Topic: Soft bodies early preview
Replies: 41
Views: 25214

Re: Soft bodies early preview

So you solve the rigid bodies and the particles in two different loops and only in the particle loop you apply impulse derived from the particle displacements? Did you try to solve both in the same loop, e.g. The final sweep would adjust positions for the particles and apply impulses on the rigid b...
by Nathanael
Wed Mar 19, 2008 5:46 pm
Forum: Research and development discussion about Collision Detection and Physics Simulation
Topic: Soft bodies early preview
Replies: 41
Views: 25214

Re: Soft bodies early preview

Great Demos!!! Are you working alone or with Erwin on this? As I can see the collision has as usual problems with tunneling. What are you using for collision between soft-bodies and rigid-bodies? Thanks a lot, Yes, tunneling is quite obvious at this point, and the effect is worsen by the fact that ...
by Nathanael
Wed Mar 19, 2008 1:11 pm
Forum: Research and development discussion about Collision Detection and Physics Simulation
Topic: Soft bodies early preview
Replies: 41
Views: 25214

Re: Soft bodies early preview

Nice demos! Very well done :-) Thanks, Yes, the solver itself is based on Matthias Muller's work, mainly because its simple to implement and provide velocities which are needed for some future features. Coupling between rigid and soft bodies is indeed currently done inside the (soft bodies) constra...
by Nathanael
Wed Mar 19, 2008 10:41 am
Forum: Research and development discussion about Collision Detection and Physics Simulation
Topic: Soft bodies early preview
Replies: 41
Views: 25214

Soft bodies early preview

Here's a (very) early preview of soft bodies implementation for Bullet. http://bulletphysics.com/ftp/pub/test/index.php?dir=physics/demos/&file=BulletSoftBody.zip Basic keys: - ']' Next sub demo. - [space] Reset scene. All comments/critics are welcome, just don't ask THE question, "when?" ^^. Enjoy.
by Nathanael
Fri Mar 14, 2008 4:02 am
Forum: Research and development discussion about Collision Detection and Physics Simulation
Topic: Angular spring damping
Replies: 6
Views: 4693

Re: Angular spring damping

If we reduce the problem to just two points, Let Xa,Xb be points position of A and B resp., Let Va,Vb be points velocity of A and B resp., Set Vr=Vb-Va, to be the relative velocity Set N=(Xb-Xa)/|Xb-Xa|, to be the direction from Xa toward Xb We can now project Vr unto a plane perpendicular to N and ...
by Nathanael
Thu Mar 13, 2008 10:11 am
Forum: Research and development discussion about Collision Detection and Physics Simulation
Topic: Angular spring damping
Replies: 6
Views: 4693

Re: Angular spring damping

You may be interested in reading that paper http://www.matthiasmueller.info/publications/posBasedDyn.pdf . Two things in there could be of interest to you, - A global damping method. - A bending (angular) constraint. Mind that the proposed solutions in the paper work a position level and in 3d. Hope...