Search found 78 matches

by Nathanael
Fri May 24, 2013 9:16 am
Forum: Links, Papers, Libraries, Demos, Movies, Comparisons
Topic: Great Physics Engine Comparison (PEEL)
Replies: 29
Views: 34559

Re: Great Physics Engine Comparison (PEEL)

I for one is really happy that Pierre published his results, regardless of supposed biases, there was a time not so long ago where posting on the Bullet forum lead to enlightening discussions instead of flame wars. This should be a technical discussion, because the reality is, most real time physics...
by Nathanael
Mon Mar 30, 2009 9:13 am
Forum: Research and development discussion about Collision Detection and Physics Simulation
Topic: GJK Warm Starting
Replies: 3
Views: 1658

Re: GJK Warm Starting

Degeneracies are still possible. Yes, right, I haven't thought about that, I'm going to check my own code :) If you store simplex vertices (position, not index) in shape local space, it should be possible to make warm-starting work for implicit primitives too, but having to apply the inverse transf...
by Nathanael
Fri Mar 13, 2009 6:41 am
Forum: Research and development discussion about Collision Detection and Physics Simulation
Topic: GJK Warm Starting
Replies: 3
Views: 1658

Re: GJK Warm Starting

For polytopes, a cheap warming is to use center masses as an initial direction, that give you some speed-up, and does not require to store anything. Now if you want to cache the last simplex, you could store it as a list of vertex pairs ([vertexIndexInA,vertexIndexInB], etc...) , rebuild and solve t...
by Nathanael
Thu Dec 04, 2008 12:43 pm
Forum: Research and development discussion about Collision Detection and Physics Simulation
Topic: EPA Simplification - Side-stepping Robustness Issues
Replies: 4
Views: 8003

Re: EPA Simplification - Side-stepping Robustness Issues

Have you compared your ideas with Bullet EPA implementation ? (btGjkEpa2.cpp)

Nathanael.
by Nathanael
Wed Oct 29, 2008 1:05 am
Forum: Research and development discussion about Collision Detection and Physics Simulation
Topic: ApplyForce() adds excess energy
Replies: 3
Views: 1482

Re: ApplyForce() adds excess energy

Its a common observation, I think the best explanation can be found here: http://www.cs.cmu.edu/~baraff/sigcourse/notesd1.pdf page 29, section 5.5

Hope it help,
Nathanael.
by Nathanael
Sat Oct 25, 2008 3:37 am
Forum: Research and development discussion about Collision Detection and Physics Simulation
Topic: Polygon soup with polygon soup collision detection
Replies: 5
Views: 2353

Re: Polygon soup with polygon soup collision detection

Is there any info or know techniques for convex decomposition? This is the first time i hear this term formally... The simplest way that I'm aware of is to recursively split the mesh with itself, (complete convex decomposition), then merge resulting convex sets based on some heuristic (aspect ratio...
by Nathanael
Fri Oct 17, 2008 3:47 am
Forum: Research and development discussion about Collision Detection and Physics Simulation
Topic: Soft Body Parameterization
Replies: 1
Views: 1561

Re: Soft Body Parameterization

It is probably possible to apply large damping on soft bodies deformations (but not global motion), to achieve some kind of Clay like behavior, but it is currently not implemented. Clay behave very much like an highly viscous fluid, with very little elastic forces, so, my guess is smoothed particle ...
by Nathanael
Mon Sep 15, 2008 10:10 am
Forum: General Bullet Physics Support and Feedback
Topic: leaks again [solved]
Replies: 8
Views: 3313

Re: leaks again

Can you update your btSoftBody.h/cpp to latest svn version, and check if the leaks gone?

Thanks,
Nathanael.
by Nathanael
Sat Sep 13, 2008 1:19 pm
Forum: General Bullet Physics Support and Feedback
Topic: friction model
Replies: 4
Views: 9018

Re: friction model

What you have is an infinitely rigid cylinder rolling over an infinitely rigid plane, no amount of 'classic' friction will ever stop the cylinder motion. Most real life objects deform slightly on contact, and provide some non-zero area contact surface, they lose some energy when regaining their orig...
by Nathanael
Sat Sep 13, 2008 10:03 am
Forum: General Bullet Physics Support and Feedback
Topic: friction model
Replies: 4
Views: 9018

Re: friction model

Part of the problem may come from the fact that when only one contact is created between your cylinder and the plane, nothing prevent/damp angular velocities about the contact normal (contacts are points, not surfaces). Try adding a bit of angular damping along that axis, that should work. Hope it h...
by Nathanael
Thu Sep 11, 2008 2:15 am
Forum: Release Announcements
Topic: Bullet 2.71 released: Disney Maya Plugin, CUDA experiments
Replies: 10
Views: 35443

Re: Bullet 2.71 released: Disney Maya Plugin, CUDA experiments

But why it should be 11% slower? Only one method is slower (btDbvtVolume::Select), when measured by the internal benchmark (btDbvt::benchmark). It may be due to the way the compiler allocate registers in that case (the method is inlined), but its not big deal, and does not mean its actually slower ...
by Nathanael
Sun Sep 07, 2008 9:30 am
Forum: Release Announcements
Topic: Bullet 2.71 released: Disney Maya Plugin, CUDA experiments
Replies: 10
Views: 35443

Re: Bullet 2.71 released: Disney Maya Plugin, CUDA experiments

DevO wrote: One question why using inline asm and not SSE intristics.
SSE intristics can be compiled on 64bit and on 32bit and GCC compilers support them too.
Can you try the lastest svn version of btDbvt.h/cpp , SSE has being re-enabled, it use intrinsics now.

Thanks,
Nathanael.
by Nathanael
Sun Aug 31, 2008 12:44 am
Forum: General Bullet Physics Support and Feedback
Topic: btGjkEpaSolver2 error
Replies: 6
Views: 2544

Re: btGjkEpaSolver2 error

I can see two likely possibilities for your problem: 1- when GjkEpa2::Penetration is called , there's just not enough stack space free to allocation instances of epa on it, if so, you can try to allocate epa on the heap, here's a quick patch to test that: case GJK::eStatus::Inside: { EPA& epa(*(new ...
by Nathanael
Sat Aug 30, 2008 4:54 am
Forum: Research and development discussion about Collision Detection and Physics Simulation
Topic: Position based dynamics collisions
Replies: 3
Views: 2087

Re: Position based dynamics collisions

You could try to express the position in triangle as barycentric coordinate let say: P0*u+P1*v+P2*(1-u-v)
then your triangle gradients simply become :
[ -N*u , -N*v , -N*(1-u-v) ]
(based on C=(q-(P0 u + P1 v + P2 (1-u-v))).N )

Hope its work and help,
Nathanael.